This file documents the gnu linker ld gnu binutils version 2. We will take the gnu linker script of efm32gg11 efm32gg11b. Arm compiler toolchain using the linker chapter 1 conventions and feedback chapter 2 overview of the linker. As a result, you have many choices to control its behavior. Gnu ld runs the linker, which creates an executable file or a library from object files created during compilation of a software project.
This file documents the internals of the gnu linker ld. Compiling, linking, and locating programming embedded. When the program is linked, the linker script is passed as an input to the linker, as shown in the following command. Using ld scripts when linking images and shared objects to link an image or shared object. For technical support, please open a support ticket. The gnu linker has a command language to specify the image format. If you target platforms that do not support linker scripts i.
Theo0option tells gcc to not perform any optimizations at all the default if no optimization level is speci. The linker script file instructs the gnu linker to locate the data, bss, and text sections in ram starting at address 0x00400000. The following is a list of the most important and immediately useful ones for embedded development. An introduction to the gnu compiler and linker thewcastalignoption this option causes gcc to issue a warning whenever a pointer cast can create alignment issues. When a package has several associated manuals, they are all listed. The best way to find out which output sections are present, is to just compile and link an example application, and inspect the generated map file if the map file is not automatically generated, you should. This document is distributed under the terms of the gnu free documentation license. A script specied in this way augments the main linker script used for the link either the default linker script or the one specied by usingt.
If the linker cannot recognize the format of an object file, it will assume that it is a linker script. If the linker can not recognize the format of an object file, it will assume that it is a linker script. Gnu manuals online gnu project free software foundation. Using the gnu linker scripts on avr uc3 devices this document highlights the main purpose of the gnu linker script, which is to control the location of code and variables in the executable. If a package has no specific manual online, the link just goes to the packages home page which is also linked to explicitly. This script iswritten in the linker command language.
This script is written in the linker command language. Currently, only gnu ld and the solaris linker supports this. Gnu linker gnu tools gnu tools by cyberthor studios. So this post is about to use the gnu linker to fill the uninitalized flash memory with a pattern. An implicit linker script will not replace the default linker script. Your linker script serves to bind symbols from files, or symbols listed in explicitly defined input sections, to the output sections. User manual the gnu linker cube32ide pdf book manual free. At the time the gnu linker did not fully support the elf object file format. Apr 04, 2018 the final step in creating an executable from object files and libraries is linking.
The linker uses a default script that compiles into the linker executable, if you do not supply one via the t command line option. Filling unused memory with the gnu linker dzone iot. User manual the gnu linker cube32ide pdf book online. Linker script tutorial most linker scripts do nothing. Certain options such as r or n affect the default linker script. However, when necessary, the linker script can alsodirect the linker to perform many other operations, using the commandsdescribed below. This command language can be quite complicated but most of what is required can be learned by careful examination of a welldocumented example.
Please see the translations readme for information on coordinating and submitting translations of this article. Use the verbose option to display the default linker script. You just need to make sure your macros dont collide with linker script syntax. The contents of the rom section will appear in the linker output file as usual. Figure 12 is an example linker command script that i will discuss in detail over the. Typically an implicit linker script would contain only symbol assignments, or the input, group, or version commands. This feature permits the linker to link against a file which appears to be an object. Since the file needs to be adapted to your application, you should copy it to your project folder and enter it under options for target linker.
The gnu linker ld is meant to cover a broad range of situations, and to be as. This table lists official gnu packages with links to their primary documentation, where available. This tells ld to produce a file called output as the result of linking the file libcrt0. The linker command script includes a command specifically for specifying a version script, and is only meaningful for elf platforms that support shared libraries. Any input files read because of an implicit linker script will be read at the position in the command line where the implicit linker script was read. The main purpose of the linker script is to describe how the sections in the input files should be mapped into the output file, and.
The gnu linker ld version 2 january 1994 steve chamberlain cygnus support. Note that specifying a script in this way merely augments the main linker script. A script specified in this way augments the main linker script used for the link read. The version script file format is documented in the gnu ld manual, but a small example would be. This is performed by a linker that accepts linker command language files called linker scripts. Many microprocessors can only access multibyte values on speci. Using the gnu linker script to know the flash and ram.
Using the gnu linker script to know the flash and ram areas. The main purpose of the linker script is to describe how the sections inthe input files should be mapped into the output file, and to controlthe memory layout of the output file. The linker needs the value of the start address, and the lengths of memory regions, in order to do any linking at all. Sep 06, 2017 using the gnu linker script to know the flash and ram areas in the application posted on september 6, 2017 by erich styger sometimes it is handy to know in the running application the start address, end address and the size of a linked section, e. Linker scripts are written in a specialized scripting language specific to the gnu ld application. Theooption produces the least optimization, whileo3produces aggressively optimized code. The main purpose of the linker script is to describe how the sections in the input files should be mapped into the output file, and to control the memory layout of the output file. The gnu linker is using the pattern 0x00 for unused bytes inside sections.
Extensions of the gnu toolchain linker scripts and their meanings. Filling unused memory with the gnu linker mcu on eclipse. The gnu linker or gnu ld is the gnu projects implementation of the unix command ld. A version script can be build directly into the linker script that you are using, or you can supply the version script as just another input file to the linker at the time that you link. The main purpose of the linker script is to describe how the sections in the input files should be mapped into the output file, and to control the memory layout of the.
The gnu linker ld is meant to cover a broad range of situations, and to be as compatible as possible with other linkers. In fact, there are no less than thirteen categories of options to choose from. The primary purpose of a linker script is to describe the memory layout of the target machine, and specify where each section of the program should be placed in memory. Mostly, it is a repository into which you can put information about gnu ld as you discover it or as you design changes to ld. Version scripts provides information that can be used by gnulinux distribution packaging tools. 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. Opaque formats include postscript, pdf, proprietary formats that can be read. This feature permits the linker to link against a file which appears to be an object or an archive, but actually merely. The final step in creating an executable from object files and libraries is linking. Other linker scripts can be supplied by using the t command line option or the long form. Using ld, the gnu linker linker scripts extras springer. An introduction to the gnu compiler and linkero0,o,o1,o2, ando3 these options tell gcc to perform varying levels of optimization on output. An introduction to the gnu compiler and linker command line options gcc supports a large list of command line options. Broken links and other corrections or suggestions can be sent to org.
If the linker cannot recognize the format of an object le, it will assume that it is a linker script. The libsymbolversions module can be used to add shared library versioning support. A predefined linker control file that fits most systems can be found in the folder \arm\gnu. A linker script may be passed to gnu ld to exercise greater control over the linking process. An introduction to the gnu compiler and linker gcc, the gnu. An ld script can be given to control how the linker combines sections, for example. This document highlights the main purpose of the gnu linker script, which is to. Minimal linker script for cortex m3 and m4 using gcc for c language applications. The first executable instruction is designated with the entry command, which appears on the first line of the preceding example. This feature permits the linker to link against a file which appears to be an object or an archive, but actually merely defines some symbol values, or uses input or group to load other objects. To engage in technical discussions or ask general questions, please. Linker merges sections in the input files into sections in the output file default merging sections of same name symbols get new addresses, and references are patched section merging can be controlled by linker script files.
Using the gnu linker script to know the flash and ram areas in the application posted on september 6, 2017 by erich styger sometimes it is handy to know in the running application the start address, end address and the size of a linked section, e. Red hat enterprise linux 3 using ld, the gnu linker. The design and implementation were optimized for the a. It is a collection of miscellaneous information with little form at this point. Opaque formats include postscript, pdf, proprietary formats that can be read and edited. Version scripts provides information that can be used by gnu linux distribution packaging tools. If the linker cannot recognize the format of an object. For options whose names are a single letter, option arguments must either follow the op.
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