Datenblatt für MPLAB® XC32 Assembler, Linker, Utilities Guide von Microchip Technology

6‘ MICRDCHIP
2013 Microchip Technology Inc. DS50002186A
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
User’s Guide
YSTEM
2013 Microchip Technology Inc. DS50002186A-page 2
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
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OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
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suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Note the following details of the code protection feature on Microchip devices:
• Microchip products meet the specification contained in their particular Microchip Data Sheet.
• Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
• There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
• Microchip is willing to work with the customer who is concerned about the integrity of their code.
• Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
QUALITY MANAGEMENT S
YSTEM
CERTIFIED BY DNV
== ISO/TS 16949 ==
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC,
FlashFlex, KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro,
PICSTART, PIC32 logo, rfPIC, SST, SST Logo, SuperFlash
and UNI/O are registered trademarks of Microchip Technology
Incorporated in the U.S.A. and other countries.
FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor,
MTP, SEEVAL and The Embedded Control Solutions
Company are registered trademarks of Microchip Technology
Incorporated in the U.S.A.
Silicon Storage Technology is a registered trademark of
Microchip Technology Inc. in other countries.
Analog-for-the-Digital Age, Application Maestro, BodyCom,
chipKIT, chipKIT logo, CodeGuard, dsPICDEM,
dsPICDEM.net, dsPICworks, dsSPEAK, ECAN,
ECONOMONITOR, FanSense, HI-TIDE, In-Circuit Serial
Programming, ICSP, Mindi, MiWi, MPASM, MPF, MPLAB
Certified logo, MPLIB, MPLINK, mTouch, Omniscient Code
Generation, PICC, PICC-18, PICDEM, PICDEM.net, PICkit,
PICtail, REAL ICE, rfLAB, Select Mode, SQI, Serial Quad I/O,
Total Endurance, TSHARC, UniWinDriver, WiperLock, ZENA
and Z-Scale are trademarks of Microchip Technology
Incorporated in the U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated
in the U.S.A.
GestIC and ULPP are registered trademarks of Microchip
Technology Germany II GmbH & Co. KG, a subsidiary of
Microchip Technology Inc., in other countries.
All other trademarks mentioned herein are property of their
respective companies.
© 2013, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 978-1-62077-521-9
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 3
Table of Contents
Preface ........................................................................................................................... 7
Part 1 – MPLAB XC32 Assembler
Chapter 1. Assembler Overview
1.1 Introduction ................................................................................................... 15
1.2 Assembler and Other Development Tools ................................................... 15
1.3 Feature Set ................................................................................................... 16
1.4 Input/Output Files ......................................................................................... 17
Chapter 2. Assembler Command-Line Options
2.1 Introduction ................................................................................................... 23
2.2 Assembler Interface Syntax ......................................................................... 23
2.3 Compilation-Driver Interface Syntax ............................................................. 24
2.4 Options that Modify the Listing Output ......................................................... 25
2.5 Options that Control Informational Output .................................................... 37
2.6 Options that Control Output File Creation .................................................... 38
2.7 Assembler Symbol-Definition and Search-Path Options .............................. 39
2.8 Compilation-Driver and Preprocessor Options ............................................. 40
Chapter 3. MPLAB XC32 Assembly Language
3.1 Introduction ................................................................................................... 41
3.2 Internal Preprocessor ................................................................................... 42
3.3 Source Code Format .................................................................................... 43
3.4 Special Characters ....................................................................................... 48
3.5 Symbols ........................................................................................................ 51
3.6 Giving Symbols Other Values ...................................................................... 52
3.7 The Special DOT Symbol ............................................................................. 52
3.8 Expressions .................................................................................................. 53
3.9 Operators ..................................................................................................... 53
3.10 Special Operators ....................................................................................... 55
Chapter 4. Assembler Directives
4.1 Introduction ................................................................................................... 57
4.2 Directives that Define Sections .................................................................... 58
4.3 Directives that Initialize Constants ............................................................... 62
4.4 Directives that Declare Symbols .................................................................. 64
4.5 Directives that Define Symbols .................................................................... 65
4.6 Directives that Modify Section Alignment ..................................................... 66
4.7 Directives that Format the Output Listing ..................................................... 68
XC32 Assembler, Linker and Utilities User’s Guide
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4.8 Directives that Control Conditional Assembly .............................................. 69
4.9 Directives for Substitution/Expansion ........................................................... 71
4.10 Directives that Include Other Files ............................................................. 75
4.11 Directives that Control Diagnostic Output .................................................. 76
4.12 Directives for Debug Information ................................................................ 77
4.13 Directives that Control Code Generation .................................................... 79
Chapter 5. Assembler Errors/Warnings/Messages
5.1 Introduction ................................................................................................... 81
5.2 Fatal Errors ................................................................................................... 82
5.3 Errors ............................................................................................................ 83
5.4 Warnings ...................................................................................................... 90
5.5 Messages ..................................................................................................... 94
Part 2 – MPLAB XC32 Object Linker
Chapter 6. Linker Overview
6.1 Introduction ................................................................................................... 97
6.2 Linker and Other Development Tools ........................................................... 97
6.3 Feature Set ................................................................................................... 98
6.4 Input/Output Files ......................................................................................... 98
Chapter 7. Linker Command-Line Interface
7.1 Introduction ................................................................................................. 105
7.2 Linker Interface Syntax ............................................................................... 106
7.3 Compilation-Driver Linker Interface Syntax ................................................ 107
7.4 Options that Control Output File Creation .................................................. 108
7.5 Options that Control Run-time Initialization ................................................ 113
7.6 Options that Control Multilib Library Selection ........................................... 114
7.7 Options that Control Informational Output .................................................. 115
7.8 Options that Modify the Link Map Output ................................................... 118
Chapter 8. Linker Scripts
8.1 Introduction ................................................................................................. 119
8.2 Overview of Linker Scripts .......................................................................... 120
8.3 Command Line Information ........................................................................ 120
8.4 Default Linker Script ................................................................................... 121
8.5 Adding a Custom Linker Script to an MPLAB X IDE Project ...................... 123
8.6 Linker Script Command Language ............................................................. 124
8.7 Expressions in Linker Scripts ..................................................................... 140
Chapter 9. Linker Processing
9.1 Introduction ................................................................................................. 147
9.2 Overview of Linker Processing ................................................................... 148
9.3 Linker Allocation ......................................................................................... 150
9.4 Global and Weak Symbols ......................................................................... 153
9.5 Initialized Data ............................................................................................ 154
Table of Contents
2013 Microchip Technology Inc. DS50002186A-page 5
9.6 Stack Allocation .......................................................................................... 157
9.7 Heap Allocation .......................................................................................... 157
9.8 PIC32MX Interrupt Vector Tables .............................................................. 158
9.9 Interrupt Vector Tables for PIC32 MCUs Featuring Dedicated Programmable
Variable Offsets .................................................................................... 159
Chapter 10. Linker Examples
10.1 Introduction ............................................................................................... 163
10.2 Highlights .................................................................................................. 163
10.3 Memory Addresses and Relocatable Code .............................................. 164
10.4 Locating a Variable at a Specific Address ................................................ 165
10.5 Locating a Function at a Specific Address ............................................... 165
10.6 Locating and Reserving Program Memory ............................................... 166
Chapter 11. Linker Errors/Warnings
11.1 Introduction ............................................................................................... 167
11.2 Fatal Errors ............................................................................................... 168
11.3 Errors ........................................................................................................ 169
11.4 Warnings .................................................................................................. 172
Part 3 – 32-Bit Utilities (including the Archiver/Librarian)
Chapter 12. MPLAB XC32 Object Archiver/Librarian
12.1 Introduction ............................................................................................... 175
12.2 Archiver/Librarian and Other Development Tools .................................... 176
12.3 Feature Set ............................................................................................... 177
12.4 Input/Output Files ..................................................................................... 177
12.5 Syntax ...................................................................................................... 177
12.6 Options ..................................................................................................... 178
12.7 Scripts ...................................................................................................... 180
Chapter 13. Other Utilities
13.1 Introduction ............................................................................................... 183
13.2 xc32-bin2hex Utility .................................................................................. 184
13.3 xc32-nm Utility .......................................................................................... 185
13.4 xc32-objdump Utility ................................................................................. 188
13.5 xc32-ranlib Utility ...................................................................................... 191
13.6 xc32-size Utility ........................................................................................ 192
13.7 xc32-strings Utility .................................................................................... 194
13.8 xc32-strip Utility ........................................................................................ 195
Part 4 – Appendices
Appendix A. Deprecated Features
A.1 Introduction ................................................................................................ 199
A.2 Assembler Directives that Define Sections ................................................ 200
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 6 2013 Microchip Technology Inc.
Appendix B. Useful Tables
B.1 Introduction ................................................................................................ 201
B.2 ASCII Character Set .................................................................................. 201
B.3 Hexadecimal to Decimal Conversion ......................................................... 202
Appendix C. GNU Free Documentation License
Glossary .....................................................................................................................205
Index ...........................................................................................................................225
Worldwide Sales and Service ...................................................................................234
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 7
Preface
INTRODUCTION
This chapter contains general information that is useful to know before using 32-bit
language tools. Items discussed include:
• Document Layout
• Conventions Used in this Guide
• Recommended Reading
• The Microchip Web Site
• myMicrochip Personalized Notification Service
• Customer Support
NOTICE TO CUSTOMERS
All documentation becomes dated, and this manual is no exception. Microchip tools and
documentation are constantly evolving to meet customer needs, so some actual dialogs
and/or tool descriptions may differ from those in this document. Please refer to our web site
(www.microchip.com) to obtain the latest documentation available.
Documents are identified with a “DS” number. This number is located on the bottom of each
page, in front of the page number. The numbering convention for the DS number is
“DSXXXXXXXXA”, where “XXXXXXXX” is the document number and “A” is the revision level
of the document.
For the most up-to-date information on development tools, see the MPLAB® X IDE online help.
Select the Help menu, and then Topics to open a list of available online help files.
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 8 2013 Microchip Technology Inc.
DOCUMENT LAYOUT
This document describes how to use GNU language tools to write code for 32-bit
applications. The document layout is as follows:
Part 1 – MPLAB XC32 Assembler
•Chapter 1. Assembler Overview – gives an overview of assembler operation.
•Chapter 2. Assembler Command-Line Options – details command-line options
for the assembler.
•Chapter 3. MPLAB XC32 Assembly Language – discusses the source
language used by the macro assembler.
•Chapter 4. Assembler Directives – describes the assembler commands in the
source code.
•Chapter 5. Assembler Errors/Warnings/Messages – provides a descriptive list
of the errors, warnings and messages.
Part 2 – MPLAB XC32 Object Linker
•Chapter 6. Linker Overview – gives an overview of linker operation.
•Chapter 7. Linker Command-Line Interface – details command-line options for
the linker.
•Chapter 8. Linker Scripts – describes how to generate and use linker scripts to
control linker operation.
•Chapter 9. Linker Processing – discusses how the linker builds an application
from input files.
•Chapter 10. Linker Examples – includes a number of 32-bit-specific linker
examples.
•Chapter 11. Linker Errors/Warnings – provides a descriptive list of the errors
and warnings.
Part 3 – 32-Bit Utilities (including the Archiver/Librarian)
•Chapter 12. MPLAB XC32 Object Archiver/Librarian – details command-line
options for the archiver/librarian.
•Chapter 13. Other Utilities – details the other utilities and their operation.
Part 4 – Appendices
•Appendix A. Deprecated Features – discusses the features considered
obsolete.
•Appendix B. Useful Tables – lists some useful tables: the ASCII character set
and hexadecimal to decimal conversion.
•Appendix C. GNU Free Documentation License – details the license
requirements for using the GNU language tools.
File>Save
Preface
2013 Microchip Technology Inc. DS50002186A-page 9
CONVENTIONS USED IN THIS GUIDE
The following conventions may appear in this documentation:
DOCUMENTATION CONVENTIONS
Description Represents Examples
Arial font:
Italic characters Referenced books MPLAB® X IDE User’s Guide
Emphasized text ...is the only compiler...
Initial caps A window the Output window
A dialog the Settings dialog
A menu selection select Enable Programmer
Quotes A field name in a window or
dialog
“Save project before build”
Underlined, italic text with
right angle bracket
A menu path File>Save
Bold characters A dialog button Click OK
A tab Click the Power tab
Text in angle brackets < > A key on the keyboard Press <Enter>, <F1>
Courier font:
Plain Courier Sample source code #define START
Filenames autoexec.bat
File paths c:\mcc18\h
Keywords _asm, _endasm, static
Command-line options -Opa+, -Opa-
Bit values 0, 1
Constants 0xFF, ’A’
Italic Courier A variable argument file.o, where file can be
any valid filename
Square brackets [ ] Optional arguments mpasmwin [options]
file [options]
Curly brackets and pipe
character: { | }
Choice of mutually exclusive
arguments; an OR selection
errorlevel {0|1}
Ellipses... Replaces repeated text var_name [,
var_name...]
Represents code supplied by
user
void main (void)
{ ...
}
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 10 2013 Microchip Technology Inc.
RECOMMENDED READING
This documentation describes how to use 32-bit language tools. Other useful
documents are listed below. The following Microchip documents are available and
recommended as supplemental reference resources.
Readme Files
For the latest information on Microchip tools, read the associated Readme files (HTML
files) included with the software.
MPLAB® XC32 C/C++ Compiler User's Guide (DS51686)
A guide to using the 32-bit C compiler. The 32-bit linker is used with this tool.
32-Bit Language Tools Libraries (DS51685)
A descriptive listing of libraries available for Microchip 32-bit devices. This includes
standard (including math) libraries and compiler built-in functions. 32-bit peripheral
libraries are described in HTML files provided with each peripheral library type.
Device-Specific Documentation
The Microchip website contains many documents that describe 32-bit device functions
and features. Among these are:
• Individual and family data sheets
• Family reference manuals
• Programmer’s reference manuals
Preface
2013 Microchip Technology Inc. DS50002186A-page 11
THE MICROCHIP WEB SITE
Microchip provides online support via our web site at www.microchip.com. This web
site is used as a means to make files and information easily available to customers.
Accessible by using your favorite Internet browser, the web site contains the following
information:
•Product Support – Data sheets and errata, application notes and sample
programs, design resources, user’s guides and hardware support documents,
latest software releases and archived software
•General Technical Support – Frequently Asked Questions (FAQs), technical
support requests, online discussion groups, Microchip consultant program
member listing
•Business of Microchip – Product selector and ordering guides, latest Microchip
press releases, listing of seminars and events, listings of Microchip sales offices,
distributors and factory representatives
myMICROCHIP PERSONALIZED NOTIFICATION SERVICE
Microchip's personal notification service helps keep customers current on their
Microchip products of interest. Subscribers will receive e-mail notification whenever
there are changes, updates, revisions or errata related to a specified product family or
development tool.
Please visit http://www.microchip.com/pcn to begin the registration process and select
your preferences to receive personalized notifications. A FAQ and registration details
are available on the page, which can be opened by selecting the link above.
When you are selecting your preferences, choosing “Development Systems” will
populate the list with available development tools. The main categories of tools are
listed below:
•Compilers – The latest information on Microchip C compilers, assemblers, linkers
and other language tools. These include all MPLAB C compilers; all MPLAB
assemblers (including MPASM™ assembler); all MPLAB linkers (including
MPLINK™ object linker); and all MPLAB librarians (including MPLIB™ object
librarian).
•Emulators – The latest information on the Microchip MPLAB REAL ICE™
In-Circuit Emulator.
•In-Circuit Debuggers – The latest information on Microchip MPLAB ICD 3
In-Circuit Debugger and PICkit™ 3 In-Circuit Debugger/Programmer.
•MPLAB® X IDE – The latest information on Microchip MPLAB X IDE, the Inte-
grated Development Environment for development systems tools. This list is
focused on the MPLAB X IDE, MPLAB X IDE Project Manager, MPLAB X Editor
and MPLAB X SIM simulator, as well as general editing and debugging features.
•Programmers – The latest information on Microchip programmers. These include
the device (production) programmers MPLAB REAL ICE in-circuit emulator,
MPLAB ICD 3 In-Circuit Debugger, MPLAB PM3 and development
(non-production) programmers PICkit 3 In-Circuit Debugger/Programmer.
•Starter/Demo Boards – These include MPLAB Starter Kit boards, PICDEM™
demonstration boards, and various other evaluation boards.
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 12 2013 Microchip Technology Inc.
CUSTOMER SUPPORT
Users of Microchip products can receive assistance through several channels:
• Distributor or Representative
• Local Sales Office
• Field Application Engineer (FAE)
• Technical Support
Customers should contact their distributor, representative or field application engineer
(FAE) for support. Local sales offices are also available to help customers. A listing of
sales offices and locations is included in the back of this document.
Technical support is available through the web site at: http://support.microchip.com.
Documentation errors or comments may be emailed to docerrors@microchip.com.
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 13
Part 1 – MPLAB XC32 Assembler
Chapter 1. Assembler Overview ................................................................................. 15
Chapter 2. Assembler Command-Line Options ........................................................ 23
Chapter 3. MPLAB XC32 Assembly Language.......................................................... 41
Chapter 4. Assembler Directives ................................................................................ 57
Chapter 5. Assembler Errors/Warnings/Messages................................................... 81
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 14 2013 Microchip Technology Inc.
NOTES:
6‘ MICROCHIP Assembler 4 { Archwer1berzflzn)] 4 l { ]
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 15
Chapter 1. Assembler Overview
1.1 INTRODUCTION
MPLAB® XC32 Assembler (xc32-as) produces relocatable machine code from sym-
bolic assembly language for the PIC32 MCU family of devices. The assembler is a
Windows® operating system console application that provides a platform for develop-
ing assembly language code. The assembler is a port of the GNU assembler from the
Free Software Foundation.
Topics covered in this chapter are:
• Assembler and Other Development Tools
• Feature Set
• Input/Output Files
1.2 ASSEMBLER AND OTHER DEVELOPMENT TOOLS
MPLAB XC32 Assembler translates user assembly source files. In addition, the
MPLAB XC32 C/C++ Compiler uses the assembler to produce its object file.
After the C preprocessor processes the assembly source file (*.S), the assembler gen-
erates a relocatable object file that can then be put into an archive or linked with other
relocatable object files and archives to create an executable file. See Figure 1-1 for an
overview of the tools process flow.
FIGURE 1-1: TOOLS PROCESS FLOW
Object File Libraries
(*.a)
Assembler
Linker
C Source Files
(*.c)
C Compiler
Source Files (*.s)
Assembly Source
Files (*.S)
Object Files
(*.o)
Executable File
(*.elf)
Archiver (Librarian)
Command Line
Simulator
Compiler
Driver
Program
MPLAB® IDE
Debug Tool
Linker Script
(*.ld)
XC32 Assembler, Linker and Utilities User’s Guide
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1.3 FEATURE SET
Notable features of the assembler include:
• Support for the MIPS32, MIPS16e and microMIPS instruction sets
• Support for ELF object format
• Available for Linux®, OS X®, and and Windows operating systems
• Rich Directive Set
• Flexible Macro Language
• Command-Line Interface
• Integrated component of MPLAB X IDE
Assembler Overview
2013 Microchip Technology Inc. DS50002186A-page 17
1.4 INPUT/OUTPUT FILES
Standard assembler input and output files are listed below.
Unlike the MPASM™ Assembler (for use with 8-bit PIC® MCUs), MPLAB XC32 Assem-
bler does not generate error files, hex files, or symbol and debug files. The XC32
assembler is capable of creating a listing file and a relocatable object file (that may or
may not contain debugging information). MPLAB Linker for PIC32 MCUs is used with
the assembler to produce the final object files, map files and a final executable file for
debugging with MPLAB X IDE (see Figure 1-1).
1.4.1 Source Files
The assembler accepts, as input, a source file that consists of PIC32 instructions,
assembler directives and comments. A sample source file is shown in Example 1-1.
EXAMPLE 1-1: SAMPLE ASSEMBLER CODE
Updated example code:
#include <xc.h>
#define IOPORT_BIT_7 (1 << 7)
.global main /* define all global symbols here */
.text
/* define which section (for example "text")
* does this portion of code resides in. Typically,
* all your code will reside in .text section as
* shown below.
*/
.set noreorder
/* This is important for an assembly programmer. This
* directive tells the assembler not to optimize
* the order of the instructions as well as not to insert
* 'nop' instructions after jumps and branches.
*/
/*********************************************************************
* main()
* This is where the PIC32 start-up code will jump to after initial
* set-up.
********************************************************************/
Extension Description
Input
.S Assembly source file to be preprocessed (recommended)
.s Source File
Output
.o Object File
.1st Listing File
Note: Microchip Technology strongly suggests an .S extension for assembly
source files. This will enable you to easily use the C compiler driver without
having to specify the option to tell the driver that the file should be treated
as an assembly file. The capitalized S also indicates that the source file
should be preprocessed by the C preprocessor before being passed to the
assembler. See the “MPLAB XC32 C/C++ Compiler User’s Guide”
(DS51686) for more details on the C compiler driver.
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 18 2013 Microchip Technology Inc.
.ent main /* directive that marks symbol 'main' as function in the ELF
* output
*/
main:
/* Call function to clear bit relevant to pin 7 of port A.
* The 'jal' instruction places the return address in the $ra
* register.
*/
ori a0, $0, IOPORT_BIT_7
jal mPORTAClearBits
nop
/* endless loop */
endless:
j endless
nop
.end main /* directive that marks end of 'main' function and its
* size in the ELF output
*/
/*********************************************************************
* mPORTAClearBits(int bits)
* This function clears the specified bits of IOPORT A.
*
* pre-condition: $ra contains return address
* Input: Bit mask in $a0
* Output: none
* Side effect: clears bits in IOPORT A
********************************************************************/
.ent mPORTAClearBits
mPORTAClearBits:
/* function prologue - save registers used in this function
* on stack and adjust stack-pointer
*/
addiu sp, sp, -4
sw s0, 0(sp)
la s0, LATACLR
sw a0, 0(s0) /* clear specified bits */
/* function epilogue - restore registers used in this function
* from stack and adjust stack-pointer
*/
lw s0, 0(sp)
addiu sp, sp, 4
/* return to caller */
jr ra
nop
.end mPORTAClearBits
Assembler Overview
2013 Microchip Technology Inc. DS50002186A-page 19
1.4.2 Object File
The assembler creates a relocatable ELF object file. The object files do not have
addresses resolved, yet, and must be linked, before they can be used for an
executable.
By default, the name of the object file created is a.out. Specify the -o option (see
Chapter 2. “Assembler Command-Line Options”) on the command line to override
the default name.
1.4.3 Listing File
The assembler has the capability to produce a listing file. The listing file is not an abso-
lute listing file, and the addresses that appear in the listing are relative to the start of its
section.
By default, the listing file is displayed on standard output. Specify the -a=<file>
option (see Chapter 2. “Assembler Command-Line Options”) on the command line
to send the listing file to a specified file.
A listing file produced by the assembler is composed of the elements listed below.
Example 1-2 shows a sample listing file.
1.4.3.1 HEADER
The header contains the name of the assembler, the name of the file being assembled,
and a page number. This is not shown if the -an option is specified.
1.4.3.2 TITLE
The title line contains the title specified by the .title directive. This is not shown if
the -an option is specified.
1.4.3.3 SUBTITLE
The subtitle line contains the subtitle specified by the .sbttl directive. This is not
shown if the -an option is specified.
1.4.3.4 HIGH-LEVEL SOURCE
High-level source will be present if the -ah option is given to the assembler. The format
for high-level source is:
<line #>:<filename> **** <source>
For example:
1:hello.c **** #include <stdio.h>
1.4.3.5 ASSEMBLER SOURCE
Assembler source will be present if the -al option is given to the assembler. The
format for assembler source is:
<line #> <addr> <encoded bytes> <source>
For example:
35 0000 80000434 ori $a0, $zero, IOPORT_BIT_7
Note 1: Line numbers may be repeated.
2: Addresses are relative to sections in this module and are not absolute.
3: Instructions are encoded in “little endian” order.
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1.4.3.6 SYMBOL TABLE
A symbol table is present if the -as option is given to the assembler. A list of defined
symbols and a list of undefined symbols will be given.
The defined symbols will have the format:
DEFINED SYMBOLS
<filename>:<line #> <section>:<addr> <symbol>
For example:
DEFINED SYMBOLS
foo.S:79 .text:00000000 main
foo.S:107 .text:00000014 mPORTAClearBits
The undefined symbols will have the format:
UNDEFINED SYMBOLS
<symbol>
For example:
UNDEFINED SYMBOLS
WDTCON
WDTCONCLR
EXAMPLE 1-2: SAMPLE ASSEMBLER LISTING FILE
GAS LISTING foo.s page 1
1 # 1 "foo.S"
2 # 1 "<built-in>"
1 .nolist
0
0
3 .list
4
5 #define IOPORT_BIT_7 (1 << 7)
6
8 .global baz /* define all global symbols here */
9
10 /* define which section (for example "text")
11 * does this portion of code resides in.
12 * Typically, all of your code will reside in
* the .text section as shown.
14 */
15 .text
16
17 /* This is important for an assembly programmer.
18 * This directive tells the assembler not to
19 * optimize the order of the instructions
20 * as well as not to insert 'nop' instructions
21 * after jumps and branches.
22 */
23 .set noreorder
24
25 .ent baz /* directive that marks symbol 'baz' as
26 * a function in ELF output
27 */
28
29 baz:
30
31 /* Call function to clear bit relevant to pin
32 * 7 in port A. The 'jal' instruction places
Assembler Overview
2013 Microchip Technology Inc. DS50002186A-page 21
33 * the return address in $ra.
34 */
35 0000 80000434 ori $a0, $zero, IOPORT_BIT_7
36 0004 0500000C jal mPORTAClearBits
37 0008 00000000 nop
38
39 /* endless loop */
40 endless:
41 000c 03000008 j endless
42 0010 00000000 nop
43
44 .end baz /* directive that marks end of 'baz'
45 * function and registers size in ELF
46 * output
47 */
DEFINED SYMBOLS
*ABS*:00000000 foo.S
*ABS*:00000001 __DEBUG
foo.S:56 .text:00000014 mPORTAClearBits
foo.S:38 .text:0000000c endless
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NOTES:
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 23
Chapter 2. Assembler Command-Line Options
2.1 INTRODUCTION
MPLAB XC32 Assembler (xc32-as) may be used on the host PC's command-line
interface (e.g., cmd.exe) as well as with the MPLAB X IDE project manager.
The MPLAB X IDE project manager automatically calls the assembler (via the xc32-gcc
compilation driver) when building a project. Many of the commonly used options listed
here are available as check boxes on the MPLAB X IDE project build-options dialog.
However, for a more advanced option, you may have to specify the option in the “Alter-
nate Settings” field of the dialog. After you build a project in MPLAB X IDE, the output
window shows the options passed to the assembler.
Topics covered in this chapter are:
• Assembler Interface Syntax
• Compilation-Driver Interface Syntax
• Options that Modify the Listing Output
• Options that Control Informational Output
• Options that Control Output File Creation
• Assembler Symbol-Definition and Search-Path Options
• Compilation-Driver and Preprocessor Options
2.2 ASSEMBLER INTERFACE SYNTAX
The assembler command line may contain options and file names. Options may appear
in any order and may be before, after or between file names. The order of file names
determines the order of assembly.
xc32-as [options|sourcefiles]...
‘--’ (two hyphens) by itself names the standard input file explicitly, as one of the files
for the assembler to translate. Except for ‘--’, any command line argument that begins
with a hyphen (‘-’) is an option. Each option changes the behavior of the assembler,
but no option changes the way another option works.
Some options require exactly one file name to follow them. The file name may either
immediately follow the option’s letter or it may be the next command line argument. For
example, to specify an output file named test.o, either of the following options would
be acceptable:
•-o test.o
•-otest.o
Note: command-line options are case sensitive.
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2.3 COMPILATION-DRIVER INTERFACE SYNTAX
The compilation-driver program (xc32-gcc) preprocesses, compiles, assembles, and
links C and assembly-language modules and library archives. This driver orchestrates
the build process so that you often don't need to know which individual programs pre-
process, compile, assemble, and link. The driver calls the appropriate individual tools
to complete the requested build process.
In practice, the assembler is usually invoked via xc32-gcc, which determines that it
should assemble an input file by its *.S or *.s filename extension. The compilation
driver sends a file with a *.S (upper case) extension through the CPP-style preproces-
sor before it passes the file to the assembler while the driver sends a file with a *.s
(lower case) extension directly to the assembler.
The basic form of the compilation-driver command line is:
xc32-gcc [options] files
To pass an assembler option from the compilation driver to the assembler, use the
-Wa,option option. The option argument should not contain white space.
EXAMPLE 2-1: EXAMPLE COMPILATION-DRIVER COMMAND LINE
xc32-gcc -mprocessor=32MX360F512L -I"./include" ASMfile.S
-o"ASMfile.o" -DMYMACRO=1 -Wa,-ah="ASMfile.lst"
For additional information on the compilation driver, see the “MPLAB XC32 C/C++
Compiler User’s Guide” (DS51686).
Note: Command-line options and filename extensions are case sensitive.
Note: To use the xc32-gcc compilation driver from MPLAB X IDE, be sure to
select the XC32 Compiler Toolchain for your project.
Assembler Command-Line Options
2013 Microchip Technology Inc. DS50002186A-page 25
2.4 OPTIONS THAT MODIFY THE LISTING OUTPUT
The following options are used to control the listing output. A listing file is helpful for
debugging and general analysis of code operation. Use the following options to
construct a listing file with information that you find useful.
•-a[suboption] [=file]
•--listing-lhs-width num
•--listing-lhs-width2 num
•--listing-rhs-width num
•--listing-cont-lines num
2.4.1 -a[suboption] [=file]
The -a option enables listing output. The -a option supports the following sub options
to further control what is included in the assembly listing:
If no sub-options are specified, the default sub-options used are hls; the -a option by
itself requests high-level, assembly, and symbolic listing. You can use other letters to
select specific options for the listing output.
The letters after the -a may be combined into one option. So for example instead of
specifying -al -an on the command line, you could specify -aln.
-ac Omit false conditionals
-ad Omit debugging directives
-ah Include high-level source
-al Include assembly
-am Include macro expansions
-an Omit forms processing
-as Include symbols
-a=file Output listing to specified file (must be in current directory).
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2.4.1.1 -ac
-ac omits false conditionals from a listing. Any lines that are not assembled because
of a false .if or .ifdef (or the .else of a true .if or .ifdef) will be omitted from
the listing. Example 2-2 shows a listing where the -ac option was not used.
Example 2-3 shows a listing for the same source where the -ac option was used.
EXAMPLE 2-2: LISTING FILE GENERATED WITH -al COMMAND LINE
OPTION
GAS LISTING asm.s page 1
1 # 1 "asm.S"
2 # 1 "<built-in>"
1 .data
0
2 .if 0
3 .if 1
4 .endif
5 .long 0
6 .if 0
7 .long 0
8 .endif
9 .else
10 .if 1
11 .endif
12 0000 02000000 .long 2
13 .if 0
14 .long 3
15 .else
16 0004 04000000 .long 4
17 .endif
18 .endif
19 .if 0
20 .long 5
21 .elseif 1
22 .if 0
23 .long 6
24 .elseif 1
25 0008 07000000 .long 7
26 .endif
27 .elseif 1
28 .long 8
29 .else
30 .long 9
31 .endif
Assembler Command-Line Options
2013 Microchip Technology Inc. DS50002186A-page 27
EXAMPLE 2-3: LISTING FILE GENERATED WITH -alc COMMAND LINE
OPTION
GAS LISTING asm.s page 1
1 # 1 "asm.S"
2 # 1 "<built-in>"
1 .data
0
0
2 .if 0
9 .else
10 .if 1
11 .endif
12 0000 02000000 .long 2
13 .if 0
15 .else
16 0004 04000000 .long 4
17 .endif
18 .endif
19 .if 0
21 .elseif 1
22 .if 0
24 .elseif 1
25 0008 07000000 .long 7
26 .endif
27 .elseif 1
29 .else
31 .endif
Note: Some lines omitted due to -ac option.
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2.4.1.2 -ad
-ad omits debugging directives from the listing. This option is useful when processing
compiler-generated assembly code containing debugging information, the compiler-
generated debugging directives will not clutter the listing. Example 2-4 shows a listing
using both the d and h sub-options. Compared to using the h sub-option alone (see the
next section), the listing is much cleaner.
EXAMPLE 2-4: LISTING FILE GENERATED WITH -alhd COMMAND LINE
OPTION
GAS LISTING test.s page 1
1 .section .mdebug.abi32
2 .previous
10 .Ltext0:
11 .align2
12 .globlmain
13 .LFB0:
14 .file 1 "src\\test.c"
1:src/test.c **** #include <xc.h>
2:src/test.c **** volatile unsigned int testval;
3:src/test.c ****
4:src/test.c **** int
5:src/test.c **** main (void)
6:src/test.c **** {
15 .loc 1 6 0
16 .setnomips16
17 .entmain
18 main:
19 .frame$fp,8,$31# vars= 0, regs= 1/0, args= 0, gp= 0
20 .mask0x40000000,-8
21 .fmask0x00000000,0
22 .setnoreorder
23 .setnomacro
24
25 0000 F8FFBD27 addiu$sp,$sp,-8
26 .LCFI0:
27 0004 0000BEAF sw$fp,0($sp)
28 .LCFI1:
29 0008 21F0A003 move$fp,$sp
30 .LCFI2:
7:src/test.c **** testval += 1;
31 .loc 1 7 0
32 000c 0000828F lw$2,%gp_rel(testval)($28)
33 0010 01004224 addiu$2,$2,1
34 0014 000082AF sw$2,%gp_rel(testval)($28)
8:src/test.c **** return 0;
35 .loc 1 8 0
36 0018 21100000 move$2,$0
9:src/test.c **** }
37 .loc 1 9 0
38 001c 21E8C003 move$sp,$fp
39 0020 0000BE8F lw$fp,0($sp)
40 0024 0800BD27 addiu$sp,$sp,8
41 0028 0800E003 j$31
42 002c 00000000 nop
Assembler Command-Line Options
2013 Microchip Technology Inc. DS50002186A-page 29
43
44 .setmacro
45 .setreorder
46 .endmain
47 .LFE0:
49
50 .commtestval,4,4
88 .Letext0:
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2.4.1.3 -ah
-ah requests a high-level language listing. High-level listings require that the assembly
source code was generated by a compiler, a debugging option like -g was given to the
compiler, and that assembly listings (-al) are also requested. -al requests an output
program assembly listing. Example 2-5 shows a listing that was generated using the
-alh command line option.
EXAMPLE 2-5: LISTING FILE GENERATED WITH -alh COMMAND LINE
OPTION
GAS LISTING tempfile.s page 1
1 .section .mdebug.abi32
2 .previous
3 .section.debug_abbrev,"",@progbits
4 .Ldebug_abbrev0:
5 .section.debug_info,"",@progbits
6 .Ldebug_info0:
7 .section.debug_line,"",@progbits
8 .Ldebug_line0:
9 0000 34000000 .text
11 .align2
12 .globlmain
13 .LFB0:
14 .file 1 "src/test.c"
1:src/test.c **** #include <xc.h>
2:src/test.c **** volatile unsigned int testval;
3:src/test.c ****
4:src/test.c **** int
5:src/test.c **** main (void)
6:src/test.c **** {
15 .loc 1 6 0
16 .setnomips16
17 .entmain
18 main:
19 .frame$sp,0,$31 # vars= 0, regs= 0/0, args= 0, gp= 0
20 .mask0x00000000,0
21 .fmask0x00000000,0
22 .setnoreorder
23 .setnomacro
24
7:src/test.c **** testval += 1;
25 .loc 1 7 0
26 0000 0000848F lw$4,%gp_rel(testval)($28)
8:src/test.c **** return 0;
9:src/test.c **** }
27 .loc 1 9 0
28 0004 21100000 move$2,$0
29 .loc 1 7 0
30 0008 01008324 addiu$3,$4,1
31 000c 000083AF sw$3,%gp_rel(testval)($28)
32 .loc 1 9 0
33 0010 0800E003 j$31
34 0014 00000000 nop
Assembler Command-Line Options
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35
36 .setmacro
37 .setreorder
38 .endmain
39 .LFE0:
40 .sizemain, .-main
41
42 .commtestval,4,4
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2.4.1.4 -al
-al requests an assembly listing. This sub-option may be used with other sub-options.
See the other examples in this section.
2.4.1.5 -am
-am expands macros in a listing. Example 2-6 shows a listing where the -am option
was not used. Example 2-7 shows a listing for the same source where the -am option
was used.
EXAMPLE 2-6: LISTING FILE GENERATED WITH -al COMMAND LINE
OP
TION
GAS LISTING foo.s page 1
1 # 1 "foo.S"
2 # 1 "<built-in>"
1 .macro sum from=0, to=5
0
0
2 .long \from
3 .if \to-\from
4 sum "(\from+1)",\to
5 .endif
6 .endm
7
8 .data
9 0000 00000000 .long 0
10 0004 0A000000 sum 10, 14
10 0B000000
10 0C000000
10 0D000000
10 0E000000
11 0018 00000000 .long 0
Assembler Command-Line Options
2013 Microchip Technology Inc. DS50002186A-page 33
EXAMPLE 2-7: LISTING FILE GENERATED WITH -alm COMMAND LINE
OPTION
GAS LISTING foo.s page 1
1 # 1 "foo.S"
2 # 1 "<built-in>"
1 .macro sum from=0, to=5
0
0
2 .long \from
3 .if \to-\from
4 sum "(\from+1)",\to
5 .endif
6 .endm
7
8 .data
9 0000 00000000 .long 0
10 sum 10, 14
10 0004 0A000000 > .long 10
10 > .if 14-10
10 > sum "(10+1)",14
10 0008 0B000000 >> .long (10+1)
10 >> .if 14-(10+1)
10 >> sum "((10+1)+1)",14
10 000c 0C000000 >>> .long ((10+1)+1)
10 >>> .if 14-((10+1)+1)
10 >>> sum "(((10+1)+1)+1)",14
10 0010 0D000000 >>>> .long (((10+1)+1)+1)
10 >>>> .if 14-(((10+1)+1)+1)
10 >>>> sum "((((10+1)+1)+1)+1)",14
10 0014 0E000000 >>>>> .long ((((10+1)+1)+1)+1)
10 >>>>> .if 14-((((10+1)+1)+1)+1)
10 >>>>> sum "(((((10+1)+1)+1)+1)+1)",14
10 >>>>> .endif
10 >>>> .endif
10 >>> .endif
10 >> .endif
10 > .endif
11 0018 00000000 .long 0
Note: > signifies expanded macro instructions.
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2.4.1.6 -an
-an turns off all forms processing that would be performed by the listing directives
.psize, .eject, .title and .sbttl. Example 2-8 shows a listing where the -an
option was not used. Example 2-9 shows a listing for the same source where the -an
option was used.
EXAMPLE 2-8: LISTING FILE GENERATED WITH -al COMMAND LINE
OPTION
GAS LISTING foo.s page 1
User's Guide Example
Listing Options
1 # 1 "foo.S"
2 # 1 "<built-in>"
1 .text
0
0
2 .title "User's Guide Example"
3 .sbttl "Listing Options"
GAS LISTING foo.s page 2
User's Guide Example
Listing Options
4 .psize 10
5
6 0000 01001A3C lui $k0, 1
7 0004 02001A3C lui $k0, 2
8 0008 03001A3C lui $k0, 3
9 .eject
GAS LISTING foo.s page 3
User's Guide Example
Listing Options
10 000c 04001A3C lui $k0, 4
11 0010 05001A3C lui $k0, 5
EXAMPLE 2-9: LISTING FILE GENERATED WITH -aln COMMAND LINE
OPTION
1 # 1 "foo.S"
2 # 1 "<built-in>"
1 .text
0
0
2 .title "User's Guide Example"
3 .sbttl "Listing Options"
4 .psize 10
5
6 0000 01001A3C lui $k0, 1
7 0004 02001A3C lui $k0, 2
8 0008 03001A3C lui $k0, 3
9 .eject
10 000c 04001A3C lui $k0, 4
11 0010 05001A3C lui $k0, 5
Assembler Command-Line Options
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2.4.1.7 -as
-as requests a symbol table listing. Example 2-10 shows a listing that was generated
using the -as command line option. Note that both defined and undefined symbols are
listed.
EXAMPLE 2-10: LISTING FILE GENERATED WITH -as COMMAND LINE
OPTION
GAS LISTING example.s page 1
DEFINED SYMBOLS
*ABS*:00000000 src\example.c
example.s:18 .text:00000000 main
*COM*:00000004 testval
UNDEFINED SYMBOLS
bar
2.4.1.8 -a=file
=file defines the name of the output file. This file must be in the current directory.
2.4.2 --listing-lhs-width num
The --listing-lhs-width option is used to set the width of the output data column
of the listing file. By default, this is set to 1 word. The following line is extracted from a
listing. The output data column is in bold text.
2 0000 54686973 .ascii "This is an example"
2 20697320
2 616E2065
2 78616D70
2 6C650000
If the option --listing-lhs-width 2 is used, then the same line will appear as
follows in the listing:
2 0000 54686973 20697320 .ascii "This is an example"
2 616E2065 78616D70
2 6C650000
2.4.3 --listing-lhs-width2 num
The --listing-lhs-width2 option is used to set the width of the continuation lines
of the output data column of the listing file. By default, this is set to 1. If the specified
width is smaller than the first line, this option is ignored. The following lines are
extracted from a listing. The output data column is in bold.
2 0000 54686973 .ascii "This is an example"
2 20697320
2 616E2065
2 78616D70
2 6C650000
If the option --listing-lhs-width2 3 is used, then the same line will appear as
follows in the listing:
2 0000 54686973 .ascii "This is an example"
2 20697320 616E2065 78616D70
2 6C650000
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2.4.4 --listing-rhs-width num
The --listing-rhs-width option is used to set the maximum width in characters
of the lines from the source file. By default, this is set to 100. The following lines are
extracted from a listing that was created without using the --listing-rhs-width
option. The text in bold are the lines from the source file.
2 0000 54686973 .ascii "This line is long"
2 206C696E
2 65206973
2 206C6F6E
2 67000000
If the option --listing-rhs-width 22 is used, then the same line will appear as
follows in the listing:
2 0000 54686973 .ascii "This line is
2 206C696E
2 65206973
2 206C6F6E
2 67000000
The line is truncated (not wrapped) in the listing, but the data is still there.
2.4.5 --listing-cont-lines num
The --listing-cont-lines option is used to set the maximum number of continu-
ation lines used for the output data column of the listing. By default, this is 8. The fol-
lowing lines are extracted from a listing that was created without using the
--listing-cont-lines option. The text in bold shows the continuation lines used
for the output data column of the listing.
2 0000 54686973 .ascii "This is a long character
sequence"
2 20697320
2 61206C6F
2 6E672063
2 68617261
Notice that the number of bytes displayed matches the number of bytes in the ASCII
string; however, if the option --listing-cont-lines 2 is used, then the output
data will be truncated after 2 continuation lines as shown below.
2 0000 54686973 .ascii "This is a long character
sequence"
2 20697320
2 61206C6F
Assembler Command-Line Options
2013 Microchip Technology Inc. DS50002186A-page 37
2.5 OPTIONS THAT CONTROL INFORMATIONAL OUTPUT
The options in this section control how information is output. Errors, warnings and
messages concerning code translation and execution are controlled through several of
the options in this section.
Any item in parentheses shows the short method of specifying the option, e.g.,
--no-warn also may be specified as -W.
2.5.1 --fatal-warnings
Warnings are treated as if they were errors.
2.5.2 --no-warn (-W)
Warnings are suppressed. If you use this option, no warnings are issued. This option
only affects the warning messages. It does not change how your file is assembled.
Errors are still reported.
2.5.3 --warn
Warnings are issued, if appropriate. This is the default behavior.
2.5.4 -J
No warnings are issued about signed overflow.
2.5.5 --help
The assembler will show a message regarding the command line usage and options.
The assembler then exits.
2.5.6 --target-help
The assembler will show a message regarding the PIC32 target-specific command-line
options. The assembler then exits.
2.5.7 --version
The assembler version number is displayed. The assembler then exits.
2.5.8 --verbose (-v)
The assembler version number is displayed. The assembler does not exit. If this is the
only command line option used, then the assembler will print out the version and wait
for entry of the assembly source through standard input. Use <CTRL>-D to send an
EOF character to end assembly.
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2.6 OPTIONS THAT CONTROL OUTPUT FILE CREATION
The options in this section control how the output file is created. For example, to
change the name of the output object file, use -o.
Any item in parentheses shows the short method of specifying the option, e.g.,
--keep-locals may be specified as -L also.
2.6.1 -g
Generate symbolic debugging information.
2.6.2 --keep-locals (-L)
Keep local symbols, i.e., labels beginning with .L (upper case only). Normally you do
not see such labels when debugging, because they are intended for the use of
programs (like compilers) that compose assembler programs. Normally both the
assembler and linker discard such symbols. This option tells the assembler to retain
those symbols in the object files.
2.6.3 -o objfile
Name the object file output objfile. In the absence of errors, there is always one
object file output when you run the assembler. By default, it has the name a.out. Use
this option (which takes exactly one filename) to give the object file a different name.
Whatever the object file is called, the assembler overwrites any existing file with the
same name.
2.6.4 -Z
Generate object file even after errors. After an error message, the assembler normally
produces no output. If for some reason, you are interested in object file output even
after the assembler gives an error message, use the -Z option. If there are any errors,
the assembler continues anyway, and writes an object file after a final warning
message of the form “n errors, m warnings, generating bad object file”.
2.6.5 -MD file
Write dependency information to file. The assembler can generate a dependency
file. This file consists of a single rule suitable for describing the dependencies of the
main source file. The rule is written to the file named in its argument. This feature can
be used in the automatic updating of makefiles.
Assembler Command-Line Options
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2.7 ASSEMBLER SYMBOL-DEFINITION AND SEARCH-PATH OPTIONS
The options in this section perform functions not defined in previous sections.
2.7.1 --defsym sym=value
Define symbol sym to given value.
2.7.2 -I dir
Use this option to add dir to the list of directories that the assembler searches for files
specified in .include directives. You may use -I as many times as necessary to
include a variety of paths. The current working directory is always searched first; after
that, the assembler searches any -I directories in the same order as they were
specified (left to right) on the command line.
When passed directly to the assembler, this option affects the search path used by the
assembler's .include directive. To affect the search path used by the C preprocessor
for a #include directive, pass the corresponding option to the xc32-gcc compilation
driver.
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2.8 COMPILATION-DRIVER AND PREPROCESSOR OPTIONS
The compilation-driver (xc32-gcc) and C preprocessor options in this section may be
useful for assembly-code projects. The compilation driver will pass the options to the
preprocessor as required. See the “MPLAB XC32 C/C++ Compiler User’s Guide”
(DS51686) for more information on the compilation driver and for a more
comprehensive list of driver options.
2.8.1 -mprocessor=device
Selects the device for which to compile (e.g., -mprocessor=32MX360F512L).
2.8.2 -Wa,option
Pass option as an option to the assembler. If option contains commas, it is split into
multiple assembler options at the commas. The option argument must not contain
white space.
2.8.3 -Dmacro=defn
Define macro macro as defn. All instances of -D on the command line are processed
before any -U options.
2.8.4 -Dmacro
Define macro macro as 1. All instances of -D on the command line are processed
before any -U options.
2.8.5 -Umacro
Undefine macro macro. -U options are evaluated after all -D options, but before any
-include and -imacros options.
2.8.6 -I dir
Add the directory dir to the head of the list of directories to be searched for #include
preprocessor header files. This can be used to override a system header file, substitut-
ing your own version, since these directories are searched before the system header
file directories. If you use more than one -I option, the directories are scanned in
left-to-right order. The standard system directories come after.
When passed to the compilation driver, this option affects the search path used by the
preprocessor's #include directive. To affect the search path used by the assembler's
.include directive, pass the corresponding option to the assembler using the -Wa
option.
2.8.7 -save-temps
Do not delete intermediate files. Place them in the current directory and name them
based on the source file. Thus, compiling foo.c with -c -save-temps would
produce the following files:
•foo.i (preprocessed file)
•foo.s (assembly language file)
•foo.o (object file)
2.8.8 -v
Print the commands executed during each stage of compilation.
2.8.9 --help
Print a description of the command-line options.
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 41
Chapter 3. MPLAB XC32 Assembly Language
3.1 INTRODUCTION
The source language accepted by the macro assembler is described here. All opcode
mnemonics and operand syntax are specific to the target device. The same assembler
application is used for compiler-generated intermediate assembly and hand-written
assembly source code.
Topics covered in this chapter are:
• Internal Preprocessor
• Source Code Format
• Special Characters
•Symbols
• Giving Symbols Other Values
• The Special DOT Symbol
• Expressions
• Operators
• Special Operators
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3.2 INTERNAL PREPROCESSOR
The assembler has an internal preprocessor. The internal processor performs the
following actions.
1. Adjusts and removes extra white space. It leaves one space or tab before the
keywords on a line, and turns any other white space on the line into a single
space.
2. Removes all comments, replacing them with a single space, or an appropriate
number of new lines.
3. Converts character constants into the appropriate numeric value.
If you have a single character (e.g., ‘b’) in your source code, it will be changed to
the appropriate numeric value. If you have a syntax error that occurs at the single
character, the assembler will not display ‘b’, but instead display the first digit of
the decimal equivalent.
For example, if you had .global mybuf, ‘b’ in your source code, the error mes-
sage would say “Error: Rest of line ignored. First ignored character is ‘9’.” Notice
the error message says ‘9’. This is because the ‘b’ was converted to its decimal
equivalent 98. The assembler is actually parsing .global mybuf,98
The internal processor does not perform the following actions.
1. macro preprocessing
2. include file handling
3. anything else you may get from your C compiler’s preprocessor
You can do include file preprocessing with the .include directive. See Chapter
4. “Assembler Directives”.
You can use the C compiler driver to get other C-style preprocessing by giving the input
file a .S suffix. See the “MPLAB XC32 C/C++ Compiler User’s Guide” (DS51686) for
more information.
If the first line of an input file is #NO_APP or if you use the -f option, white space and
comments are not removed from the input file. Within an input file, you can ask for white
space and comment removal in certain portions by putting a line that says #APP before
the text that may contain white space or comments, and putting a line that says
#NO_APP after this text. This feature is mainly intended to support assembly
statements in compilers whose output is otherwise free of comments and white space.
Note: Excess white space, comments and character constants cannot be used
in the portions of the input text that are not preprocessed.
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3.3 SOURCE CODE FORMAT
Assembly source code consists of statements and white spaces.
White space is one or more spaces or tabs. White space is used to separate pieces of
a source line. White space should be used to make your code easier for people to read.
Unless within character constants, any white space means the same as exactly one
space.
Each statement has the following general format and is followed by a new line.
[label:][mnemonic[operands] ][; comment]
OR
[label:][directive[arguments] ][; comment]
• Label
•Mnemonic
•Directive
• Operands
•Arguments
•Comments
3.3.1 Label
A label is one or more characters chosen from the set composed of all letters, digits,
the underline character (_), and the period (.). Labels may not begin with a decimal
digit, except for the special case of a local symbol. (See Section 3.5.1 “Local Sym-
bols” for more information.) Case is significant. There is no length limit; all characters
are significant.
Label definitions must be immediately followed by a colon. A space, a tab, an end of
line, or assembler mnemonic or directive may follow the colon.
Label definitions may appear on a line by themselves and will reference the next
address.
The value of a label after linking is the absolute address of a location in memory.
3.3.2 Mnemonic
Mnemonics tell the assembler which machine instructions to assemble. For example,
addition (ADD), jumps (J), or loads (LUI). Unlike labels that you create yourself, mne-
monics are provided by the PIC32 MCU assembly language. Mnemonics are not case
sensitive.
See the data sheet of your target PIC32 MCU for more details on the CPU
instruction-set mnemonics available for the device.
The assembler also supports a number of synthesized/macro instructions intended to
make writing assembly code easier. The LI (load immediate) instruction is an example
of a synthetic macro instruction. The assembler generates two machine instructions to
load a 32-bit constant value into a register from this single synthetic instruction.
[label:] [mnemonic [operands] ] [; comment]
OR
[label:] [directive [arguments] ] [; comment]
Note: Excess white space, comments and character constants cannot be used in
the portions of the input text that are not preprocessed.
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3.3.3 Assembler Syntax
The assembler synthesizes instructions for:
• A 32-bit Load Immediate
• A load from a memory location
• An extended branch conditional
• A two-operand form of some three-operand instructions
• An unaligned load/store instruction
Assembly directives, such as .set noat, .set nomacro, and .set noreorder,
disable these normally helpful features for cases where you require full control over the
generated code. See Section 4.13 “Directives that Control Code Generation”.
3.3.4 Directive
Assembler directives are commands that appear in the source code but are not trans-
lated directly into machine code. Directives are used to control the assembler, its input,
output and data allocation. The first character of a directive is a dot (.). More details
are provided in Chapter 4. “Assembler Directives” on the available directives.
3.3.5 Operands
Each machine instruction takes from 0 up to 4 operands. (See the appropriate data
sheet of your target PIC32 MCU for a full list of machine instructions.) These operands
give information to the instruction on the data that should be used and the storage loca-
tion for the instruction. Operands must be separated from mnemonics by one or more
spaces or tabs.
Separate multiple operands with commas. If commas do not separate your operands,
the assembler displays a warning and takes its best guess on the separation of the
operands. For most PIC32 MCU instructions, an operand consists of a core
general-purpose register, label, literal, or basereg+offset.
3.3.5.1 GENERAL-PURPOSE REGISTER OPERANDS
The PIC32 MCU core contains thirty-two 32-bit general purpose registers used for inte-
ger operations and address calculation. Most of the PIC32 MCU instructions require
one or more GPR operands, either for the source, the destination, or both.
Register operands are distinguished with a preceding dollar sign ('$'). The register
number immediately follows the dollar sign. Example 3-1 shows assembly source code
using register number operands.
However, if you use the compilation driver (xc32-gcc) to preprocess the source code
with the CPP-style preprocessor before assembling, you can take advantage of macros
that are provided in the xc.h header file that is provided with the C compiler. These
macros map conventional register names to the corresponding register number.
Example 3-2 shows assembly source code using conventional register names for oper-
ands. See the “MPLAB XC32 C/C++ Compiler User’s Guide” (DS51686) for additional
information on PIC32 MCU register conventions and the compiler's runtime
environment.
EXAMPLE 3-1: ASSEMBLY SOURCE CODE WITH REGISTER NUMBER
OPERANDS
.text
# Add Word
li $2, 123
li $3, 456
add $4, $2, $3
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2013 Microchip Technology Inc. DS50002186A-page 45
EXAMPLE 3-2: ASSEMBLY SOURCE CODE WITH CONVENTIONAL
REGISTER NAMES
#include <xc.h>
.text
/* Add Word */
li v0, 123 /* v0 is a return-value register */
li v1, 456 /* v1 is a return-value register */
add a0, v0, v1 /* a0 is an argument register */
3.3.5.2 LITERAL-VALUE OPERANDS
Literal values can be hexadecimal, octal, binary, or decimal format. Hexadecimal num-
bers are distinguished by a leading 0x. Octal numbers are distinguished by a leading
0. Binary numbers are distinguished by a leading 0B or 0b. Decimal numbers require
no special leading or trailing character.
Example:
0xe, 016, 0b1110 and 14 all represent the literal value 14.
-5 represents the literal value -5.
symbol represents the value of symbol.
3.3.5.3 BASEREG+OFFSET OPERANDS
Load and store operations select the memory location using a BaseReg+Offset oper-
and. For an operand of this type, the effective address is formed by adding the 32-bit
signed offset to the contents of a base register. A PIC32 MCU data sheet shows this
type of operand as Mem[R+offset].
EXAMPLE 3-3: USING ASSEMBLY SOURCE CODE WITH
BASEREG+OFFSET OPERANDS
#include <xc.h>
.data
.align 4
MY_WORD_DATA:
.word 0x10203040, 0x8090a0b0
.text
.global example
/* Store Word */
example:
la v0, MY_WORD_DATA
lui v1,0x1111
ori v1,v1,0x4432
lui a0,0x5555
ori a0,a0,0x1123
sw v1, 0(v0) /* Mem[GPR[v0]+0] <- GPR[v1] */
sw a0, 4(v0) /* Mem[GPR[v0]+4] <- GPR[a0] */
lw a1, 0(v0) /* GPR[a1] <- Mem[GPR[v0]+0] */
b .
The C compiler supports global-pointer relative (gp-rel) addressing. Loads and stores
to data lying within 32 KB of either side of the address stored in the gp register (64 KB
total) can be performed in a single instruction using the gp register as the base register.
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The C compiler's -Gnum option controls the maximum size of global and static data
items that can be addressed in one instruction instead of two. The compiler's default
gnum value is 8 bytes, which is large enough to hold all simple scalar variables.
EXAMPLE 3-4: ASSEMBLY SOURCE CODE WITH GP-RELATIVE
ADDRESSING
.align 2
.globl foo
.set nomips32
.ent foo
foo:
.set noreorder
.set nomacro
lw $3,%gp_rel(testval)($28)
addiu $2,$3,1
sw $2,%gp_rel(testval)($28)
j $31
nop
.set macro
.set reorder
.end foo
There are a few potential pitfalls to using gp-relative addressing:
• You must take special care when writing assembler code to declare global (i.e.,
public or external) data items correctly:
- Writable, initialized data of gnum bytes or less must be put explicitly into the
.sdata section, for example:
.sdata
small: .word 0x12345678
- Global common data must be declared with the correct size, for example:
.comm small, 4
.comm big, 100
- Small external variables must also be declared correctly, for example:
.extern smallext, 4
• If your program has a very large number of small data items or constants, the C
compiler's -G8 option may still try to push more than 64 KB of data into the ''small''
region; the symptom will be obscure relocation errors (''relocation truncated'')
when linking. Fix it by disabling gp-relative addressing with the compiler's -G0
option and/or reducing the space reserved in the small data sections (i.e. .sbss
and .sdata) in your assembly code.
3.3.6 Arguments
Each directive takes 0 to 3 arguments. These arguments give additional information to
the directive on how it should carry out the command. Arguments must be separated
from directives by one or more spaces or tabs. Commas must separate multiple argu-
ments. More details on the available directives are provided in Chapter 4. “Assembler
Directives”.
Note: To utilize gp-relative addressing, the compiler and assembler must group all
of the “small” variables and constants into one of the “small” sections. See
the MPLAB® XC32 C/C++ Compiler User's Guide (DS51686) for more
information on the global pointer and the -G option.
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3.3.7 Comments
Comments can be represented in the assembler in one of two ways described below.
3.3.7.1 SINGLE LINE COMMENT
This type of comment extends from the comment character to the end of the line. For
a single line comment, use a number/hash sign (#).
3.3.7.2 MULTI-LINE COMMENT
This type of comment can span multiple lines. For a multi-line comment, use
/* ... */. These comments cannot be nested.
Example:
/* All
of these
lines
are
comments */
Note: This comment character differs from the character recognized by the
MPASM assembler and the MPLAB Assembler for PIC24 MCUs and dsPIC
DSCs.
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3.4 SPECIAL CHARACTERS
A constant is a value written so that its value is known by inspection, without knowing
any context. Examples are:
.byte 74, 0112, 0b01001010, 0x4A, 0x4a, ’J’, ’\J’#All the same value
.ascii "Ring the bell\7" #A string constant
.float 0f-31415926535897932384626433832795028841971.693993751E-40
3.4.1 Numeric Constants
The assembler distinguishes two kinds of numbers according to how they are stored in
the machine. Integers are numbers that would fit into a long in the C language.
Floating-point numbers are IEEE 754 floating-point numbers.
3.4.1.1 INTEGERS
A binary integer is ‘0b’ or ‘0B’ followed by zero or more of the binary digits ‘01’.
An octal integer is ‘0’ followed by zero or more of the octal digits ‘01234567’.
A decimal integer starts with a non-zero digit followed by zero or more decimal digits
‘0123456789’.
A hexadecimal integer is ‘0x’ or ‘0X’ followed by one or more hexadecimal digits
‘0123456789abcdefABCDEF’.
To denote a negative integer, use the prefix operator ‘-’.
3.4.1.2 FLOATING-POINT NUMBERS
A floating-point number is represented in IEEE 754 format. A floating-point number is
written by writing (in order):
• An optional prefix, which consists of the digit ‘0’, followed by the letter ‘e’, ‘f’ or ‘d’
in upper or lower case. Because floating point constants are used only with
.float and .double directives, the precision of the binary representation is
independent of the prefix.
• An optional sign: either ‘+’ or ‘-’.
• An optional integer part: zero or more decimal digits.
• An optional fractional part: ‘.’ followed by zero or more decimal digits.
• An optional exponent, consisting of:
- An ‘E’ or ‘e’.
- Optional sign: either ‘+’ or ‘-’.
- One or more decimal digits.
At least one of the integer part or fractional part must be present. The floating-point
number has the usual base-10 value.
Floating-point numbers are computed independently of any floating-point hardware in
the computer running the assembler.
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3.4.2 Character Constants
There are two kinds of character constants. A character stands for one character in one
byte and its value may be used in numeric expressions. A string can contain potentially
many bytes and their values may not be used in arithmetic expressions.
3.4.2.1 CHARACTERS
A single character may be written as a single quote immediately followed by that char-
acter, or as a single quote immediately followed by that character and another single
quote. The assembler accepts the following escape characters to represent special
control characters:
TABLE 3-1: SPECIAL CHARACTERS AND USAGES
The value of a character constant in a numeric expression is the machine’s byte-wide
code for that character. The assembler assumes your character code is ASCII.
3.4.2.2 STRINGS
A string is written between double quotes. It may contain double quotes or null
characters. The way to get special characters into a string is to escape the characters,
preceding them with a backslash ‘\’ character. The same escape sequences that apply
to strings also apply to characters.
3.4.2.3 GENERAL SYNTAX RULES
Table 3-2 summarizes the general syntax rules that apply to the assembler:
Escape Character Description Hex
Value
\a Bell (alert) character 07
\b Backspace character 08
\f Form-feed character 0C
\n New-line character 0A
\r Carriage return character 0D
\t Horizontal tab character 09
\v Vertical tab character 0B
\\ Backslash 5C
\? Question mark character 3F
\" Double quote character 22
\digit digit digit Octal character code. The numeric code is 3 octal digits.
\x hex-digits Hex character code. All trailing hex digits are combined.
Either upper or lower case x works.
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TABLE 3-2: SYNTAX RULES
Character Character Description Syntax Usage
.period begins a directive
#number/hash begin single-line comment
/* slash, asterisk begin multiple-line comment
*/ asterisk, slash end multiple-line comment
:colon end a label definition
none required begin a literal value
’c’ character in single quotes specifies single character value
"string" character string in double quotes specifies a character string
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3.5 SYMBOLS
A symbol is one or more characters chosen from the set composed of all letters, digits,
the underline character (_), and the period (.). Symbols may not begin with a digit. The
case of letters is significant (e.g., foo is a different symbol than Foo). There is no length
limit and all characters are significant.
Each symbol has exactly one name. Each name in an assembly language program
refers to exactly one symbol. You may use that symbol name any number of times in a
program.
• Local Symbols
• Giving Symbols Other Values
• The Special DOT Symbol
• Predefined Symbols
3.5.1 Local Symbols
Local symbols are used when temporary scope for a label is needed. There are ten
local symbol names, which can be reused throughout the program. They may be
referred to using the names ‘0’, ‘1’, ..., ‘9’. To define a local symbol, write a label of the
form ‘N’, ‘N’, ..., ‘N’ (where N represents any digit 0-9). To refer to the most recent pre-
vious definition of that symbol, write ‘Nb’, using the same digit as when you defined the
label. To refer to the next definition of a local label, write ‘Nf’. The ‘b’ stands for
“backwards” and the ‘f’ stands for “forwards”.
There is no restriction on how you can use these labels, and you can reuse them too.
You can repeatedly define the same local label (using the same number 'N'), although
you can refer to only the most recently defined local label of that number (for a back-
wards reference) or the next definition of a specific local label for a forward reference.
Also note that the first 10 local labels (‘0:’. . . ‘9:’) are implemented in a slightly more
efficient manner than the others.
Here is an example:
EXAMPLE 3-5: SYMBOL USAGE
1: b 1f
2: b 1b
1: b 2f
2: b 1b
Which is the equivalent of:
label_1: b label_3
label_2: b label_1
label_3: b label_4
label_4: b label_3
Local symbol names are only a notational device. They are immediately transformed
into more conventional symbol names before the assembler uses them. These conven-
tional symbol names are stored in the symbol table and appear in error messages and
optionally emitted to the object file.
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3.6 GIVING SYMBOLS OTHER VALUES
A symbol can be given an arbitrary value by writing a symbol, followed by an equals
sign '=', followed by an expression.
Example:
VAR = 4
3.7 THE SPECIAL DOT SYMBOL
The special symbol ‘.’ refers to the current address being processed by the assembler.
Thus, the expression ‘melvin: .long .’ defines melvin to contain its own address.
Assigning a value to . is treated the same as an .org directive. Thus, the expression
‘.=.+4’ is the same as saying ‘.space 4’.
When used in an executable section, ‘.’ refers to a Program Counter address. On a
PIC32 MCU, the Program Counter increments by 4 for each 32-bit instruction word.
User code should take care to properly align instructions after modifying the dot
symbol.
3.7.1 Giving Symbols Other Values
A symbol can be given an arbitrary value by writing a symbol, followed by an equals
sign ‘=’, followed by an expression.
Example:
VAR = 4
3.7.2 The Special DOT Symbol
The special symbol ‘.’ refers to the current address being processed by the assembler.
Thus, the expression ‘melvin: .long .’ defines melvin to contain its own address.
Assigning a value to . is treated the same as an .org directive. Thus, the expression
‘.=.+4’ is the same as saying ‘.space 4’.
When used in an executable section, ‘.’ refers to a Program Counter address. On a
PIC32 MCU, the Program Counter increments by 4 for each 32-bit instruction word.
User code should take care to properly align instructions after modifying the dot
symbol.
3.7.3 Predefined Symbols
The assembler predefines several symbols which can be tested by conditional
directives in source code.
TABLE 3-3: PREDEFINED SYMBOLS
Symbol Definition
P32MX PIC32MX target device family
P32MZ PIC32MZ target device family
HAS_MIPS32R2 Device supports the MIPS32r2 Instruction Set
HAS_MIPS16 Device supports the MIPS16e Instruction Set
HAS_MICROMIPS Device supports the microMIPS Instruction Set
HAS_DSPR2 Device supports the DSPr2 engine
HAS_MCU Device supports the MIPS MCU extensions
HAS_L1CACHE Device has an L1 data and program cache
HAS_VECTOROFFSETS Device uses configurable offsets for the vector table
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3.8 EXPRESSIONS
An expression specifies an address or numeric value. White space may precede and/or
follow an expression. The result of an expression must be an absolute number or an
offset into a particular section. When an expression is not absolute and does not pro-
vide enough information for the assembler to know its section, the assembler
terminates and generates an error message.
3.8.1 Empty Expressions
An empty expression has no value: it is just white space or null. Wherever an absolute
expression is required, you may omit the expression, and the assembler assumes a
value of (absolute) 0.
3.8.2 Integer Expressions
An integer expression is one or more arguments delimited by operators. Arguments are
symbols, numbers or subexpressions. Subexpressions are a left parenthesis ‘(’ fol-
lowed by an integer expression, followed by a right parenthesis ‘)’; or a prefix operator
followed by an argument.
Integer expressions involving symbols in program memory are evaluated in Program
Counter (PC) units. In MIPS32 mode, the Program Counter increments by 4 for each
instruction word. For example, to branch to the next instruction after label L, specify L+4
as the destination.
Example:
b L+4
3.9 OPERATORS
Operators are arithmetic functions, like + or %. Prefix operators are followed by an
argument. Infix operators appear between their arguments. Operators may be
preceded and/or followed by white space.
Prefix operators have higher precedence than infix operators. Infix operators have an
order of precedence dependent on their type.
3.9.1 Prefix Operators
The assembler has the following prefix operators. Each takes one argument, which
must be absolute.
TABLE 3-4: PREFIX OPERATORS
Operator Description Example
-Negation. Two’s complement negation. -1
~Bit-wise not. One’s complement. ~flags
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3.9.2 Infix Operators
Infix operators take two arguments, one on either side. Operators have a precedence,
by type, as shown in the table below; but, operations with equal precedence are per-
formed left to right. Apart from + or –, both operators must be absolute, and the result
is absolute.
TABLE 3-5: INFIX OPERATORS
Operator Description Example
Arithmetic
*Multiplication 5 * 4 (=20)
/Division. Truncation is the same as the C operator ‘/’. 23 / 4 (=5)
%Remainder 30 % 4 (=2)
<< Shift Left. Same as the C operator ‘<<’ 2 << 1 (=4)
>> Shift Right. Same as the C operator ‘>>’ 2 >> 1 (=1)
Bit-Wise
&Bit-wise And 4 & 6 (=4)
^Bit-wise Exclusive Or 4 ^ 6 (=2)
!Bit-wise Or Not 0x1010 ! 0x5050
(=0xBFBF)
|Bit-wise Inclusive Or 2 | 4 (=6)
Simple Arithmetic
+Addition. If either argument is absolute, the result has the
section of the other argument. You may not add together
arguments from different sections.
4 + 10 (=14)
-Subtraction. If the right argument is absolute, the result
has the section of the left argument. If both arguments
are in the same section, the result is absolute. You may
not subtract arguments from different sections.
14 - 4 (=10)
Relational
== Equal to .if (x == y)
!= Not equal to (also <>).if (x != y)
<Less than .if (x < 5)
<= Less than or equal to .if (y <= 0)
>Greater than .if (x > a)
>= Greater than or equal to .if (x >= b)
Logical
&& Logical AND .if ((x > 1) &&
(x < 10))
|| Logical OR .if ((y != x)
|| (y < 100))
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3.10 SPECIAL OPERATORS
The assembler provides a set of special operators for each of the following actions:
• Obtaining the Size of a Specific Section
• Obtaining the Starting Address of a Specific Section
• Obtaining the End Address of a Specific Section
3.10.1 Obtaining the Size of a Specific Section
The .sizeof.(section_name) operator can be used to obtain the size in bytes of
a specific section after the link process has occurred. For example, to find the final size
of the .data section, use:
.word .sizeof.(.data)
3.10.2 Obtaining the Starting Address of a Specific Section
The .startof.(section_name) operator can be used to obtain the starting
address of a specific section after the link process has occurred. For example, to obtain
the starting address of the .data section, use:
.word .sizeof.(.data)
3.10.3 Obtaining the Ending Address of a Specific Section
The .endof.(section_name) operator can be used to obtain the ending address of a
specific section after the link process has occurred. For example, to obtain the starting
address of the .data section, use:
.word .sizeof.(.data)
TABLE 3-6: SPECIAL OPERATORS
Operators Description
.sizeof.(name)Get size of section name in address units
.startof.(name)Get starting address of section name
.endof.(name) Get ending address of section name
DD
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NOTES:
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 57
Chapter 4. Assembler Directives
4.1 INTRODUCTION
Directives are assembler commands that appear in the source code but are not usually
translated directly into opcodes. They are used to control the assembler: its input,
output, and data allocation.
While there are many significant similarities with directives supported by the 16-bit
MPLAB Assembler for PIC24 MCUs and dsPIC DSCs (xc16-as), there are many
differences in the directive set supported by the 32-bit MPLAB XC32 Assembler
(xc32-as).
Topics covered in this chapter are:
• Directives that Define Sections
• Directives that Initialize Constants
• Directives that Declare Symbols
• Directives that Define Symbols
• Directives that Modify Section Alignment
• Directives that Format the Output Listing
• Directives that Control Conditional Assembly
• Directives for Substitution/Expansion
• Directives that Include Other Files
• Directives that Control Diagnostic Output
• Directives for Debug Information
• Directives that Control Code Generation
Note: Assembler directives are not target instructions (ADD, XOR, JAL, etc). For
instruction set information, consult your target-device data sheet
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4.2 DIRECTIVES THAT DEFINE SECTIONS
Sections are locatable blocks of code or data that will occupy contiguous locations in
the 32-bit device memory. Three sections are pre-defined: .text for executable code,
.data for initialized data and .bss for uninitialized data. Other sections may be
defined; the linker defines several that are useful for locating data in specific areas of
32-bit memory.
Section directives are:
•.bss
•.data
•.pushsection name
•.popsection
•.section name [, “flags”] (deprecated)
• .section name [, attr1[,…,attrn]]
•.text
.bss
Definition
Assemble the following statements onto the end of the .bss (uninitialized data)
section.
The bss section is used for local common variable storage. You may allocate address
space in the bss section, but you may not dictate data to load into it before your pro-
gram executes. When your program starts running, all the contents of the bss section
are zeroed bytes.
Use the .bss directive to switch into the bss section and then define symbols as usual.
You may assemble only zero values into the section. Typically the section will contain
only symbol definitions and .skip directives
Example
# The following symbols (B1 and B2) will be placed in
# the uninitialized data section.
.bss
B1: .space 4 # 4 bytes reserved for B1
B2: .space 1 # 1 byte reserved for B2
.data
Definition
Assemble the following statements onto the end of the .data (initialized data) section.
Example
# The following symbols (D1 and D2) will be placed in
# the initialized data section.
.data
D1: .long 0x12345678 # 4 bytes
D2: .byte 0xFF # 1 byte
The linker collects initial values for section .data (and other sections defined with the
data attribute) and creates a data initialization template. This template can be pro-
cessed during application start-up to transfer initial values into memory. For C applica-
tions, a library function is called for this purpose automatically. Assembly projects can
utilize this library by linking with the libpic32 library. For more information, see the
discussion of Section 9.5.3 “Run-Time Library Support” in Initialized Data.
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.pushsection name
This directive pushes the current section onto the top of the section stack and then
replaces the current section with name. Every .pushsection should have a matching
.popsection.
.popsection
Replace the current section description with the top section on the section stack. This
section is popped off the stack.
.section name [, “flags”] (deprecated)
.section name [, attr1[,...,attrn]]
Assemble the following code into a section named name. If the character * is specified
for name, the assembler will generate a unique name for the section based on the input
file name in the format filename.s.scnn, where n represents the number of auto-
generated section names.
Sections named * can be used to conserve memory because the assembler will not
add alignment padding to these sections. Sections that are not named * may be com-
bined across several files, so the assembler must add padding in order to guarantee
the requested alignment.
If the optional argument is not present, the section attributes depend on the section
name. A table of reserved section names with implied attributes is given in Reserved
Section Names with Implied Attributes. If the section name matches a reserved name,
the implied attributes will be assigned to that section. If the section name is not recog-
nized as a reserved name, the default attribute will be data (initialized storage in data
memory).
Implied attributes for reserved section names other than [.text, .data, .bss] are
deprecated.
A warning will be issued if implied attributes for these reserved sections are used.
If the first optional argument is quoted, it is taken as one or more flags that describe the
section attributes. Quoted section flags are deprecated. (See Appendix
A. “Deprecated Features”). A warning will be issued if quoted section flags are used.
If the first optional argument is not quoted, it is taken as the first element of an attribute
list. Attributes may be specified in any order, and are case-insensitive. Two categories
of section attributes exist: attributes that represent section types, and attributes that
modify section types.
4.2.1 Attributes That Represent Section Types
Attributes that represent section types are mutually exclusive. At most, one of the attri-
butes listed below may be specified for a given section.
TABLE 4-1: ATTRIBUTES THAT REPRESENT SECTION TYPES
Attribute Description
code Executable code in program memory
data Initialized storage in data memory
bss Uninitialized storage in data memory
persist Persistent storage in data memory
ramfunc Function in data memory
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4.2.2 Attributes that Modify Section Types
Depending on the attribute, all or some section types may be modified by it, as below
Table Table 4-2 in word file
4.2.3 Combining Attributes that Modify Section Types
The following section names are available for user applications:
TABLE 4-2: ATTRIBUTES THAT MODIFY SECTION TYPES
Attribute Description
Attribute applies to:
code data bss persist ramfunc
address(a) Locate at absolute address a x x x x
near Locate in the first 64k of memory x x x
reverse Align the ending address +1 x x x
align(n) Align the starting address x x x x x
noload Allocate, do not load x x x x x
keep Keep section against garbage
collection
xxx x x
TABLE 4-3: COMBINING ATTRIBUTES THAT MODIFY SECTION TYPES
address near reverse align noload keep
address xx xx
near xxxxx
reverse xxx
align xx xx
noload xxx x x
keep xxx xx
TABLE 4-4: RESERVED SECTION NAMES
Section
Name Generated by Mapped in the
linker script to
Implied
Attributes
.text Compiler- or assembler generated instructions code
.text.* Functions when compiled with
-ffunction-sections are output to uniquely named sections of
this form
code
.startup C start-up code/ left in the linker script for backwards compatibility kseg0_boot_mem code
.app_excpt General-Exception handler kseg0_boot_mem code
.reset Reset handler kseg0_boot_mem code
.bev_excpt BEV-Exception handler kseg0_boot_mem code
.vector_n Interrupt Vector n kseg0_boot_mem code
.rodata Strings and C data declared const code
.rodata.* Constant data when compiled with -fdata-sections are output
to uniquely named sections of this form
code
.data Variables >n bytes (compiled -Gn) with an initial value. data
.data.* Large initialized variables compiled with -fdata-sections data
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Section Directive Examples
.section foo ;foo is initialized data memory.
.section bar,bss,align(256) ;bar is uninitialized data memory, aligned.
.section *,data,near ;section is near initialized data memory.
.section buf1,bss,address(0xa0000800);buf1 is uninitialized data memory at 0xa0000800.
.section *, code ;section is in program memory
.text
Definition
Assemble the following statements onto the end of the .text (executable code)
section.
Example
.text
.ent _main_entry
_main_entry:
jal main
nop
jal exit
nop
1:
b 1b
nop
.end _main_entry
.ramfunc RAM-functions data
.bss Uninitialized data bss
.lit4 /
.lit8
Constants (usually floating point) which the assembler decides to
store in memory rather than in the instruction stream. Used for
gp-relative addressing.
data
.sdata Variables <=n bytes (compiled -Gn) with an initial value. Used for
gp-relative addressing.
data
.sdata.* Small variables compiled with -fdata-sections. Used for
gp-relative addressing
data
.sbss Uninitialized variables <=n bytes (compiled -Gn). Used for
gp-relative addressing.
data
.sbss.* Small uninitialized variables compiled with -fdata-sections.
Used for gp-relative addressing.
data
.bss Uninitialized larger variables data
.bss.* Uninitialized variables compiled with -fdata-sections. data
.heap Heap used for dynamic memory data
.stack Minimum space reserved for stack data
.debug* DWARF debug information info
.line DWARF debug information info
.comment #ident/.ident strings info
.reginfo Information section info
TABLE 4-4: RESERVED SECTION NAMES (CONTINUED)
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4.3 DIRECTIVES THAT INITIALIZE CONSTANTS
Constant initialization directives are:
•.ascii “string1” [, ..., “stringn”]
•.asciz “string1” [, ..., “stringn”]
•.byte expr1[, ..., exprn]
•.double value1[, ..., valuen]
•.float value1[, ..., valuen]
•.single value1[, ..., valuen]
•.hword expr1[, ..., exprn]
•.int expr1[, ..., exprn]
•.long expr1[, ..., exprn]
•.short expr1[, ..., exprn]
•.string “str”
•.word expr1[, ..., exprn]
.ascii “string1” [, ..., “stringn”]
.ascii expects zero or more string literals separated by commas. It assembles each
string (with no automatic trailing zero byte) into consecutive addresses.
.asciz “string1” [, ..., “stringn”]
.asciz is just like .ascii, but each string is followed by a zero byte. The "z" in
.asciz stands for "zero". This directive is a synonym for .string.
.byte expr1[, ..., exprn]
.byte expects zero or more expressions, separated by commas. Each expression is
assembled into the next byte in the current section.
.double value1[, ..., valuen]
Assembles one or more double-precision (64-bit) floating-point constants into
consecutive addresses in little-endian format. Floating point numbers are in IEEE
format (see Section 3.4.1.2 “Floating-Point Numbers”).
The following statements are equivalent:
.double 12345.67
.double 1.234567e4
.double 1.234567e04
.double 1.234567e+04
.double 1.234567E4
.double 1.234567E04
.double 1.234567E+04
Alternatively, you can specify the hexadecimal encoding of a floating-point constant.
The following statements are equivalent and encode the value 12345.67 as a 64-bit
double-precision number:
.double 0e:40C81CD5C28F5C29
.double 0f:40C81CD5C28F5C29
.double 0d:40C81CD5C28F5C29
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.float value1[, ..., valuen]
Assembles one or more single-precision (32-bit) floating-point constants into
consecutive addresses in little-endian format. It has the same effect as .single.
Floating point numbers are in IEEE format (see Section 3.4.1.2 “Floating-Point
Numbers”).
The following statements are equivalent:
.float 12345.67
.float 1.234567e4
.float 1.234567e04
.float 1.234567e+04
.float 1.234567E4
.float 1.234567E04
.float 1.234567E+04
Alternatively, you can specify the hexadecimal encoding of a floating-point constant.
The following statements are equivalent and encode the value 12345.67 as a 32-bit
double-precision number:
.float 0e:4640E6AE
.float 0f:4640E6AE
.float 0d:4640E6AE
.single value1[, ..., valuen]
Assembles one or more single-precision (32-bit) floating-point constants into
consecutive addresses in little-endian format. This directive is a synonym for .float.
Floating point numbers are in IEEE format (see Section 3.4.1.2 “Floating-Point
Numbers”).
.hword expr1[, ..., exprn]
Assembles one or more 2-byte numbers into consecutive addresses in little-endian
format. This directive is a synonym for .short.
.int expr1[, ..., exprn]
Assembles one or more 4-byte numbers into consecutive addresses in little-endian
format. This directive is a synonym for .long.
.long expr1[, ..., exprn]
Assembles one or more 4-byte numbers into consecutive addresses in little-endian
format. This directive is a synonym for .int.
.short expr1[, ..., exprn]
Assembles one or more 2-byte numbers into consecutive addresses in little-endian
format. This directive is a synonym for .hword.
.string “str”
This directive is a synonym for .asciz.
.word expr1[, ..., exprn]
Assembles one or more 4-byte numbers into consecutive addresses in little-endian
format.
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4.4 DIRECTIVES THAT DECLARE SYMBOLS
Declare symbol directives are:
•.comm symbol, length [, algn]
•.extern symbol
•.global symbol .globl symbol
•.lcomm symbol, length
•.weak symbol
.comm symbol, length [, algn]
.comm declares a common symbol named symbol. When linking, a common symbol
in one object file may be merged with a defined or common symbol of the same name
in another object file. If the linker does not see a definition for the symbol - just one or
more common symbols - then it will allocate length bytes of uninitialized memory.
length must be an absolute expression. If the linker sees multiple common symbols
with the same name, and they do not all have the same size, it will allocate space using
the largest size.
The .comm directive takes an optional third argument. If algn is specified, it is the
desired alignment of the symbol, specified as a byte boundary (for example, an align-
ment of 16 means that the least significant 4 bits of the address should be zero). The
alignment must be an absolute expression, and it must be a power of two. If linker allo-
cates uninitialized memory for the common symbol, it will use the alignment when plac-
ing the symbol. If no alignment is specified, the assembler will set the alignment to the
largest power of two less than or equal to the size of the symbol, up to a maximum of 1.
.extern symbol
The .extern directive declares a symbol name that may be used in the current mod-
ule, but it is defined as global in a different module. However, all symbols are extern
by default so this directive is optional.
.global symbol
.globl symbol
The .global directive declares a symbol that is defined in the current module and is
available to other modules. .global makes the symbol visible to the linker. If you
define symbol in your partial program, its value is made available to other partial pro-
grams that are linked with it. Otherwise, symbol takes its attributes from a symbol of the
same name from another file linked into the same program.
Both spellings (.globl and .global) are accepted, for compatibility with other
assemblers.
.lcomm symbol, length
Reserve length bytes for a local common denoted by symbol. The section and value
of symbol are those of the new local common. The addresses are allocated in the .bss
section, so that at run-time, the bytes start off zeroed. symbol is not declared global
so it is normally not visible to the linker.
.weak symbol
Marks the symbol named symbol as weak. When a weak-defined symbol is linked with
a normal-defined symbol, the normal-defined symbol is used with no error. When a
weak-defined symbol is linked and the symbol is not defined, the value of the weak
symbol becomes zero with no error.
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4.5 DIRECTIVES THAT DEFINE SYMBOLS
Define symbol directives are:
•.equ symbol, expression
•.equiv symbol, expression
.equ symbol, expression
This directive sets the value of symbol to expression. You may set a symbol any
number of times in assembly. If you set a global symbol, the value stored in the object
file is the last value equated to it.
.equiv symbol, expression
Like .equ, except that the assembler will signal an error if symbol is already defined.
Note that a symbol which has been referenced but not actually defined is considered
to be undefined.
Except for the contents of the error message, this directive is roughly equivalent to:
.ifdef SYM
.err
.endif
.equ SYM,VAL
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4.6 DIRECTIVES THAT MODIFY SECTION ALIGNMENT
Directives that explicitly modify section alignment are listed below.
•.align [algn[, fill]]
•.fill repeat[, size[, value]]
•.org new-lc[, fill]
•.skip size[, fill]
•.space size[, fill]
•.struct expression
.align [algn[, fill]]
The .align directive pads the location counter (in the current subsection) to a partic-
ular storage boundary. The first expression (which must be absolute) is the alignment
required specified as the number of low-order zero bits the location counter must have
after advancement.
The assembler accepts algn values from 0 up to 15. A .align 0 turns off the auto-
matic alignment used by the data creating pseudo-ops. You must make sure that data
is properly aligned. Reinstate auto alignment with a .align pseudo instruction.
The second expression (also absolute) gives the fill value to be stored in the pad-
ding bytes. It (and the comma) may be omitted. If it is omitted, the padding bytes are
zero by default. You may wish to use 0xFF for FLASH regions of memory.
.fill repeat[, size[, value]]
Reserve repeat copies of size bytes. repeat may be zero or more. size may be zero
or more, but if it is more than 8, then it is deemed to have the value 8. The content of
each repeat bytes is taken from an 8-byte number. The highest order 4 bytes are zero.
The lowest order 4 bytes are value rendered in the little-endian byte-order. Each size
bytes in a repetition is taken from the lowest order size bytes of this number.
size is optional. If the first comma and following tokens are absent, size is assumed
to be 1.
value is optional. If the second comma and value are absent, value is assumed
zero.
Example:
.text
.fill 0x3, 1, 0xFF
.align 2
mylabel: b .
Note: User code must take care to properly align an instruction following a direc-
tive that modifies the section alignment or location counter.
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.org new-lc[, fill]
The .org directive advances the location counter of the current section to new-lc.
new-lc is either an absolute expression or an expression with the same section as the
current subsection. That is, you can't use .org to cross sections: if new-lc has the
wrong section, the .org directive is ignored. If the section of new-lc is absolute,
xc32-as issues a warning, then pretends the section of new-lc is the same as the
current subsection.
.org may only increase the location counter, or leave it unchanged; you cannot use
.org to move the location counter backwards.
Because the assembler tries to assemble programs in one pass, new-lc may not be
undefined.
Beware that the origin is relative to the start of the section, not to the start of the
subsection.
When the location counter (of the current subsection) is advanced, the intervening
bytes are filled with fill, which should be an absolute expression. If the comma and
fill are omitted, fill defaults to zero.
.skip size[, fill]
.space size[, fill]
These directives emit size bytes, each of value fill. Both size and fill are
absolute expressions. If the comma and fill are omitted, fill is assumed to be
zero.
.struct expression
Switch to the absolute section, and set the section offset to expression, which must
be an absolute expression. You might use this as follows:
.struct 0
field1:
.struct field1 + 4
field2:
.struct field2 + 4
field3:
This would define the symbol field1 to have the value 0, the symbol field2 to have
the value 4, and the symbol field3 to have the value 8. Assembly would be left in the
absolute section, and you would need to use a .section directive of some sort to
change to some other section before further assembly.
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4.7 DIRECTIVES THAT FORMAT THE OUTPUT LISTING
Output listing format directives are:
•.eject
•.list
•.nolist
•.psize lines[, columns]
•.sbttl “subheading”
•.title “heading”
.eject
Force a page break at this point when generating assembly listings.
.list
Controls (in conjunction with .nolist) whether assembly listings are generated. This
directive increments an internal counter (which is one initially). Assembly listings are
generated if this counter is greater than zero.
Only functional when listings are enabled with the -a command line option and forms
processing has not been disabled with the -an command line option.
.nolist
Controls (in conjunction with .list) whether assembly listings are generated. This
directive decrements an internal counter (which is one initially). Assembly listings are
generated if this counter is greater than zero.
Only functional when listings are enabled with the -a command line option and forms
processing has not been disabled with the -an command line option.
.psize lines[, columns]
Declares the number of lines, and optionally, the number of columns to use for each
page when generating listings.
If you do not use .psize, listings use a default line count of 60. You may omit the
comma and columns specification; the default width is 200 columns.
The assembler generates formfeeds whenever the specified number of lines is
exceeded (or whenever you explicitly request one, using .eject).
If you specify lines as 0, no formfeeds are generated save those explicitly specified with
.eject.
.sbttl “subheading”
Use subheading as a subtitle (third line, immediately after the title line) when generat-
ing assembly listings. This directive affects subsequent pages, as well as the current
page, if it appears within ten lines of the top.
.title “heading”
Use heading as the title (second line, immediately after the source file name and page
number) when generating assembly listings.
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4.8 DIRECTIVES THAT CONTROL CONDITIONAL ASSEMBLY
Conditional assembly directives are:
•.else
•.elseif expr
•.endif
•.if expr
.else
Used in conjunction with the .if directive to provide an alternative path of assembly
code should the .if evaluate to false.
.elseif expr
Used in conjunction with the .if directive to provide an alternative path of assembly
code should the .if evaluate to false and a second condition exists.
.endif
Marks the end of a block of code that is only assembled conditionally.
.if expr
Marks the beginning of a section of code that is only considered part of the source
program being assembled if the argument expr is non-zero. The end of the conditional
section of code must be marked by an .endif; optionally, you may include code for
the alternative condition, flagged by .else.
The assembler also supports the following variants of .if.
.ifdecl symbol
Assembles the following section of code if the specified symbol has been defined. Note
that a symbol which has been referenced, but not yet defined, is considered to be
undefined.
.ifc string1,string2
This directive assembles the following section of code if the two strings are the same.
The strings may be optionally quoted with single quotes. If they are not quoted, the first
string stops at the first comma, and the second string stops at the end of the line.
Strings which contain whitespace should be quoted. The string comparison is case
sensitive.
.ifeq absolute-expression
This directive assembles the following section of code if the argument is zero.
.ifeqs string1,string2
This directive is another form of .ifc. The strings must be quoted using double
quotes.
.ifge absolute-expression
This directive assembles the following section of code if the argument is greater than
or equal to zero.
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.ifgt absolute-expression
This directive assembles the following section of code if the argument is greater than
zero.
.ifle absolute-expression
This directive assembles the following section of code if the argument is less than or
equal to zero.
.iflt absolute-expression
This directive assembles the following section of code if the argument is less than zero.
.ifnc string1,string2
This directive is like .ifc, but the sense of the test is reversed: this assembles the
following section of code if the two strings are not the same.
.ifndef symbol
This directive assembles the following section of code if the specified symbol has not
been defined. Both spelling variants are equivalent. Note a symbol which has been
referenced but not yet defined is considered to be undefined.
.ifnotdef symbol
This directive is the same as .ifndef.
.ifne absolute-expression
This directive assembles the following section of code if the argument is not equal to
zero (in other words, this is equivalent to .if).
.ifnes string1,string2
This directive is like .ifeqs, but the sense of the test is reversed: this assembles the
following section of code if the two strings are not the same.
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4.9 DIRECTIVES FOR SUBSTITUTION/EXPANSION
Substitution/expansion directives are:
•.exitm
•.irp symbol, value1 [, ..., valuen] ... .endr
•.irpc symbol, value ... .endr
•.macro
.exitm
Exit early from the current macro definition. See .macro directive.
.irp symbol, value1
[, ..., valuen]
...
.endr
Evaluate a sequence of statements assigning different values to symbol. The
sequence of statements starts at the .irp directive, and is terminated by a .endr
directive. For each value, symbol is set to value, and the sequence of statements is
assembled. If no value is listed, the sequence of statements is assembled once, with
symbol set to the null string. To refer to symbol within the sequence of statements,
use \symbol.
For example, assembling
.irp reg,0,1,2,3
lw $a\reg, 1032+\reg($sp)
.endr
is equivalent to assembling
lw $a0,1032+0($sp)
lw $a1,1032+1($sp)
lw $a2,1032+2($sp)
lw $a3,1032+3($sp)
.irpc symbol, value
...
.endr
Evaluate a sequence of statements assigning different values to symbol. The
sequence of statements starts at the .irpc directive, and is terminated by an .endr
directive. For each character in value, symbol is set to the character, and the
sequence of statements is assembled. If no value is listed, the sequence of statements
is assembled once, with symbol set to the null string. To refer to symbol within the
sequence of statements, use \symbol.
For example, assembling
.irpc reg,0123
lw $a\reg, 1032+\reg($sp)
.endr
is equivalent to assembling
lw $a0,1032+0($sp)
lw $a1,1032+1($sp)
lw $a2,1032+2($sp)
lw $a3,1032+3($sp)
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.macro
The directives .macro and .endm allow you to define macros that generate assembly
output. For example, this definition specifies a macro SUM that puts a sequence of
numbers into memory:
.macro SUM from=0, to=5
.long \from
.if \+o-\from
SUM "(\from+1)", \+o
.endif
.endm
With that definition, 'SUM 0,5' is equivalent to this assembly input:
.long 0
.long 1
.long 2
.long 3
.long 4
.long 5
.macro macname
.macro macname macargs …
Begin the definition of a macro called macname. If your macro definition requires argu-
ments, specify their names after the macro name, separated by commas or spaces.
You can supply a default value for any macro argument by following the name with
=deflt. For example, these are all valid .macro statements:
•.macro comm
Begin the definition of a macro called comm, which takes no arguments.
•.macro plus1 p, p1
.macro plus1 p p1
Either statement begins the definition of a macro called plus1, which takes two
arguments; within the macro definition, write \p or \p1 to evaluate the arguments.
•.macro reserve_str p1=0 p2
Begin the definition of a macro called reserve_str, with two arguments. The
first argument has a default value, but not the second. After the definition is com-
plete, you can call the macro either as 'reserve_str a,b' (with \p1 evaluating
to a and \p2 evaluating to b), or as 'reserve_str ,b' (with \p1 evaluating as
the default, in this case '0', and \p2 evaluating to b).
When you call a macro, you can specify the argument values either by position, or by
keyword. For example, 'SUM 9,17' is equivalent to 'sum to=9, from=17'.
.endm
Mark the end of a macro definition.
.exitm
Exit early from the current macro definition.
Assembler Directives
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\@
The assembler maintains a counter of how many macros it has executed in this
pseudo-variable; you can copy that number to your output with \@, but only within a
macro definition. In the following example, a recursive macro is used to allocate an arbi-
trary number of labeled buffers
.macro make_buffers num,size
BUF\@: .space \size
.if (\num - 1)
make_buffers (\num - 1),\size
.endif
.endm
.bss
# create BUF0..BUF3, 16 bytes each
make_buffers 4,16
This example macro expands as shown in the following listing:
6 make_buffers (\num - 1),\size
7 .endif
8 .endm
9
10 .bss
11 # create BUF0..BUF3, 16 bytes each
12 make_buffers 4,16
12 > BUF0:.space 16
12 0000 > .space 16
12 > .if (4-1)
12 > make_buffers (4-1),16
12 >> BUF1:.space 16
12 0010 >> .space 16
12 >> .if ((4-1)-1)
12 >> make_buffers ((4-1)-1),16
12 >>> BUF2:.space 16
12 0020 >>> .space 16
12 >>> .if (((4-1)-1)-1)
12 >>> make_buffers (((4-1)-1)-1),16
12 >>>> BUF3:.space 16
12 0030 >>>> .space 16
12 >>>> .if ((((4-1)-1)-1)-1)
12 >>>> make_buffers ((((4-1)-1)-1)-1),16
12 >>>> .endif
12 >>> .endif
12 >> .endif
12 > .endif
.purgem "name"
Undefine the macro name, so that later uses of the string will not be expanded. See
.macro directive on the preceding page.
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.rept count ... .endr
Repeat the sequence of lines between the .rept directive and the next .endr
directive count times.
For example, assembling
.rept 3
.long 0
.endr
is equivalent to assembling
.long 0
.long 0
.long 0
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4.10 DIRECTIVES THAT INCLUDE OTHER FILES
Directives that include data from other files are:
•.incbin "file"[,skip[,count]]
•.include "file"
.incbin "file"[,skip[,count]]
The .incbin directive includes file verbatim at the current location. The file is
assumed to contain binary data. The search paths used can be specified with the -I
command-line option (see Chapter 2. “Assembler Command-Line Options”).
Quotation marks are required around file.
The skip argument skips a number of bytes from the start of the file. The count
argument indicates the maximum number of bytes to read. Note that the data is not
aligned in any way, so it is the user's responsibility to make sure that proper alignment
is provided both before and after the .incbin directive.
.include "file"
Provides a way to include supporting files at specified points in your source code. The
code is assembled as if it followed the point of the .include. When the end of the
included file is reached, assembly of the original file continues at the statement
following the .include.
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4.11 DIRECTIVES THAT CONTROL DIAGNOSTIC OUTPUT
Miscellaneous directives are:
•.abort
•.err
•.error "string"
•.fail expression
•.ident "comment"
•.print "string"
•.version "string"
•.warning "string"
.abort
Prints out the message “.abort detected. Abandoning ship.” and exits the program.
.err
If the assembler sees an .err directive, it will print an error message, and unless the
-Z option was used, it will not generate an object file. This directive can be used to
signal an error in conditionally compiled code.
.error "string"
Similar to .err, except that the specified string is printed.
.fail expression
Generates an error or a warning. If the value of the expression is 500 or more,
xc32-as will print a warning message. If the value is less than 500, as will print an
error message. The message will include the value of expression. This can
occasionally be useful inside complex nested macros or conditional assembly.
.ident "comment"
Appends comment to the section named .comment. This section is created if it does
not exist. The linker will ignore this section when allocating memory, but will combine
all.comment sections together, in link order.
.print "string"
Prints string on the standard output during assembly.
.version "string"
This directive creates a .note section and places into it an ELF formatted note of type
NT_VERSION. The note's name is set to string. .version is supported when the
output file format is ELF; otherwise, it is ignored.
.warning "string"
Similar to the directive .error, but emits a warning.
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4.12 DIRECTIVES FOR DEBUG INFORMATION
Debug information directives are:
•.ent function
•.end
•.file fileno "filename"
•.fmask mask, offset
•.frame framereg, frameoffset, retreg
•.loc fileno, lineno [columnno]
•.mask mask, offset
•.size name, expression
•.sleb128 expr1 [, ..., exprn]
•.type name, description
•.uleb128 expr1[,...,exprn]
.ent function
This directive marks the function symbol as a function similarly to the generic .type
directive.
.end
End program.
.file fileno "filename"
When emitting dwarf2 line-number information .file assigns filenames to the
.debug_line file name table. The fileno operand should be a unique positive inte-
ger to use as the index of the entry in the table. The filename operand is a C string
literal.
The detail of filename indices is exposed to the user because the filename table is
shared with the .debug_info section of the dwarf2 debugging information, and thus
the user must know the exact indices that table entries will have.
.fmask mask, offset
Not used for current PIC32 MCUs. Maintain mask 0x00000000 and offset 0.
.frame framereg, frameoffset, retreg
This directive describes the shape of the stack frame. The virtual frame pointer in use
is framereg; normally this is either $fp or $sp. The frame pointer is frameoffset
bytes below the canonical frame address (CFA), which is the value of the stack pointer
on entry to the function. The return address is initially located in retreg until it is saved
as indicated in .mask.
.loc fileno, lineno [columnno]
The object file's debugging information contains a line-number matrix that correlates an
assembly instruction to a line and column of source code. The .loc directive will add
a matrix row corresponding to the assembly instruction immediately following the direc-
tive. The fileno, lineno, and columnno will be applied to the debug state machine
before the row is added.
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.mask mask, offset
Indicate which of the integer registers are saved in the current function's stack frame.
mask is interpreted a bit mask in which bit n set indicates that register n is saved. The
registers are saved in a block located offset bytes from the canonical frame address
(CFA), which is the value of the stack pointer on entry to the function.
.size name, expression
This directive sets the size associated with a symbol name. The size in bytes is com-
puted from expression which can make use of label arithmetic. This directive is
typically used to set the size of function symbols.
.sleb128 expr1 [, ..., exprn]
sleb128 stands for “signed little endian base 128.” This is a compact, variable-length
representation of numbers used by the DWARF symbolic-debugging format.
.type name, description
This sets the type of symbol name to be either a function symbol or an object symbol.
There are five different syntaxes supported for the type description field, in order to
provide compatibility with various other assemblers. The syntaxes supported are:
.type <name>,#function
.type <name>,#object
.type <name>,@function
.type <name>,@object
.type <name>,%function
.type <name>,%object
.type <name>,"function"
.type <name>,"object"
.type <name> STT_FUNCTION
.type <name> STT_OBJECT
.uleb128 expr1[,...,exprn]
uleb128 stands for “unsigned little endian base 128.” This is a compact, variable-length
representation of numbers used by the DWARF symbolic-debugging format.
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4.13 DIRECTIVES THAT CONTROL CODE GENERATION
Directives controlling assembler code-generation behavior are:
•.set noat
•.set at
•.set noautoextend
•.set autoextend
•.set nomacro
•.set macro
•.set mips16e
•.set nomips16e
•.set noreorder
•.set reorder
.set noat
When synthesizing some address formats, the assembler may require a scratch regis-
ter. By default, the assembler will quietly use the at ($1) register, which is reserved as
an assembler temporary by convention. In some cases, the compiler should not use
that register. The .set noat directive prevents the assembler from quietly using that
register.
.set at
Allow the assembler to quietly use the at ($1) register.
.set noautoextend
By default, MIPS16 instructions are automatically extended to 32 bits when necessary.
The directive .set noautoextend will turn this off. When .set noautoextend is
in effect, any 32-bit instruction must be explicitly extended with the .e modifier (e.g.,
li.e $4,1000). The directive .set autoextend may be used to once again
automatically extend instructions when necessary.
.set autoextend
Enable auto-extension of MIPS16 instructions to 32 bits.
.set nomacro
The assembler supports synthesized instructions, an instruction mnemonic that syn-
thesizes into multiple machine instructions. For instance, the sleu instruction assem-
bles into an sltu instruction and an xori instruction. The .set nomacro directive
causes the assembler to emit a warning message when an instruction expands into
more than one machine instruction.
.set macro
Suppress warnings for synthesized instructions.
.set mips16e
Assemble with the MIPS16e ISA extension.
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.set nomips16e
Do not assemble with the MIPS16e ISA extension.
.set noreorder
By default, the assembler attempts to fill a branch or delay slot automatically by
reordering the instructions around it. This feature can be very useful.
Occasionally, you'll want to retain precise control over your instruction ordering. Use
the .set noreorder directive to tell the assembler to suppress this feature until it
encounters a .set reorder directive.
.set reorder
Allow the assembler to reorder instructions to fill a branch or delay slot.
.set micromips
Assemble with the microMIPS ISA mode.
.set nomicromips
Do not assemble with the microMIPS ISA mode.
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 81
Chapter 5. Assembler Errors/Warnings/Messages
5.1 INTRODUCTION
MPLAB Assembler for PIC32 MCUs (xc32-as) generates errors, warnings and mes-
sages. A descriptive list of the most common diagnostic messages from the assembler
is shown here.
Topics covered in this chapter are:
• Fatal Errors
• Errors
• Warnings
• Messages
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5.2 FATAL ERRORS
The following errors indicate that an internal error has occurred in the assembler.
Please contact Microchip Technology (http://support.microchip.com) for support if the
assembler generates any of the fatal errors listed below. Be sure to provide full details
about the source code and command-line options causing the error.
• Bad char = '%c'
• Bad defsym; format is --defsym name=value
• Bad return from bfd_install_relocation: %x
• Broken assembler. No assembly attempted.
• Can't allocate elf private section data: %s
• Can't continue
• Can't create group: %s
• Can't extend frag %u chars
• Can't open a bfd on stdout %s
• Can't start writing .mdebug section: %s
• Cannot write to output file
• Could not write .mdebug section: %s
• Dwarf2 is not supported for this object file format
• Emulations not handled in this configuration
• Error constructing %s pseudo-op table: %s
• Expr.c(operand): bad atof_generic return val %d
• Failed sanity check
• Failed to read instruction table %s\n
• Failed to set up debugging information: %s
• Index into stored_fixups[] out of bounds
• Inserting into symbol table failed: %s
• Internal: bad mips opcode (bits 0x%lx undefined): %s %s.
• Internal: bad mips opcode (mask error): %s %s.
• Internal: bad mips opcode (unknown extension operand type `+%c'): %s %s.
• Internal: bad mips opcode (unknown operand type `%c'): %s %s.
• Internal error, line %d, %s
• Internal error: unknown dwarf2 format
• Internal: can't hash `%s': %s
• Invalid abi -mabi=%s
• Invalid listing option `%c'
• Macros nested too deeply
• Missing emulation mode name
• Multiple emulation names specified
• No compiled in support for 64 bit object file
• No object file generated
• Rva not supported
• Rva without symbol
• Too many fixups
• Unrecognized emulation name `%s'
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5.3 ERRORS
The errors listed below usually indicate an error in the assembly source code or
command-line options passed to the assembler.
Symbol
.abort detected. Abandoning ship.
User error invoked with the .abort directive.
.else without matching .if
A .else directive was seen without a preceding .if directive.
.elseif after .else
A .elseif directive specified after a .else directive. Modify your code so that the
.elseif directive comes before the .else directive.
.elseif without matching .if
A .elseif directive was seen without a preceding .if directive.
.endfunc missing for previous .func
A .endfunc directive is missing for a previous .func directive.
.endif without .if
A .endif directive was seen without a preceding .if directive.
.err encountered.
User error invoked with the .err directive.
.Ifeqs syntax error
Two comma-separated, double-quoted strings were not passed as arguments to the
.ifeqs directive.
.Set pop with no .set push
Attempting to pop options off of an empty option stack. Use .set push before .set
pop.
.Size expression too complicated to fix up
The .size expression can be constant or use label subtraction.
A
A bignum with underscores may not have more than 8 hex digits in any word.
A bignum constant must not have more than 8 hex digits in a single word.
A bignum with underscores must have exactly 4 words.
A bignum constant using the underscore notation must have exactly four 8-hexdigit
parts.
Absolute sections are not supported.
This assembler does not support the absolute section command.
Alignment not a power of 2.
The alignment value must be a power of 2. Modify the alignment to be a power of 2.
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Alignment too large: 15. Assumed.
An alignment greater than 15 was requested. The assembler automatically continues
with a alignment value of 15.
Arg/static registers overlap.
A MIPS32 mode save/restore uses overlapping registers for args and statics.
Argument must be a string.
The argument to a .error or .warning directive must be a double-quoted string.
Attempt to allocate data in common section.
This directive attempts to allocate data to a section that isn't allocatable. Allocate the
data to another section instead.
Attempt to get value of unresolved symbol name
The assembler could not get the value of an unresolved symbol.
Attempt to set value of section symbol.
Assignments to section symbols are not legal.
B
Backward ref to unknown label label:
The referenced label is either not seen or not defined here.
Bad .common segment name
Could not determine an appropriate alignment value for a .comm symbol. A previously
seen .comm symbol may be incorrect.
Bad escaped character in string.
The string uses a non-standard backslash-escaped character.
Bad expression.
The expression type cannot be determined or an operand is not of the correct type for
the expression type.
Bad floating literal: %s.
The token could not be converted to a floating-point value.
Bad floating-point constant: exponent overflow.
The token could not be converted to a floating-point value because of exponent
overflow.
Bad floating-point constant: unknown error code=%d.
The token could not be converted to a floating-point value.
Bad format for ifc or ifnc.
The arguments to the ifc or ifnc directive are incorrect. They must be 2
comma-separated, double-quoted strings.
Bad or irreducible absolute expression.
The absolute expression had an unexpected operator type.
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Bad register expression.
The DWARF debugging directive has an invalid register expression.
Bignum invalid.
The bignum value specified in the expression is not valid.
C
Can't parse register list.
In MIPS32 mode, the register list is invalid.
Can't resolve value for symbol `%s'.
The assembler could not get a real value for the symbol.
Constant too large.
When sign extending a constant offset from a base register, the constant was too large.
Could not skip to num in file filename
The skip parameter to the .incbin directive was invalid for the given file.
D
Duplicate else.
Each .if directive can have only up to one corresponding .else directive.
E
End of file inside conditional.
The assembler identified a missing conditional-end directive. Terminate the conditional
before the end of the file.
End of macro inside conditional.
The assembler identified a missing macro-end directive. Terminate the macro before
the end of the file.
Expected address expression.
The expression was illegal, absent, or bignum but it should have been a constant
address.
Expected comma after %s.
The arguments for this directive must be separated by a comma.
Expected comma after name `%s' in .size directive.
The arguments for this directive must be separated by a comma.
Expected quoted string.
The argument should be a quoted string.
Expected simple number.
This argument must be a simple number.
Expected symbol name.
This argument must be a symbol name.
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Expression out of range.
The expression is out of range for the directive or instruction (e.g. 32-bit value when a
32-bit value is expected)
Expression too complex.
The expression should be a symbol or constant.
F
File not found: %s.
The file specified to a directive (such as .incbin) could not be opened as specified.
File number %ld already allocated.
The file number passed to a .file directive is already in use.
File number less than one.
The file number passed to a .file directive must be > 1.
Floating point number invalid.
The floating-point number is invalid.
G
Global symbols not supported in common sections.
External symbols are not supported in MRI common sections.
I
Ignoring attempt to redefine symbol name
The symbol being redefined by the .weakext directive has already been defined.
Improper insert size
The width of the field specified to an INS instruction was not valid for the shift position.
Improper extract size
The width of the field specified to an EXT instruction was not valid for the shift position.
Instruction insn requires absolute expression.
This instruction requires a constant expression.
Invalid astatic register list
The aregs field of a MIPS32e extended SAVE/RESTORE instruction specified an
invalid astatic register list.
Invalid arg register list.
The aregs field of a MIPS32e extended SAVE/RESTORE instruction specified an
invalid arg register list.
Invalid coprocessor 0 register number.
An invalid coprocessor 0 register number was passed to this instruction.
Invalid coprocessor sub-selection value (%ld), not in range 0-7.
The coprocessor sub-selection value must be in the range 0-7.
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Invalid frame size
The frame size is not valid and could not be encoded.
Invalid identifier for .ifdef.
The specified identifier is not a valid name. It must begin with a legal character.
Invalid register list.
In MIPS32 mode, the register list contained an invalid register.
Invalid segment %s.
Attempting to change the location counter in an invalid segment.
Invalid static register list.
The static register list should include only $s2-$s8
J
Jump to misaligned address (0x%lx).
The jump target address is not aligned.
Junk at end of line, first unrecognized character is char
There are extraneous characters after the expected input.
Junk at end of line, first unrecognized character valued 0xval
There are extraneous characters after the expected input.
L
Load/store address overflow (max 32 bits).
The load/store address is greater than 32 bits wide. Make sure that the label is correct.
Local label is not defined.
A referenced local label was never defined.
Lui expression not in range 0..65535.
The Load Upper Immediate expression should be within the 32-bit range.
N
New line in title.
The title heading string should be enclosed in double quotes.
No such section.
The section name specified in a .global directive does not exist. (e.g. .global foo
.myscn)
Non-constant expression in .elseif statement
The .elseif statement requires a constant expr expression. The argument of the
.elseif directive must be a constant value able to be resolved on the first pass of the
directive. Ensure that any .equ of a symbol used in this argument is located before the
directive. See Section 4.8 “Directives that Control Conditional Assembly” for
more details.
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Non-constant expression in .if statement.
The .if statement requires a constant expr expression. The argument of the .if
directive must be a constant value able to be resolved on the first pass of the directive.
Ensure that any .equ of a symbol used in this argument is located before the directive.
See Section 4.8 “Directives that Control Conditional Assembly” for more details.
`Noreorder' must be set before `nomacro'.
Set noreorder before setting nomacro.
Number (0x%lx) larger than 32 bits.
Loading a value greater than 32 bits wide into a register.
Number larger than 64 bits.
Loading a value greater than 64 bits wide into HI/LO registers.
O
Offset too large.
The offset must be within the signed-extended 32-bit range.
Opcode not supported on this processor.
The instruction opcode is not supported on PIC32 MCUs.
Operand overflow.
The operand is not within the allowed range for this instruction.
Operation combines symbols in different segments.
The left-hand side of the expression and the right-hand side of the expression are
located in two different sections. The assembler does not know how to handle this
expression.
R
Register value used as expression.
An expression's operator is a register rather than a valid operator.
Relocation reloc isn't supported by the current ABI.
This relocation isn't supported by the PIC32 little-endian ELF output format.
S
Seek to end of .incbin file failed `%s'.
Could not find the end of the file specified by .incbin
Skip (%ld) + count (%ld) larger than file size (%ld).
The .incbin skip value + count value is greater than the size of the file.
Store insn found in delay slot of noreorder code.
Consider moving the store in front of the branch and using a nop in the delay instead.
Symbol `%s' can not be both weak and common.
Both the .weak directive and .comm directive were used on the same symbol within
the same source file.
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Symbol name is already defined.
The symbol cannot be redefined.
Symbol definition loop encountered at `%s'.
The symbol could not be defined because a self-referential loop was encountered. A
symbol's definition cannot depend on its own value.
Syntax error in .startof. Or .sizeof.
The assembler found either .startof. or .sizeof., but did not find the beginning
parenthesis '(' or ending parenthesis ')'.
T
This string may not contain '\0'.
The string must be a valid C string and cannot contain '\0'.
Treating warnings as errors.
The assembler has been instruction to treat all warnings as errors with the
--fatal-warnings command-line option.
U
Unassigned file number num
The .loc directive specifies a file number that is not yet in use.
Unclosed '('.
An open '(' is unmatched with a closing ')'. Add the missing ')'.
Unexpected register in list.
In MIPS32 mode, an invalid register was used. Check the operands for this instruction.
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5.4 WARNINGS
The assembler generates warnings when an assumption is made so that the
assembler could continue assembling a flawed program. Warnings should not be
ignored. Each warning should be specifically looked at and corrected to ensure that the
assembler understands what was intended. Warning messages can sometimes point
out bugs in your program.
Symbol
.end directive missing or unknown symbol
The .end function debugging-info directive is missing or the associated symbol is not
defined. Make sure that the .end directive is placed appropriately after the .ent
directive.
.end directive without a preceding .ent directive.
The .end function debugging-info directive does not have an associated .ent directive
to mark the symbol as a function. Make sure that the .end directive is positioned
appropriately after a .ent directive.
.end not in text section
The .end function debugging-info directive must be in a section with executable code.
.end symbol does not match .ent symbol.
The .end function debugging-info directive's function argument does not match the
preceding .ent directive's function argument. Make sure that the .end directive is
positioned appropriately after its corresponding .ent directive.
.endr encountered without preceding .rept, .irc, or .irp
The .endr directive ends a .rept, .irc, or .irp sequence; however this .endr
directive does not have a preceding .rept, .irc, or .irp directive. Make sure that
the .endr directive is positioned correctly in your code.
.ent or .aent not in text section.
The .ent function debugging-info directive must be in a section containing executable
code.
.fail expr encountered
If the value of the your .fail expression is 500 or more, the assembler will print a
warning message. The message will include the value of expression.
.fill size clamped to 8
The .fill size value may be zero or more, but if it is more than 8, then it is deemed
to have the value 8.
.frame outside of .ent
The .frame directive describes the stack frame and therefore must be used within a
function.
.incbin count zero, ignoring filename
The .incbin count should be greater than zero. reading zero bytes from a file has no
effect.
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.mask/.fmask outside of .ent
The .mask/.fmask stack-frame information should be defined within a .ent function.
Make sure that the .mask/.fmask directive is positioned correctly within the source
code.
.popsection without corresponding .pushsection; ignored
The assembler cannot pop a section off of the section stack without pushing one onto
the stack first.
.previous without corresponding .section; ignored
There's no previous section swap with the current section. Make sure that the
.previous directive is positioned correctly within the source code.
.space repeat count is negative, ignored.
The .space size argument must be greater than 0.
.space repeat count is zero, ignored.
The .space size argument must be greater than 0.
A
Alignment negative: 0 assumed.
The .align alignment must be a non-negative power-of-two value. .align 0 turns off
the automatic alignment used by the data creating pseudo-ops.
Alignment too large: 15 assumed.
The .align alignment value is greater than 15. The valid range is [0,15].
D
Divide by zero.
DIV instruction with $zero register as RT.
Division by zero.
This expression attempts to divide by zero. Check the operands.
E
Extended instruction in delay slot.
A MIPS32e extended instruction may not be placed in a jump delay slot as it will cause
undefined behavior. Move the instruction out of the delay slot.
F
Floating point constant too large.
The hexadecimal encoding of a floating-point constant is too large. Make sure that your
floating-point value is encoded correctly in the 32-bit or 64-bit IEEE format.
I
Ignoring changed section attributes for name
If section attributes are specified the second time the assembler sees a particular sec-
tion, then they should be the same as the first time the assembler saw the section
attributes. The assembler assumes that the first set of section attributes was correct.
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Ignoring changed section entity size for name
The section entity size should be the same the second time the assembler sees a par-
ticular section. The assembler assumes that the section entity size the first time it saw
the section was correct.
Ignoring changed section type for name
The section type should be the same the second time the assembler sees a particular
section. The assembler assumes that the section type the first time it saw the section
was correct.
Ignoring incorrect section type for name
When switching to a special predefined section by name, the section's type should
match the predefined type. The assembler uses the predefined type for the section.
Immediate for %s not in range 0..1023 (%lu).
The debugger Break code was not in the valid range. Normal user code should not use
this instruction reserved for debugger use.
Improper shift amount (%lu).
The shift value for a shift instruction (e.g. SLL, SRA, SRL) is out of range.
Instruction sne: Instruction %s: result is always false.
The result of the condition tested by the SNE instruction is always false. (e.g. The s
operand is the zero register and t is a nonzero constant expression.)
Instruction seq: result is always true.
The result of the condition tested by the SEQ instruction is always false. (e.g. The s
operand is the zero register and t is the constant 0.)
Invalid merge entity size.
The section merge entity size must be non-negative.
Invalid number.
The constant was in an unrecognized format. Check the constant's prefix and radix.
J
Jump address range overflow (0x%lx).
The target address of the jump instruction is outside the 228-byte “page”.
L
Left operand is a bignum; integer 0 assumed.
The left operand in the expression is a bignum rather than an integer. The assembler
performs expression evaluation on only integers so it assumes integer 0 for this
operand.
Left operand is a float; integer 0 assumed.
The left operand in the expression is a float rather than an integer. The assembler
performs expression evaluation on only integers so it assumes integer 0 for this
operand.
Assembler Errors/Warnings/Messages
2013 Microchip Technology Inc. DS50002186A-page 93
Line numbers must be positive; line number %d rejected.
This directive accepts only positive integers for the line number.
M
Missing close quote; (assumed).
The single-character quote is not properly closed.
Missing operand; zero assumed.
An operand (probably the right-size operand) is missing in the expression. The
assembler assumes integer 0 and continues.
O
Operand overflow.
The constant expression used as in the (basereg+offset) operand accepts only 32-bit
signed constants.
R
Repeat < 0; .fill ignored.
The repeat argument to the .fill directive must be non-negative.
Right operand is a bignum; integer 0 assumed.
The right operand in the expression is a bignum rather than an integer. The assembler
performs expression evaluation on only integers so it assumes integer 0 for this
operand.
Right operand is a float; integer 0 assumed.
The right operand in the expression is a float rather than an integer. The assembler
performs expression evaluation on only integers so it assumes integer 0 for this
operand.
S
Setting incorrect section attributes for name
When setting section attributes on a special section, the section's attributes should
match those of the predefined type. The assembler uses the predefined type for the
section.
Setting incorrect section type for name
When setting section attributes on a special section, the section's attributes should
match those of the predefined type. The assembler uses the predefined type for the
section.
Size negative; .fill ignored.
The size argument to the .fill directive must be non-negative.
T
Tried to set unrecognized symbol: name
The symbol in the .set directive was not a recognized PIC32 MCU assembler symbol.
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DS50002186A-page 94 2013 Microchip Technology Inc.
Truncated file filename, num1 of num2 bytes read.
The number of bytes read from the .incbin file was fewer than the number specified
in the counts argument.
U
Unknown escape \escape in string; ignored.
The string contains an unrecognized backslash-escaped character. Check that the
character following the backslash is correct.
Used $at without .set noat.
This code is using the $at (assembler temporary) register, but the assembler may use
it when generating synthesized macro instruction. Use the .set noat directive to tell
the assembler not to quietly use this register
5.5 MESSAGES
The assembler generates messages when a non-critical assumption is made so that
the assembler could continue assembling a flawed program. Messages may be
ignored. However, messages can sometimes point out bugs in your program.
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 95
Part 2 – MPLAB XC32 Object Linker
Chapter 6. Linker Overview......................................................................................... 97
Chapter 7. Linker Command-Line Interface............................................................. 105
Chapter 8. Linker Scripts........................................................................................... 119
Chapter 9. Linker Processing ................................................................................... 147
Chapter 10. Linker Examples .................................................................................... 163
Chapter 11. Linker Errors/Warnings......................................................................... 167
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 96 2013 Microchip Technology Inc.
NOTES:
6‘ MICROCHIP V c Cumpner J, Assemb‘er Arcmver (Lmranam ¢ Linker Cummand Lme
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 97
Chapter 6. Linker Overview
6.1 INTRODUCTION
MPLAB XC32 Object Linker (xc32-ld) produces binary code from relocatable object
code and archives for the PIC32 MCU family of devices. The 32-bit linker is a Windows
console application that provides a platform for developing executable code. The linker
is a part of the GNU linker from the Free Software Foundation.
Topics covered in this chapter are:
• Linker and Other Development Tools
• Feature Set
• Input/Output Files
6.2 LINKER AND OTHER DEVELOPMENT TOOLS
The PIC32 linker translates object files from the PIC32 assembler, and archives files
from the PIC32 archiver/librarian, into an executable file. See Figure 6-1 for an
overview of the tools process flow.
FIGURE 6-1: TOOLS PROCESS FLOW
Object File Libraries
(*.a)
Assembler
Linker
C/C++ Source Files
(*.c, *.cpp)
C Compiler
Source Files (*.s)
Assembly Source
Files (*.S)
Object Files
(*.o)
Executable File
(*.elf)
Archiver (Librarian)
Command Line
Simulator
Compiler
Driver
Program
MPLAB® X IDE
Debug Tool
Linker Script
(*.ld)
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6.3 FEATURE SET
Notable features of the linker include:
• User-defined minimum stack allocation
• User-defined heap allocation
• Available for Windows
• Linker scripts for all current PIC32 devices
• Command-Line Interface
• Integrated component of MPLAB X IDE
6.4 INPUT/OUTPUT FILES
Linker input and output files are listed below.
TABLE 6-1: LINKER FILES
Unlike the Microchip MPLINK™ linker, the 32-bit linker does not generate absolute
listing files. The 32-bit linker is capable of creating a map file and a binary ELF file (that
may or may not contain debugging information). For text output similar to MPLINK's
listing file, run the ELF file through the xc32-objdump binary utility.
6.4.1 Object Files
Relocatable code produced by the assembler. The linker accepts the ELF object file
format.
6.4.2 Library Files
A collection of object files grouped together for convenience.
6.4.3 Linker Script File
Linker scripts, or command files:
• Instruct the linker where to locate sections
• Specify memory ranges for a given part
• Can be customized to locate user-defined sections at specific addresses
For more on linker script files, see Chapter 8. “Linker Scripts”.
Extension Description
Input
.o Object Files
.a Library Files
.ld Linker Script File
Output
.elf, .out Linker Output Files
.map Map File
Linker Overview
2013 Microchip Technology Inc. DS50002186A-page 99
EXAMPLE 6-1: LINKER SCRIPT
OUTPUT_FORMAT("elf32-tradlittlemips")
OUTPUT_ARCH(pic32mx)
ENTRY(_reset)
MEMORY
{
kseg0_program_mem(rx): ORIGIN=0x9D000000, LENGTH=0x8000
kseg0_boot_mem : ORIGIN=0x9FC00490, LENGTH=0x970
exception_mem : ORIGIN=0x9FC01000, LENGTH=0x1000
kseg1_boot_mem : ORIGIN=0xBFC00000, LENGTH=0x490
debug_exec_mem : ORIGIN=0xBFC02000, LENGTH=0xFF0
config3 : ORIGIN=0xBFC02FF0, LENGTH=0x4
config2 : ORIGIN=0xBFC02FF4, LENGTH=0x4
config1 : ORIGIN=0xBFC02FF8, LENGTH=0x4
config0 : ORIGIN=0xBFC02FFC, LENGTH=0x4
kseg1_data_mem (w!x): ORIGIN=0xA0000000, LENGTH=0x2000
sfrs : ORIGIN=0xBF800000, LENGTH=0x100000
}
SECTIONS
{
.text ORIGIN(kseg0_program_mem) :
{
_text_begin = . ;
*(.text .stub .text.* )
*(.mips16.fn.*)
*(.mips16.call.*)
_text_end = . ;
} >kseg0_program_mem =0
.data :
{
_data_begin = . ;
*(.data .data.* .gnu.linkonce.d.*)
KEEP (*(.gnu.linkonce.d.*personality*))
*(.data1)
} >kseg1_data_mem AT>kseg0_program_mem
.bss :
{
*(.dynbss)
*(.bss .bss.* )
*(COMMON)
. = ALIGN(32 / 8) ;
} >kseg1_data_mem
.stack ALIGN(4) :
{
. += _min_stack_size ;
} >kseg1_data_mem
}
Note: This simplified linker-script example is for illustrative purposes only; it is not
a complete, working, linker script.
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6.4.4 Linker Output Files
By default, the name of the linker output binary file is a.out. You can override the
default name by specifying the -o option on the command line. The MPLAB X IDE proj-
ect manager uses the -o option to name the output file projectname.elf, where
projectname is the name of your MPLAB X IDE project.
The format of the binary file is an Executable and Linking Format (ELF) file. The Exe-
cutable and Linking Format was originally developed and published by UNIX System
Laboratories (USL) as part of the Application Binary Interface (ABI). The ELF specifi-
cation is the result of the work of the Tool Interface Standards (TIS) Committee, an
association of members of the microcomputer industry formed to work toward
standardization of the software interfaces visible to development tools.
The debugging information within the ELF file is in the DWARF Debugging Information
format. Also a result of the work of the TIS Committee, the DWARF format uses a series
of debugging entries to define a low-level representation of a source program. A
DWARF consumer, such as MPLAB X IDE, can then use the representation to create
an accurate picture of the original source program
6.4.5 Map File
The map files produced by the linker consist of:
• Archive Member Table – lists the name of any members from archive files that are
included in the link.
• Memory Usage Report – shows the starting address and length of all output
sections in program memory and data memory. It also shows a percent utilization
of memory in the region.
• Memory Configuration – lists all of the memory regions defined for the link.
• Linker Script and Memory Map – shows modules, sections and symbols that are
included in the link as specified in the linker script.
• Outside Cross Reference Table (optional) - shows symbols, sorted by name. For
each symbol, a list of file names is given. If the symbol is defined, the first file
listed is the location of the definition. The remaining files listed contain references
to the symbol.
Linker Overview
2013 Microchip Technology Inc. DS50002186A-page 101
EXAMPLE 6-2: MAP FILE
Archive member included because of file (symbol)
size\libc.a(general-exception.o)
size/crt0.o (_general_exception_context)
size\libc.a(default-general-exception-handler.o)
size\libc.a(general-exception.o) (_general_exception_handler)
size\libc.a(default-bootstrap-exception-handler.o)
size/crt0.o (_bootstrap_exception_handler)
size\libc.a(default-on-reset.o)
size/crt0.o (_on_reset)
size\libc.a(default-on-bootstrap.o)
size/crt0.o (_on_bootstrap)
size\libc.a(default-nmi-handler.o)
size/crt0.o (_nmi_handler)
Microchip PIC32 Memory-Usage Report
kseg0 Program-Memory Usage
section address length (dec) Description
------- ---------- -------------- -----------
.text 0x9d000000 0x678 1656 Application's executable code
.rodata 0x9d000678 0x14 20 Read-only constant data
.data 0x9d00068c 0xf 244 Data-initialization template
.sdata 0x9d000780 0x4 4 Small data-initialization template
Total kseg0_program_mem used:
0x784 1924 0.4% of 0x80000
kseg0 Boot-Memory Usage
section address length (dec) Description
------- ---------- -------------- -----------
.startup 0x9fc00490 0x1e0 480 C startup code
Total kseg0_boot_mem used:
0x1e0 480 19.9% of 0x970
Exception-Memory Usage
section address length (dec) Description
------- ---------- -------------- -----------
.app_excpt 0x9fc01180 0x10 16 General-Exception handler
.vector_1 0x9fc01220 0x8 8 Interrupt Vector 1
Total exception_mem used :
0x18 24 0.6% of 0x1000
kseg1 Boot-Memory Usage
section address length (dec) Description
------- ---------- -------------- -----------
.reset 0xbfc00000 0x10 16 Reset handler
.bev_excpt 0xbfc00380 0x10 16 BEV-Exception handler
Total kseg1_boot_mem used :
0x20 32 2.7% of 0x490
-----------------------------------------------
Total Program Memory used :
0x99c 2460 0.5% of 0x81e00
-----------------------------------------------
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DS50002186A-page 102 2013 Microchip Technology Inc.
kseg1 Data-Memory Usage
section address length (dec) Description
------- ---------- -------------- -----------
.data 0xa0000000 0xf4 244 Initialized data
.sdata 0xa00000f4 0x4 4 Small initialized data
.sbss 0xa00000f8 0x4 4 Small uninitialized data
.bss 0xa00000fc 0x10c 268 Uninitialized data
.heap 0xa0000208 0x800 2048 Dynamic Memory heap
.stack 0xa0000a08 0x400 1024 Min space reserved for stack
Total kseg1_data_mem used :
0xe08 3592 11.0% of 0x8000
--------------------------------------------------------------
Total Data Memory used :
0xe08 3592 11.0% of 0x8000
--------------------------------------------------------------
Memory Configuration
Name Origin Length Attributes
kseg0_program_mem 0x9d000000 0x00080000 xr
kseg0_boot_mem 0x9fc00490 0x00000970
exception_mem 0x9fc01000 0x00001000
kseg1_boot_mem 0xbfc00000 0x00000490
config0 0xbfc02ffc 0x00000004
kseg1_data_mem 0xa0000000 0x00008000 w !x
sfrs 0xbf800000 0x00100000
*default* 0x00000000 0xffffffff
Linker script and memory map
LOAD size/crt0.o
0x00000800 _min_heap_size = 0x800
START GROUP
LOAD size\libc.a
LOAD size\libm.a
LOAD size\libmchp_peripheral_32MX360F512L.a
END GROUP
LOAD C:/xc32-Tools/bin/../lib/gcc/pic32mx/3.4.4/size\libgcc.a
0x00000400 PROVIDE (_min_stack_size, 0x400)
0x00000000 PROVIDE (_min_heap_size, 0x0)
LOAD ./proc/32MX360F512L\processor.o
0x00000001 PROVIDE (_vector_spacing, 0x1)
0x9fc01000 _ebase_address = 0x9fc01000
0xbfc00000 _RESET_ADDR = 0xbfc00000
0xbfc00380 _BEV_EXCPT_ADDR = 0xbfc00380
0x9fc01180 _GEN_EXCPT_ADDR = (_ebase_address + 0x180)
.reset 0xbfc00000 0x10
*(.reset)
.reset 0xbfc00000 0x10 size/crt0.o
0xbfc00000 _reset
.bev_excpt 0xbfc00380 0x10
*(.bev_handler)
.bev_handler 0xbfc00380 0x10 size/crt0.o
.vector_0 0x9fc01200 0x0
*(.vector_0)
.startup 0x9fc00490 0x1e0
*(.startup)
.startup 0x9fc00490 0x1e0 size/crt0.o
Linker Overview
2013 Microchip Technology Inc. DS50002186A-page 103
.text 0x9d000000 0x678
0x9d000000 _text_begin = .
*(.text .stub .text.* .gnu.linkonce.t.*)
.text 0x9d000000 0x18 size/crt0.o
.text 0x9d000018 0x110 intermediate\object.o
0x9d000089 testfunct
0x9d0000a0 main
0x9d000018 foo
.text 0x9d000128 0xc intermediate est.o
0x9d000128 mylabel
.text.general_exception
0x9d000134 0xd0 size\libc.a(general-exception.o)
0x9d000134 _general_exception_context
.text._general_exception_handler
0x9d0005bc 0x8 size\libc.a(default-general-exception-handler.o)
0x9d0005bc _general_exception_handler
.text._bootstrap_exception_handler
0x9d0005c4 0x8 size\libc.a(default-bootstrap-exception-handler.o)
0x9d0005c4 _bootstrap_exception_handler
.text._on_reset
0x9d0005cc 0x8 size\libc.a(default-on-reset.o)
0x9d0005cc _on_reset
.text._on_bootstrap
0x9d0005d4 0x8 size\libc.a(default-on-bootstrap.o)
0x9d0005d4 _on_bootstrap
.text 0x9d0005dc 0x18 size\libc.a(default-nmi-handler.o)
0x9d0005dc _nmi_handler
.sdata 0xa00000f4 0x4 load address 0x9d000780
0xa00000f4 _sdata_begin = .
.heap 0xa0000208 0x800
0xa0000208 _heap = .
0xa0000a08 . = (. + _min_heap_size)
*fill* 0xa0000208 0x800 00
.stack 0xa0000a08 0x400
0xa0000e08 . = (. + _min_stack_size)
*fill* 0xa0000a08 0x400 00
.ramfunc 0xa0001000 0x0 load address 0x9d000784
0xa0001000 _ramfunc_begin = .
*(.ramfunc .ramfunc.*)
0xa0001000 . = ALIGN (0x4)
0xa0008000 _stack =
(_ramfunc_length >0x0)?
(_ramfunc_begin - 0x4):0xa0008000
OUTPUT(test-2.elf elf32-tradlittlemips)
Cross Reference Table
Symbol File
PORTE ./proc/32MX360F512L\processor.o
size\libc.a(default-nmi-handler.o)
size\libc.a(general-exception.o)
intermediate/test.o
size/crt0.o
foo intermediate\cobject.o
main intermediate\cobject.o
size/crt0.o
mylabel intermediate\asmobject.o
funct intermediate\cobject.o
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DS50002186A-page 104 2013 Microchip Technology Inc.
NOTES:
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 105
Chapter 7. Linker Command-Line Interface
7.1 INTRODUCTION
MPLAB XC32 Object Linker (xc32-ld) may be used on the command line interface as
well as with MPLAB X IDE.
Topics covered in this chapter are:
• Linker Interface Syntax
• Compilation-Driver Linker Interface Syntax
• Options that Control Output File Creation
• Options that Control Run-time Initialization
• Options that Control Informational Output
• Options that Modify the Link Map Output
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 106 2013 Microchip Technology Inc.
7.2 LINKER INTERFACE SYNTAX
The linker supports a plethora of command-line options, but in actual practice few of
them are used in any particular context.
xc32-ld [options] file...
For instance, a frequent use of xc32-ld is to link object files and archives to produce
a binary file. To link a file hello.o:
xc32-ld -o output hello.o -lpic32
This tells xc32-ld to produce a file called output as the result of linking the file
hello.o with the archive libpic32.a.
When linking a C application, there are typically several archives (also known as “librar-
ies”) which are included in the link command. The list of archives may be specified
within --start-group, --end-group options to help resolve circular references:
xc32-ld -o output hello.o --start-group -lpic32 -lm -lc --end-group
The command-line options to xc32-ld may be specified in any order, and may be
repeated at will. Repeating most options with a different argument will either have no
further effect, or override prior occurrences (those further to the left on the command
line) of that option. Options that may be meaningfully specified more than once are
noted in the descriptions below.
Non-option arguments are object files that are to be linked together. They may follow,
precede or be mixed in with command-line options, except that an object file argument
may not be placed between an option and its argument.
Usually the linker is invoked with at least one object file, but you can specify other forms
of binary input files using -l and the script command language. If no binary input files
are specified, the linker does not produce any output, and issues the message ‘No
input files’.
If the linker cannot recognize the format of an object file, it will assume that it is a linker
script. A script specified in this way augments the main linker script used for the link
(either the default linker script or the one specified by using -T). This feature permits
the linker to link against a file that appears to be an object or an archive, but actually
merely defines some symbol values, or uses INPUT or GROUP to load other objects.
For options whose names are a single letter, option arguments must either follow the
option letter without intervening white space, or be given as separate arguments
immediately following the option that requires them.
For options whose names are multiple letters, either one dash or two can precede the
option name; for example, -trace-symbol and --trace-symbol are equivalent.
There is one exception to this rule. Multiple-letter options that begin with the letter o can
only be preceded by two dashes.
Arguments to multiple-letter options must either be separated from the option name
by an equals sign, or be given as separate arguments immediately following the
option that requires them. For example, --trace-symbol srec and
--trace-symbol=srec are equivalent. Unique abbreviations of the names of
multiple-letter options are accepted.
Note: command-line options are case sensitive.
Linker Command-Line Interface
2013 Microchip Technology Inc. DS50002186A-page 107
7.3 COMPILATION-DRIVER LINKER INTERFACE SYNTAX
In practice, the linker is usually invoked via xc32-gcc, the compilation driver. The basic
form of the compilation-driver command line is:
xc32-gcc [options] files
To pass a linker option from the compilation driver to the linker, use the -Wl,option
option.
EXAMPLE 7-1: COMPILATION-DRIVER COMMAND LINE
xc32-gcc -mprocessor=32MX360F512L "input.o" -o"output.elf"
-Os -Wl,--defsym=_min_heap_size=2048,-Map="mapfile.map",
--cref,--report-mem
Calling the linker via the compilation driver has a few advantages over calling the linker
directly.
• The driver's -mprocessor option allows the driver to pass the correct
device-specific include-file and library search paths to the linker. For instance,
when specifying -mprocessor=32MX360F512L, the driver passes the
corresponding device-specific library search path,
pic32mx/lib/proc/32MX360F512L, to the linker. This path allows the linker to
find the correct default linker script and processor library for the target device.
• The driver accepts the C compiler's optimization, ISA mode, and floating-point
support options required to select the appropriate multilib permutation. For exam-
ple, when passing the -Os size optimization option, the driver passes
pic32mx/lib/size as a library search path so that the linker uses the
pre-compiled libraries optimized for size. See the “MPLAB XC32 C/C++ Compiler
User’s Guide” (DS51686) for more information on the C compiler's multilib
feature.
Note: Command-line options and filename extensions are case sensitive.
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DS50002186A-page 108 2013 Microchip Technology Inc.
7.4 OPTIONS THAT CONTROL OUTPUT FILE CREATION
Output file creation options are:
•-( archives -), --start-group archives, --end-group
•-d, -dc, -dp
•--defsym sym=expr
•--discard-all (-x)
•--discard-locals (-X)
• --fill=option
•--gc-sections
•--library name (-l name)
•--library-path <dir> (-L <dir>)
•-nodefaultlibs
•-nostartfiles
•-nostdlib
•--output file (-o file)
•--p PROC
•--relocatable (-r, -i, -Ur)
•--retain-symbols-file file
•--section-start sectionname=org
•--script file (-T file)
•--strip-all (-s)
•--strip-debug (-S)
•-Tbss address
•-Tdata address
•-Ttext address
•--undefined symbol (-u symbol)
•--no-undefined
•--wrap symbol
7.4.1 -( archives -), --start-group archives,
--end-group
Start and end a group.
The archives should be a list of archive files. They may be either explicit file names, or
-l options. The specified archives are searched repeatedly until no new undefined
references are created. Normally, an archive is searched only once in the order that it
is specified on the command line. If a symbol in that archive is needed to resolve an
undefined symbol referred to by an object in an archive that appears later on the
command line, the linker would not be able to resolve that reference. By grouping the
archives, they will all be searched repeatedly until all possible references are resolved.
Using this option has a significant performance cost. It is best to use it only when there
are unavoidable circular references between two or more archives.
7.4.2 -d, -dc, -dp
Force common symbols to be defined.
Assign space to common symbols even if a relocatable output file is specified (with -r).
The script command FORCE_COMMON_ALLOCATION has the same effect.
Linker Command-Line Interface
2013 Microchip Technology Inc. DS50002186A-page 109
7.4.3 --defsym sym=expr
Define a symbol.
Create a global symbol in the output file, containing the absolute address given by
expr. You may use this option as many times as necessary to define multiple symbols
in the command line. A limited form of arithmetic is supported for the expr in this
context: you may give a hexadecimal constant or the name of an existing symbol, or
use + and - to add or subtract hexadecimal constants or symbols.
7.4.4 --discard-all (-x)
Discard all local symbols.
7.4.5 --discard-locals (-X)
Discard temporary local symbols.
7.4.6 --fill=option
--fill=option
Fill unused program memory. The format is:
--fill=[wn:]expression[@address[:end_address] | unused]
address and end_address will specify the range of program memory addresses to fill.
If end_address is not provided, then the expression will be written to the specific mem-
ory location at address address. The optional literal value unused may be specified to
indicate that all unused memory will be filled. If none of the location parameters are pro-
vided, all unused memory will be filled. expression will describe how to fill the specified
memory. The following options are available:
Single value:
xc32-ld --fill=0x12345678@unused
Range of values:
xc32-ld --fill=1,2,3,4,097@0x9d000650:0x9d000750
Incrementing value:
xc32-ld --fill=7+=711@unused
By default, the linker will fill using data that is instruction-word length. For 32-bit
devices, the default fill width is 32 bits. However, you may specify the value width using
[wn:], where n is the fill value's width and n belongs to [1, 2, 4, 8]. Multiple fill options
may be specified on the command line; the linker will always process fill options at
specific locations first.
7.4.7 --gc-sections
Enable garbage collection of unused input sections. This option is not compatible with
-r. The default behavior (of not performing this garbage collection) can be restored by
specifying --no-gc-sections on the command line.
When link-time garbage collection is in use, marking sections that should not be elimi-
nated is often useful. Mark the section by surrounding an input section's wildcard entry
with KEEP(), as in KEEP(*(.init)) or KEEP(SORT_BY_NAME(*)(.ctors)).
Note: There should be no white space between sym, the equals sign (“=”) and
expr.
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7.4.8 --library name (-l name)
Search for library name.
Add archive file name to the list of files to link. This option may be used any number of
times. xc32-ld will search its path-list for occurrences of libname.a for every name
specified. The linker will search an archive only once, at the location where it is speci-
fied on the command line. If the archive defines a symbol that was undefined in some
object that appeared before the archive on the command line, the linker will include the
appropriate file(s) from the archive. However, an undefined symbol in an object appear-
ing later on the command line will not cause the linker to search the archive again. See
the -( option for a way to force the linker to search archives multiple times. You may
list the same archive multiple times on the command line.
If the format of the archive file is not recognized, the linker will ignore it. Therefore, a
version mismatch between libraries and the linker may result in “undefined symbol”
errors.
7.4.9 --library-path <dir> (-L <dir>)
Add <dir> to library search path.
Add path <dir> to the list of paths that xc32-ld will search for archive libraries and
xc32-ld control scripts. You may use this option any number of times. The directories
are searched in the order in which they are specified on the command line. All -L
options apply to all -l options, regardless of the order in which the options appear. The
library paths can also be specified in a link script with the SEARCH_DIR command.
Directories specified this way are searched at the point in which the linker script
appears in the command line.
7.4.10 -nodefaultlibs
Do not use the standard system libraries when linking. Only the libraries you specify
are passed to the linker. The compiler may generate calls to memcmp, memset and
memcpy. These entries are usually resolved by entries in the standard compiler librar-
ies. These entry points should be supplied through some other mechanism when this
option is specified.
7.4.11 -nostartfiles
Do not pass the default prebuilt C startup file (pic32mx/lib/crt0.o) to the linker.
You will provide your own version of the startup code for the application.
7.4.12 -nostdlib
Do not use the standard system startup files or libraries when linking. No startup files
and only the libraries you specify are passed to the linker. The compiler may generate
calls to memcmp, memset and memcpy. These entries are usually resolved by entries
in standard compiler libraries. These entry points should be supplied through some
other mechanism when this option is specified.
7.4.13 --output file (-o file)
Set output ELF file name.
Use file as the name for the program produced by xc32-ld; if this option is not
specified, the name a.out is used by default.
7.4.14 --p PROC
Specify the target processor (e.g., 32MX795F512L).
Specify a target processor for the link.
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7.4.15 --relocatable (-r, -i, -Ur)
Generate relocatable output.
I.e., generate an output file that can in turn serve as input to xc32-ld. This is often
called partial linking. If this option is not specified, an absolute file is produced.
7.4.16 --retain-symbols-file file
Keep only symbols listed in file.
Retain only the symbols listed in the file file, discarding all others. file is simply a
flat file, with one symbol name per line. This option is especially useful in environments
where a large global symbol table is accumulated gradually, to conserve run-time
memory. --retain-symbols-file does not discard undefined symbols, or symbols
needed for relocations. You may only specify --retain-symbols-file once in the
command line. It overrides -s and -S.
7.4.17 --section-start sectionname=org
Locate a section in the output file at the absolute address given by org. You may use
this option as many times as necessary to locate multiple sections in the command line.
org must be a single hexadecimal integer; for compatibility with other linkers, you may
omit the leading ‘0x’ that is usually associated with hexadecimal values.
7.4.18 --script file (-T file)
Read linker script.
Read link commands from the file file. These commands replace xc32-ld’s default
link script (rather than adding to it), so file must specify everything necessary to
describe the target format. If file does not exist, xc32-ld looks for it in the directories
specified by any preceding -L options. Multiple -T options accumulate.
7.4.19 --strip-all (-s)
Strip all symbols. Omit all symbol information from the output file.
7.4.20 --strip-debug (-S)
Strip debugging symbols. Omit debugger symbol information (but not all symbols) from
the output file.
7.4.21 -Tbss address
Set address of .bss section.
Use address as the starting address for the bss segment of the output file. address
must be a single hexadecimal integer; for compatibility with other linkers, you may omit
the leading ‘0x’ that is usually associated with hexadecimal values.
Normally the address of this section is specified in a linker script.
7.4.22 -Tdata address
Set address of .data section.
Use address as the starting address for the data segment of the output file. address
must be a single hexadecimal integer; for compatibility with other linkers, you may omit
the leading ‘0x’ that is usually associated with hexadecimal values.
Normally the address of this section is specified in a linker script.
Note: There should be no white space between sectionname, the equals sign
(=), and org.
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7.4.23 -Ttext address
Set address of .text section.
Use address as the starting address for the text segment of the output file. address
must be a single hexadecimal integer; for compatibility with other linkers, you may omit
the leading ‘0x’ that is usually associated with hexadecimal values.
Normally the address of this section is specified in a linker script.
7.4.24 --undefined symbol (-u symbol)
Start with undefined reference to symbol.
Force symbol to be entered in the output file as an undefined symbol. Doing this may,
for example, trigger linking of additional modules from standard libraries. -u may be
repeated with different option arguments to enter additional undefined symbols.
7.4.25 --no-undefined
Allow no undefined symbols.
7.4.26 --wrap symbol
Use wrapper functions for symbol
Use a wrapper function for symbol. Any undefined reference to symbol will be resolved
to __wrap_symbol. Any undefined reference to __real_symbol will be resolved to
symbol. This can be used to provide a wrapper for a system function. The wrapper
function should be called __wrap_symbol. If it wishes to call the system function, it
should call __real_symbol.
Here is a trivial example:
void *
__wrap_malloc (int c)
{
printf ("malloc called with %ld\n", c);
return __real_malloc (c);
}
If you link other code with this file using --wrap malloc, then all calls to malloc will
call the function __wrap_malloc instead. The call to __real_malloc in
__wrap_malloc will call the real malloc function. You may wish to provide a
__real_malloc function as well, so that links without the --wrap option will
succeed. If you do this, you should not put the definition of __real_malloc in the
same file as __wrap_malloc; if you do, the assembler may resolve the call before the
linker has a chance to wrap it to malloc.
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7.5 OPTIONS THAT CONTROL RUN-TIME INITIALIZATION
Run-time initialization options are:
•--data-init
•--no-data-init
•--defsym=_min_stack_size=size
•--defsym=_min_heap_size=size
7.5.1 --data-init
Support initialized data. (This is the default.)
Create a special output section named .dinit as a template for the run-time initializa-
tion of data. The C start-up module in libpic32.a interprets this template and copies ini-
tial data values into initialized data sections. Other data sections (such as .bss) are
cleared before the main() function is called. Note that the persistent data section
(.pbss) is not affected by this option.
The
7.5.2 --no-data-init
Do not support initialized data.
Suppress the template which is normally created to support run-time initialization of
data. When this option is specified, the linker will select a shorter form of the C start-up
module in libpic32.a. If the application includes data sections which require initializa-
tion, a warning message will be generated and the initial data values discarded.
Storage for the data sections will be allocated as usual.
7.5.3 --defsym=_min_stack_size=size
The default linker script provides a minimum stack size of 1024 bytes. Use the
--defsym option to define the _min_stack_size symbol to change this default
size value. Note that the actual effective stack size may be larger than the minimum
size.
xc32-gcc foo.c -Wl,--defsym=_min_stack_size=1536
7.5.4 --defsym=_min_heap_size=size
The default linker script provides a heap size of 0 bytes. Use the --defsym option to
define the _min_heap_size symbol to change this default size value. The linker creates
a heap with a size defined by this value.
xc32-gcc foo.c -Wl,--defsym=_min_heap_size=2048
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7.6 OPTIONS THAT CONTROL MULTILIB LIBRARY SELECTION
Multilibs are a set of prebuilt target libraries. Each target library in the multilib gets built
with a different set of compiler options. Multilibs provide the linker with the capability to
match a target library with the compiler options used to build an application. The pre-
built target libraries represent the most common combinations of compiler options.
When the compilation driver is called to link an application, the driver chooses the ver-
sion of the target library that corresponds to the application options. These options
should be passed to the compilation driver, not the linker proper. The compilation driver
then translates the options to the appropriate -L library search path when calling the
linker.Size versus speed (-Os vs. -O3)
Select either -Os to optimize for size or -O0 through -O3 to optimize for speed.
-O0
Select the unoptimized multilib target-library permutation. (This is the default for the
command-line interface, but MPLAB X IDE's project manager may pass one of the
other optimization options by default.)
-O1
Select the multilib target-library permutation built with optimization level 1.
-O2
Select the multilib target-library permutation built with optimization level 2. This optimi-
zation level provides a good balance between execution speed and code size. This
multilib optimization level is a good choice for most applications.
-O3
Select the multilib target-library permutation built with optimization level 3. This
optimization maximizes execution speed.
-Os
Select the multilib target-library permutation built optimized for code size, for example:
xc32-gcc foo.o -Os -o project.elf
7.6.1 Instruction Set Mode (MIPS32/MIPS16E/microMIPS
Selects multilib permutation based on -mips16 or -mmicromips or -mips32r2, for
example:
xc32-gcc foo.o -O3 -mips16 -o project.elf
7.6.2 Software floating-point versus no floating-point support
The no-float library permutations typically have significantly less overhead than the
floating-point library permutations. If your application does not require floating-point
support, use this option.
-mno-float
Selects the multilib target-library permutation that does not support software
floating-point operations.
Example:
xc32-gcc foo.o -Os -mno-mips16 -mno-float -o project.elf
-msoft-float
Selects the multilib-target-library permutation with full software floating-point support.
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7.7 OPTIONS THAT CONTROL INFORMATIONAL OUTPUT
Information output options are:
•--check-sections
•--no-check-sections
•--help
•--no-warn-mismatch
•--report-mem
•--trace (-t)
•--trace-symbol symbol (-y symbol)
•-V
•--verbose
•--version (-v)
•--warn-common
•--warn-once
•--warn-section-align
7.7.1 --check-sections
Check section addresses for overlaps. (This is the default.) Normally the linker will
perform this check, and it will produce a suitable error message if it finds an overlap.
7.7.2 --no-check-sections
Do not check section addresses for overlaps. Use for diagnosing memory allocation
issues only.
7.7.3 --help
Print option help.
Print a summary of the command-line options on the standard output and exit.
7.7.4 --no-warn-mismatch
Do not warn about mismatched input files.
Normally xc32-ld will give an error if you try to link together input files that are
mismatched for some reason, perhaps because they have been compiled for different
processors or for different endiannesses. This option tells xc32-ld that it should
silently permit such possible errors. This option should only be used with care, in cases
when you have taken some special action that ensures that the linker errors are
inappropriate.
7.7.5 --report-mem
Print a memory usage report.
Print a summary of memory usage to standard output during the link. This report also
appears in the link map.
7.7.6 --trace (-t)
Trace file.
Print the names of the input files as xc32-ld processes them.
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7.7.7 --trace-symbol symbol (-y symbol)
Trace mentions of symbol.
Print the name of each linked file in which symbol appears. This option may be given
any number of times. This option is useful when you have an undefined symbol in your
link but do not know where the reference is coming from.
7.7.8 -V
Print version and other information.
7.7.9 --verbose
Output lots of information during link.
Display the version number for xc32-ld. Display the input files that can and cannot be
opened. Display the linker script if using a default built-in script.
7.7.10 --version (-v)
Print version information.
7.7.11 --warn-common
Warn about duplicate common symbols.
Warn when a common symbol is combined with another common symbol or with a
symbol definition. This option allows you to find potential problems from combining
global symbols. There are three kinds of global symbols, illustrated here by C
examples:
int i = 1;
A definition, which goes in the initialized data section of the output file.
extern int i;
An undefined reference, which does not allocate space. There must be either a
definition or a common symbol for the variable somewhere.
int i;
A common symbol. If there are only (one or more) common symbols for a variable, it
goes in the uninitialized data area of the output file.
The linker merges multiple common symbols for the same variable into a single
symbol. If they are of different sizes, it picks the largest size. The linker turns a common
symbol into a declaration, if there is a definition of the same variable.
The --warn-common option can produce five kinds of warnings. Each warning
consists of a pair of lines: the first describes the symbol just encountered, and the
second describes the previous symbol encountered with the same name. One or both
of the two symbols will be a common symbol.
Turning a common symbol into a reference, because there is already a definition for the
symbol.
file(section): warning: common of ‘symbol’ overridden by definition
file(section): warning: defined here
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Turning a common symbol into a reference, because a later definition for the symbol is
encountered. This is the same as the previous case, except that the symbols are
encountered in a different order.
file(section): warning: definition of ‘symbol’ overriding common
file(section): warning: common is here
Merging a common symbol with a previous same-sized common symbol.
file(section): warning: multiple common of ‘symbol’
file(section): warning: previous common is here
Merging a common symbol with a previous larger common symbol.
file(section): warning: common of ‘symbol’ overridden by larger common
file(section): warning: larger common is here
Merging a common symbol with a previous smaller common symbol. This is the same
as the previous case, except that the symbols are encountered in a different order.
file(section): warning: common of ‘symbol’ overriding smaller common
file(section): warning: smaller common is here
7.7.12 --warn-once
Warn only once for each undefined symbol, rather than once per module that refers to
it.
7.7.13 --warn-section-align
Note that section-alignment gaps are normal. This option helps you identify ways to
minimize gaps.
Warn if start of section changes due to alignment. This means a gap has been intro-
duced into the (normally sequential) allocation of memory. Typically, an input section
will set the alignment. The address will only be changed if it is not explicitly specified;
that is, if the SECTIONS command does not specify a start address for the section.
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7.8 OPTIONS THAT MODIFY THE LINK MAP OUTPUT
Link map output modifying options are:
•--cref
•--print-map (-M)
•-Map file
7.8.1 --cref
Output cross reference table.
If a linker map file is being generated, the cross-reference table is printed to the map
file. Otherwise, it is printed on the standard output. The format of the table is intention-
ally simple, so that a script may easily process it if necessary. The symbols are printed
out, sorted by name. For each symbol, a list of file names is given. If the symbol is
defined, the first file listed is the location of the definition. The remaining files contain
references to the symbol.
7.8.2 --print-map (-M)
Print map file on standard output. A link map provides information about the link,
including the following:
• Where object files and symbols are mapped into memory.
• How common symbols are allocated.
• All archive members included in the link, with a mention of the symbol which
caused the archive member to be brought in.
7.8.3 -Map file
Write a map file.
Print a link map to the file file. See the description of the --print-map (-M)
option.
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
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Chapter 8. Linker Scripts
8.1 INTRODUCTION
Linker scripts are used to control MPLAB XC32 Object Linker (xc32-ld) functions. By
default, the linker uses a built-in linker script with a device-specific include file. How-
ever, you can also customize your linker script for specialized control of the linker in
your application.
Topics covered in this chapter are:
• Overview of Linker Scripts
• Command Line Information
• Default Linker Script
• Adding a Custom Linker Script to an MPLAB X IDE Project
• Linker Script Command Language
• Expressions in Linker Scripts
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8.2 OVERVIEW OF LINKER SCRIPTS
Linker scripts control all aspects of the link process, including:
• allocation of data memory and program memory
• mapping of sections from input files into the output file
• construction of special data structures (such as interrupt vector tables)
Linker scripts are text files that contain a series of commands. Each command is either
a keyword, possibly followed by arguments, or an assignment to a symbol.
8.3 COMMAND LINE INFORMATION
Linker scripts are specified on the command line using either the -T option or the
--script option (see Section 7.4 “Options that Control Output File Creation”):
xc32-ld -o output.elf input.o --script mylinkerscript.ld
If the linker is invoked through xc32-gcc, add the -Wl, prefix to allow the option to be
passed to the linker:
xc32-gcc -o output.elf input.o -Wl,--script,mylinkerscript.ld
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8.4 DEFAULT LINKER SCRIPT
For PIC32MX Devices Only:
If no linker script is specified on the command line, the linker will use an internal version
known as the built-in default linker script. The default linker script has section mapping
that is appropriate for all PIC32 MCUs. It uses an INCLUDE directive to include the
device-specific memory regions.
The default linker script is appropriate for most PIC32 MCU applications. Only applica-
tions with specific memory-allocation needs will require an application-specific linker
script. The default linker script can be examined by invoking the linker with the
--verbose option:
xc32-ld --verbose
In a normal tool-suite installation, a copy of the default linker script is located at
\pic32mx\lib\ldscripts\elf32pic32mx.x. Note that this file is only a copy of
the default linker script. The script that the linker uses is internal to the linker.
The device-specific portion of the linker script is located in
\pic32mx\lib\proc\device\procdefs.ld, where device is the device value
specified to the -mprocessor compilation-driver (xc32-gcc) option.
For PIC32MZ and Later Devices:
Single-file linker script for PIC32MZ and later devices: The linker script for PIC32MZ
devices are contained within a single file (e.g.
pic32mx/lib/proc/32MZ2048ECH100/p32MZ2048ECH100.ld). This eliminates the
dependency on two files (elf32pic32mx.x and procdefs.ld) used by the older
linker-script model. Like before, the xc32-gcc compilation driver will pass the
device-specific linker script to the linker when building with -mprocessor=device option.
The default linker script maps each standard input section to one or more specific
MEMORY regions. In turn, each MEMORY region maps to an address segment on the
PIC32 MCU (e.g. kseg0, kseg1). See the Section 3 of the PIC32MX Family Reference
Manual (DS61115) for a full description of the user/kernel address segments.
Note: The “MPLAB XC32 C/C++ Compiler User’s Guide” (DS51686) examines
the contents of the default linker script in detail. The discussion applies to
both assembly-code and C-code projects.
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The table below shows how the default linker script maps standard sections to
MEMORY regions.
TABLE 8-1: PIC32 RESERVED, STANDARD SECTION NAMES IN DEFAULT LINKER SCRIPT
Section Name Generated by Final Location Default linker-script
MEMORY region
.reset Reset handler Executable boot-code segment kseg0_boot_mem
.bev_excpt BEV-Exception handler Executable boot-code segment kseg0_boot_mem
.app_excpt General-Exception handler Executable boot-code segment kseg0_boot_mem
.vector_n Interrupt Vector n Executable boot-code segment kseg0_boot_mem
.startup C startup code Executable boot-code segment kseg0_boot_mem
.text Compiler- or assembler-generated
instructions
Executable code segment kseg0_program_mem
.rodata Strings and C data declared const Read-only data segment kseg0_program_mem
.sdata2 Small initialized constant global
and static data
Read-only data segment kseg0_program_mem
.sbss2 Uninitialized constant global and
static data (i.e., variables which
will always be zero)
Read-only data segment kseg0_program_mem
.data Variables >n bytes (compiled -Gn)
with an initial value. Values copied
from program memory to data
memory at C startup.
Initialized data segment kseg1_data_mem &
kseg0_program_mem
.sdata Variables <=n bytes (compiled
-Gn) with an initial value. Used for
gp-relative addressing.
Small initialized data segment kseg1_data_mem &
kseg0_program_mem
.lit4 / .lit8 Constants (usually floating point)
which the assembler decides to
store in memory rather than in the
instruction stream. Used for
gp-relative addressing.
Small initialized data segment kseg1_data_mem &
kseg0_program_mem
.sbss Uninitialized variables <=n bytes
(compiled -Gn). Used for
gp-relative addressing.
Small zero-filled segment kseg1_data_mem
.bss Uninitialized larger variables Zero-filled segment kseg1_data_mem
.heap Heap used for dynamic memory Reserved by linker script kseg1_data_mem
.stack Minimum space reserved for stack Reserved by linker script kseg1_data_mem
.ramfunc RAM-functions, copied from pro-
gram memory to data memory at C
startup
Initialized data segment kseg1_data_mem &
kseg0_program_mem
.reginfo
.stab*
.debug*
Debug information Not in load image n/a
.line DWARF debug information Not in load image n/a
.comment #ident/.ident strings Not in load image n/a
Note: The table above contains sections that are no longer mapped in the linker script. Starting with XC32 v2.00,
the best-fit allocator allocates them.
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8.5 ADDING A CUSTOM LINKER SCRIPT TO AN MPLAB X IDE PROJECT
The standard default 32-bit linker scripts are general purpose and will satisfy the
demands of most applications. However, an occasion may arise where a custom linker
script is required.
Copy the default linker-script file (e.g.,
pic32mx/lib/proc/32MZ2048ECH100/p32MZ2048ECH100.ld) in your applica-
tion's project directory. Add the new *.ld file to your project. It should now appear in
the project tree under “Linker Files”.
Customizations that you make to your new *.ld file should now affect your project.
You may wish to retain unused sections in a custom linker script, since unused sections
will not impact application memory usage. If a section must be removed for a custom
script, C style comments can be used to disable it.
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8.6 LINKER SCRIPT COMMAND LANGUAGE
Linker scripts are text files that contain a series of commands. Each command is either
a keyword, possibly followed by arguments, or an assignment to a symbol. Multiple
commands may be separated using semicolons. White space is generally ignored, but
there are some cases where white space is significant. For instance, white space is
required around operators.
Strings such as file or format names can normally be entered directly. If the file name
contains a character such as a comma which would otherwise serve to separate file
names, the file name may be specified in double quotes. There is no way to use a
double quote character in a file name.
Comments may be included just as in C, delimited by /* and */. As in C, comments
are syntactically equivalent to white space.
8.6.1 Basic Linker Script Concepts
The linker combines input files into a single output file. The output file and each input
file are in a special data format known as an ELF object file format. Each file is called
an object file. Each object file has, among other things, a list of sections. A section in
an input file is called an input section; similarly, a section in the output file is an output
section.
Each section in an object file has a name and a size. Most sections also have an
associated block of data, known as the section contents. A section may be marked as
loadable, which mean that the contents should be loaded into memory when the output
file is run. A section with no contents may be allocatable, which means that an area in
memory should be set aside, but nothing in particular should be loaded there (in some
cases this memory must be zeroed out).
Every loadable or allocatable output section has two addresses. The first is the VMA,
or virtual memory address. This is the address the section will have when the output
file is run. The second is the LMA, or load memory address. This is the address at
which the section will be loaded. In most cases, the two addresses will be the same.
An example of when they might be different is when a section is intended to contain
RAM-located functions (e.g. the default .ramfunc section). In this case, the
program-memory address would be the LMA and the data-memory address would be
the VMA.
The sections in an object file can be viewed by using the xc32-objdump program with
the -h option.
Every object file also has a list of symbols, known as the symbol table. A symbol may
be defined or undefined. Each symbol has a name, and each defined symbol has an
address, among other information. If a C program is compiled into an object file, a
defined symbol will be created for every defined function and global or static variable.
Every undefined function or global variable which is referenced in the input file will
become an undefined symbol.
Symbols in an object file can be viewed by using the xc32-nm program, or by using
the xc32-objdump program with the -t option.
Note: Both the VMA and the LMA use the PIC32 MCU's virtual address. See the
PIC32MX Family Reference Manual (DS61115) for a description of the
PIC32MX Virtual-to-Physical Fixed Memory Mapping. In addition, the
family reference manual describes the PIC32 memory layout.
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8.6.2 Commands Dealing with Files
Several linker script commands deal with files.
INCLUDE filename
Include the linker script filename at this point. The file will be searched for in the current
directory, and in any directory specified with the -L option. Calls to INCLUDE may be
nested up to 10 levels deep.
INPUT(file, file, ...)
INPUT(file file ...)
The INPUT command directs the linker to include the named files in the link, as though
they were named on the command line. The linker will first try to open the file in the
current directory. If it is not found, the linker will search through the archive library
search path. See the description of -L in Section 7.4.9 “--library-path <dir>
(-L <dir>)”.
If INPUT (-lfile) is used, xc32-ld will transform the name to libfile.a, as with
the command line argument -l.
When the INPUT command appears in an implicit linker script, the files will be included
in the link at the point at which the linker script file is included. This can affect archive
searching.
GROUP(file, file, ...)
GROUP(file file ...)
The GROUP command is like INPUT, except that the named files should all be archives,
and they are searched repeatedly until no new undefined references are created. See
the description of archives in Section 7.4.1 “-( archives -), --start-group
archives, --end-group”.
OPTIONAL(file, file, ...)
OPTIONAL(file file ...)
The OPTIONAL command is analogous to the INPUT command, except that the named
files are not required for the link to succeed. This is particularly useful for specifying
archives (or libraries) that may or may not be installed with the compiler. The default
linker scripts provided with the XC32 compiler use the OPTIONAL directive to link the
device-specific peripheral libraries.
OUTPUT(filename)
The OUTPUT command names the output file. Using OUTPUT(filename) in the linker
script is exactly like using -o filename on the command line (see
Section 7.4.13 “--output file (-o file)”). If both are used, the command line
option takes precedence.
SEARCH_DIR(path)
The SEARCH_DIR command adds path to the list of paths where the linker looks for
archive libraries. Using SEARCH_DIR(path) is exactly like using -L path on the
command line (see Section 7.4.9 “--library-path <dir> (-L <dir>)”). If both
are used, then the linker will search both paths. Paths specified using the command
line option are searched first.
STARTUP(filename)
The STARTUP command is just like the INPUT command, except that filename will
become the first input file to be linked, as though it were specified first on the command
line.
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8.6.3 Assigning Values to Symbols
A value may be assigned to a symbol in a linker script. This will define the symbol as a
global symbol.
8.6.3.1 SIMPLE ASSIGNMENTS
A symbol may be assigned using any of the C assignment operators:
symbol = expression ;
symbol += expression ;
symbol -= expression ;
symbol *= expression ;
symbol /= expression ;
symbol <<= expression ;
symbol >>= expression ;
symbol &= expression ;
symbol |= expression ;
The first case will define symbol to the value of expression. In the other cases, symbol
must already be defined, and the value will be adjusted accordingly.
The special symbol name ‘.’ indicates the location counter. This symbol may be only
used within a SECTIONS command.
The semicolon after expression is required.
Expressions are defined in Section 8.7 “Expressions in Linker Scripts”.
Symbol assignments may appear as commands in their own right, or as statements
within a SECTIONS command, or as part of an output section description in a
SECTIONS command.
The section of the symbol will be set from the section of the expression; for more
information, see Section 8.7.6 “The Section of an Expression”.
Here is an example showing the three different places that symbol assignments may
be used:
floating_point = 0;
SECTIONS
{
.text ORIGIN(kseg0_program_mem) :
{
_text_begin = . ;
*(.text .stub .text.* )
_text_end = . ;
} >kseg0_program_mem =0
_bdata = (. + 3) & ~ 3;
.data : { *(.data) }
}
In this example, the symbol floating_point will be defined as zero. The symbol
_text_end will be defined as the address following the last .text input section. The
symbol _bdata will be defined as the address following the .text output section
aligned upward to a 4-byte boundary.
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8.6.3.2 PROVIDE
In some cases, it is desirable for a linker script to define a symbol only if it is referenced
and is not defined by any object included in the link. For example, traditional linkers
defined the symbol etext. However, ANSI C requires that etext may be used as a
function name without encountering an error. The PROVIDE keyword may be used to
define a symbol, such as etext, only if it is referenced but not defined. The syntax is
PROVIDE(symbol = expression).
Here is an example of using PROVIDE to define etext:
SECTIONS
{
.text :
{
*(.text)
_etext = .;
PROVIDE(etext = .);
}
}
The PIC32 default linker script uses the PROVIDE command to define the default
_min_stack_size, _min_heap_size, and _vector_spacing symbol values.
PROVIDE(_min_stack_size = 0x400) ;
PROVIDE(_min_heap_size = 0) ;
PROVIDE(_vector_spacing = 0x00000001);
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8.6.4 MEMORY Command
The linker’s default configuration permits allocation of all available memory. This can
be overridden by using the MEMORY command.
The MEMORY command describes the location and size of blocks of memory in the
target. It can be used to describe which memory regions may be used by the linker and
which memory regions it must avoid. Sections may then be assigned to particular
memory regions. The linker will set section addresses based on the memory regions
and will warn about regions that become too full. The linker will not shuffle sections
around to fit into the available regions.
The syntax of the MEMORY command is:
MEMORY
{
name [(attr)] : ORIGIN = origin, LENGTH = len
...
}
The name is a name used in the linker script to refer to the region. The region name
has no meaning outside of the linker script. Region names are stored in a separate
name space, and will not conflict with symbol names, file names or section names.
Each memory region must have a distinct name.
The attr string must consist only of the following characters:
If an unmapped section matches any of the listed attributes other than !, it will be
placed in the memory region. The ! attribute reverses this test, so that an unmapped
section will be placed in the memory region only if it does not match any of the listed
attributes.
The origin is an expression for the start address of the memory region. The expression
must evaluate to a constant before memory allocation is performed, which means that
section relative symbols may not be used. The keyword ORIGIN may be abbreviated
to org or o (but not, for example, ORG).
The len is an expression for the size in bytes of the memory region. As with the origin
expression, the expression must evaluate to a constant before memory allocation is
performed. The keyword LENGTH may be abbreviated to len or l.
In the following example, we specify that there are two memory regions available for
allocation: one starting at 0 for 48 kilobytes, and the other starting at 0x800 for two
kilobytes. The linker will place into the rom memory region every section which is not
explicitly mapped into a memory region, and is either read-only or executable. The
linker will place other sections which are not explicitly mapped into a memory region
into the ram memory region.
MEMORY
{
rom (rx) : ORIGIN = 0, LENGTH = 48K
ram (!rx) : org = 0x800, l = 2K
}
RRead-only section
WRead/write section
XExecutable section
AAllocatable section
IInitialized section
LSame as I
!Invert the sense of any of the following attributes
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Once a memory region is defined, the linker can be directed to place specific output
sections into that memory region by using the >region output section attribute. For
example, to specify a memory region named mem, use >mem in the output section
definition. If no address was specified for the output section, the linker will set the
address to the next available address within the memory region. If the combined output
sections directed to a memory region are too large for the region, the linker will issue
an error message.
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8.6.5 SECTIONS Command
The SECTIONS command tells the linker how to map input sections into output sections
and how to place the output sections in memory.
The format of the SECTIONS command is:
SECTIONS
{
sections-command
sections-command
...
}
Each SECTIONS command may be one of the following:
• an ENTRY command (see Section 8.6.6 “Other Linker Script Commands”)
• a symbol assignment (see Section 8.6.3 “Assigning Values to Symbols”)
• an output section description
• an overlay description
The ENTRY command and symbol assignments are permitted inside the SECTIONS
command for convenience in using the location counter in those commands. This can
also make the linker script easier to understand because those commands can be used
at meaningful points in the layout of the output file.
Output section descriptions and overlay descriptions are described below.
If a SECTIONS command does not appear in the linker script, the linker will place each
input section into an identically named output section in the order that the sections are
first encountered in the input files. If all input sections are present in the first file, for
example, the order of sections in the output file will match the order in the first input file.
The first section will be at address zero.
8.6.5.1 INPUT SECTION DESCRIPTION
The most common output section command is an input section description.
The input section description is the most basic linker script operation. Output sections
tell the linker how to lay out the program in memory. Input section descriptions tell the
linker how to map the input files into the memory layout.
An input section description consists of a file name optionally followed by a list of
section names in parentheses.
The file name and the section name may be wildcard patterns, which are described
further below.
The most common input section description is to include all input sections with a
particular name in the output section. For example, to include all input .text sections,
one would write:
*(.text)
Here the * is a wildcard which matches any file name. To exclude a list of files from
matching the file name wildcard, EXCLUDE_FILE may be used to match all files except
the ones specified in the EXCLUDE_FILE list. For example:
*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)
will cause all .ctors sections from all files except crtend.o and otherfile.o to
be included.
There are two ways to include more than one section:
*(.text .rodata)
*(.text) *(.rodata)
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The difference between these is the order in which the .text and .rodata input
sections will appear in the output section. In the first example, they will be intermingled.
In the second example, all .text input sections will appear first, followed by all
.rodata input sections.
A file name can be specified to include sections from a particular file. This would be
useful if one of the files contain special data that needs to be at a particular location in
memory. For example:
data.o(.data)
If a file name is specified without a list of sections, then all sections in the input file will
be included in the output section. This is not commonly done, but it may be useful on
occasion. For example:
data.o
When a file name is specified which does not contain any wild card characters, the
linker will first see if the file name was also specified on the linker command line or in
an INPUT command. If not, the linker will attempt to open the file as an input file, as
though it appeared on the command line. This differs from an INPUT command
because the linker will not search for the file in the archive search path.
8.6.5.2 INPUT SECTION WILDCARD PATTERNS
In an input section description, either the file name or the section name or both may be
wildcard patterns.
The file name of * seen in many examples is a simple wildcard pattern for the file name.
The wildcard patterns are like those used by the UNIX shell.
When a file name is matched with a wildcard, the wildcard characters will not match a
/ character (used to separate directory names on UNIX). A pattern consisting of a
single * character is an exception; it will always match any file name, whether it
contains a / or not. In a section name, the wildcard characters will match a / character.
File name wildcard patterns only match files which are explicitly specified on the
command line or in an INPUT command. The linker does not search directories to
expand wild cards.
If a file name matches more than one wildcard pattern, or if a file name appears
explicitly and is also matched by a wildcard pattern, the linker will use the first match in
the linker script. For example, this sequence of input section descriptions is probably
in error, because the data.o rule will not be used:
.data : { *(.data) }
.data1 : { data.o(.data) }
Normally, the linker will place files and sections matched by wild cards in the order in
which they are seen during the link. This can be changed by using the SORT keyword,
which appears before a wildcard pattern in parentheses (e.g., SORT(.text*)). When
the SORT keyword is used, the linker will sort the files or sections into ascending order
by name before placing them in the output file.
To verify where the input sections are going, use the -M linker option to generate a map
file. The map file shows precisely how input sections are mapped to output sections.
*matches any number of characters
?matches any single character
[chars]matches a single instance of any of the chars; the - character may be used to
specify a range of characters, as in [a-z] to match any lower case letter
\quotes the following character
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This example shows how wildcard patterns might be used to partition files. This linker
script directs the linker to place all .text sections in .text and all .bss sections in
.bss. The linker will place the .data section from all files beginning with an upper
case character in .DATA; for all other files, the linker will place the .data section in
.data.
SECTIONS {
.text : { *(.text) }
.DATA : { [A-Z]*(.data) }
.data : { *(.data) }
.bss : { *(.bss) }
}
8.6.5.3 INPUT SECTION FOR COMMON SYMBOLS
A special notation is needed for common symbols, because common symbols do not
have a particular input section. The linker treats common symbols as though they are
in an input section named COMMON.
File names may be used with the COMMON section just as with any other input sections.
This will place common symbols from a particular input file in one section, while
common symbols from other input files are placed in another section.
In most cases, common symbols in input files will be placed in the .bss section in the
output file. For example:
.bss { *(.bss) *(COMMON) }
If not otherwise specified, common symbols will be assigned to section .bss.
8.6.5.4 INPUT SECTION EXAMPLE
The following example is a complete linker script. It tells the linker to read all of the
sections from file all.o and place them at the start of output section outputa which
starts at location 0x10000. All of section .input1 from file foo.o follows immedi-
ately, in the same output section. All of section .input2 from foo.o goes into output
section outputb, followed by section .input1 from foo1.o. All of the remaining
.input1 and .input2 sections from any files are written to output section outputc.
SECTIONS {
outputa 0x10000 :
{
all.o
foo.o (.input1)
}
outputb :
{
foo.o (.input2)
foo1.o (.input1)
}
outputc :
{
*(.input1)
*(.input2)
}
}
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8.6.5.5 OUTPUT SECTION DESCRIPTION
The full description of an output section looks like this:
name [address] [(type)] : [AT(lma)]
{
output-section-command
output-section-command
...
} [>region] [AT>lma_region] [=fillexp]
Most output sections do not use most of the optional section attributes.
The white space around name and address is required. The colon and the curly
braces are also required. The line breaks and other white space are optional.
A section name may consist of any sequence of characters, but a name which contains
any unusual characters such as commas must be quoted.
Each output-section-command may be one of the following:
• a symbol assignment (see Section 8.6.3 “Assigning Values to Symbols”)
• an input section description (see Section 8.6.5.1 “Input Section Description”)
• data values to include directly (see Section 8.6.5.7 “Output Section Data”)
8.6.5.6 OUTPUT SECTION ADDRESS
The address is an expression for the VMA (the virtual memory address) of the output
section. If address is not provided, the linker will set it based on region if present, or
otherwise based on the current value of the location counter.
If address is provided, the address of the output section will be set to precisely that.
If neither address nor region is provided, then the address of the output section will
be set to the current value of the location counter aligned to the alignment requirements
of the output section. The alignment requirement of the output section is the strictest
alignment of any input section contained within the output section.
For example,
.text . : { *(.text) }
and
.text : { *(.text) }
are subtly different. The first will set the address of the .text output section to the
current value of the location counter. The second will set it to the current value of the
location counter aligned to the strictest alignment of a .text input section.
The address may be an arbitrary expression (see Section 8.7 “Expressions in Linker
Scripts”). For example, to align the section on a 0x10 byte boundary, so that the
lowest four bits of the section address are zero, the command could look like this:
.text ALIGN(0x10) : { *(.text) }
This works because ALIGN returns the current location counter aligned upward to the
specified value.
Specifying address for a section will change the value of the location counter.
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8.6.5.7 OUTPUT SECTION DATA
Explicit bytes of data may be inserted into an output section by using BYTE, SHORT,
LONG or QUAD as an output section command. Each keyword is followed by an
expression in parentheses providing the value to store. The value of the expression is
stored at the current value of the location counter.
The BYTE, SHORT, LONG and QUAD commands store one, two, four and eight bytes
(respectively). For example, this command will store the four byte value of the symbol
addr:
LONG(addr)
After storing the bytes, the location counter is incremented by the number of bytes
stored. When using data commands in a program memory section, it is important to
note that the linker considers program memory to be 32-bits wide, even though only 24
bits are physically implemented. Therefore, the most significant 8 bits of a LONG data
value are not loaded into device memory.
Data commands only work inside a section description and not between them, so the
following will produce an error from the linker:
SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } }
whereas this will work:
SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } }
The FILL command may be used to set the fill pattern for the current section. It is
followed by an expression in parentheses. Any otherwise unspecified regions of
memory within the section (for example, gaps left due to the required alignment of input
sections) are filled with the two least significant bytes of the expression, repeated as
necessary. A FILL statement covers memory locations after the point at which it occurs
in the section definition; by including more than one FILL statement, different fill
patterns may be used in different parts of an output section.
This example shows how to fill unspecified regions of memory with the value 0x9090:
FILL(0x9090)
The FILL command is similar to the =fillexp output section attribute (see
Section 8.6.5.9 “Output Section Attributes”), but it only affects the part of the
section following the FILL command, rather than the entire section. If both are used,
the FILL command takes precedence.
8.6.5.8 OUTPUT SECTION DISCARDING
The linker will not create an output section which does not have any contents. This is
for convenience when referring to input sections that may or may not be present in any
of the input files. For example:
.foo { *(.foo) }
will only create a .foo section in the output file if there is a .foo section in at least one
input file.
If anything other than an input section description is used as an output section
command, such as a symbol assignment, then the output section will always be
created, even if there are no matching input sections.
The special output section name /DISCARD/ may be used to discard input sections.
Any input sections which are assigned to an output section named /DISCARD/ are not
included in the output file.
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8.6.5.9 OUTPUT SECTION ATTRIBUTES
To review, the full description of an output section is:
name [address] [(type)] : [AT(lma)]
{
output-section-command
output-section-command
...
} [>region] [AT>lma_region] [:phdr :phdr ...] [=fillexp]
name, address and output-section-command have already been described. In
the following sections, the remaining section attributes will be described.
8.6.5.10 OUTPUT SECTION TYPE
Each output section may have a type. The type is a keyword in parentheses. The
following types are defined:
NOLOAD
The section should be marked as not loadable, so that it will not be loaded into memory
when the program is run.
DSECT, COPY, INFO, OVERLAY
These type names are supported for backward compatibility with older MIPS and GNU
assemblers but are rarely used. They all have the same effect: the section should be
marked as not allocatable, so that no memory is allocated for the section when the
program is run.
The linker normally sets the attributes of an output section based on the input sections
which map into it. This can be overridden by using the section type. For example, in the
script sample below, the ROM section is addressed at memory location 0 and does not
need to be loaded when the program is run. The contents of the ROM section will appear
in the linker output file as usual.
SECTIONS {
ROM 0 (NOLOAD) : { ... }
...
}
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8.6.5.11 OUTPUT SECTION LMA
Every section has a virtual address (VMA) and a load address (LMA). The address
expression which may appear in an output section description sets the VMA.
The linker will normally set the LMA equal to the VMA. This can be changed by using
the AT keyword. The expression lma that follows the AT keyword specifies the load
address of the section. Alternatively, with AT>lma_region expression, a memory
region may be specified for the section’s load address. See Section 8.6.4 “MEMORY
Command”.
This feature is designed to make it easy to build a ROM image. For example, the
following linker script creates three output sections: one called .text, which starts at
0xBFC00000, one called .mdata, which is loaded at the end of the .text section
even though its VMA is 0xA0000000, and one called .bss to hold uninitialized data at
address 0xA0001000. The symbol _data is defined with the value 0xA0000000,
which shows that the location counter holds the VMA value, not the LMA value.
SECTIONS
{
.text 0xBFC00000: { *(.text) _etext = . ; }
.mdata 0xA0000000:
AT ( ADDR (.text) + SIZEOF (.text) )
{ _data = . ; *(.data); _edata = . ; }
.bss 0xA0001000:
{ _bstart = . ; *(.bss) *(COMMON) ; _bend = . ;}
}
The run-time initialization code for use with a program generated with this linker script
would include a function to copy the initialized data from the ROM image to its run-time
address. The initialization function could take advantage of the symbols defined by the
linker script.
Writing such a function would rarely be necessary, however. These functions are pro-
vided by the C compiler's startup and initialization code. See the “MPLAB® C/C++
Compiler User's Guide” (DS51686) for more information on the startup code provided
with the compiler. The assembly source code for the startup routine is provided in
\pic32-libs\c\startup\crt0.S.
8.6.5.12 OUTPUT SECTION REGION
A section can be assigned to a previously defined region of memory by using >region.
See Section 8.6.4 “MEMORY Command”.
Here is a simple example:
MEMORY { rom : ORIGIN = 0x1000, LENGTH = 0x1000 }
SECTIONS { ROM : { *(.text) } >rom }
8.6.5.13 OUTPUT SECTION FILL
A fill pattern can be set for an entire section by using =fillexp. fillexp as an
expression. Any otherwise unspecified regions of memory within the output section (for
example, gaps left due to the required alignment of input sections) will be filled with the
two least significant bytes of the value, repeated as necessary.
The fill value can also be changed with a FILL command in the output section
commands; see Section 8.6.5.7 “Output Section Data”.
Here is a simple example:
SECTIONS { .text : { *(.text) } =0x9090 }
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8.6.5.14 OVERLAY DESCRIPTION
An overlay description provides an easy way to describe sections which are to be
loaded as part of a single memory image but are to be run at the same memory
address. At run time, some sort of overlay manager will copy the overlaid sections in
and out of the run-time memory address as required, perhaps by simply manipulating
addressing bits.
Overlays are described using the OVERLAY command. The OVERLAY command is
used within a SECTIONS command, like an output section description. The full syntax
of the OVERLAY command is as follows:
OVERLAY [start] : [NOCROSSREFS] [AT ( ldaddr )]
{
secname1
{
output-section-command
output-section-command
...
} [:phdr...] [=fill]
secname2
{
output-section-command
output-section-command
...
} [:phdr...] [=fill]
...
} [>region] [:phdr...] [=fill]
Everything is optional except OVERLAY (a keyword), and each section must have a
name (secname1 and secname2 above). The section definitions within the OVERLAY
construct are identical to those within the general SECTIONS construct, except that no
addresses and no memory regions may be defined for sections within an OVERLAY.
The sections are all defined with the same starting address. The load addresses of the
sections are arranged such that they are consecutive in memory starting at the load
address used for the OVERLAY as a whole (as with normal section definitions, the load
address is optional, and defaults to the start address; the start address is also optional,
and defaults to the current value of the location counter).
If the NOCROSSREFS keyword is used, and there are any references among the
sections, the linker will report an error. Since the sections all run at the same address,
it normally does not make sense for one section to refer directly to another.
For each section within the OVERLAY, the linker automatically defines two symbols. The
symbol __load_start_secname is defined as the starting load address of the
section. The symbol __load_stop_secname is defined as the final load address of
the section. Any characters within secname which are not legal within C identifiers are
removed. C (or assembler) code may use these symbols to move the overlaid sections
around as necessary.
At the end of the overlay, the value of the location counter is set to the start address of
the overlay plus the size of the largest section.
Here is an example. Remember that this would appear inside a SECTIONS construct.
OVERLAY 0x9D001000 : AT (0xA0004000)
{
.text0 { o1/*.o(.text) }
.text1 { o2/*.o(.text) }
}
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This will define both .text0 and .text1 to start at address 0x9D001000. .text0
will be loaded at address 0x9D001000, and .text1 will be loaded immediately after
.text0. The following symbols will be defined: __load_start_text0,
__load_stop_text0, __load_start_text1, __load_stop_text1.
C code to copy overlay .text1 into the overlay area might look like the following:
extern char __load_start_text1, __load_stop_text1;
memcpy ((char *) 0x9D001000, &__load_start_text1,
&__load_stop_text1 - &__load_start_text1);
The OVERLAY command is a convenience, since everything it does can be done using
the more basic commands. The above example could have been written identically as
follows.
.text0 0x9D001000: AT (0x9D004000) { o1/*.o(.text) }
__load_start_text0 = LOADADDR (.text0);
__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
.text1 0x9D001000: AT(0x9D004000+SIZEOF(.text0))
{o2/*.o(.text) }
__load_start_text1 = LOADADDR (.text1);
__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
. = 0x9D001000+ MAX (SIZEOF (.text0), SIZEOF (.text1));
8.6.6 Other Linker Script Commands
There are several other linker script commands, which are described briefly:
ASSERT(exp, message)
Ensure that exp is non-zero. If it is zero, then exit the linker with an error code, and print
message.
ENTRY(symbol)
Specify symbol as the first instruction to execute in the program. The linker will record
the address of this symbol in the output object file header. This does not affect the
Reset instruction at address zero, which must be generated in some other way. By
convention, the 32-bit linker scripts construct a GOTO __reset instruction at address
zero.
EXTERN(symbol symbol ...)
Force symbol to be entered in the output file as an undefined symbol. Doing this may,
for example, trigger linking of additional modules from standard libraries. Several
symbols may be listed for each EXTERN, and EXTERN may appear multiple times. This
command has the same effect as the -u command line option.
FORCE_COMMON_ALLOCATION
This command has the same effect as the -d command line option: to make 32-bit
linker assign space to common symbols even if a relocatable output file is specified
(-r).
NOCROSSREFS(section section ...)
This command may be used to tell 32-bit linker to issue an error about any references
among certain output sections. In certain types of programs, when one section is
loaded into memory, another section will not be. Any direct references between the two
sections would be errors.
The NOCROSSREFS command takes a list of output section names. If the linker detects
any cross references between the sections, it reports an error and returns a non-zero
exit status. The NOCROSSREFS command uses output section names, not input section
names.
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OUTPUT_ARCH(bfdarch)
Specify a particular output machine architecture. The bfdarch value is always
pic32mx for Microchip PIC32 MCUs.
OUTPUT_FORMAT(format_name)
The OUTPUT_FORMAT command names the object file format to use for the output file.
The format_name value is always elf32-tradlittlemips for Microchip PIC32
MCUs.
TARGET(format_name)
The TARGET command names the object file format to use when reading input files. It
affects subsequent INPUT and GROUP commands. The format_name value should
remain elf32-tradlittlemips for Microchip PIC32 MCUs.
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8.7 EXPRESSIONS IN LINKER SCRIPTS
The syntax for expressions in the linker script language is identical to that of C
expressions. All expressions are evaluated as 32-bit integers.
You can use and set symbol values in expressions.
The linker defines several special purpose built-in functions for use in expressions.
8.7.1 Constants
All constants are integers.
As in C, the linker considers an integer beginning with 0 to be octal, and an integer
beginning with 0x or 0X to be hexadecimal. The linker considers other integers to be
decimal.
In addition, you can use the suffixes K and M to scale a constant by 1024 or 1024*1024
respectively. For example, the following all refer to the same quantity:
_fourk_1 = 4K;
_fourk_2 = 4096;
_fourk_3 = 0x1000;
8.7.2 Symbol Names
Unless quoted, symbol names start with a letter, underscore, or period and may include
letters, digits, underscores, periods and hyphens. Unquoted symbol names must not
conflict with any keywords. You can specify a symbol which contains odd characters or
has the same name as a keyword by surrounding the symbol name in double quotes:
"SECTION" = 9;
"with a space" = "also with a space" + 10;
Since symbols can contain many non-alphabetic characters, it is safest to delimit
symbols with spaces. For example, A-B is one symbol, whereas A - B is an
expression involving subtraction.
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8.7.3 The Location Counter
The special linker variable dot ‘.’ always contains the current output location counter.
Since the . always refers to a location in an output section, it may only appear in an
expression within a SECTIONS command. The ‘.’ symbol may appear anywhere that
an ordinary symbol is allowed in an expression.
Assigning a value to ‘.’ will cause the location counter to be moved. This may be used
to create holes in the output section. The location counter may never be moved
backwards.
SECTIONS
{
output :
{
file1(.text)
. = . + 1000;
file2(.text)
. += 1000;
file3(.text)
} = 0x1234;
}
In the previous example, the .text section from file1 is located at the beginning of
the output section output. It is followed by a 1000 byte gap. Then the .text section
from file2 appears, also with a 1000 byte gap following before the .text section
from file3. The notation = 0x1234 specifies what data to write in the gaps.
‘.’ actually refers to the byte offset from the start of the current containing object.
Normally this is the SECTIONS statement, whose start address is 0, hence ‘.’ can be
used as an absolute address. If ‘.’ is used inside a section description, however, it
refers to the byte offset from the start of that section, not an absolute address. So, in a
script like this:
SECTIONS
{
. = 0x100
.text: {
*(.text)
. = 0x200
}
. = 0x500
.data: {
*(.data)
. += 0x600
}
}
the .text section will be assigned a starting address of 0x100 and a size of exactly
0x200 bytes, even if there is not enough data in the .text input sections to fill this
area. (If there is too much data, an error will be produced because this would be an
attempt to move ‘.’ backwards). The .data section will start at 0x500 and it will have
an extra 0x600 bytes worth of space after the end of the values from the .data input
sections and before the end of the .data output section itself.
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8.7.4 Operators
The linker recognizes the standard C set of arithmetic operators, with the standard
bindings and precedence levels:
TABLE 8-2: PRECEDENCE OF OPERATORS
8.7.5 Evaluation
The linker evaluates expressions lazily. It only computes the value of an expression
when absolutely necessary.
The linker needs some information, such as the value of the start address of the first
section, and the origins and lengths of memory regions, in order to do any linking at all.
These values are computed as soon as possible when the linker reads in the linker
script.
However, other values (such as symbol values) are not known or needed until after
storage allocation. Such values are evaluated later, when other information (such as
the sizes of output sections) is available for use in the symbol assignment expression.
The sizes of sections cannot be known until after allocation, so assignments dependent
upon these are not performed until after allocation.
Some expressions, such as those depending upon the location counter ‘.’, must be
evaluated during section allocation.
If the result of an expression is required, but the value is not available, then an error
results. For example, a script like the following:
SECTIONS
{
.text 9+this_isnt_constant :
{ *(.text) }
}
will cause the error message “non-constant expression for initial address”.
Precedence Associativity Operators Description
1 (highest) left ! - ~ Prefix operators
2left* / % multiply, divide, modulo
3left+ - add, subtract
4left>> << bit shift right, left
5left== != > < <= >= Relational
6left&bitwise and
7left|bitwise or
8left&& logical and
9left|| logical or
10 right ? : Conditional
11 (lowest) right &= += -= *= /= Symbol assignments
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8.7.6 The Section of an Expression
When the linker evaluates an expression, the result is either absolute or relative to
some section. A relative expression is expressed as a fixed offset from the base of a
section.
The position of the expression within the linker script determines whether it is absolute
or relative. An expression which appears within an output section definition is relative
to the base of the output section. An expression which appears elsewhere will be
absolute.
A symbol set to a relative expression will be relocatable if you request relocatable
output using the -r option. That means that a further link operation may change the
value of the symbol. The symbol’s section will be the section of the relative expression.
A symbol set to an absolute expression will retain the same value through any further
link operation. The symbol will be absolute, and will not have any particular associated
section.
You can use the built-in function ABSOLUTE to force an expression to be absolute when
it would otherwise be relative. For example, to create an absolute symbol set to the
address of the end of the output section .data:
SECTIONS
{
.data : { *(.data) _edata = ABSOLUTE(.); }
}
If ABSOLUTE were not used, _edata would be relative to the .data section.
8.7.7 Built-in Functions
The linker script language includes a number of built-in functions for use in linker script
expressions.
8.7.7.1 ABSOLUTE(EXP)
Return the absolute (non-relocatable, as opposed to non-negative) value of the
expression exp. Primarily useful to assign an absolute value to a symbol within a
section definition, where symbol values are normally section relative.
8.7.7.2 ADDR(SECTION)
Return the absolute address (the VMA) of the named section. Your script must
previously have defined the location of that section. In the following example,
symbol_1 and symbol_2 are assigned identical values:
SECTIONS { ...
.output1 :
{
start_of_output_1 = ABSOLUTE(.);
...
}
.output :
{
symbol_1 = ADDR(.output1);
symbol_2 = start_of_output_1;
}
...
}
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8.7.7.3 ALIGN(EXP)
Return the location counter (.) aligned to the next exp boundary. exp must be an
expression whose value is a power of two. This is equivalent to
(. + exp - 1) & ~(exp - 1)
ALIGN doesn’t change the value of the location counter; it just does arithmetic on it.
Here is an example which aligns the output .data section to the next 0x2000 byte
boundary after the preceding section and sets a variable within the section to the next
0x8000 boundary after the input sections:
SECTIONS { ...
.data ALIGN(0x2000): {
*(.data)
variable = ALIGN(0x8000);
}
...
}
The first use of ALIGN in this example specifies the location of a section because it is
used as the optional address attribute of a section definition (see
Section 8.6.5 “SECTIONS Command”). The second use of ALIGN is used to define
the value of a symbol.
The built-in function NEXT is closely related to ALIGN.
8.7.7.4 BLOCK(EXP)
This is a synonym for ALIGN, for compatibility with older linker scripts. It is most often
seen when setting the address of an output section.
8.7.7.5 DEFINED(SYMBOL)
Return 1 if symbol is in the linker global symbol table and is defined; otherwise return
0. You can use this function to provide default values for symbols. For example, the
following script fragment shows how to set a global symbol begin to the first location
in the .text section, but if a symbol called begin already existed, its value is
preserved:
SECTIONS { ...
.text : {
begin = DEFINED(begin) ? begin : . ;
...
}
...
}
8.7.7.6 KEEP(SECTION)
When link-time garbage collection is in use (--gc-sections), marking sections that
should not be eliminated is often useful. This is accomplished by surrounding an input
section's wildcard entry with KEEP(), as in KEEP(*(.init)) or
KEEP(SORT_BY_NAME(*)(.ctors)).
8.7.7.7 LOADADDR(SECTION)
Return the absolute LMA of the named section. This is normally the same as ADDR, but
it may be different if the AT attribute is used in the output section definition (see
Section 8.6.5 “SECTIONS Command”).
8.7.7.8 MAX(EXP1, EXP2)
Returns the maximum of exp1 and exp2.
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8.7.7.9 MIN(EXP1, EXP2)
Returns the minimum of exp1 and exp2.
8.7.7.10 NEXT(EXP)
Return the next unallocated address that is a multiple of exp. This function is
equivalent to ALIGN(exp).
8.7.7.11 SIZEOF(SECTION)
Return the size in bytes of the named section, if that section has been allocated. If the
section has not been allocated when this is evaluated, the linker will report an error. In
the following example, symbol_1 and symbol_2 are assigned identical values:
SECTIONS{ ...
.output {
.start = . ;
...
.end = . ;
}
symbol_1 = .end - .start ;
symbol_2 = SIZEOF(.output);
...
}
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NOTES:
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
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Chapter 9. Linker Processing
9.1 INTRODUCTION
How the MPLAB XC32 Object Linker (xc32-ld) builds an application from input files is
discussed here.
Topics covered in this chapter are:
• Overview of Linker Processing
•Linker Allocation
• Global and Weak Symbols
• Initialized Data
• Stack Allocation
• Heap Allocation
• PIC32MX Interrupt Vector Tables
• Interrupt Vector Tables for PIC32 MCUs Featuring Dedicated Programmable
Variable Offsets
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9.2 OVERVIEW OF LINKER PROCESSING
A linker combines one or more object files, with optional archive files, into a single
executable output file. The object files contain relocatable sections of code and data
which the linker will allocate into target memory. The entire process is controlled by a
linker script, also known as a link command file. A linker script is required for every link.
The link process may be broken down into 5 steps:
1. Loading Input Files
2. Allocating Memory
3. Resolving Symbols
4. Computing Absolute Addresses
5. Building the Output File
9.2.1 Loading Input Files
The initial task of the linker is to interpret link command options and load input files. If
a linker script is specified, that file is opened and interpreted. Otherwise an internal
default linker script is used. In either case, the linker script provides a description of the
target device, including specific memory region information. See Chapter 8. “Linker
Scripts” for more details.
Next the linker opens all of the input object files. Each input file is checked to make sure
the object format is compatible. If the object format is not compatible, an error is
generated. The contents of each input file are then loaded into internal data structures.
Typically each input file will contain multiple sections of code or data. Each section
contains a list of relocation entries which associate locations in a section’s raw data
with relocatable symbols.
9.2.2 Allocating Memory
After all of the input files have been loaded, the linker allocates memory. This is
accomplished by assigning each input section to an output section. The relation
between input and output sections is defined by a section map in the linker script. An
output section may or may not have the same name as an input section. Each output
section is then assigned to a memory region in the target device.
If an input section is not explicitly assigned to an output section, the linker will allocate
the unassigned section according to section attributes. For more information about
linker allocation, see Section 9.3 “Linker Allocation”.
9.2.3 Resolving Symbols
Once memory has been allocated, the linker begins the process of resolving symbols.
Symbols defined in each input section have offsets that are relative to the beginning of
the section. The linker converts these values into output section offsets.
Next, the linker attempts to match all external symbol references with a corresponding
symbol definition. Multiple definitions of the same external symbol result in an error. If
an external symbol is not found, an attempt is made to locate the symbol definition in
an archive file. If the symbol definition is found in an archive, the corresponding archive
module is loaded.
Modules loaded from archives may contain additional symbol references, so the
process continues until all external symbol references have matching definitions.
External symbols that are defined as “weak” receive special processing, as explained
in Section 9.4 “Global and Weak Symbols”. If any external symbol reference
Note: Input sections are derived from source code by the compiler or the
assembler. Output sections are created by the linker.
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remains undefined, an error is generated.
9.2.4 Creating Special Sections
After the symbols have been resolved, the linker constructs any special input or output
sections that are required. For example, the linker constructs a special input section
named .dinit to support initialized data. Section.dinit is an initialization template that
is interpreted by the C run-time library. For more information about initialized data, see
Section 9.5 “Initialized Data”.
9.2.5 Computing Absolute Addresses
After the special sections have been created, the final sizes of all output sections are
known. The linker then computes absolute addresses for all output sections and
external symbols. Each output section is checked to make sure it falls within its
assigned memory regions. If any section falls outside of its memory region, an error is
generated. Any symbols defined in the linker script are also computed.
9.2.6 Building the Output File
Finally, the linker builds the output file. Relocation entries in each section are patched
using absolute addresses. If the address computed for a symbol does not fit in the
relocation entry, a link error results. This can occur, for example, when one module ref-
erences a variable which it thinks is in a “small data” section, while the other defines it
in a non-small section.
A link map is also generated if requested with the appropriate option. The link map
includes a memory usage report, which shows the starting address and length of all
sections in data memory and program memory. For more information about the link
map, see Section 6.4.5 “Map File”.
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9.3 LINKER ALLOCATION
Linker allocation is controlled by the linker script, and proceeds in three steps:
1. Mapping Input Sections to Output Sections
2. Assigning Output Sections to Regions
3. Allocating Unmapped Sections
Steps 1 and 2 are performed by a sequential memory allocator. Input sections which
appear in the linker script are assigned to specific memory regions in the target
devices. Addresses within a memory region are allocated sequentially, beginning with
the lowest address and growing upwards.
Step 3 is performed by a best-fit memory allocator. Input sections which do not appear
in the linker script are assigned to memory regions according to their attributes. The
best-fit allocator makes efficient use of any remaining memory, including gaps between
output sections that may have been left by the sequential allocator.
9.3.1 Mapping Input Sections to Output Sections
Input sections are grouped and mapped into output sections, according to the section
map. When an output section contains several different input sections, the exact
ordering of input sections may be important. For example, consider the following output
section definition:
/* Code Sections */
.text ORIGIN(kseg0_program_mem) :
{
*(.text .stub .text.* .gnu.linkonce.t.*)
*(.mips16.fn.*)
*(.mips16.call.*)
} >kseg0_program_mem =0
Here the output section named .text is defined. Notice that the contents of this
section are specified within curly braces {}. After the closing brace,
>kseg0_program_mem indicates that this output section should be assigned to
memory region kseg0_program_mem.
The contents of output section .text may be interpreted as follows:
• Input sections named .text and .stub and input sections that match the wild-
card patterns .text.* and .gnu.linkonce.t.* are collected and mapped
into the output section. Grouping these sections ensures locality of reference.
• Input sections that match the wildcard pattern .mips16.fn.* are collected and
mapped into the output section.
• Input sections that match the wildcard pattern .mips16.call.* are collected
and mapped into the output section.
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9.3.2 Assigning Output Sections to Regions
Once the sizes of all output sections are known, they are assigned to memory regions.
Normally a region is specified in the output section definition. If a region is not specified,
the first defined memory region will be used.
Memory regions are filled sequentially, from lower to higher addresses, in the same
order that sections appear in the section map. A location counter, unique to each
region, keeps track of the next available memory location. There are two conditions
which may cause gaps in the allocation of memory within a region:
1. The section map specifies an absolute address for an output section, or
2. The output section has a particular alignment requirement.
In either case, any intervening memory between the current location counter and the
absolute (or aligned) address is skipped. The exact address of all items allocated in
memory may be determined from the link map file.
For a section containing an aligned memory block (with the aligned attribute in C or
.align directive in assembly), the section must also be aligned, to the same (or
greater) alignment value. If two or more input sections have different alignment
requirements, the largest alignment is used for the output section.
9.3.3 Allocating Unmapped Sections
After all sections that appear in the section map are allocated, any remaining sections
are considered to be unmapped. Unmapped sections are allocated according to sec-
tion attributes. The linker uses a best-fit memory allocator to determine the most effi-
cient arrangement in memory. The primary emphasis of the best-fit allocator is the
reduction or elimination of memory gaps due to address alignment restrictions. By con-
vention, most standard sections such as the .text, .data, .bss, or .ramfunc sec-
tion are not explicitly mapped in linker scripts, thus providing maximum flexibility for the
best-fit memory allocator. The exception is the “small” data sections used for gp-
relative addressing. Because these sections must be grouped together, they are
mapped in the linker script. A future toolchain release may allow the “small” data
sections to be allocated by the best-fit allocator.
Section attributes affect memory allocation as described below. For a general
discussion of section attributes, see Section A.2 “Assembler Directives that Define
Sections”.
code
The code attribute specifies that a section should be allocated in program memory, as
defined by region kseg0_program_mem in the linker script. The following attributes
may be used in conjunction with code and will further specify the allocation:
• address() specifies an absolute address
• align() specifies alignment of the section starting address
data
The data attribute specifies that a section should be allocated as initialized storage in
data memory, as defined by regions kseg0_data_mem & kseg1_data_mem in the linker
script. The following attributes may be used in conjunction with data and will further
specify the allocation:
• address() specifies an absolute address
• near specifies the first 64K of data memory
• align() specifies alignment of the section starting address
• reverse() specifies alignment of the section ending address + 1
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bss
The bss attribute specifies that a section should be allocated as uninitialized storage in
data memory, as defined by region kseg0_data_mem & kseg1_data_mem in the linker
script. The following attributes may be used in conjunction with bss and will further
specify the allocation:
• address() specifies an absolute address
• near specifies the first 64K of data memory
• align() specifies alignment of the section starting address
• reverse() specifies alignment of the section ending address + 1
persist
The persist attribute specifies that a section should be allocated as persistent storage
in data memory, as defined by region kseg0_data_mem & kseg1_data_mem in the
linker script. Persistent storage is not cleared or initialized by the C run-time library. The
following attributes may be used in
• conjunction with persist and will further specify the allocation:
• address() specifies an absolute address
• near specifies the first 64K of data memory
• align() specifies alignment of the section starting address
• reverse() specifies alignment of the section ending address + 1
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9.4 GLOBAL AND WEAK SYMBOLS
When a symbol reference appears in an object file without a corresponding definition,
the symbol is declared external. By default, external symbols have global binding and
are referred to as global symbols. External symbols may be explicitly declared with
weak binding, using the __weak__ attribute in C or the .weak directive in assembly
language.
As the name implies, global symbols are visible to all input files involved in the link.
There must be one (and only one) definition for every global symbol referenced. If a
global definition is not found among the input files, archives will be searched and the
first archive module found that contains the needed definition will be loaded. If a
definition is not found for a global symbol, a link error is reported.
Weak symbols share the same name space as global symbols, but are handled differ-
ently. Multiple definitions of a weak symbol are permitted. If a weak definition is not
found among the input files, archives are not searched and a value of 0 is assumed for
all references to the weak symbol. A global symbol definition of the same name will take
precedence over a weak definition (or the lack of one). In essence, weak symbols are
considered optional and may be replaced by global symbols, or ignored entirely.
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9.5 INITIALIZED DATA
The linker provides automatic support for initialized variables in data memory. Variables
are allocated in sections. Each data section is declared with a flag that indicates
whether it is initialized, or not initialized.
To control the initialization of the various data sections, the linker constructs a data ini-
tialization template. The template is allocated in program memory, and is processed at
start-up by the run-time library. When the application main program takes control, all
variables in data memory have been initialized.
• Standard Data Section Names
• Data Initialization Template
• Run-Time Library Support
9.5.1 Standard Data Section Names
Traditionally, linkers based on the GNU technology support three sections in the linked
binary file:
The name “bss” dates back several decades, and means memory “Block Started by
Symbol”. By convention, bss memory is filled with zeros during program start-up. The
traditional section names are considered to have implied attributes as listed in
Table 9-1. The code attribute indicates that the section contains executable code and
should be loaded in program memory. The bss attribute indicates that the section con-
tains data storage that is not initialized, but will be filled with zeros at program start-up.
The data attribute indicates that the section contains data storage that receives initial
values at start-up.
Assembly applications may define additional sections with explicit attributes using the
section directive described in Section “Directives that Define Sections”. For C applica-
tions, the 32-bit compiler will automatically define sections to contain variables and
functions as needed. For more information on the attributes of variables and functions
that may result in automatic section definition, see the “MPLAB XC32 C/C++ Compiler
User’s Guide” (DS51686).
TABLE 9-1: TRADITIONAL SECTION NAMES
Section Name Description Attribute
.text executable code code
.data data memory that receives initial values data
.bss data memory that is not initialized bss
Note: Whenever a section directive is used, all declarations that follow are
assembled into the named section. This continues until another section
directive appears, or the end of file. For more information on defining
sections and section attributes, see Section X.Y “Directives that Define
Sections”.
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9.5.2 Data Initialization Template
As noted in Section 9.5.1 “Standard Data Section Names”, the 32-bit Language
Tools support BSS-type sections (memory that is not initialized) as well as data-type
sections (memory that receives initial values). The data-type sections receive initial val-
ues at start-up, and the BSS-type sections are filled with zeros. A generic data initial-
ization template is used that supports any number of arbitrary BSS-type sections or
data-type sections. The data initialization template is created by the linker and is loaded
into an output section named .dinit in program memory. Start-up code in the
run-time library interprets the template and initializes data memory accordingly.
The data initialization template contains one record for each output section in data
memory. The template is terminated by a null instruction word. The format of a data
initialization record is:
/* data init record */
struct data_record {
char *dst; /* destination address */
unsigned int len; /* length in bytes */
unsigned int format:7; /* format code */
char dat[0]; /* variable length data */
};
The first element of the record is a pointer to the section in data memory. The second
and third elements are the section length and format code, respectively. The last ele-
ment is an optional array of data bytes. For BSS-type sections, no data bytes are
required.
The format code has two possible values.
TABLE 9-2: FORMAT CODE VALUES
Format Code Description
0Fill the output section with zeros
1Copy 4 bytes of data from each instruction word in the data array
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9.5.3 Run-Time Library Support
In order to initialize variables in data memory, the data initialization template must be
processed at start-up, before the application's main function takes control. For C pro-
grams, this task is performed by C start-up modules in the runtime library. Assembly
language programs can also use the C start-up modules by linking with libpic32.a.
To utilize a start-up module, the application must allow the run-time library to take con-
trol at device Reset. This happens automatically for C programs. The application’s
main() function is invoked after the start-up module has completed its work. Assembly
language programs should use the following naming conventions to specify which
routine takes control at device Reset.
Note that the first entry name (_reset) includes one leading underscore characters. The
second entry name (main) includes no leading underscore character. On device Reset,
the startup module is called and it performs the following:
1. Initialize Stack Pointer
2. The data initialization template in section .dinit is read, causing all uninitial-
ized sections to be cleared, and all initialized sections to be initialized with values
read from program memory.
3. Copy RAM functions from program flash to data memory an initialize bus matrix
registers.
4. The function main is called with no parameters.
5. If main returns, the processor will reset.
The alternate start-up module is linked when the --no-data-init option is specified.
It performs the same operations, except for step (2), which is omitted. The alternate
start-up module is smaller than the primary module, and can be selected to conserve
program memory if data initialization is not required.
Source code for both modules is provided in the src directory of the MPLAB XC32 C
compiler installation directory. The start-up modules may be modified if necessary. For
example, if an application requires main to be called with parameters, a conditional
assembly directive may be switched to provide this support.
TABLE 9-3: TABLE MAIN ENTRY POINTS
Main Entry Name Description
_reset Takes control immediately after device Reset
main Takes control after the start-up module completes its work
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9.6 STACK ALLOCATION
The MPLAB C compiler for PIC32 MCUs dedicates general-purpose register 29 as the
software Stack Pointer. All processor stack operations, including function calls, inter-
rupts, and exceptions use the software stack. The stack grows downward from high
addresses to low addresses.
By default, 32-bit linker dynamically allocates the largest stack possible from unused
data memory. Previous releases used output sections specified in the linker script to
allocate the stack.
The location and size of the stack is reported in the link map output file and the
Memory-Usage Report, under the heading Dynamic Memory Usage. Applications can
ensure that at least a minimum sized stack is available by specifying the size on the
linker command line using the --defsym=_min_stack_size=size linker command line
option. An example of allocating a stack of 2048 bytes using the command line is:
xc32-gcc foo.c -Wl,--defsym=_min_stack_size=2048.
The linker script a default _min_stack_size of 1024.
The linker's reported size of the .stack section is the minimum size required to avoid
a link error. The effective stack size is usually larger than the reported .stack section
size.
9.7 HEAP ALLOCATION
The C runtime heap is an uninitialized area of data memory that is used for dynamic
memory allocation using the standard C library dynamic memory-management func-
tions, calloc, malloc, and realloc. If you do not use any of these functions (directly or
indirectly), then you do not need to allocate a heap. By default, the heap size is 0.
If you do want to use dynamic memory allocation, either directly, by calling one of the
memory allocation functions, or indirectly, by using a standard C library function that
uses one of these functions, then a heap must be created. A heap is created by spec-
ifying its size on the linker command line using the --defsym=_min_heap_size
linker command line option. An example of allocating a heap of 512 bytes using the
command line is:
xc32-gcc foo.c -Wl,--defsym=_min_heap_size=512
The linker allocates the heap immediately before the stack. The location and size of the
heap are reported in the link map output file and in the Memory-Usage Report, under
the heading Dynamic Memory Usage. If the requested size is not available, the linker
reports an error.
The heap is now dynamically allocated by the linker. Previous releases used output
sections specified in the linker script to allocate the heap.
Note: See the “MPLAB XC32 C/C++ Compiler User’s Guide” (DS51686) for more
information on the compiler's usage of the stack.
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9.8 PIC32MX INTERRUPT VECTOR TABLES
The vector address of a given interrupt is calculated using Exception Base (EBASE
<31:12>) register, which provides a 4 KB page-aligned base address value located in
the kernel segment (kseg) address space. (EBASE is a CPU register.) The address is
calculated by using EBASE and VS (INTCTL <9:5>) values. The VS bits provide the
vector spacing between adjacent vector addresses.
The linker script creates the corresponding Interrupt Vector Table as follows:
PROVIDE(_vector_spacing = 0x00000001);
_ebase_address = 0x9FC01000;
SECTIONS
{
.app_excpt _GEN_EXCPT_ADDR :
{
KEEP(*(.gen_handler))
} > exception_mem
.vector_0 _ebase_address + 0x200 :
{
KEEP(*(.vector_0))
} > exception_mem
ASSERT (_vector_spacing == 0 || SIZEOF(.vector_0) <=
(_vector_spacing << 5),
"function at exception vector 0 too large")
.vector_1 _ebase_address + 0x200 +
(_vector_spacing << 5) * 1 :
{
KEEP(*(.vector_1))
} > exception_mem
ASSERT (_vector_spacing == 0 || SIZEOF(.vector_1) <=
(_vector_spacing << 5),
"function at exception vector 1 too large")
.vector_2 _ebase_address + 0x200 +
(_vector_spacing << 5) * 2 :
{
KEEP(*(.vector_2))
} > exception_mem
/* … */
.vector_63 _ebase_address + 0x200 +
(_vector_spacing << 5) * 63 :
{
KEEP(*(.vector_63))
} > exception_mem
ASSERT (_vector_spacing == 0 || SIZEOF(.vector_63) <=
(_vector_spacing << 5),
"function at exception vector 63 too large")
}
Each vector in the table is created as an output section located at an absolute address
based on values of the _ebase_address and _vector_spacing symbols. There is
one output section for each of the 64 vectors in the table.
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2013 Microchip Technology Inc. DS50002186A-page 159
9.9 INTERRUPT VECTOR TABLES FOR PIC32 MCUS FEATURING DEDICATED
PROGRAMMABLE VARIABLE OFFSETS
Some PIC32 families feature variable offsets for vector spacing. This feature allows the
interrupt vector spacing to be configured according to application needs. A specific
interrupt vector offset can be set for each vector using its associated OFFxxx register.
For details on the interrupt vector-table variable offset feature, refer to the PIC32 Family
Reference Manual (DS61108) and also the data sheet for your specific PIC32 MCU.
The XC32 toolchain provides a device-specific default linker script and a corresponding
object file that work together with the default runtime startup code. The following table
shows the files, located in /pic32mx/lib/proc/<devicename>, that are used to
initialized vector-table offset registers.
Device linker script <devicename>.ld
Vector Offset initialization vector_offset_init.o
Device runtime startup code crt0_<boot_isa>.o
9.9.1 Device-specific Linker Script
The application source code is responsible for creating a .vector_n input section for
each interrupt vector. The C/C++ compiler creates this section when either the
vector(n) or at_vector(n) attribute is applied to the interrupt service routine. In
assembly code, use the .section directive to create a new named section.
The device-specific linker script creates a single output section named .vectors that
groups all of the individual .vector_n input sections from the project. The start of the
interrupt-vector table is mapped to the address (_ebase_address + 0x200). The
default value of the _ebase_address symbol is also provided in the linker script.
For each vector, the linker script also creates a symbol named __vector_offset_n
whose value is the offset of the vector address from the _ebase_address address.
PROVIDE(_ebase_address = 0x9D000000);
SECTIONS
{
/* Interrupt vector table with vector offsets */
.vectors _ebase_address + 0x200 :
{
/* Symbol __vector_offset_n points to .vector_n if it exists,
* otherwise points to the default handler. The
* vector_offset_init.o module then provides a .data section
* containing values used to initialize the vector-offset SFRs
* in the crt0 startup code.
*/
__vector_offset_0 = (DEFINED(__vector_dispatch_0) ? (. - _ebase_address) : __vector_offset_default);
KEEP(*(.vector_0))
__vector_offset_1 = (DEFINED(__vector_dispatch_1) ? (. - _ebase_address) : __vector_offset_default);
KEEP(*(.vector_1))
__vector_offset_2 = (DEFINED(__vector_dispatch_2) ? (. - _ebase_address) : __vector_offset_default);
KEEP(*(.vector_2))
/* … */
__vector_offset_190 = (DEFINED(__vector_dispatch_190) ? (. - _ebase_address) : __vector_offset_default);
KEEP(*(.vector_190))
}
}
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9.9.2 Vector-Offset Initialization Module
The vector-offset initialization module (vector_offset_init.o) uses the
__vector_offset_n symbols defined in the default linker script. The value of each
symbol is the offset of the vector’s address from the ebase register’s address. The vec-
tor-offset initialization module, uses the symbol value to create a .data section using
the address of the corresponding OFFxxx special function register. This means that the
standard linker-generated data-initialization template contains the values used to ini-
tialize the OFFxxx registers.
.section
.data.__vector_offset_BF810540,data,keep,address(0xBF810540)
.word __vector_offset_0
.word __vector_offset_1
.word __vector_offset_2
.word __vector_offset_3
.word __vector_offset_4
.word __vector_offset_5
.word __vector_offset_6
9.9.3 Runtime Startup-Code Data Initialization
With these .data sections added to the project and the linker-generated data-
initialization template, the standard runtime startup code initializes the OFFxxx special
function registers as regular initialized data. No special code is required in the startup
code to initialize the OFFxxx registers.
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9.9.4 Example Vector-Table Assembly Source Code
The following example shows how to create a vector dispatch for interrupt vector 0. The
vector dispatch is a jump from the vector table to the actual Interrupt Service Routine
(ISR).
/* Input section .vector_0 is mapped to the .vectors output
* section in the linker script.
*/
.globl _vector_dispatch_0
.section .vector_0,code
.align 2
.set nomips16
.ent __vector_dispatch_0
__vector_dispatch_0:
/* Jump to the actual ISR code */
j isrvector0
nop
.end __vector_dispatch_0
.size __vector_dispatch_0, .-__vector_dispatch_0
The following example shows how to place the Interrupt Service Routine directly into
the vector table. The mapping in the linker script will automatically adjust the vector
spacing to accommodate the function’s code.
/* Input section .vector_0 is mapped to the .vectors output
* section in the linker script.
*/
.section .vector_0,code
.align 2
.globl isrvector0
.set nomips16
.set nomicromips
.ent isrvector0
isrvector0:
.set noat
/* Interrupt Service Routine code directly in the vector table.
* Be sure to preserve registers as appropriate for an ISR.
*/
eret
.set at
.end isrvector0
.size isrvector0, .-isrvector0
From XC32 C code, use the standard vector(n) and at_vector(n) function attri-
butes on your ISR function. Refer to the “MPLAB XC32 C/C++ Compiler User’s Guide”
(DS51686) for further information on these function attributes.
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Chapter 10. Linker Examples
10.1 INTRODUCTION
The 32-bit compiler and assembler each provide a syntax that can be used to designate
certain elements of an application for special handling. In C, a rich set of attributes are
available to modify variable and function definitions (see the “MPLAB XC32 C/C++
Compiler User’s Guide” (DS51686). In assembly language, variables and functions are
abstracted into memory sections, which become inputs to the linker. The assembler
provides another set of attributes that are available to modify section definitions (see
Section 4.6 “Directives that Modify Section Alignment”).
This chapter includes a number of 32-bit specific linker examples and shows the
equivalent syntax in C and assembly language.
10.2 HIGHLIGHTS
Topics covered in this chapter are:
• Memory Addresses and Relocatable Code
• Locating a Variable at a Specific Address
• Locating a Function at a Specific Address
• Locating and Reserving Program Memory
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10.3 MEMORY ADDRESSES AND RELOCATABLE CODE
For most applications it is preferable to write fully relocatable source code, thus allow-
ing the linker to determine the exact addresses in memory where functions and vari-
ables are placed. The final address of external symbols in memory can be determined
from the link map output, as shown in this excerpt:
...
.text 0x9d0000f0 0x64
.text 0x9d0000f0 0x64 test.o
0x9d0000f0 myfunc
0x9d000110 main
.text._DefaultInterrupt 0x9d000154 0x48
.text._DefaultInterrupt 0x9d000154 0x48 c:/program files/
microchip/xc32/v1.20/bin/
../lib/gcc/pic32mx/4.5.2/
../../../../pic32mx/
lib\libpic32.a
defaultinterrupt.o)
0x9d000154 _DefaultInterrupt...
In some cases it is necessary for the programmer to specify the address where a cer-
tain variable or function should be located. Traditionally this is done by creating a
user-defined section and writing a custom linker script. The 32-bit assembler and com-
piler provide a set of attributes that can be used to specify absolute addresses and
memory spaces directly in source code. When these attributes are used, custom linker
scripts are not required.
Note: By specifying an absolute address, the programmer assumes the respon-
sibility to ensure the specified address is reasonable and available. If the
specified address is out of range, or conflicts with a statically allocated
resource, a link error will occur.
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2013 Microchip Technology Inc. DS50002186A-page 165
10.4 LOCATING A VARIABLE AT A SPECIFIC ADDRESS
In this example, array buf1 is located at a specific address in data memory. The
address of buf1 can be confirmed by executing the program in the simulator, or by
examining the link map.
#include "stdio.h"
int __attribute__((address(0xa0000200))) buf1[128];
The equivalent array definition in assembly language appears below. The .align
directive is optional and represents the default alignment in data memory. Use of * as
a section name causes the assembler to generate a unique name based on the source
file name.
.globl buf1
.section *,address(0xa0000200),bss
.align 2
.type buf1, @object
.size buf1, 512
buf1:
.space 512
10.5LOCATING A FUNCTION AT A SPECIFIC ADDRESS
In this example, function func is located at a specific address.
#include "stdio.h"
void __attribute__((address(0x9d002000))) func()
{}
The equivalent function definition in assembly language appears below. The .align
directive is optional and represents the default alignment in program memory. Use of *
as a section name causes the assembler to generate a unique name based on the
source file name.
.section *,address(0x9d002000),code
.align 2
.globl func
func:
......
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10.6 LOCATING AND RESERVING PROGRAM MEMORY
In this example, a block of program memory is reserved for a special purpose, such as
a bootloader. An arbitrary sized function is allocated in the block, with the remaining
space reserved for expansion or other purposes.
The following output section definition is added to a custom linker script:
BOOT_START = 0x9d00A200;
BOOT_LEN = 0x400;
my_boot BOOT_START :
{
*(my_boot);
. = BOOT_LEN; /* advance dot to the maximum length */
} > kseg0_program_mem
Note the “dot assignment” (.=) that appears inside the section definition after the input
sections. Dot is a special variable that represents the location counter, or next fill point,
in the current section. It is an offset relative to the start of the section. The statement in
effect says “no matter how big the input sections are, make sure the output section is
full size.”
The following C function will be allocated in the reserved block:
void __attribute__((section("my_boot"))) func1()
{
/* etc. */
}
The equivalent assembly language would be:
.section my_boot,code
.align 2
.globl func1
func1:
......
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Chapter 11. Linker Errors/Warnings
11.1 INTRODUCTION
MPLAB XC32 Object Linker (xc32-ld) generates errors and warnings. A descriptive list
of these outputs is shown here. This list shows only the most common diagnostic
messages from the linker.
Topics covered in this appendix are:
• Fatal Errors
• Errors
• Warnings
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11.2 FATAL ERRORS
The following errors indicate that an internal error has occurred in the linker. If the linker
emits any of the fatal errors listed below and you're using a custom linker script, check
that the script specifies OUTPUT_FORMAT (elf32-tradlittlemips) and
OUTPUT_ARCH (pic32mx). Other values may cause the linker to operate in an unsup-
ported mode. Also check that you are passing only fully supported options on the
linker's command line. Finally, make sure that no other applications have the linker's
input or output files locked.
If the fatal error occurs with the correct OUTPUT_FORMAT, OUTPUT_ARCH, and
command-line options, contact Microchip Technology at http://support.microchip.com
for engineering support. Be sure to provide full details about the source code and
command-line options that caused the error.
• Bfd backend error: bfd_reloc_ctor unsupported
• Bfd_hash_allocate failed creating symbol %s
• Bfd_hash_lookup failed: %e
• Bfd_hash_lookup for insertion failed: %e
• Bfd_hash_table_init failed: %e
• Bfd_hash_table_init of cref table failed: %e
• Bfd_link_hash_lookup failed: %e
• Bfd_new_link_order failed
• Bfd_record_phdr failed: %e
• Can't set bfd default target to `%s': %e
• Can not create link hash table: %e
• Can not make object file: %e
• Cannot represent machine `%s'
• Could not read relocs: %e
• Could not read symbols
• Cref_hash_lookup failed: %e
• Error closing file `%s'
• Error writing file `%s'
• Failed to create hash table
• Failed to merge target specific data
• File not recognized: %e
• Final close failed: %e
• Final link failed: %e
• Hash creation failed
• Out of memory during initialization
• Symbol `%t' missing from main hash table
• Target %s not found
• Target architecture respecified
• Unknown architecture: %s
• Unknown demangling style `%s'
• Unknown language `%s' in version information
Linker Errors/Warnings
2013 Microchip Technology Inc. DS50002186A-page 169
11.3 ERRORS
The linker errors listed below usually indicate an error in the linker script or
command-line options passed to the linker. An error could also indicate a problem with
one or more of the input object files or archives.
Symbols
--gc-sections and -r may not be used together
The garbage-collection sections option and the relocatable-output option are not com-
patible. Remove either the --gc-sections option or the --relocatable option.
--relax and -r may not be used together
The relaxation option and the relocatable output option are not compatible. Remove
one of the options.
A
A heap is required, but has not been specified.
A heap must be specified when using Standard C input/output functions
Assignment to location counter invalid outside of SECTION
An assignment to the special dot symbol can be done only during allocation within a
SECTION. Check the location of the assignment statement in the linker script.
B
Bad --unresolved-symbols option: option
The --unresolved-symbols method option was invalid. Note that this option is
unsupported. Try the default --unresolved-symbols=report-all instead.
C
Can not PROVIDE assignment to location counter
An assignment to the special dot symbol can be done only during allocation. A
PROVIDE command cannot use an assignment to the location counter. Remove the
erroneous statement from the linker script.
Can not set architecture: arch_name
If you're using a custom linker script, check that the OUTPUT_ARCH (pic32mx) com-
mand appears in the linker script. The PIC32 MCU linker currently supports only the
'pic32mx' arch.
Cannot move location counter backwards (from addr1 to addr2)
The next dot-symbol value must be greater than the current dot-symbol value.
Could not allocate data memory.
The linker could not find a way to allocate all of the sections that have been assigned
to region ‘kseg0_data_memory/kseg1_data_memory’.
Could not allocate program memory.
The linker could not find a way to allocate all of the sections that have been assigned
to region ‘kseg0_program_memory’.
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D
Dangerous relocation: relocation_type
A symbol was resolved but the usage is dangerous. This can occur, for example, when
the code uses GP-relative addressing but the _gp initialization symbol was not defined.
The _gp symbol is normally defined in the linker script.
--data-init and --no-data-init options can not be used together.
--data-init creates a special output section named .dinit as a template for the
run-time initialization of data, --no-data-init does not. Only one option can be
used.
F
File format not recognized; treating as linker script
One of the input files was not a recognized ELF object or archive. The linker assumes
that it is a linker script.
G
Group ended before it began (--help for usage)
The -) option appeared on the command line before the -( option. Check that the
group is specified correctly on the linker command line.
I
Illegal use of name section
The section name is reserved. For instance, the special output-section name
/DISCARD/ may be used to discard input sections. Any input sections which are
assigned to an output section named /DISCARD/ are not included in the output file.
You should not create your own output section named /DISCARD/.
Includes nested too deeply
The maximum include depth is 10.
Invalid argument to option --section-start
The argument to --section-start must be sectionname=org. org must be a
single hexadecimal integer. There should be no white space between sectionname,
the equals sign (=), and org.
Invalid assignment to location counter
The assignment to the special dot symbol was invalid.
Invalid syntax in flags
The section flags are invalid. The accepted flags are: a r w x l.
M
Macros nested too deeply
The maximum macro nesting depth is 10.
May not nest groups (--help for usage)
An archive group is already started. Use the -) option to close the current group before
starting another group with the -( option.
Linker Errors/Warnings
2013 Microchip Technology Inc. DS50002186A-page 171
Member %b in archive is not an object
The archive member is not a valid object. Check that the library archive is correct for
the Microchip MPLAB XC32 C/C++ Compiler.
Missing argument(s) to option --section-start
The required argument to --section-start must be sectionname=org.
Multiple definition of name
The linker discovered a symbol that is defined multiple times. Eliminate the extraneous
definition(s).
Multiple startup files
The linker script is attempting to set a startup file, but a startup file has already been
set. There should be only one startup file specified in the linker script.
N
No input files
The linker did not find an input file specified on the command line. There was nothing
for the linker to do. Check that you are passing the correct object file names to the
linker.
Nonconstant expression for name
name must be a nonconstant expression.
Not enough memory for stack (num bytes available).
There was not enough memory free to allocate the minimum-sized stack.
R
region region is full (filename section secname).
The memory region region is full, but section secname has been assigned to it.
Reloc refers to symbol name which is not being output
An instruction references a symbol that is not being output.
Relocation truncated to fit relocation_type name.
This error indicates that the relocated value of name is too large for its intended use.
This can happen when an address is out of range for the instruction in question. Check
that the symbol is both declared and defined in the intended section. For instance, a
variable's declaration and definition must both be either const or non-const.
Relocation truncated to fit: relocation_type name against undefined symbol
name
This error can occur if the symbol does not exist. For instance, the code calls a function
that has not been defined.
U
Undefined MEMORY region region referenced in expression
The expression referenced a MEMORY region that does not exist in the linker script.
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11.4 WARNINGS
The linker generates warnings when an assumption is made so that the linker could
continue linking a flawed program. Warnings should not be ignored. Each warning
should be specifically looked at and corrected to ensure that the linker understands
what was intended. Warning messages can sometimes point out bugs in your program.
C
Cannot find entry symbol name
If the linker cannot find the specified entry symbol and it is not a number. Use the first
address in the text section.
Changing start of section name by num bytes
The linker is changing the start of the indicated section due to alignment.
D
data initialization has been turned off, therefore section secname will not be
initialized.
The specified section requires initialization, but data initialization has been turned off;
so, the initial data values are discarded. Storage for the data sections will be allocated
as usual.
I
initial values were specified for a non-loadable data section (name). These
values will be ignored.
By definition, a persistent data section implies data that is not initialized; therefore the
values are discarded. Storage for the section will be allocated as usual.
R
Redeclaration of memory region name
The MEMORY region has been declared more than once in the linker script.
U
Undefined reference to name
The symbol is undefined.
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Part 3 – 32-Bit Utilities (including the Archiver/Librarian)
Chapter 12. MPLAB XC32 Object Archiver/Librarian.............................................. 175
Chapter 13. Other Utilities ......................................................................................... 183
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Chapter 12. MPLAB XC32 Object Archiver/Librarian
12.1 INTRODUCTION
The MPLAB XC32 Object Archiver/Librarian (xc32-ar) creates, modifies and extracts
files from archives. This tool is one of several utilities. An “archive” is a single file hold-
ing a collection of other files in a structure that makes it possible to retrieve the original
individual files (called “members” of the archive).
The 32-bit archiver/librarian can maintain archives whose members have names of any
length; however, if an f modifier is used, the file names will be truncated to 15 charac-
ters.
The archiver is considered a binary utility because archives of this sort are most often
used as “libraries” holding commonly needed subroutines.
The archiver creates an index to the symbols defined in relocatable object modules in
the archive when you specify the modifier s. Once created, this index is updated in the
archive whenever the archiver makes a change to its contents (save for the q update
operation). An archive with such an index speeds up linking to the library and allows
routines in the library to call each other without regard to their placement in the archive.
You may use xc32-nm -s or xc32-nm --print-armap to list this index table. If an
archive lacks the table, another form of the 32-bit archiver/librarian called
xc32-ranlib can be used to add only the table.
The 32-bit archiver/librarian is designed to be compatible with two different facilities.
You can control its activity using command-line options or, if you specify the single
command line option -M, you can control it with a script supplied via standard input.
Topics covered in this chapter are:
• Archiver/Librarian and Other Development Tools
• Feature Set
• Input/Output Files
•Syntax
• Options
•Scripts
V AR 0 Compiler ¢ Assemb‘er Archiver (Librarian) J, Lin Ker Command Line
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12.2 ARCHIVER/LIBRARIAN AND OTHER DEVELOPMENT TOOLS
The 32-bit librarian creates an archive file from object files created by the 32-bit assem-
bler. Archive files may then be linked by the 32-bit linker with other relocatable object
files to create an executable file. See Figure 12-1 for an overview of the tools process
flow.
FIGURE 12-1: MPLAB X IDE TOOLS PROCESS FLOW
Object File Libraries
(*.a)
Assembler
Linker
C Source Files
(*.c)
C Compiler
Source Files (*.s)
Assembly Source
Files (*.S)
Object Files
(*.o)
Executable File
(*.elf)
Archiver (Librarian)
Command Line
Simulator
Compiler
Driver
Program
MPLAB® X
IDE Debug
Linker Script
(*.ld)
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12.3 FEATURE SET
Notable features of the assembler include:
• Available for Linux x86, Mac OS X, and Windows
• Command Line Interface
12.4 INPUT/OUTPUT FILES
The 32-bit archiver/librarian generates archive files (.a). An archive file is a single file
holding a collection of other files in a structure that makes it possible to retrieve the orig-
inal individual files (called members of the archive). All objects are processed in the
ELF object-file format.
xc32-ar is considered a binary utility because archives of this sort are most often used
as libraries holding commonly needed subroutines.
12.5 SYNTAX
xc32-ar [-]P[MOD [RELPOS] [COUNT]] ARCHIVE [MEMBER...]
xc32-ar -M [ <mri-script ]
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12.6 OPTIONS
When you use the 32-bit archiver/librarian with command-line options, the archiver
insists on at least two arguments to execute: one key letter specifying the operation
(optionally accompanied by other key letters specifying modifiers), and the archive
name.
xc32-ar [-]P[MOD [RELPOS][COUNT]] ARCHIVE [MEMBER...]
Most operations can also accept further MEMBER arguments, specifying archive
members. Without specifying members, the entire archive is used.
The 32-bit archiver/librarian allows you to mix the operation code P and modifier flags
MOD in any order, within the first command line argument. If you wish, you may begin
the first command line argument with a dash.
The P key letter specifies what operation to execute; it may be any of the following, but
you must specify only one of them.
Note: command-line options are case sensitive.
TABLE 12-1: OPERATION TO EXECUTE
Option Function
dDelete modules from the archive. Specify the names of modules to be deleted as
MEMBER...; the archive is untouched if you specify no files to delete.
If you specify the v modifier, the 32-bit archiver/librarian lists each module as it is
deleted.
mUse this operation to move members in an archive.
The ordering of members in an archive can make a difference in how programs are
linked using the library, if a symbol is defined in more than one member.
If no modifiers are used with m, any members you name in the MEMBER arguments
are moved to the end of the archive; you can use the a, b or i modifiers to move
them to a specified place instead.
pPrint the specified members of the archive, to the standard output file. If the v
modifier is specified, show the member name before copying its contents to
standard output. If you specify no MEMBER arguments, all the files in the archive are
printed.
qAppend the files MEMBER... into ARCHIVE.
rInsert the files MEMBER... into ARCHIVE (with replacement).
If one of the files named in MEMBER... does not exist, the archiver displays an
error message, and leaves undisturbed any existing members of the archive
matching that name. By default, new members are added at the end of the file; but
you may use one of the modifiers a, b or i to request placement relative to some
existing member. The modifier v used with this operation elicits a line of output for
each file inserted, along with one of the letters a or r to indicate whether the file was
appended (no old member deleted) or replaced.
tDisplay a table listing the contents of ARCHIVE, or those of the files listed in
MEMBER..., that are present in the archive. Normally only the member name is
shown; if you also want to see the modes (permissions), timestamp, owner, group
and size, you can request that by also specifying the v modifier. If you do not
specify a MEMBER, all files in the archive are listed.
For example, if there is more than one file with the same name (fie) in an archive
(b.a), then xc32-ar t b.a fie lists only the first instance; to see them all, you
must ask for a complete listing in xc32-ar t b.a.
xExtract members (named MEMBER) from the archive. You can use the v modifier
with this operation, to request that the archiver list each name as it extracts it.
If you do not specify a MEMBER, all files in the archive are extracted.
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A number of modifiers (MOD) may immediately follow the P key letter to specify
variations on an operation’s behavior.
TABLE 12-2: MODIFIERS
Option Function
aAdd new files after an existing member of the archive. If you use the modifier a,
the name of an existing archive member must be present as the RELPOS
argument, before the ARCHIVE specification.
bAdd new files before an existing member of the archive. If you use the modifier
b, the name of an existing archive member must be present as the RELPOS
argument, before the ARCHIVE specification. (Same as i.)
cCreate the archive. The specified ARCHIVE is always created if it did not exist,
when you requested an update. But a warning is issued unless you specify in
advance that you expect to create it, by using this modifier.
fTruncate names in the archive. The 32-bit archiver/librarian will normally permit
file names of any length. This will cause it to create archives that are not compat-
ible with the native archiver program on some systems. If this is a concern, the f
modifier may be used to truncate file names when putting them in the archive.
iInsert new files before an existing member of the archive. If you use the modifier
i, the name of an existing archive member must be present as the RELPOS
argument, before the ARCHIVE specification. (Same as b.)
lThis modifier is accepted but not used.
NUses the COUNT parameter. This is used if there are multiple entries in the
archive with the same name. Extract or delete instance COUNT of the given
name from the archive.
oPreserve the original dates of members when extracting them. If you do not
specify this modifier, files extracted from the archive are stamped with the time of
extraction.
PUse the full path name when matching names in the archive. The 32-bit
archiver/librarian cannot create an archive with a full path name (such archives
are not POSIX compliant), but other archive creators can. This option will cause
the archiver to match file names using a complete path name, which can be
convenient when extracting a single file from an archive created by another tool.
sWrite an object-file index into the archive, or update an existing one, even if no
other change is made to the archive. You may use this modifier flag either with
any operation, or alone. Running xc32-ar s on an archive is equivalent to
running ranlib on it.
SDo not generate an archive symbol table. This can speed up building a large
library in several steps. The resulting archive cannot be used with the linker. In
order to build a symbol table, you must omit the S modifier on the last execution
of the archiver, or you must run ranlib on the archive.
uNormally, xc32-ar r... inserts all files listed into the archive. If you would like to
insert only those of the files you list that are newer than existing members of the
same names, use this modifier. The u modifier is allowed only for the operation r
(replace). In particular, the combination qu is not allowed, since checking the
timestamps would lose any speed advantage from the operation q.
vThis modifier requests the verbose version of an operation. Many operations
display additional information, such as file names processed when the modifier v
is appended.
VThis modifier shows the version number of the 32-bit archiver/librarian.
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12.7 SCRIPTS
If you use the single command line option -M with the archiver, you can control its
operation with a rudimentary command language.
xc32-ar -M [ <SCRIPT ]
This form of the 32-bit archiver/librarian operates interactively if standard input is com-
ing directly from a terminal. During interactive use, the archiver prompts for input (the
prompt is AR >), and continues executing even after errors. If you redirect standard
input to a script file, no prompts are issued, and the 32-bit archiver/librarian abandons
execution (with a nonzero exit code) on any error.
The archiver command language is not designed to be equivalent to the command-line
options; in fact, it provides somewhat less control over archives. The only purpose of
the command language is to ease the transition to the 32-bit archiver/librarian for
developers who already have scripts written for the MRI “librarian” program.
The syntax for the 32-bit archiver/librarian command language is straightforward:
• commands are recognized in upper or lower case; for example, LIST is the same
as list. In the following descriptions, commands are shown in upper case for
clarity.
• a single command may appear on each line; it is the first word on the line.
• empty lines are allowed, and have no effect.
• comments are allowed; text after either of the characters “*” or “;” is ignored.
• Whenever you use a list of names as part of the argument to an xc32-ar
command, you can separate the individual names with either commas or blanks.
Commas are shown in the explanations below, for clarity.
• “+” is used as a line continuation character; if “+” appears at the end of a line, the
text on the following line is considered part of the current command.
Table shows the commands you can use in archiver scripts, or when using the archiver
interactively. Three of them have special significance.
ARCHIVER SCRIPTS COMMANDS
Option Function
OPEN or CREATE Specify a “current archive”, which is a temporary file
required for most of the other commands.
SAVE Commits the changes so far specified by the script.
Prior to SAVE, commands affect only the temporary
copy of the current archive.
ADDLIB ARCHIVE
ADDLIB ARCHIVE (MODULE,
MODULE,...MODULE)
Add all the contents of ARCHIVE (or, if specified,
each named MODULE from ARCHIVE) to the current
archive.
Requires prior use of OPEN or CREATE.
ADDMOD MEMBER, MEMBER, ...
MEMBER
Add each named MEMBER as a module in the current
archive.
Requires prior use of OPEN or CREATE.
CLEAR Discard the contents of the current archive, canceling
the effect of any operations since the last SAVE. May
be executed (with no effect) even if no current
archive is specified.
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CREATE ARCHIVE Creates an archive, and makes it the current archive
(required for many other commands). The new
archive is created with a temporary name; it is not
actually saved as ARCHIVE until you use SAVE. You
can overwrite existing archives; similarly, the
contents of any existing file named ARCHIVE will not
be destroyed until SAVE.
DELETE MODULE, MODULE, ...
MODULE
Delete each listed MODULE from the current archive;
equivalent to xc32-ar -d ARCHIVE MODULE ...
MODULE.
Requires prior use of OPEN or CREATE.
DIRECTORY ARCHIVE (MODULE,
... MODULE) [OUTPUTFILE]
List each named MODULE present in ARCHIVE. The
separate command VERBOSE specifies the form of
the output: when verbose output is off, output is like
that of xc32-ar -t ARCHIVE MODULE.... When
verbose output is on, the listing is like xc32-ar -tv
ARCHIVE MODULE....
Output normally goes to the standard output stream;
however, if you specify OUTPUTFILE as a final
argument, the 32-bit archiver/librarian directs the out-
put to that file.
END Exit from the archiver with a 0 exit code to indicate
successful completion. This command does not save
the output file; if you have changed the current
archive since the last SAVE command, those
changes are lost.
EXTRACT MODULE, MODULE, ...
MODULE
Extract each named MODULE from the current
archive, writing them into the current directory as
separate files. Equivalent to xc32-ar -x ARCHIVE
MODULE....
Requires prior use of OPEN or CREATE.
LIST Display full contents of the current archive, in
“verbose” style regardless of the state of VERBOSE.
The effect is like xc32-ar tv ARCHIVE. (This
single command is a 32-bit archiver/librarian
enhancement, rather than present for MRI
compatibility.)
Requires prior use of OPEN or CREATE.
OPEN ARCHIVE Opens an existing archive for use as the current
archive (required for many other commands). Any
changes as the result of subsequent commands will
not actually affect ARCHIVE until you next use SAVE.
REPLACE MODULE, MODULE, ...
MODULE
In the current archive, replace each existing MODULE
(named in the REPLACE arguments) from files in the
current working directory. To execute this command
without errors, both the file, and the module in the
current archive, must exist.
Requires prior use of OPEN or CREATE.
VERBOSE Toggle an internal flag governing the output from
DIRECTORY. When the flag is on, DIRECTORY
output matches output from xc32-ar -tv ....
SAVE Commits your changes to the current archive and
actually saves it as a file with the name specified in
the last CREATE or OPEN command.
Requires prior use of OPEN or CREATE.
ARCHIVER SCRIPTS COMMANDS (CONTINUED)
Option Function
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NOTES:
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 183
Chapter 13. Other Utilities
13.1 INTRODUCTION
Besides the MPLAB XC32 Object Archiver/Librarian (xc32-ar), there are several other
binary utilities available for use with the MPLAB XC32 Assembler and Linker.
Topics covered in this chapter are:
Utility Description
xc32-bin2hex Utility Converts a linked object file into an Intel® hex file.
xc32-nm Utility Lists symbols from an object file.
xc32-objdump Utility Displays information about object files.
xc32-ranlib Utility Generates an index from the contents of an archive and
stores it in the archive.
xc32-size Utility List file section sizes and total size.
xc32-strings Utility Prints the printable character sequences.
xc32-strip Utility Discards all symbols from an object file.
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13.2 xc32-bin2hex UTILITY
The binary-to-hexadecimal (xc32-bin2hex) utility converts binary files (from the
32-bit linker) to Intel hex format files, suitable for loading into device programmers.
• Input/Output Files
•Syntax
• Options
13.2.1 Input/Output Files
• Input: ELF formatted binary object files
• Output: Intel hex files
13.2.2 Syntax
Command line syntax is:
xc32-bin2hex [options] file
Example 13.1: hello.elf
Convert the absolute ELF executable file hello.elf to hello.hex
xc32-bin2hex hello.elf
13.2.3 Options
The following options are supported.
EXAMPLE 13-2: -v OPTION OUTPUT
writing hello.hex
section PC address byte address length (w/pad) actual length (dec)
------- ---------- ------------ -------------- --------------------
.reset 0 0 0x8 0x6 (6)
.text 0x100 0x200 0x6a28 0x4f9e (20382)
.dinit 0x3614 0x6c28 0xda4 0xa3b (2619)
.const 0x3ce6 0x79cc 0x40 0x30 (48)
.ivt 0x4 0x8 0xf8 0xba (186)
.aivt 0x84 0x108 0xf8 0xba (186)
Total program memory used (bytes): 0x5b83 (23427)
TABLE 13-1: xc32-bin2hex OPTIONS
Option Function
-a, --sort Sort sections by address
-i, --virtual Use virtual addresses
-p, --physical Use physical addresses (default)
-v, --verbose Print verbose messages
-?, --help Print a help screen
Note: See the PIC32MX Family Reference Manual (DS61115) for a description of
the PIC32MX Virtual-to-Physical Fixed Memory Mapping.
Other Utilities
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13.3 xc32-nm UTILITY
The xc32-nm utility produces a list of symbols from object files. Each item in the list
consists of the symbol value, symbol type and symbol name.
• Input Files
•Syntax
• Options
• Output Formats
13.3.1 Input Files
• Input: ELF object file. If no object files are listed as arguments, xc32-nm assumes
the file a.out.
13.3.2 Syntax
Command line syntax is:
xc32-nm [ -A | -o | --print-file-name ]
[ -a | --debug-syms ] [ -B ]
[ --defined-only ] [ -u | --undefined-only ]
[ -f format | --format=format ] [ -g | --extern-only ]
[ --help ] [-l | --line-numbers ]
[ -n | -v | --numeric-sort ] [-omf=format]
[ -p | --no-sort ]
[ -P | --portability ] [ -r | --reverse-sort ]
[ -s --print-armap ] [ --size-sort ]
[ -t radix | --radix=radix ] [ -V | --version ]
[ OBJFILE... ]
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13.3.3 Options
The long and short forms of options, shown in Table 13-2 as alternatives, are
equivalent.
TABLE 13-2: xc32-nm OPTIONS
Option Function
-A
-o
--print-file-name
Precede each symbol by the name of the input file (or archive
member) in which it was found, rather than identifying the
input file once only, before all of its symbols.
-a
--debug-syms
Display all symbols, even debugger-only symbols; normally
these are not listed.
-B The same as --format=bsd.
--defined-only Display only defined symbols for each object file.
-u
--undefined-only
Display only undefined symbols (those external to each object
file).
-f format
--format=format
Use the output format format, which can be bsd, sysv or
posix. The default is bsd. Only the first character of format
is significant; it can be either upper or lower case.
-g
--extern-only
Display only external symbols.
--help Show a summary of the options to xc32-nm and exit.
-l
--line-numbers
For each symbol, use debugging information to try to find a
filename and line number. For a defined symbol, look for the
line number of the address of the symbol. For an undefined
symbol, look for the line number of a relocation entry that
refers to the symbol. If line number information can be found,
print it after the other symbol information.
-n
-v
--numeric-sort
Sort symbols numerically by their addresses, rather than
alphabetically by their names.
-p
--no-sort
Do not bother to sort the symbols in any order; print them in
the order encountered.
-P
--portability
Use the POSIX.2 standard output format instead of the default
format. Equivalent to -f posix.
-r
--reverse-sort
Reverse the order of the sort (whether numeric or alphabetic);
let the last come first.
-s
--print-armap
When listing symbols from archive members, include the
index: a mapping (stored in the archive by xc32-ar or
xc32-ranlib) of which modules contain definitions for which
names.
--size-sort Sort symbols by size. The size is computed as the difference
between the value of the symbol and the value of the symbol
with the next higher value. The size of the symbol is printed,
rather than the value.
-t radix
--radix=radix
Use radix as the radix for printing the symbol values. It must
be d for decimal, o for octal or x for hexadecimal.
-V
--version
Show the version number of xc32-nm and exit.
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13.3.4 Output Formats
The symbol value is in the radix selected by the options, or hexadecimal by default.
If the symbol type is lowercase, the symbol is local; if uppercase, the symbol is global
(external). Table 13-3 shows the symbol types:
TABLE 13-3: SYMBOL TYPES
Symbol Description
A The symbol’s value is absolute, and will not be changed by further linking.
B The symbol is in the uninitialized data section (known as BSS).
C The symbol is common. Common symbols are uninitialized data. When linking,
multiple common symbols may appear with the same name. If the symbol is
defined anywhere, the common symbols are treated as undefined references.
D The symbol is in the initialized data section.
N The symbol is a debugging symbol.
R The symbol is in a read only data section.
T The symbol is in the text (code) section.
U The symbol is undefined.
V The symbol is a weak object. When a weak defined symbol is linked with a normal
defined symbol, the normal defined symbol is used with no error. When a weak
undefined symbol is linked and the symbol is not defined, the value of the weak
symbol becomes zero with no error.
W The symbol is a weak symbol that has not been specifically tagged as a weak
object symbol. When a weak defined symbol is linked with a normal defined
symbol, the normal defined symbol is used with no error. When a weak undefined
symbol is linked and the symbol is not defined, the value of the weak symbol
becomes zero with no error.
? The symbol type is unknown, or object file format specific.
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13.4 xc32-objdump UTILITY
The xc32-objdump utility displays information about one or more object files. The
options control what particular information to display. The output can provide
information similar to that of a disassembly listing.
• Input Files
•Syntax
• Options
13.4.1 Input Files
• Input: Object archive files. If no object files are listed as arguments,
xc32-objdump assumes the file a.out.
13.4.2 Syntax
Command line syntax is:
xc32-objdump [ -a | --archive-headers ]
[ -d | --disassemble ]
[ -D | --disassemble-all ]
[ -f | --file-headers ]
[ --file-start-context ]
[ -g | --debugging ]
[ -h | --section-headers | --headers ]
[ -H | --help ]
[ -j name | --section=name ]
[ -l | --line-numbers ]
[ -M options | --disassembler-options=options]
[ --prefix-addresses]
[ -r | --reloc ]
[ -s | --full-contents ]
[ -S | --source ]
[ --[no-]show-raw-insn ]
[ --start-address=address ]
[ --stop-address=address ]
[ -t | --syms ]
[ -V | --version ]
[ -w | --wide ]
[ -x | --all-headers ]
[ -z | --disassemble-zeros ]
OBJFILE...
OBJFILE… are the object files to be examined. When you specify archives,
xc32-objdump shows information on each of the member object files.
Other Utilities
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13.4.3 Options
The long and short forms of options, shown in Table 13-4, as alternatives, are
equivalent. At least one of the following options -a, -d, -D, -f, -g, -G, -h,
-H, -p, -r, -R, -S, -t, -T, -V or -x must be given.
TABLE 13-4: xc32-objdump OPTIONS
Option Function
-a
--archive-header
If any of the OBJFILE files are archives, display the archive
header information (in a format similar to ls -l). Besides
the information you could list with xc32-ar tv,
xc32-objdump -a shows the object file format of each
archive member.
-d
--disassemble
Display the assembler mnemonics for the machine
instructions from OBJFILE. This option only disassembles
those sections that are expected to contain instructions.
-D
--disassemble-all
Like -d, but disassemble the contents of all sections, not
just those expected to contain instructions.
-f
--file-header
Display summary information from the overall header of
each of the OBJFILE files.
--file-start-context Specify that when displaying inter-listed source
code/disassembly (assumes ‘-S’) from a file that has not
yet been displayed, extend the context to the start of the file.
-g
--debugging
Display debugging information. This attempts to parse
debugging information stored in the file and print it out using
a C like syntax. Only certain types of debugging information
have been implemented.
-h
--section-header
--header
Display summary information from the section headers of
the object file.
File segments may be relocated to nonstandard addresses,
for example by using the -Ttext, -Tdata or -Tbss
options to ld. However, some object file formats, such as
a.out, do not store the starting address of the file
segments. In those situations, although ld relocates the
sections correctly, using xc32-objdump -h to list the file
section headers cannot show the correct addresses.
Instead, it shows the usual addresses, which are implicit for
the target.
-H
--help
Print a summary of the options to xc32-objdump and exit.
-j name
--section=name
Display information only for section name.
-l
--line-numbers
Label the display (using debugging information) with the
filename and source line numbers corresponding to the
object code or relocs shown. Only useful with -d, -D or
-r.
-M options
--disassembler-
options=options
Pass target specific information to the disassembler. The
PIC32 device supports the following target specific options:
symbolic - Will perform symbolic disassembly.
--prefix-addresses When disassembling, print the complete address on each
line. This is the older disassembly format.
-r
--reloc
Print the relocation entries of the file. If used with -d or -D,
the relocations are printed interspersed with the
disassembly.
-s
--full-contents
Display the full contents of any sections requested.
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-S
--source
Display source code intermixed with disassembly, if
possible. Implies -d.
--show-raw-insn When disassembling instructions, print the instruction in
hex, as well as in symbolic form. This is the default except
when --prefix-addresses is used.
--no-show-raw-insn When disassembling instructions, do not print the
instruction bytes. This is the default when
--prefix-addresses is used.
--start-address=address Start displaying data at the specified address. This affects
the output of the -d, -r and -s options.
--stop-address=address Stop displaying data at the specified address. This affects
the output of the -d, -r and -s options.
-t
--syms
Print the symbol table entries of the file. This is similar to the
information provided by the xc32-nm program.
-V
--version
Print the version number of xc32-objdump and exit.
-w
--wide
Format some lines for output devices that have more than
80 columns.
-x
--all-header
Display all available header information, including the
symbol table and relocation entries. Using -x is equivalent
to specifying all of -a -f -h -r -t.
-z
--disassemble-zeroes
Normally the disassembly output will skip blocks of zeros.
This option directs the disassembler to disassemble those
blocks, just like any other data.
TABLE 13-4: xc32-objdump OPTIONS (CONTINUED)
Option Function
Other Utilities
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13.5 xc32-ranlib UTILITY
The xc32-ranlib utility generates an index to the contents of an archive and stores
it in the archive. The index lists each symbol defined by a member of an archive that is
a relocatable object file. You may use xc32-nm -s or xc32-nm --print-armap to
list this index. An archive with such an index speeds up linking to the library and allows
routines in the library to call each other without regard to their placement in the archive.
Running xc32-ranlib is completely equivalent to executing xc32-ar -s (i.e., the
32-bit archiver/librarian with the -s option).
• Input/Output Files
•Syntax
• Options
13.5.1 Input/Output Files
• Input: Archive file
• Output: Archive file
13.5.2 Syntax
Command line syntax is:
xc32-ranlib [-v | -V | --version] ARCHIVE
xc32-ranlib [-h | --help]
13.5.3 Options
The long and short forms of options, shown here as alternatives, are equivalent.
TABLE 13-5: xc32-ranlib OPTIONS
Option Function
-v
-V
--version
Show the version number of xc32-ranlib
-h
--help
Print a help message
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13.6 xc32-size UTILITY
The xc32-size utility lists the section sizes, and the total size, for each of the object
or archive files in its argument list. By default, one line of output is generated for each
object file or each module in an archive.
• Input/Output Files
•Syntax
• Options
•Example
13.6.1 Input/Output Files
• Input: Object or archive file(s)
• Output: Standard output
13.6.2 Syntax
The xc32-size command-line syntax is:
xc32-size [ -A | -B | --format=compatibility ]
[ --help ]
[ -d | -o | -x | --radix= number]
[ -t | --totals ]
[ -V | --version ]
[objfile...]
13.6.3 Options
The xc32-size options are shown below.
Note: The linker's --report-mem memory-usage report provides additional
information on memory usage.
TABLE 13-6: xc32-size OPTIONS
Option Function
-A
-B
--format=compatibility
Using one of these options, you can choose whether the out-
put from gnu size resembles output from System V size (using
-A or --format=sysv), or Berkeley size (using -B or
--format=berkeley). The default is the one-line format
similar to Berkeley's.
--help Show a summary of acceptable arguments and options.
-d
-o
-x
--radix=number
Using one of these options, you can control whether the size
of each section is given in decimal (-d or --radix=10); octal
(-o or --radix=8); or hexadecimal (-x or --radix=16). In
--radix=number, only the three values (8, 10, 16) are
supported. The total size is always given in two radices;
decimal and hexadecimal for -d or -x output, or octal and
hexadecimal if you're using -o.
-t
--totals
Show totals of all objects listed (Berkeley format listing mode
only).
-V
--version
Display the version number of xc32-size.
Other Utilities
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13.6.4 Example
Here is an example of the Berkeley (default) format of output from size:
xc32-size --format=Berkeley ranlib size
text data bss dec hex filename
294880 81920 11592 388392 5ed28 ranlib
294880 81920 11888 388688 5ee50 size
This is the same data, but displayed closer to System V conventions:
xc32-size --format=SysV ranlib size
ranlib :
section size addr
.text 294880 8192
.data 81920 303104
.bss 11592 385024
Total 388392
size :
section size addr
.text 294880 8192
.data 81920 303104
.bss 11888 385024
Total 388688
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13.7 xc32-strings UTILITY
For each file given, the xc32-strings utility prints the printable character sequences
that are at least 4 characters long (or the number given in the options) and are followed
by an unprintable character. By default, it only prints the strings from the initialized and
loaded sections of object files; for other types of files, it prints the strings from the whole
file.
xc32-strings is mainly useful for determining the contents of non-text files.
• Input/Output Files
•Syntax
• Options
13.7.1 Input/Output Files
• Input: ELF object file
• Output: Standard output
13.7.2 Syntax
Command line syntax is:
xc32-strings [-a | --all | -] [-f | --print-file-name]
[--help] [-min-len | -n min-len | --bytes=min-len]
[-t radix | --radix=radix] [-v | --version] FILE...
13.7.3 Options
The long and short forms of options, shown in Table 13-7 as alternatives, are
equivalent.
TABLE 13-7: xc32-strings OPTIONS
Option Function
-a
--all
-
Do not scan only the initialized and loaded sections of object files;
scan the whole files.
-f
--print-file-name
Print the name of the file before each string.
--help Print a summary of the program usage on the standard output and
exit.
-min-len
-n min-len
--bytes=min-len
Print sequences of characters that are at least -min-len
characters long, instead of the default 4.
-t radix
--radix=radix
Print the offset within the file before each string. The single
character argument specifies the radix of the offset - o for octal, x
for hexadecimal or d for decimal.
-v
--version
Print the program version number on the standard output and exit.
Other Utilities
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13.8 xc32-strip UTILITY
The xc32-strip utility discards all symbols from the object and archive files
specified. At least one file must be given. xc32-strip modifies the files named in its
argument, rather than writing modified copies under different names.
• Input/Output Files
•Syntax
• Options
13.8.1 Input/Output Files
• Input: Object or archive files
• Output: Object or archive files. If no object or archive files are listed as arguments,
xc32-strip assumes the file a.out.
13.8.2 Syntax
Command line syntax is:
xc32-strip [ -g | -S | --strip-debug ] [ --help ]
[ -K symbolname | --keep-symbol=symbolname ]
[ -N symbolname | --strip-symbol=symbolname ]
[ -o file ]
[ -p | --preserve-dates ]
[ -R sectionname | --remove-section=sectionname ]
[ -s | --strip-all ] [--strip-unneeded]
[ -v | --verbose ] [ -V | --version ]
[ -x | --discard-all ] [ -X | --discard-locals ]
OBJFILE...
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13.8.3 Options
The long and short forms of options, shown in Table 13-8 as alternatives, are equivalent.
TABLE 13-8: xc32-strip OPTIONS
Option Function
-g
-S
--strip-debug
Remove debugging symbols only.
--help Show a summary of the options to xc32-strip and
exit.
-K symbolname
--keep-symbol=symbolname
Keep only symbol symbolname from the source file.
This option may be given more than once.
-N symbolname
--strip-symbol=symbolname
Remove symbol symbolname from the source file.
This option may be given more than once, and may
be combined with strip options other than -K.
-o file Put the stripped output in file, rather than replacing
the existing file. When this argument is used, only
one OBJFILE argument may be specified.
-p
--preserve-dates
Preserve the access and modification dates of the
file.
-R sectionname
--remove-section=sectionname
Remove any section named sectionname from the
output file. This option may be given more than once.
Note that using this option inappropriately may make
the output file unusable.
-s
--strip-all
Remove all symbols.
--strip-unneeded Remove all symbols that are not needed for
relocation processing.
-v
--verbose
Verbose output: list all object files modified. In the
case of archives, xc32-strip -v lists all members
of the archive.
-V
--version
Show the version number for xc32-strip.
-x
--discard-all
Remove non-global symbols.
-X
--discard-locals
Remove compiler-generated local symbols.
(These usually start with L or “.”.)
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USER’S GUIDE
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Part 4 – Appendices
Appendix A. Deprecated Features............................................................................ 199
Appendix B. Useful Tables ........................................................................................ 201
Appendix C. GNU Free Documentation License ..................................................... 203
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NOTES:
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Appendix A. Deprecated Features
A.1 INTRODUCTION
The features described below are considered to be obsolete and have been replaced
with more advanced functionality. Projects that depend on deprecated features will
work properly with versions of the language tools cited. The use of a deprecated fea-
ture will result in a warning; programmers are encouraged to revise their projects in
order to eliminate any dependency on deprecated features. Support for these features
may be removed entirely in future versions.
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A.2 ASSEMBLER DIRECTIVES THAT DEFINE SECTIONS
The following .section directive format was deprecated in XC32 v2.00. The new
directive format may be found in Section 4.2 “Directives that Define Sections”.
.section name [, flags] [, @type]
Use the .section directive to assemble the following code into a section named
name. The optional flags argument is a quoted string which may contain any
combination of the following characters:
asection is allocatable
wsection is writable
xsection is executable
The @type argument may be one of:
@progbits Normal section with contents
@nobits Section does not contain data (i.e., section only occupies space)
The following section names are recognized:
Section Directive Examples
.section foo,"aw",@progbits #foo is initialized
#data memory.
.section fob,"aw",@nobits #fob is uninitialized
#(but also not zeroed)
#data memory.
.section bar,"ax",@progbits #bar is in program memory
TABLE A-1: SECTION NAMES
Section Name Default Flag
.text x
.data d
.bss b
Note: Ensure that double quotes are used around flags. If the optional argument
to the .section directive is not quoted, it is taken as a sub-section
number. Remember, a single character in single quotes (i.e., ‘b’) is
converted by the preprocessor to a number.
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USER’S GUIDE
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Appendix B. Useful Tables
B.1 INTRODUCTION
Here are some useful tables included for reference.
• ASCII Character Set
• Hexadecimal to Decimal Conversion
B.2 ASCII CHARACTER SET
This table lists the ASCII standard character set.
Least
Significant
Nibble
Most Significant Nibble
HEX01234567
0NUL DLE Space 0 @ P ` p
1SOH DC1 ! 1 A Q a q
2STX DC2 " 2 B R b r
3ETX DC3 # 3 C S c s
4EOT DC4 $ 4 D T d t
5ENQ NAK % 5 E U e u
6ACK SYN & 6 F V f v
7Bell ETB ' 7 G W g w
8BS CAN ( 8 H X h x
9HT EM ) 9 I Y i y
ALF SUB * : J Z j z
BVT ESC + ; K [ k {
CFF FS , < L \ l |
DCR GS – = M ] m }
ESO RS . > N ^ n ~
FSI US / ? O _ o DEL
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B.3 HEXADECIMAL TO DECIMAL CONVERSION
This table describes how to convert hexadecimal to decimal. For each hex digit, find
the associated decimal value. Add the numbers together.
For example, hex A38F converts to 41871 as follows:
High Byte Low Byte
Hex 1000 Dec Hex 100 Dec Hex 10 Dec Hex 1 Dec
00000000
1 4096 1 256 1 16 1 1
2 8192 2 512 2 32 2 2
3 12288 3 768 3 48 3 3
4 16384 4 1024 4 64 4 4
5 20480 5 1280 5 80 5 5
6 24576 6 1536 6 96 6 6
7 28672 7 1792 7 112 7 7
8 32768 8 2048 8 128 8 8
9 36864 9 2304 9 144 9 9
A 40960 A 2560 A 160 A 10
B 45056 B 2816 B 176 B 11
C 49152 C 3072 C 192 C 12
D 53248 D 3328 D 208 D 13
E 57344 E 3584 E 224 E 14
F 61440 F 3840 F 240 F 15
Hex 1000’s Digit Hex 100’s Digit Hex 10’s Digit Hex 1’s Digit Result
40960 768 128 15 41871 Decimal
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LINKER AND UTILITIES
USER’S GUIDE
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Appendix C. GNU Free Documentation License
Copyright (C) 2010 Microchip Technology Inc.
Permission is granted to copy, distribute and/or modify this document under the terms
of the GNU Free Documentation License, Version 1.3 or any later version published by
the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and
no Back-Cover Texts.
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NOTES:
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Glossary
A
Absolute Section
A GCC compiler section with a fixed (absolute) address that cannot be changed by the
linker.
Absolute Variable/Function
A variable or function placed at an absolute address using the OCG compiler’s @
address syntax.
Access Memory
PIC18 Only – Special registers on PIC18 devices that allow access regardless of the
setting of the Bank Select Register (BSR).
Access Entry Points
Access entry points provide a way to transfer control across segments to a function
which may not be defined at link time. They support the separate linking of boot and
secure application segments.
Address
Value that identifies a location in memory.
Alphabetic Character
Alphabetic characters are those characters that are letters of the Arabic alphabet
(a,b,…,z,A,B, …,Z).
Alphanumeric
Alphanumeric characters are comprised of alphabetic characters and decimal digits
(0,1, …, 9).
ANDed Breakpoints
Set up an ANDed condition for breaking, i.e., breakpoint 1 AND breakpoint 2 must
occur at the same time before a program halt. This can only be accomplished if a data
breakpoint and a program memory breakpoint occur at the same time.
Anonymous Structure
16-bit C Compiler – An unnamed structure.
PIC18 C Compiler – An unnamed structure that is a member of a C union. The
members of an anonymous structure may be accessed as if they were members of the
enclosing union. For example, in the following code, hi and lo are members of an
anonymous structure inside the union caster.
union castaway
int intval;
struct {
char lo; //accessible as caster.lo
char hi; //accessible as caster.hi
};
} caster;
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ANSI
American National Standards Institute is an organization responsible for formulating
and approving standards in the United States.
Application
A set of software and hardware that may be controlled by a PIC® microcontroller.
Archive/Archiver
An archive/library is a collection of relocatable object modules. It is created by
assembling multiple source files to object files, and then using the archiver/librarian to
combine the object files into one archive/library file. An archive/library can be linked
with object modules and other archives/libraries to create executable code.
ASCII
American Standard Code for Information Interchange is a character set encoding that
uses 7 binary digits to represent each character. It includes upper and lower case
letters, digits, symbols and control characters.
Assembly/Assembler
Assembly is a programming language that describes binary machine code in a
symbolic form. An assembler is a language tool that translates assembly language
source code into machine code.
Assigned Section
A GCC compiler section which has been assigned to a target memory block in the linker
command file.
Asynchronously
Multiple events that do not occur at the same time. This is generally used to refer to
interrupts that may occur at any time during processor execution.
Asynchronous Stimulus
Data generated to simulate external inputs to a simulator device.
Attribute
GCC Characteristics of variables or functions in a C program which are used to
describe machine-specific properties.
Attribute, Section
GCC Characteristics of sections, such as “executable”, “readonly”, or “data” that can
be specified as flags in the assembler .section directive.
B
Binary
The base two numbering system that uses the digits 0-1. The rightmost digit counts
ones, the next counts multiples of 2, then 22 = 4, etc.
Bookmarks
Use bookmarks to easily locate specific lines in a file.
Select Toggle Bookmarks on the Editor toolbar to add/remove bookmarks. Click other
icons on this toolbar to move to the next or previous bookmark.
Breakpoint
Hardware Breakpoint: An event whose execution will cause a halt.
Software Breakpoint: An address where execution of the firmware will halt. Usually
achieved by a special break instruction.
Glossary
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Build
Compile and link all the source files for an application.
C
C\C++
C is a general-purpose programming language which features economy of expression,
modern control flow and data structures, and a rich set of operators. C++ is the
object-oriented version of C.
Calibration Memory
A special function register or registers used to hold values for calibration of a PIC
microcontroller on-board RC oscillator or other device peripherals.
Central Processing Unit
The part of a device that is responsible for fetching the correct instruction for execution,
decoding that instruction, and then executing that instruction. When necessary, it works
in conjunction with the arithmetic logic unit (ALU) to complete the execution of the
instruction. It controls the program memory address bus, the data memory address
bus, and accesses to the stack.
Clean
Clean removes all intermediary project files, such as object, hex and debug files, for
the active project. These files are recreated from other files when a project is built.
COFF
Common Object File Format. An object file of this format contains machine code,
debugging and other information.
Command Line Interface
A means of communication between a program and its user based solely on textual
input and output.
Compiled Stack
A region of memory managed by the compiler in which variables are statically allocated
space. It replaces a software or hardware stack when such mechanisms cannot be
efficiently implemented on the target device.
Compiler
A program that translates a source file written in a high-level language into machine
code.
Conditional Assembly
Assembly language code that is included or omitted based on the assembly-time value
of a specified expression.
Conditional Compilation
The act of compiling a program fragment only if a certain constant expression, specified
by a preprocessor directive, is true.
Configuration Bits
Special-purpose bits programmed to set PIC microcontroller modes of operation. A
Configuration bit may or may not be preprogrammed.
Control Directives
Directives in assembly language code that cause code to be included or omitted based
on the assembly-time value of a specified expression.
CPU
See Central Processing Unit.
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Cross Reference File
A file that references a table of symbols and a list of files that references the symbol. If
the symbol is defined, the first file listed is the location of the definition. The remaining
files contain references to the symbol.
D
Data Directives
Data directives are those that control the assembler’s allocation of program or data
memory and provide a way to refer to data items symbolically; that is, by meaningful
names.
Data Memory
On Microchip MCU and DSC devices, data memory (RAM) is comprised of General
Purpose Registers (GPRs) and Special Function Registers (SFRs). Some devices also
have EEPROM data memory.
Data Monitor and Control Interface (DMCI)
The Data Monitor and Control Interface, or DMCI, is a tool in MPLAB X IDE. The
interface provides dynamic input control of application variables in projects.
Application-generated data can be viewed graphically using any of 4
dynamically-assignable graph windows.
Debug/Debugger
See ICE/ICD.
Debugging Information
Compiler and assembler options that, when selected, provide varying degrees of
information used to debug application code. See compiler or assembler documentation
for details on selecting debug options.
Deprecated Features
Features that are still supported for legacy reasons, but will eventually be phased out
and no longer used.
Device Programmer
A tool used to program electrically programmable semiconductor devices such as
microcontrollers.
Digital Signal Controller
A A digital signal controller (DSC) is a microcontroller device with digital signal
processing capability, i.e., Microchip dsPIC DSC devices.
Digital Signal Processing\Digital Signal Processor
Digital signal processing (DSP) is the computer manipulation of digital signals,
commonly analog signals (sound or image) which have been converted to digital form
(sampled). A digital signal processor is a microprocessor that is designed for use in
digital signal processing.
Directives
Statements in source code that provide control of the language tool’s operation.
Download
Download is the process of sending data from a host to another device, such as an
emulator, programmer or target board.
DWARF
Debug With Arbitrary Record Format. DWARF is a debug information format for ELF
files.
Glossary
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E
EEPROM
Electrically Erasable Programmable Read Only Memory. A special type of PROM that
can be erased electrically. Data is written or erased one byte at a time. EEPROM
retains its contents even when power is turned off.
ELF
Executable and Linking Format. An object file of this format contains machine code.
Debugging and other information is specified in with DWARF. ELF/DWARF provide
better debugging of optimized code than COFF.
Emulation/Emulator
See ICE/ICD.
Endianness
The ordering of bytes in a multi-byte object.
Environment
MPLAB PM3 – A folder containing files on how to program a device. This folder can be
transferred to a SD/MMC card.
Epilogue
A portion of compiler-generated code that is responsible for deallocating stack space,
restoring registers and performing any other machine-specific requirement specified in
the runtime model. This code executes after any user code for a given function,
immediately prior to the function return.
EPROM
Erasable Programmable Read Only Memory. A programmable read-only memory that
can be erased usually by exposure to ultraviolet radiation.
Error/Error File
An error reports a problem that makes it impossible to continue processing your
program. When possible, an error identifies the source file name and line number
where the problem is apparent. An error file contains error messages and diagnostics
generated by a language tool.
Event
A description of a bus cycle which may include address, data, pass count, external
input, cycle type (fetch, R/W), and time stamp. Events are used to describe triggers,
breakpoints and interrupts.
Executable Code
Software that is ready to be loaded for execution.
Export
Send data out of the MPLAB IDE/MPLAB X IDE in a standardized format.
Expressions
Combinations of constants and/or symbols separated by arithmetic or logical
operators.
Extended Microcontroller Mode
In extended microcontroller mode, on-chip program memory as well as external
memory is available. Execution automatically switches to external if the program
memory address is greater than the internal memory space of the PIC18 device.
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Extended Mode (PIC18 MCUs)
In Extended mode, the compiler will utilize the extended instructions (i.e., ADDFSR,
ADDULNK, CALLW, MOVSF, MOVSS, PUSHL, SUBFSR and SUBULNK) and the indexed
with literal offset addressing.
External Label
A label that has external linkage.
External Linkage
A function or variable has external linkage if it can be referenced from outside the
module in which it is defined.
External Symbol
A symbol for an identifier which has external linkage. This may be a reference or a
definition.
External Symbol Resolution
A process performed by the linker in which external symbol definitions from all input
modules are collected in an attempt to resolve all external symbol references. Any
external symbol references which do not have a corresponding definition cause a linker
error to be reported.
External Input Line
An external input signal logic probe line (TRIGIN) for setting an event based upon
external signals.
External RAM
Off-chip Read/Write memory.
F
Fatal Error
An error that will halt compilation immediately. No further messages will be produced.
File Registers
On-chip data memory, including General Purpose Registers (GPRs) and Special
Function Registers (SFRs).
Filter
Determine by selection what data is included/excluded in a trace display or data file.
Fixup
The process of replacing object file symbolic references with absolute addresses after
relocation by the linker.
Flash
A type of EEPROM where data is written or erased in blocks instead of bytes.
FNOP
Forced No Operation. A forced NOP cycle is the second cycle of a two-cycle
instruction. Since the PIC microcontroller architecture is pipelined, it prefetches the
next instruction in the physical address space while it is executing the current
instruction. However, if the current instruction changes the program counter, this
prefetched instruction is explicitly ignored, causing a forced NOP cycle.
Frame Pointer
A pointer that references the location on the stack that separates the stack-based
arguments from the stack-based local variables. Provides a convenient base from
which to access local variables and other values for the current function.
Glossary
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Free-Standing
An implementation that accepts any strictly conforming program that does not use
complex types and in which the use of the features specified in the library clause (ANSI
‘89 standard clause 7) is confined to the contents of the standard headers <float.h>,
<iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>, <stddef.h> and
<stdint.h>.
G
GPR
General Purpose Register. The portion of device data memory (RAM) available for
general use.
H
Halt
A stop of program execution. Executing Halt is the same as stopping at a breakpoint.
Heap
An area of memory used for dynamic memory allocation where blocks of memory are
allocated and freed in an arbitrary order determined at runtime.
Hex Code\Hex File
Hex code is executable instructions stored in a hexadecimal format code. Hex code is
contained in a hex file.
Hexadecimal
The base 16 numbering system that uses the digits 0-9 plus the letters A-F (or a-f). The
digits A-F represent hexadecimal digits with values of (decimal) 10 to 15. The rightmost
digit counts ones, the next counts multiples of 16, then 162 = 256, etc.
High Level Language
A language for writing programs that is further removed from the processor than
assembly.
I
ICE/ICD
In-Circuit Emulator/In-Circuit Debugger: A hardware tool that debugs and programs a
target device. An emulator has more features than an debugger, such as trace.
In-Circuit Emulation/In-Circuit Debug: The act of emulating or debugging with an
in-circuit emulator or debugger.
-ICE/-ICD: A device (MCU or DSC) with on-board in-circuit emulation or debug circuitry.
This device is always mounted on a header board and used to debug with an in-circuit
emulator or debugger.
ICSP
In-Circuit Serial Programming. A method of programming Microchip embedded
devices using serial communication and a minimum number of device pins.
IDE
Integrated Development Environment, as in MPLAB IDE/MPLAB X IDE.
Identifier
A function or variable name.
IEEE
Institute of Electrical and Electronics Engineers.
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Import
Bring data into the MPLAB IDE/MPLAB X IDE from an outside source, such as from a
hex file.
Initialized Data
Data which is defined with an initial value. In C,
int myVar=5;
defines a variable which will reside in an initialized data section.
Instruction Set
The collection of machine language instructions that a particular processor
understands.
Instructions
A sequence of bits that tells a central processing unit to perform a particular operation
and can contain data to be used in the operation.
Internal Linkage
A function or variable has internal linkage if it can not be accessed from outside the
module in which it is defined.
International Organization for Standardization
An organization that sets standards in many businesses and technologies, including
computing and communications. Also known as ISO.
Interrupt
A signal to the CPU that suspends the execution of a running application and transfers
control to an Interrupt Service Routine (ISR) so that the event may be processed. Upon
completion of the ISR, normal execution of the application resumes.
Interrupt Handler
A routine that processes special code when an interrupt occurs.
Interrupt Service Request (IRQ)
An event which causes the processor to temporarily suspend normal instruction
execution and to start executing an interrupt handler routine. Some processors have
several interrupt request events allowing different priority interrupts.
Interrupt Service Routine (ISR)
Language tools – A function that handles an interrupt.
MPLAB IDE/MPLAB X IDE – User-generated code that is entered when an interrupt
occurs. The location of the code in program memory will usually depend on the type of
interrupt that has occurred.
Interrupt Vector
Address of an interrupt service routine or interrupt handler.
L
L-value
An expression that refers to an object that can be examined and/or modified. An l-value
expression is used on the left-hand side of an assignment.
Latency
The time between an event and its response.
Library/Librarian
See Archive/Archiver.
Glossary
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Linker
A language tool that combines object files and libraries to create executable code,
resolving references from one module to another.
Linker Script Files
Linker script files are the command files of a linker. They define linker options and
describe available memory on the target platform.
Listing Directives
Listing directives are those directives that control the assembler listing file format. They
allow the specification of titles, pagination and other listing control.
Listing File
A listing file is an ASCII text file that shows the machine code generated for each C
source statement, assembly instruction, assembler directive, or macro encountered in
a source file.
Little Endian
A data ordering scheme for multibyte data whereby the least significant byte is stored
at the lower addresses.
Local Label
A local label is one that is defined inside a macro with the LOCAL directive. These
labels are particular to a given instance of a macro’s instantiation. In other words, the
symbols and labels that are declared as local are no longer accessible after the ENDM
macro is encountered.
Logic Probes
Up to 14 logic probes can be connected to some Microchip emulators. The logic probes
provide external trace inputs, trigger output signal, +5V, and a common ground.
Loop-Back Test Board
Used to test the functionality of the MPLAB REAL ICE in-circuit emulator.
LVDS
Low Voltage Differential Signaling. A low noise, low-power, low amplitude method for
high-speed (gigabits per second) data transmission over copper wire.
With standard I/0 signaling, data storage is contingent upon the actual voltage level.
Voltage level can be affected by wire length (longer wires increase resistance, which
lowers voltage). But with LVDS, data storage is distinguished only by positive and
negative voltage values, not the voltage level. Therefore, data can travel over greater
lengths of wire while maintaining a clear and consistent data stream.
Source: http://www.webopedia.com/TERM/L/LVDS.html.
M
Machine Code
The representation of a computer program that is actually read and interpreted by the
processor. A program in binary machine code consists of a sequence of machine
instructions (possibly interspersed with data). The collection of all possible instructions
for a particular processor is known as its “instruction set”.
Machine Language
A set of instructions for a specific central processing unit, designed to be usable by a
processor without being translated.
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Macro
Macro instruction. An instruction that represents a sequence of instructions in
abbreviated form.
Macro Directives
Directives that control the execution and data allocation within macro body definitions.
Makefile
Export to a file the instructions to Make the project. Use this file to Make your project
outside of MPLAB IDE/MPLAB X IDE, i.e., with a make.
Make Project
A command that rebuilds an application, recompiling only those source files that have
changed since the last complete compilation.
MCU
Microcontroller Unit. An abbreviation for microcontroller. Also uC.
Memory Model
For C compilers, a representation of the memory available to the application. For the
PIC18 C compiler, a description that specifies the size of pointers that point to program
memory.
Message
Text displayed to alert you to potential problems in language tool operation. A message
will not stop operation.
Microcontroller
A highly integrated chip that contains a CPU, RAM, program memory, I/O ports and
timers.
Microcontroller Mode
One of the possible program memory configurations of PIC18 microcontrollers. In
microcontroller mode, only internal execution is allowed. Thus, only the on-chip
program memory is available in microcontroller mode.
Microprocessor Mode
One of the possible program memory configurations of PIC18 microcontrollers. In
microprocessor mode, the on-chip program memory is not used. The entire program
memory is mapped externally.
Mnemonics
Text instructions that can be translated directly into machine code. Also referred to as
opcodes.
Module
The preprocessed output of a source file after preprocessor directives have been
executed. Also known as a translation unit.
MPASM™ Assembler
Microchip Technology’s relocatable macro assembler for PIC microcontroller devices,
KeeLoq® devices and Microchip memory devices.
MPLAB Language Tool for Device
Microchip’s C compilers, assemblers and linkers for specified devices. Select the type
of language tool based on the device you will be using for your application, e.g., if you
will be creating C code on a PIC18 MCU, select the MPLAB C Compiler for PIC18
MCUs.
Glossary
2013 Microchip Technology Inc. DS50002186A-page 215
MPLAB ICD
Microchip in-circuit debugger that works with MPLAB IDE/MPLAB X IDE. See ICE/ICD.
MPLAB IDE/MPLAB X IDE
Microchip’s Integrated Development Environment. MPLAB IDE/MPLAB X IDE comes
with an editor, project manager and simulator.
MPLAB PM3
A device programmer from Microchip. Programs PIC18 microcontrollers and dsPIC
digital signal controllers. Can be used with MPLAB IDE/MPLAB X IDE or stand-alone.
Replaces PRO MATE II.
MPLAB REAL ICE™ In-Circuit Emulator
Microchip’s next-generation in-circuit emulator that works with MPLAB IDE/MPLAB X
IDE. See ICE/ICD.
MPLAB SIM
Microchip’s simulator that works with MPLAB IDE/MPLAB X IDE in support of PIC MCU
and dsPIC DSC devices.
MPLIB™ Object Librarian
Microchip’s librarian that can work with MPLAB IDE/MPLAB X IDE. MPLIB librarian is
an object librarian for use with COFF object modules created using either MPASM
assembler (mpasm or mpasmwin v2.0) or MPLAB C18 C Compiler.
MPLINK™ Object Linker
MPLINK linker is an object linker for the Microchip MPASM assembler and the
Microchip C18 C compiler. MPLINK linker also may be used with the Microchip MPLIB
librarian. MPLINK linker is designed to be used with MPLAB IDE/MPLAB X IDE, though
it does not have to be.
MRU
Most Recently Used. Refers to files and windows available to be selected from MPLAB
IDE/MPLAB X IDE main pull down menus.
N
Native Data Size
For Native trace, the size of the variable used in a Watch window must be of the same
size as the selected device’s data memory: bytes for PIC18 devices and words for
16-bit devices.
Nesting Depth
The maximum level to which macros can include other macros.
Node
MPLAB IDE/MPLAB X IDE project component.
Non-Extended Mode (PIC18 MCUs)
In Non-Extended mode, the compiler will not utilize the extended instructions nor the
indexed with literal offset addressing.
Non Real Time
Refers to the processor at a breakpoint or executing single-step instructions or MPLAB
IDE/MPLAB X IDE being run in simulator mode.
Non-Volatile Storage
A storage device whose contents are preserved when its power is off.
m Ogtions>Develogment Mode
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NOP
No Operation. An instruction that has no effect when executed except to advance the
program counter.
O
Object Code/Object File
Object code is the machine code generated by an assembler or compiler. An object file
is a file containing machine code and possibly debug information. It may be
immediately executable or it may be relocatable, requiring linking with other object files,
e.g., libraries, to produce a complete executable program.
Object File Directives
Directives that are used only when creating an object file.
Octal
The base 8 number system that only uses the digits 0-7. The rightmost digit counts
ones, the next digit counts multiples of 8, then 82 = 64, etc.
Off-Chip Memory
Off-chip memory refers to the memory selection option for the PIC18 device where
memory may reside on the target board, or where all program memory may be supplied
by the emulator. The Memory tab accessed from Options>Development Mode
provides the Off-Chip Memory selection dialog box.
Opcodes
Operational Codes. See Mnemonics.
Operators
Symbols, like the plus sign ‘+’ and the minus sign ‘-’, that are used when forming
well-defined expressions. Each operator has an assigned precedence that is used to
determine order of evaluation.
OTP
One Time Programmable. EPROM devices that are not in windowed packages. Since
EPROM needs ultraviolet light to erase its memory, only windowed devices are
erasable.
P
Pass Counter
A counter that decrements each time an event (such as the execution of an instruction
at a particular address) occurs. When the pass count value reaches zero, the event is
satisfied. You can assign the Pass Counter to break and trace logic, and to any
sequential event in the complex trigger dialog.
PC
Personal Computer or Program Counter.
PC Host
Any PC running a supported Windows operating system.
Persistent Data
Data that is never cleared or initialized. Its intended use is so that an application can
preserve data across a device Reset.
Phantom Byte
An unimplemented byte in the dsPIC architecture that is used when treating the 24-bit
instruction word as if it were a 32-bit instruction word. Phantom bytes appear in dsPIC
hex files.
Glossary
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PIC MCUs
PIC microcontrollers (MCUs) refers to all Microchip microcontroller families.
PICkit 2 and 3
Microchip’s developmental device programmers with debug capability through Debug
Express. See the Readme files for each tool to see which devices are supported.
Plug-ins
The MPLAB IDE/MPLAB X IDE has both built-in components and plug-in modules to
configure the system for a variety of software and hardware tools. Several plug-in tools
may be found under the Tools menu.
Pod
The enclosure for an in-circuit emulator or debugger. Other names are “Puck”, if the
enclosure is round, and “Probe”, not be confused with logic probes.
Power-on-Reset Emulation
A software randomization process that writes random values in data RAM areas to
simulate uninitialized values in RAM upon initial power application.
Pragma
A directive that has meaning to a specific compiler. Often a pragma is used to convey
implementation-defined information to the compiler. MPLAB C30 uses attributes to
convey this information.
Precedence
Rules that define the order of evaluation in expressions.
Production Programmer
A production programmer is a programming tool that has resources designed in to
program devices rapidly. It has the capability to program at various voltage levels and
completely adheres to the programming specification. Programming a device as fast
as possible is of prime importance in a production environment where time is of the
essence as the application circuit moves through the assembly line.
Profile
For MPLAB SIM simulator, a summary listing of executed stimulus by register.
Program Counter
The location that contains the address of the instruction that is currently executing.
Program Counter Unit
16-bit assembler – A conceptual representation of the layout of program memory. The
program counter increments by 2 for each instruction word. In an executable section,
2 program counter units are equivalent to 3 bytes. In a read-only section, 2 program
counter units are equivalent to 2 bytes.
Program Memory
MPLAB IDE/MPLAB X IDE – The memory area in a device where instructions are
stored. Also, the memory in the emulator or simulator containing the downloaded target
application firmware.
16-bit assembler/compiler – The memory area in a device where instructions are
stored.
Project
A project contains the files needed to build an application (source code, linker script
files, etc.) along with their associations to various build tools and build options.
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Prologue
A portion of compiler-generated code that is responsible for allocating stack space,
preserving registers and performing any other machine-specific requirement specified
in the runtime model. This code executes before any user code for a given function.
Prototype System
A term referring to a user's target application, or target board.
Psect
The OCG equivalent of a GCC section, short for program section. A block of code or
data which is treated as a whole by the linker.
PWM Signals
Pulse Width Modulation Signals. Certain PIC MCU devices have a PWM peripheral.
Q
Qualifier
An address or an address range used by the Pass Counter or as an event before
another operation in a complex trigger.
R
Radix
The number base, hex, or decimal, used in specifying an address.
RAM
Random Access Memory (Data Memory). Memory in which information can be
accessed in any order.
Raw Data
The binary representation of code or data associated with a section.
Read Only Memory
Memory hardware that allows fast access to permanently stored data but prevents
addition to or modification of the data.
Real Time
When an in-circuit emulator or debugger is released from the halt state, the processor
runs in Real Time mode and behaves exactly as the normal chip would behave. In Real
Time mode, the real time trace buffer of an emulator is enabled and constantly captures
all selected cycles, and all break logic is enabled. In an in-circuit emulator or debugger,
the processor executes in real time until a valid breakpoint causes a halt, or until the
user halts the execution.
In the simulator, real time simply means execution of the microcontroller instructions as
fast as they can be simulated by the host CPU.
Recursive Calls
A function that calls itself, either directly or indirectly.
Recursion
The concept that a function or macro, having been defined, can call itself. Great care
should be taken when writing recursive macros; it is easy to get caught in an infinite
loop where there will be no exit from the recursion.
Reentrant
A function that may have multiple, simultaneously active instances. This may happen
due to either direct or indirect recursion or through execution during interrupt
processing.
Glossary
2013 Microchip Technology Inc. DS50002186A-page 219
Relaxation
The process of converting an instruction to an identical, but smaller instruction. This is
useful for saving on code size. MPLAB XC32 currently knows how to relax a CALL
instruction into an RCALL instruction. This is done when the symbol that is being called
is within +/- 32k instruction words from the current instruction.
Relocatable
An object whose address has not been assigned to a fixed location in memory.
Relocatable Section
16-bit assembler – A section whose address is not fixed (absolute). The linker assigns
addresses to relocatable sections through a process called relocation.
Relocation
A process performed by the linker in which absolute addresses are assigned to
relocatable sections and all symbols in the relocatable sections are updated to their
new addresses.
ROM
Read Only Memory (Program Memory). Memory that cannot be modified.
Run
The command that releases the emulator from halt, allowing it to run the application
code and change or respond to I/O in real time.
Run-time Model
Describes the use of target architecture resources.
Runtime Watch
A Watch window where the variables change in as the application is run. See individual
tool documentation to determine how to set up a runtime watch. Not all tools support
runtime watches.
S
Scenario
For MPLAB SIM simulator, a particular setup for stimulus control.
Section
The GCC equivalent of an OCG psect. A block of code or data which is treated as a
whole by the linker.
Section Attribute
A GCC characteristic ascribed to a section (e.g., an access section).
Sequenced Breakpoints
Breakpoints that occur in a sequence. Sequence execution of breakpoints is
bottom-up; the last breakpoint in the sequence occurs first.
Serialized Quick Turn Programming
Serialization allows you to program a serial number into each microcontroller device
that the Device Programmer programs. This number can be used as an entry code,
password or ID number.
Shell
The MPASM assembler shell is a prompted input interface to the macro assembler.
There are two MPASM assembler shells: one for the DOS version and one for the
Windows version.
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Simulator
A software program that models the operation of devices.
Single Step
This command steps though code, one instruction at a time. After each instruction,
MPLAB IDE/MPLAB X IDE updates register windows, watch variables, and status
displays so you can analyze and debug instruction execution. You can also single step
C compiler source code, but instead of executing single instructions, MPLAB
IDE/MPLAB X IDE will execute all assembly level instructions generated by the line of
the high level C statement.
Skew
The information associated with the execution of an instruction appears on the
processor bus at different times. For example, the executed opcodes appears on the
bus as a fetch during the execution of the previous instruction, the source data address
and value and the destination data address appear when the opcodes is actually
executed, and the destination data value appears when the next instruction is
executed. The trace buffer captures the information that is on the bus at one instance.
Therefore, one trace buffer entry will contain execution information for three
instructions. The number of captured cycles from one piece of information to another
for a single instruction execution is referred to as the skew.
Skid
When a hardware breakpoint is used to halt the processor, one or more additional
instructions may be executed before the processor halts. The number of extra
instructions executed after the intended breakpoint is referred to as the skid.
Source Code
The form in which a computer program is written by the programmer. Source code is
written in a formal programming language which can be translated into machine code
or executed by an interpreter.
Source File
An ASCII text file containing source code.
Special Function Registers (SFRs)
The portion of data memory (RAM) dedicated to registers that control I/O processor
functions, I/O status, timers or other modes or peripherals.
SQTP
See Serialized Quick Turn Programming.
Stack, Hardware
Locations in PIC microcontroller where the return address is stored when a function call
is made.
Stack, Software
Memory used by an application for storing return addresses, function parameters, and
local variables. This memory is dynamically allocated at runtime by instructions in the
program. It allows for reentrant function calls.
Stack, Compiled
A region of memory managed and allocated by the compiler in which variables are
statically assigned space. It replaces a software stack when such mechanisms cannot
be efficiently implemented on the target device. It precludes reentrancy.
MPLAB Starter Kit for Device
Microchip’s starter kits contains everything needed to begin exploring the specified
device. View a working application and then debug and program you own changes.
Glossary
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Static RAM or SRAM
Static Random Access Memory. Program memory you can read/write on the target
board that does not need refreshing frequently.
Status Bar
The Status Bar is located on the bottom of the MPLAB IDE/MPLAB X IDE window and
indicates such current information as cursor position, development mode and device,
and active tool bar.
Step Into
This command is the same as Single Step. Step Into (as opposed to Step Over) follows
a CALL instruction into a subroutine.
Step Over
Step Over allows you to debug code without stepping into subroutines. When stepping
over a CALL instruction, the next breakpoint will be set at the instruction after the CALL.
If for some reason the subroutine gets into an endless loop or does not return properly,
the next breakpoint will never be reached. The Step Over command is the same as
Single Step except for its handling of CALL instructions.
Step Out
Step Out allows you to step out of a subroutine which you are currently stepping
through. This command executes the rest of the code in the subroutine and then stops
execution at the return address to the subroutine.
Stimulus
Input to the simulator, i.e., data generated to exercise the response of simulation to
external signals. Often the data is put into the form of a list of actions in a text file.
Stimulus may be asynchronous, synchronous (pin), clocked and register.
Stopwatch
A counter for measuring execution cycles.
Storage Class
Determines the lifetime of the memory associated with the identified object.
Storage Qualifier
Indicates special properties of the objects being declared (e.g., const).
Symbol
A symbol is a general purpose mechanism for describing the various pieces which
comprise a program. These pieces include function names, variable names, section
names, file names, struct/enum/union tag names, etc. Symbols in MPLAB IDE/MPLAB
X IDE refer mainly to variable names, function names and assembly labels. The value
of a symbol after linking is its value in memory.
Symbol, Absolute
Represents an immediate value such as a definition through the assembly .equ
directive.
System Window Control
The system window control is located in the upper left corner of windows and some
dialogs. Clicking on this control usually pops up a menu that has the items “Minimize,”
“Maximize,” and “Close.”
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T
Target
Refers to user hardware.
Target Application
Software residing on the target board.
Target Board
The circuitry and programmable device that makes up the target application.
Target Processor
The microcontroller device on the target application board.
Template
Lines of text that you build for inserting into your files at a later time. The MPLAB Editor
stores templates in template files.
Tool Bar
A row or column of icons that you can click on to execute MPLAB IDE/MPLAB X IDE
functions.
Trace
An emulator or simulator function that logs program execution. The emulator logs
program execution into its trace buffer which is uploaded to MPLAB IDE/MPLAB X
IDE’s trace window.
Trace Memory
Trace memory contained within the emulator. Trace memory is sometimes called the
trace buffer.
Trace Macro
A macro that will provide trace information from emulator data. Since this is a software
trace, the macro must be added to code, the code must be recompiled or reassembled,
and the target device must be programmed with this code before trace will work.
Trigger Output
Trigger output refers to an emulator output signal that can be generated at any address
or address range, and is independent of the trace and breakpoint settings. Any number
of trigger output points can be set.
Trigraphs
Three-character sequences, all starting with ??, that are defined by ISO C as
replacements for single characters.
U
Unassigned Section
A section which has not been assigned to a specific target memory block in the linker
command file. The linker must find a target memory block in which to allocate an
unassigned section.
Uninitialized Data
Data which is defined without an initial value. In C,
int myVar;
defines a variable which will reside in an uninitialized data section.
Upload
The Upload function transfers data from a tool, such as an emulator or programmer, to
the host PC or from the target board to the emulator.
Glossary
2013 Microchip Technology Inc. DS50002186A-page 223
USB
Universal Serial Bus. An external peripheral interface standard for communication
between a computer and external peripherals over a cable using bi-serial transmission.
USB 1.0/1.1 supports data transfer rates of 12 Mbps. Also referred to as high-speed
USB, USB 2.0 supports data rates up to 480 Mbps.
V
Vector
The memory locations that an application will jump to when either a Reset or interrupt
occurs.
Volatile
A variable qualifier which prevents the compiler applying optimizations that affect how
the variable is accessed in memory.
W
Warning
MPLAB IDE/MPLAB X IDE – An alert that is provided to warn you of a situation that
would cause physical damage to a device, software file, or equipment.
16-bit assembler/compiler – Warnings report conditions that may indicate a problem,
but do not halt processing. In MPLAB C30, warning messages report the source file
name and line number, but include the text ‘warning:’ to distinguish them from error
messages.
Watch Variable
A variable that you may monitor during a debugging session in a Watch window.
Watch Window
Watch windows contain a list of watch variables that are updated at each breakpoint.
Watchdog Timer (WDT)
A timer on a PIC microcontroller that resets the processor after a selectable length of
time. The WDT is enabled or disabled and set up using Configuration bits.
Workbook
For MPLAB SIM stimulator, a setup for generation of SCL stimulus.
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NOTES:
6‘ MICROCHIP
MPLAB® XC32 ASSEMBLER,
LINKER AND UTILITIES
USER’S GUIDE
2013 Microchip Technology Inc. DS50002186A-page 225
Index
Symbols
. ................................................................................ 52
.abort........................................................................ 76
.align ........................................................................ 66
.ascii......................................................................... 62
.asciz........................................................................ 62
.bss .......................................................................... 58
.bss section .....................................................111, 132
.byte ......................................................................... 62
.comm ...................................................................... 64
.comm symbol, length .............................................. 64
.data ......................................................................... 58
.data section........................................................... 111
.double ..................................................................... 62
.eject ........................................................................ 68
.else ......................................................................... 69
.elseif........................................................................ 69
.end .......................................................................... 77
.endif ........................................................................ 69
.endm ....................................................................... 72
.endr....................................................................71, 74
.ent ........................................................................... 77
.equ .......................................................................... 65
.equiv ....................................................................... 65
.err............................................................................ 76
.error ........................................................................ 76
.exitm ..................................................................71, 72
.extern ...................................................................... 64
.fail ........................................................................... 76
.file ........................................................................... 77
.fill............................................................................. 66
.float ......................................................................... 63
.fmask ...................................................................... 77
.frame....................................................................... 77
.global ...................................................................... 64
.globl ........................................................................ 64
.hword ...................................................................... 63
.ident ........................................................................ 76
.if .............................................................................. 69
.ifc ............................................................................ 69
.ifdecl........................................................................ 69
.ifeq .......................................................................... 69
.ifeqs ........................................................................ 69
.ifge .......................................................................... 69
.ifgt ........................................................................... 70
.ifle ........................................................................... 70
.iflt ............................................................................ 70
.ifnc .......................................................................... 70
.ifndef ....................................................................... 70
.ifne .......................................................................... 70
.ifnes ........................................................................ 70
.ifnotdef .................................................................... 70
.incbin....................................................................... 75
.include..........................................................39, 42, 75
.int ............................................................................ 63
.irp ............................................................................ 71
.irpc .......................................................................... 71
.lcomm...................................................................... 64
.list............................................................................ 68
.loc............................................................................ 77
.long ......................................................................... 63
.macro ...................................................................... 72
.mask........................................................................ 78
.nolist........................................................................ 68
.org ........................................................................... 67
.popsection............................................................... 59
.print ......................................................................... 76
.psize........................................................................ 68
.purgem .................................................................... 73
.pushsection ............................................................. 59
.rept .......................................................................... 74
.sbttl.......................................................................... 68
.section name................................................... 59, 200
.set at ....................................................................... 79
.set autoextend......................................................... 79
.set macro ................................................................ 79
.set mips16e............................................................. 79
.set noat ................................................................... 79
.set noautoextend..................................................... 79
.set nomacro ............................................................ 79
.set nomips16e......................................................... 80
.set noreorder........................................................... 80
.set reorder............................................................... 80
.short ........................................................................ 63
.single....................................................................... 63
.size.......................................................................... 78
.sizeof....................................................................... 55
.skip.......................................................................... 67
.sleb128.................................................................... 78
.space....................................................................... 67
.startof. ..................................................................... 55
.string ....................................................................... 63
.struct ....................................................................... 67
.text .......................................................................... 61
.text section ............................................................ 112
.title........................................................................... 68
.type ......................................................................... 78
.uleb128 ................................................................... 78
.version..................................................................... 76
.warning.................................................................... 76
.weak................................................................ 64, 153
.word ........................................................................ 63
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-( -) ......................................................................... 108
/@............................................................................. 73
A
-a .............................................................................. 25
a.out ............................................................19, 38, 110
-a=file ....................................................................... 35
-ac ............................................................................ 26
Accessing Data ........................................................ 55
-ad ............................................................................ 28
ADDR ..................................................................... 143
-ah ............................................................................ 30
-al ............................................................................. 32
ALIGN .................................................................... 144
Allocatable Section................................................. 128
Allocating Memory.................................................. 148
-am ........................................................................... 32
-an ............................................................................ 34
ar utility................................................................... 175
Archiver .................................................................. 175
Command-Line Interface ................................ 178
Scripts ............................................................. 180
Arguments................................................................ 46
-as ............................................................................ 35
ASCII Character Set............................................... 201
Assembler
Command-Line Interface .................................. 23
Directives .................................................... 44, 57
Overview ........................................................... 15
Source............................................................... 19
ASSERT................................................................. 138
Assigning Output Sections to Regions................... 151
Assigning Values.................................................... 126
B
BaseReg+Offset....................................................... 45
bin2hex utility ......................................................... 184
Binary File .............................................................. 100
BLOCK ................................................................... 144
Building the Output File.......................................... 149
Built-in Functions.................................................... 143
ADDR.............................................................. 143
ALIGN ............................................................. 144
BLOCK............................................................ 144
DEFINED ........................................................ 144
KEEP .............................................................. 144
LOADADDR .................................................... 144
MAX ................................................................ 144
MIN ................................................................. 145
NEXT .............................................................. 145
SIZEOF ........................................................... 145
C
Character Constants ................................................ 49
Characters................................................................ 49
--check-sections ..................................................... 115
Code Control Directives
.set at ................................................................ 79
.set autoextend ................................................. 79
.set macro ......................................................... 79
.set mips16e...................................................... 79
.set noat ............................................................ 79
.set noautoextend.............................................. 79
.set nomacro ..................................................... 79
.set nomips16e.................................................. 80
.set noreorder....................................................80
.set reorder........................................................ 80
Command-Line Information
Linker Scripts .................................................. 120
Command-Line Interface
Archiver/Librarian ............................................ 178
Assembler ......................................................... 23
Linker .............................................................. 105
Comments ........................................................ 47, 124
Computing Absolute Addresses ............................. 149
Conditional Assembly Directives
.else................................................................... 69
.elseif................................................................. 69
.endif ................................................................. 69
.if ....................................................................... 69
.ifc...................................................................... 69
.ifdecl................................................................. 69
.ifeq ................................................................... 69
.ifeqs.................................................................. 69
.ifge ................................................................... 69
.ifgt .................................................................... 70
.ifle..................................................................... 70
.iflt...................................................................... 70
.ifnc.................................................................... 70
.ifndef ................................................................ 70
.ifne ................................................................... 70
.ifnes.................................................................. 70
.ifnotdef ............................................................. 70
Constants ............................................................... 140
Floating-Point Numbers .................................... 48
Integer ............................................................... 48
Numeric............................................................. 48
COPY ..................................................................... 135
--cref ....................................................................... 118
Customer Support .................................................... 12
D
-d ............................................................................ 108
-dc .......................................................................... 108
Debug Information Directives
.end ................................................................... 77
.ent .................................................................... 77
.file..................................................................... 77
.fmask................................................................ 77
.frame ................................................................ 77
.loc..................................................................... 77
.mask................................................................. 78
.size................................................................... 78
.sleb128............................................................. 78
.type .................................................................. 78
.uleb128 ............................................................ 78
Declare Symbols Directives
.comm ............................................................... 64
.extern ............................................................... 64
.global................................................................ 64
.globl.................................................................. 64
.lcomm............................................................... 64
Index
2013 Microchip Technology Inc. DS50002186A-page 227
.weak ................................................................ 64
Define Symbols Directives
.equ................................................................... 65
.equiv ................................................................ 65
DEFINED ............................................................... 144
--defsym ............................................................39, 109
--defsym=_min_heap_size..................................... 113
--defsym=_min_stack_size .................................... 113
Diagnostic Control Directives
.abort................................................................. 76
.err .................................................................... 76
.error ................................................................. 76
.fail .................................................................... 76
.ident ................................................................. 76
.print.................................................................. 76
.version ............................................................. 76
.warning ............................................................ 76
Directive ................................................................... 44
Directives
Alignment.......................................................... 66
Assembler......................................................... 57
Conditional........................................................ 69
Debug Information ............................................ 77
Declare Symbols............................................... 64
Define Symbols................................................. 65
Initialization ....................................................... 62
Miscellaneous ................................................... 76
Output Listing.................................................... 68
Section.............................................................. 58
Substitution/Expansion ..................................... 71
--discard-all ............................................................ 109
--discard-locals....................................................... 109
Documentation
Conventions........................................................ 9
Layout ................................................................. 8
DOT Symbol ............................................................ 52
Dot Variable ........................................................... 141
-dp.......................................................................... 108
DSECT................................................................... 135
E
Empty Expressions .................................................. 53
--end-group ............................................................ 108
ENTRY................................................................... 138
Escape Characters .................................................. 49
Evaluation .............................................................. 142
Examples, Linker ................................................... 163
EXCLUDE_FILE .................................................... 130
Executable Section ................................................ 128
Expressions ............................................................. 53
Expressions, Empty ................................................. 53
Expressions, Integer ................................................ 53
EXTERN ................................................................ 138
F
--fatal-warnings ........................................................ 37
File Commands, Linker Scripts
GROUP........................................................... 125
INCLUDE ........................................................ 125
INPUT ............................................................. 125
OUTPUT ......................................................... 125
SEARCH_DIR................................................. 125
STARTUP ....................................................... 125
File Extensions
Assembler ................................................... 17, 98
Linker ................................................................ 98
Files
Library ............................................................... 98
Linker Output .................................................. 100
Linker Script ...................................................... 98
Listing................................................................ 19
Map ................................................................. 100
Object.......................................................... 19, 98
Source............................................................... 17
Floating-Point Numbers ........................................... 48
FORCE_COMMON_ALLOCATION ....................... 138
Functions, Locating ................................................ 165
G
Garbage Collection ................................................ 144
--gc-sections........................................................... 109
Global Symbols ...................................................... 153
GPRs........................................................................ 44
GROUP .................................................................. 125
H
Header ..................................................................... 19
Heap Allocation ...................................................... 157
--help ................................................................ 37, 115
Hexadecimal to Decimal Conversion ..................... 202
High-level Source............................................... 19, 30
I
-I ............................................................................... 39
-i ............................................................................. 111
INCLUDE ............................................................... 125
Include Files Directives
.incbin................................................................ 75
.include.............................................................. 75
Infix Operators.......................................................... 54
INFO....................................................................... 135
Informational Output Options, Assembler
--fatal-warnings ................................................. 37
--help................................................................. 37
-J ....................................................................... 37
--no-warn........................................................... 37
--target-help ...................................................... 37
-v ....................................................................... 37
--verbose........................................................... 37
--version ............................................................ 37
-W ..................................................................... 37
--warn................................................................ 37
Informational Output Options, Linker
--check-sections.............................................. 115
--help............................................................... 115
--no-check-sections......................................... 115
--no-warn-mismatch ........................................ 115
--report-mem ................................................... 115
-t...................................................................... 115
--trace.............................................................. 115
--trace-symbol ................................................. 116
-V .................................................................... 116
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 228 2013 Microchip Technology Inc.
-v ..................................................................... 116
--verbose......................................................... 116
--version .......................................................... 116
--warn-common ............................................... 116
--warn-once..................................................... 117
--warn-section-align......................................... 117
-y ..................................................................... 116
Initializated Section ................................................ 128
Initialization Directives
.ascii.................................................................. 62
.asciz................................................................. 62
.byte .................................................................. 62
.double .............................................................. 62
.float .................................................................. 63
.hword ............................................................... 63
.int ..................................................................... 63
.long .................................................................. 63
.short ................................................................. 63
.single................................................................ 63
.string ................................................................ 63
.word ................................................................. 63
Initialized Section ................................................... 128
INPUT .................................................................... 125
Input Section
Common Symbols........................................... 132
Example .......................................................... 132
Wildcard Patterns............................................ 131
Integer Expressions ................................................. 53
Integers .................................................................... 48
Internal Preprocessor............................................... 42
Internet Address, Microchip...................................... 11
Invert Sense ........................................................... 128
J
-J .............................................................................. 37
K
K Suffix................................................................... 140
KEEP...................................................................... 144
--keep-locals............................................................. 38
L
-L ...................................................................... 38, 110
-l ............................................................................. 110
Label .................................................................. 43, 51
LENGTH................................................................. 128
Librarian ................................................................. 175
Command-Line Interface ................................ 178
Scripts ............................................................. 180
--library ................................................................... 110
Library Files.............................................................. 98
--library-path........................................................... 110
Link Map Options, Linker
--cref................................................................ 118
-M.................................................................... 118
-Map................................................................ 118
--print-map ...................................................... 118
Linker
Allocation ........................................................ 150
Command-Line Interface ................................ 105
Examples ........................................................ 163
File Extensions.................................................. 98
Output File....................................................... 100
Overview ........................................................... 97
Processing ...................................................... 147
Linker Scripts.......................................................... 119
Command Language....................................... 124
Command-Line Information.............................120
Concepts ......................................................... 124
Expressions..................................................... 140
File .................................................................... 98
File Commands...............................................125
Other Commands............................................ 138
Listing Files .............................................................. 19
Listing Output Options, Assembler........................... 25
-a=file ................................................................ 35
-ac ..................................................................... 26
-ad ..................................................................... 28
-ah ..................................................................... 30
-al ...................................................................... 32
-am .................................................................... 32
-an ............................................................... 34, 35
--listing-cont-lines .............................................. 36
--listing-lhs-width ............................................... 35
--listing-lhs-width2 ............................................. 35
--listing-rhs-width............................................... 36
--listing-cont-lines ..................................................... 36
--listing-lhs-width ...................................................... 35
--listing-lhs-width2 .................................................... 35
--listing-rhs-width ...................................................... 36
Literals...................................................................... 45
LMA ........................................................ 124, 136, 144
Load Memory Address ........................... 124, 136, 144
LOADADDR ........................................................... 144
Loading Input Files .................................................148
Local Symbols .......................................................... 51
Location Counter .................................................... 141
Location Counter Directives
.align.................................................................. 66
.fill...................................................................... 66
.org .................................................................... 67
.skip................................................................... 67
.space................................................................ 67
.struct ................................................................ 67
M
-M ........................................................................... 118
M Suffix ..................................................................140
-Map ....................................................................... 118
Map File.................................................................. 100
Mapping Sections...................................................150
MAX........................................................................ 144
-MD........................................................................... 38
MEMORY Command..............................................128
! ....................................................................... 128
A...................................................................... 128
I ....................................................................... 128
L ...................................................................... 128
R...................................................................... 128
W..................................................................... 128
X...................................................................... 128
MIN......................................................................... 145
Index
2013 Microchip Technology Inc. DS50002186A-page 229
Mnemonic ................................................................ 43
Modification Options, Archiver/Librarian
a...................................................................... 179
b...................................................................... 179
c ...................................................................... 179
f....................................................................... 179
i ....................................................................... 179
l ....................................................................... 179
N ..................................................................... 179
o...................................................................... 179
P ..................................................................... 179
S ..................................................................... 179
s ...................................................................... 179
u...................................................................... 179
V ..................................................................... 179
v ...................................................................... 179
myMicrochip Personalized Notification Service ....... 11
N
NEXT ..................................................................... 145
nm utility................................................................. 185
--no-check-sections................................................ 115
NOCROSSREFS ................................................... 138
-nodefaultlibs.......................................................... 110
NOLOAD................................................................ 135
-nostartfiles ............................................................ 110
-nostdlib ................................................................. 110
--no-undefined........................................................ 112
--no-warn.................................................................. 37
--no-warn-mismatch ............................................... 115
Numeric Constants .................................................. 48
O
-o.......................................................................38, 110
objdump utility ........................................................ 188
Object Files .........................................................19, 98
Operands ................................................................. 44
BaseReg+Offset ............................................... 45
General Purpose Registers .............................. 44
Literal Value...................................................... 45
Operators ..........................................................53, 142
Infix ................................................................... 54
Prefix................................................................. 53
Options, Archiver/Librarian
d...................................................................... 178
m..................................................................... 178
p...................................................................... 178
q...................................................................... 178
r....................................................................... 178
t....................................................................... 178
x ...................................................................... 178
Options, Assembler
Informational Output ......................................... 37
Listing Output.................................................... 25
Output File Creation.......................................... 38
Search Path ...................................................... 39
Symbol Definition.............................................. 39
Options, Linker
Informational Output ....................................... 115
Link Map Output ............................................. 118
Output File Creation........................................ 108
Run-time Initialization...................................... 113
Options, pic320-nm
--no-sort .......................................................... 186
Options, pic320-objdump
--disassemble-zeroes...................................... 190
Options, xc32-nm
-A .................................................................... 186
-a..................................................................... 186
-B .................................................................... 186
--debug-syms .................................................. 186
--defined-only .................................................. 186
--extern-only.................................................... 186
-f...................................................................... 186
--format= ......................................................... 186
-g..................................................................... 186
--help............................................................... 186
-l ...................................................................... 186
--line-numbers................................................. 186
-n..................................................................... 186
--numeric-sort.................................................. 186
-o..................................................................... 186
-P .................................................................... 186
-p..................................................................... 186
--portability ...................................................... 186
--print-armap ................................................... 186
--print-file-name............................................... 186
-r...................................................................... 186
--radix=............................................................ 186
--reverse-sort .................................................. 186
-s ..................................................................... 186
--size-sort ........................................................ 186
-t...................................................................... 186
-u..................................................................... 186
--undefined-only .............................................. 186
-V .................................................................... 186
-v ..................................................................... 186
--version .......................................................... 186
Options, xc32-objdump
-a..................................................................... 189
--all-header...................................................... 190
--archive-header.............................................. 189
-D .................................................................... 189
-d..................................................................... 189
--debugging..................................................... 189
--disassemble.................................................. 189
--disassemble-all............................................. 189
--disassembler-options=.................................. 189
-f...................................................................... 189
--file-header..................................................... 189
--file-start-context ............................................ 189
--full-contents .................................................. 189
-g..................................................................... 189
-H .................................................................... 189
-h..................................................................... 189
--header .......................................................... 189
--help............................................................... 189
-j ...................................................................... 189
-l ...................................................................... 189
--line-numbers................................................. 189
-M.................................................................... 189
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 230 2013 Microchip Technology Inc.
--no-show-raw-insn ......................................... 190
--prefix-addresses ........................................... 189
-r...................................................................... 189
--reloc.............................................................. 189
-S .................................................................... 190
-s ..................................................................... 189
--section= ........................................................ 189
--section-header.............................................. 189
--show-raw-insn............................................... 190
--source........................................................... 190
--start-address=............................................... 190
--stop-address=............................................... 190
--syms ............................................................. 190
-t...................................................................... 190
-V .................................................................... 190
--version .......................................................... 190
-w .................................................................... 190
--wide .............................................................. 190
-x ..................................................................... 190
Options, xc32-ranlib
-V .................................................................... 191
-v ..................................................................... 191
--version .......................................................... 191
Options, xc32-strings
-....................................................................... 194
-a..................................................................... 194
--all .................................................................. 194
--bytes= ........................................................... 194
-f...................................................................... 194
--help............................................................... 194
-n..................................................................... 194
--print-file-name............................................... 194
--radix=............................................................ 194
-t...................................................................... 194
-v ..................................................................... 194
--version .......................................................... 194
Options, xc32-strip
--discard-all ..................................................... 196
-g..................................................................... 196
--help............................................................... 196
-K .................................................................... 196
--keep-symbol= ............................................... 196
-N .................................................................... 196
-o..................................................................... 196
-p..................................................................... 196
--preserve-dates.............................................. 196
-R .................................................................... 196
--remove-section= ........................................... 196
-S .................................................................... 196
-s ..................................................................... 196
--strip-all .......................................................... 196
--strip-debug.................................................... 196
--strip-symbol= ................................................ 196
--strip-unneeded.............................................. 196
-V .................................................................... 196
-v ..................................................................... 196
--verbose......................................................... 196
--version .......................................................... 196
-X .................................................................... 196
-x ..................................................................... 196
Options,xc32-objdump
-z ..................................................................... 190
Options,xc32-strip
--discard-locals................................................ 196
ORG ....................................................................... 128
ORIGIN................................................................... 128
Other Linker Script Commands
ASSERT.......................................................... 138
ENTRY ............................................................ 138
EXTERN.......................................................... 138
FORCE_COMMON_ALLOCATION ................ 138
NOCROSSREFS ............................................ 138
OUTPUT_ARCH ............................................. 139
OUTPUT_FORMAT ........................................ 139
TARGET.......................................................... 139
Other Options, Assembler
--defsym ............................................................ 39
-I ........................................................................ 39
OUTPUT................................................................. 125
--output ................................................................... 110
Output File Creation Options, Assembler
--keep-locals...................................................... 38
-L ....................................................................... 38
-MD ................................................................... 38
-o ....................................................................... 38
-Z....................................................................... 38
Output File Options, Linker
-( -) .................................................................. 108
-d ..................................................................... 108
-dc ................................................................... 108
--defsym .......................................................... 109
--discard-all ..................................................... 109
--discard-locals................................................ 109
-dp ................................................................... 108
--end-group ..................................................... 108
--gc-sections.................................................... 109
-i ...................................................................... 111
-L ..................................................................... 110
-l ...................................................................... 110
--library ............................................................ 110
--library-path.................................................... 110
-nodefaultlibs................................................... 110
-nostartfiles...................................................... 110
-nostdlib........................................................... 110
--no-undefined................................................. 112
-o ..................................................................... 110
--output............................................................ 110
-r...................................................................... 111
--relocateable .................................................. 111
--retain-symbols-file......................................... 111
-S..................................................................... 111
-s ..................................................................... 111
--script ............................................................. 111
--section-start .................................................. 111
--start-group .................................................... 108
--strip-all .......................................................... 111
--strip-debug.................................................... 111
-T..................................................................... 111
-Tbss ............................................................... 111
-Tdata.............................................................. 111
Index
2013 Microchip Technology Inc. DS50002186A-page 231
-Ttext............................................................... 112
-u..................................................................... 112
--undefined...................................................... 112
-Ur................................................................... 111
--wrap.............................................................. 112
-X .................................................................... 109
-x..................................................................... 109
Output Formats, xc32-nm
?...................................................................... 187
A ..................................................................... 187
B ..................................................................... 187
C ..................................................................... 187
D ..................................................................... 187
N ..................................................................... 187
R ..................................................................... 187
T...................................................................... 187
U ..................................................................... 187
V ..................................................................... 187
W .................................................................... 187
Output Listing Directives
.eject ................................................................. 68
.list .................................................................... 68
.nolist ................................................................ 68
.psize ................................................................ 68
.sbttl .................................................................. 68
.title ................................................................... 68
Output Section
Address........................................................... 133
Attributes......................................................... 135
Data ................................................................ 134
Description...................................................... 133
Discarding....................................................... 134
Fill ................................................................... 136
LMA ................................................................ 136
Region ............................................................ 136
Type................................................................ 135
COPY ...................................................... 135
DSECT .................................................... 135
INFO ........................................................ 135
NOLOAD ................................................. 135
OVERLAY................................................ 135
OUTPUT_ARCH .................................................... 139
OUTPUT_FORMAT ............................................... 139
OVERLAY .............................................................. 135
Overlay Description................................................ 137
Overview
Assembler......................................................... 15
Linker ................................................................ 97
P
--p PROC ............................................................... 110
PIC32MX Interrupt
Vector Tables.................................................. 158
Precedence.......................................................54, 142
Prefix Operators....................................................... 53
Preprocessor, Internal.............................................. 42
--print-map ............................................................. 118
Process Flow
Assembler......................................................... 15
Librarian.......................................................... 176
Linker ................................................................ 97
Processing, Linker.................................................. 147
Program Memory, Locating and Reserving............ 166
PROVIDE ............................................................... 127
R
-r............................................................................. 111
ranlib utility ............................................................. 191
Read/Write Section ................................................ 128
Reading, Recommended ......................................... 10
Read-Only Section ................................................. 128
relocatable................................................................ 19
Relocatable Code................................................... 164
--relocateable ......................................................... 111
--report-mem .......................................................... 115
Reserved Names ..................................................... 51
Resolving Symbols................................................. 148
--retain-symbols-file................................................ 111
Run-time Initialization Options, Linker
--defsym=_min_heap_size.............................. 113
--defsym=_min_stack_size ............................. 113
S
-S............................................................................ 111
-s ............................................................................ 111
--script .................................................................... 111
Scripts
Librarian .......................................................... 180
Scripts, Archiver/Librarian
ADDLIB ........................................................... 180
ADDMOD ........................................................ 180
CLEAR ............................................................ 180
CREATE ................................................. 180, 181
DELETE .......................................................... 181
DIRECTORY................................................... 181
END ................................................................ 181
EXTRACT ....................................................... 181
LIST ................................................................ 181
OPEN...................................................... 180, 181
REPLACE ....................................................... 181
SAVE ...................................................... 180, 181
VERBOSE....................................................... 181
SEARCH_DIR ........................................................ 125
Section Directives
.bss ................................................................... 58
.data .................................................................. 58
.popsection........................................................ 59
.pushsection...................................................... 59
.section name............................................ 59, 200
.text ................................................................... 61
Section of an Expression ....................................... 143
SECTIONS Command ........................................... 130
--section-start ......................................................... 111
Simple Assignments............................................... 126
size utility................................................................ 192
SIZEOF .................................................................. 145
Source Code ............................................................ 43
Source Files ............................................................. 17
Special Operators .................................................... 55
.endof.(name).................................................... 55
.sizeof................................................................ 55
.startof ............................................................... 55
XC32 Assembler, Linker and Utilities User’s Guide
DS50002186A-page 232 2013 Microchip Technology Inc.
Stack Allocation...................................................... 157
--start-group ........................................................... 108
Starting Address....................................................... 55
STARTUP .............................................................. 125
Statement Format .................................................... 43
Strings ...................................................................... 49
strings utility ........................................................... 194
strip utility ............................................................... 195
--strip-all ................................................................. 111
--strip-debug........................................................... 111
Substitution/Expansion Directives
.endm ................................................................ 72
.endr............................................................ 71, 74
.exitm .......................................................... 71, 72
.irpc ................................................................... 71
.macro ............................................................... 72
.purgem............................................................. 73
.rept................................................................... 74
/@ ..................................................................... 73
irp ...................................................................... 71
Subtitle ............................................................... 19, 68
Symbol Names....................................................... 140
Symbol Table ......................................20, 35, 124, 144
Syntax
Archiver/Librarian............................................ 177
Assembler ......................................................... 23
Linker .............................................................. 106
xc32-bin2hex................................................... 184
xc32-nm .......................................................... 185
xc32-objdump ................................................. 188
xc32-ranlib ...................................................... 191
xc32-strings..................................................... 194
xc32-strip ........................................................ 195
T
-T............................................................................ 111
-t ............................................................................. 115
TARGET................................................................. 139
--target-help.............................................................. 37
-Tbss ...................................................................... 111
-Tdata..................................................................... 111
Title .......................................................................... 68
Title Line................................................................... 19
--trace..................................................................... 115
--trace-symbol ........................................................ 116
-Ttext ...................................................................... 112
U
-u ............................................................................ 112
--undefined ............................................................. 112
-Ur .......................................................................... 111
USB........................................................................ 223
Utilities.................................................................... 173
V
-V............................................................................ 116
-v ...................................................................... 37, 116
Variables, Locating................................................. 165
--verbose .......................................................... 37, 116
--version ........................................................... 37, 116
Virtual Memory Address................................. 124, 136
VMA................................................................ 124, 136
W
-W............................................................................. 37
--warn ....................................................................... 37
--warn-common ...................................................... 116
--warn-once ............................................................ 117
--warn-section-align................................................ 117
Watchdog Timer .....................................................223
Weak Symbols .......................................................153
Web Site, Microchip ................................................. 11
White Space ............................................................. 43
--wrap ..................................................................... 112
X
-X............................................................................ 109
-x ............................................................................ 109
xc32................................................................ 189, 196
xc32-ar utility ..........................................................175
xc32-bin2hex utility.................................................184
xc32-nm utility ........................................................ 185
xc32-objdump utility................................................ 188
xc32-ranlib utility.....................................................191
xc32-size utility ....................................................... 192
xc32-strings utility................................................... 194
xc32-strip utility.......................................................195
Y
-y ............................................................................ 116
Z
-Z .............................................................................. 38
Index
2013 Microchip Technology Inc. DS50002186A-page 233
NOTES:
6‘ MICROCHIP AMERICAS ASIA/PACIFIC ASIA/PACIFIC EUROPE
DS50002186A-page 234 2013 Microchip Technology Inc.
AMERICAS
Corporate Office
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Chandler, AZ 85224-6199
Tel: 480-792-7200
Fax: 480-792-7277
Technical Support:
http://www.microchip.com/
support
Web Address:
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Tel: 678-957-9614
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Tel: 972-818-7423
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China - Qingdao
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China - Shanghai
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Fax: 86-21-5407-5066
China - Shenyang
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China - Shenzhen
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China - Wuhan
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Taiwan - Taipei
Tel: 886-2-2508-8600
Fax: 886-2-2508-0102
Thailand - Bangkok
Tel: 66-2-694-1351
Fax: 66-2-694-1350
EUROPE
Austria - Wels
Tel: 43-7242-2244-39
Fax: 43-7242-2244-393
Denmark - Copenhagen
Tel: 45-4450-2828
Fax: 45-4485-2829
France - Paris
Tel: 33-1-69-53-63-20
Fax: 33-1-69-30-90-79
Germany - Munich
Tel: 49-89-627-144-0
Fax: 49-89-627-144-44
Italy - Milan
Tel: 39-0331-742611
Fax: 39-0331-466781
Netherlands - Drunen
Tel: 31-416-690399
Fax: 31-416-690340
Spain - Madrid
Tel: 34-91-708-08-90
Fax: 34-91-708-08-91
UK - Wokingham
Tel: 44-118-921-5869
Fax: 44-118-921-5820
Worldwide Sales and Service
08/20/13