LD ¶

2.1 Command-line Options ¶

The linker supports a plethora of command-line options, but in actual practice few of them are used in any particular context. For instance, a frequent use of ld is to link standard Unix object files on a standard, supported Unix system. On such a system, to link a file hello.o:

ld -o output /lib/crt0.o hello.o -lc

This tells ld to produce a file called output as the result of linking the file /lib/crt0.o with hello.o and the library libc.a, which will come from the standard search directories. (See the discussion of the ‘-l’ option below.)

Some of the command-line options to ld may be specified at any point in the command line. However, options which refer to files, such as ‘-l’ or ‘-T’, cause the file to be read at the point at which the option appears in the command line, relative to the object files and other file options. Repeating non-file 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 which may be meaningfully specified more than once are noted in the descriptions below.

Non-option arguments are object files or archives which 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’, ‘-R’, and the script command language. If no binary input files at all 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 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. Specifying a script in this way merely augments the main linker script, with the extra commands placed after the main script; use the ‘-T’ option to replace the default linker script entirely, but note the effect of the INSERT command. See Linker Scripts.

For options whose names are a single letter, option arguments must either follow the option letter without intervening whitespace, 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. Note—there is one exception to this rule. Multiple letter options that start with a lower case ’o’ can only be preceded by two dashes. This is to reduce confusion with the ‘-o’ option. So for example ‘-omagic’ sets the output file name to ‘magic’ whereas ‘--omagic’ sets the NMAGIC flag on the output.

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 foo’ and ‘--trace-symbol=foo’ are equivalent. Unique abbreviations of the names of multiple-letter options are accepted.

Note—if the linker is being invoked indirectly, via a compiler driver (e.g. ‘gcc’) then all the linker command-line options should be prefixed by ‘-Wl,’ (or whatever is appropriate for the particular compiler driver) like this:

  gcc -Wl,--start-group foo.o bar.o -Wl,--end-group

This is important, because otherwise the compiler driver program may silently drop the linker options, resulting in a bad link. Confusion may also arise when passing options that require values through a driver, as the use of a space between option and argument acts as a separator, and causes the driver to pass only the option to the linker and the argument to the compiler. In this case, it is simplest to use the joined forms of both single- and multiple-letter options, such as:

  gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map

Here is a table of the generic command-line switches accepted by the GNU linker:

@file

Read command-line options from file. The options read are inserted in place of the original @file option. If file does not exist, or cannot be read, then the option will be treated literally, and not removed.

Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively.

-a keyword ¶

This option is supported for HP/UX compatibility. The keyword argument must be one of the strings ‘archive’, ‘shared’, or ‘default’. ‘-aarchive’ is functionally equivalent to ‘-Bstatic’, and the other two keywords are functionally equivalent to ‘-Bdynamic’. This option may be used any number of times.

--audit AUDITLIB ¶

Adds AUDITLIB to the DT_AUDIT entry of the dynamic section. AUDITLIB is not checked for existence, nor will it use the DT_SONAME specified in the library. If specified multiple times DT_AUDIT will contain a colon separated list of audit interfaces to use. If the linker finds an object with an audit entry while searching for shared libraries, it will add a corresponding DT_DEPAUDIT entry in the output file. This option is only meaningful on ELF platforms supporting the rtld-audit interface.

-b input-format ¶

--format=input-format

ld may be configured to support more than one kind of object file. If your ld is configured this way, you can use the ‘-b’ option to specify the binary format for input object files that follow this option on the command line. Even when ld is configured to support alternative object formats, you don’t usually need to specify this, as ld should be configured to expect as a default input format the most usual format on each machine. input-format is a text string, the name of a particular format supported by the BFD libraries. (You can list the available binary formats with ‘objdump -i’.) See BFD.

You may want to use this option if you are linking files with an unusual binary format. You can also use ‘-b’ to switch formats explicitly (when linking object files of different formats), by including ‘-b input-format’ before each group of object files in a particular format.

The default format is taken from the environment variable GNUTARGET. See Environment Variables. You can also define the input format from a script, using the command TARGET; see Commands Dealing with Object File Formats.

-c MRI-commandfile ¶

--mri-script=MRI-commandfile

For compatibility with linkers produced by MRI, ld accepts script files written in an alternate, restricted command language, described in MRI Compatible Script Files. Introduce MRI script files with the option ‘-c’; use the ‘-T’ option to run linker scripts written in the general-purpose ld scripting language. If MRI-cmdfile does not exist, ld looks for it in the directories specified by any ‘-L’ options.

-d ¶

-dc

-dp

These three options are equivalent; multiple forms are supported for compatibility with other linkers. They 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. See Other Linker Script Commands.

--depaudit AUDITLIB ¶

-P AUDITLIB

Adds AUDITLIB to the DT_DEPAUDIT entry of the dynamic section. AUDITLIB is not checked for existence, nor will it use the DT_SONAME specified in the library. If specified multiple times DT_DEPAUDIT will contain a colon separated list of audit interfaces to use. This option is only meaningful on ELF platforms supporting the rtld-audit interface. The -P option is provided for Solaris compatibility.

--enable-linker-version ¶

Enables the LINKER_VERSION linker script directive, described in Output Section Data. If this directive is used in a linker script and this option has been enabled then a string containing the linker version will be inserted at the current point.

Note - this location of this option on the linker command line is significant. It will only affect linker scripts that come after it on the command line, or which are built into the linker.

--disable-linker-version ¶

Disables the LINKER_VERSION linker script directive, so that it does not insert a version string. This is the default.

--enable-non-contiguous-regions ¶

This option avoids generating an error if an input section does not fit a matching output section. The linker tries to allocate the input section to subseque nt matching output sections, and generates an error only if no output section is large enough. This is useful when several non-contiguous memory regions are available and the input section does not require a particular one. The order in which input sections are evaluated does not change, for instance:

  MEMORY {
    MEM1 (rwx) : ORIGIN = 0x1000, LENGTH = 0x14
    MEM2 (rwx) : ORIGIN = 0x1000, LENGTH = 0x40
    MEM3 (rwx) : ORIGIN = 0x2000, LENGTH = 0x40
  }
  SECTIONS {
    mem1 : { *(.data.*); } > MEM1
    mem2 : { *(.data.*); } > MEM2
    mem3 : { *(.data.*); } > MEM3
  }

  with input sections:
  .data.1: size 8
  .data.2: size 0x10
  .data.3: size 4

  results in .data.1 affected to mem1, and .data.2 and .data.3
  affected to mem2, even though .data.3 would fit in mem3.

This option is incompatible with INSERT statements because it changes the way input sections are mapped to output sections.

--enable-non-contiguous-regions-warnings ¶

This option enables warnings when --enable-non-contiguous-regions allows possibly unexpected matches in sections mapping, potentially leading to silently discarding a section instead of failing because it does not fit any output region.

-e entry ¶

--entry=entry

Use entry as the explicit symbol for beginning execution of your program, rather than the default entry point. If there is no symbol named entry, the linker will try to parse entry as a number, and use that as the entry address (the number will be interpreted in base 10; you may use a leading ‘0x’ for base 16, or a leading ‘0’ for base 8). See Setting the Entry Point, for a discussion of defaults and other ways of specifying the entry point.

--exclude-libs lib,lib,... ¶

Specifies a list of archive libraries from which symbols should not be automatically exported. The library names may be delimited by commas or colons. Specifying --exclude-libs ALL excludes symbols in all archive libraries from automatic export. This option is available only for the i386 PE targeted port of the linker and for ELF targeted ports. For i386 PE, symbols explicitly listed in a .def file are still exported, regardless of this option. For ELF targeted ports, symbols affected by this option will be treated as hidden.

--exclude-modules-for-implib module,module,... ¶

Specifies a list of object files or archive members, from which symbols should not be automatically exported, but which should be copied wholesale into the import library being generated during the link. The module names may be delimited by commas or colons, and must match exactly the filenames used by ld to open the files; for archive members, this is simply the member name, but for object files the name listed must include and match precisely any path used to specify the input file on the linker’s command-line. This option is available only for the i386 PE targeted port of the linker. Symbols explicitly listed in a .def file are still exported, regardless of this option.

-E ¶

--export-dynamic

--no-export-dynamic

When creating a dynamically linked executable, using the -E option or the --export-dynamic option causes the linker to add all symbols to the dynamic symbol table. The dynamic symbol table is the set of symbols which are visible from dynamic objects at run time.

If you do not use either of these options (or use the --no-export-dynamic option to restore the default behavior), the dynamic symbol table will normally contain only those symbols which are referenced by some dynamic object mentioned in the link.

If you use dlopen to load a dynamic object which needs to refer back to the symbols defined by the program, rather than some other dynamic object, then you will probably need to use this option when linking the program itself.

You can also use the dynamic list to control what symbols should be added to the dynamic symbol table if the output format supports it. See the description of ‘--dynamic-list’.

Note that this option is specific to ELF targeted ports. PE targets support a similar function to export all symbols from a DLL or EXE; see the description of ‘--export-all-symbols’ below.

--export-dynamic-symbol=glob ¶

When creating a dynamically linked executable, symbols matching glob will be added to the dynamic symbol table. When creating a shared library, references to symbols matching glob will not be bound to the definitions within the shared library. This option is a no-op when creating a shared library and ‘-Bsymbolic’ or ‘--dynamic-list’ are not specified. This option is only meaningful on ELF platforms which support shared libraries.

--export-dynamic-symbol-list=file ¶

Specify a ‘--export-dynamic-symbol’ for each pattern in the file. The format of the file is the same as the version node without scope and node name. See VERSION Command for more information.

-EB ¶

Link big-endian objects. This affects the default output format.

-EL ¶

Link little-endian objects. This affects the default output format.

-f name ¶

--auxiliary=name

When creating an ELF shared object, set the internal DT_AUXILIARY field to the specified name. This tells the dynamic linker that the symbol table of the shared object should be used as an auxiliary filter on the symbol table of the shared object name.

If you later link a program against this filter object, then, when you run the program, the dynamic linker will see the DT_AUXILIARY field. If the dynamic linker resolves any symbols from the filter object, it will first check whether there is a definition in the shared object name. If there is one, it will be used instead of the definition in the filter object. The shared object name need not exist. Thus the shared object name may be used to provide an alternative implementation of certain functions, perhaps for debugging or for machine-specific performance.

This option may be specified more than once. The DT_AUXILIARY entries will be created in the order in which they appear on the command line.

-F name ¶

--filter=name

When creating an ELF shared object, set the internal DT_FILTER field to the specified name. This tells the dynamic linker that the symbol table of the shared object which is being created should be used as a filter on the symbol table of the shared object name.

If you later link a program against this filter object, then, when you run the program, the dynamic linker will see the DT_FILTER field. The dynamic linker will resolve symbols according to the symbol table of the filter object as usual, but it will actually link to the definitions found in the shared object name. Thus the filter object can be used to select a subset of the symbols provided by the object name.

Some older linkers used the -F option throughout a compilation toolchain for specifying object-file format for both input and output object files. The GNU linker uses other mechanisms for this purpose: the -b, --format, --oformat options, the TARGET command in linker scripts, and the GNUTARGET environment variable. The GNU linker will ignore the -F option when not creating an ELF shared object.

-fini=name ¶

When creating an ELF executable or shared object, call NAME when the executable or shared object is unloaded, by setting DT_FINI to the address of the function. By default, the linker uses _fini as the function to call.

-g ¶

Ignored. Provided for compatibility with other tools.

-G value ¶

--gpsize=value

Set the maximum size of objects to be optimized using the GP register to size. This is only meaningful for object file formats such as MIPS ELF that support putting large and small objects into different sections. This is ignored for other object file formats.

-h name ¶

-soname=name

When creating an ELF shared object, set the internal DT_SONAME field to the specified name. When an executable is linked with a shared object which has a DT_SONAME field, then when the executable is run the dynamic linker will attempt to load the shared object specified by the DT_SONAME field rather than using the file name given to the linker.

-i ¶

Perform an incremental link (same as option ‘-r’).

-init=name ¶

When creating an ELF executable or shared object, call NAME when the executable or shared object is loaded, by setting DT_INIT to the address of the function. By default, the linker uses _init as the function to call.

-l namespec ¶

--library=namespec

Add the archive or object file specified by namespec to the list of files to link. This option may be used any number of times. If namespec is of the form :filename, ld will search the library path for a file called filename, otherwise it will search the library path for a file called libnamespec.a.

On systems which support shared libraries, ld may also search for files other than libnamespec.a. Specifically, on ELF and SunOS systems, ld will search a directory for a library called libnamespec.so before searching for one called libnamespec.a. (By convention, a .so extension indicates a shared library.) Note that this behavior does not apply to :filename, which always specifies a file called filename.

The linker will search an archive only once, at the location where it is specified on the command line. If the archive defines a symbol which was undefined in some object which 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 appearing 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.

This type of archive searching is standard for Unix linkers. However, if you are using ld on AIX, note that it is different from the behaviour of the AIX linker.

-L searchdir ¶

--library-path=searchdir

Add path searchdir to the list of paths that ld will search for archive libraries and 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. Directories specified on the command line are searched before the default directories. All -L options apply to all -l options, regardless of the order in which the options appear. -L options do not affect how ld searches for a linker script unless -T option is specified.

If searchdir begins with = or $SYSROOT, then this prefix will be replaced by the sysroot prefix, controlled by the ‘--sysroot’ option, or specified when the linker is configured.

The default set of paths searched (without being specified with ‘-L’) depends on which emulation mode ld is using, and in some cases also on how it was configured. See Environment Variables.

The 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.

-m emulation ¶

Emulate the emulation linker. You can list the available emulations with the ‘--verbose’ or ‘-V’ options.

If the ‘-m’ option is not used, the emulation is taken from the LDEMULATION environment variable, if that is defined.

Otherwise, the default emulation depends upon how the linker was configured.

--remap-inputs=pattern=filename ¶

--remap-inputs-file=file

These options allow the names of input files to be changed before the linker attempts to open them. The option --remap-inputs=foo.o=bar.o will cause any attempt to load a file called foo.o to instead try to load a file called bar.o. Wildcard patterns are permitted in the first filename, so --remap-inputs=foo*.o=bar.o will rename any input file that matches foo*.o to bar.o.

An alternative form of the option --remap-inputs-file=filename allows the remappings to be read from a file. Each line in the file can contain a single remapping. Blank lines are ignored. Anything from a hash character (‘#’) to the end of a line is considered to be a comment and is also ignored. The mapping pattern can be separated from the filename by whitespace or an equals (‘=’) character.

The options can be specified multiple times. Their contents accumulate. The remappings will be processed in the order in which they occur on the command line, and if they come from a file, in the order in which they occur in the file. If a match is made, no further checking for that filename will be performed.

If the replacement filename is /dev/null or just NUL then the remapping will actually cause the input file to be ignored. This can be a convenient way to experiment with removing input files from a complicated build environment.

Note that this option is position dependent and only affects filenames that come after it on the command line. Thus:

  ld foo.o --remap-inputs=foo.o=bar.o

Will have no effect, whereas:

  ld --remap-inputs=foo.o=bar.o foo.o 

Will rename the input file foo.o to bar.o.

Note - these options also affect files referenced by INPUT statements in linker scripts. But since linker scripts are processed after the entire command line is read, the position of the remap options on the command line is not significant.

If the verbose option is enabled then any mappings that match will be reported, although again the verbose option needs to be enabled on the command line before the remaped filenames appear.

If the -Map or --print-map options are enabled then the remapping list will be included in the map output.

-M ¶

--print-map

Print a link map to the standard output. A link map provides information about the link, including the following:

• Where object files 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.
• The values assigned to symbols.

  Note - symbols whose values are computed by an expression which involves a reference to a previous value of the same symbol may not have correct result displayed in the link map. This is because the linker discards intermediate results and only retains the final value of an expression. Under such circumstances the linker will display the final value enclosed by square brackets. Thus for example a linker script containing:

     foo = 1
     foo = foo * 4
     foo = foo + 8
  

  will produce the following output in the link map if the -M option is used:

     0x00000001                foo = 0x1
     [0x0000000c]                foo = (foo * 0x4)
     [0x0000000c]                foo = (foo + 0x8)
  

  See Expressions in Linker Scripts for more information about expressions in linker scripts.

• How GNU properties are merged.

  When the linker merges input .note.gnu.property sections into one output .note.gnu.property section, some properties are removed or updated. These actions are reported in the link map. For example:

  Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
  

  This indicates that property 0xc0000002 is removed from output when merging properties in foo.o, whose property 0xc0000002 value is 0x1, and bar.o, which doesn’t have property 0xc0000002.

  Updated property 0xc0010001 (0x1) to merge foo.o (0x1) and bar.o (0x1)
  

  This indicates that property 0xc0010001 value is updated to 0x1 in output when merging properties in foo.o, whose 0xc0010001 property value is 0x1, and bar.o, whose 0xc0010001 property value is 0x1.

• On some ELF targets, a list of fixups inserted by --relax

  foo.o: Adjusting branch at 0x00000008 towards "far" in section .text
  

  This indicates that the branch at 0x00000008 in foo.o, targeting the symbol "far" in section .text, has been replaced by a trampoline.

--print-map-discarded ¶

--no-print-map-discarded

Print (or do not print) the list of discarded and garbage collected sections in the link map. Enabled by default.

--print-map-locals ¶

--no-print-map-locals

Print (or do not print) local symbols in the link map. Local symbols will have the text ‘(local)’ printed before their name, and will be listed after all of the global symbols in a given section. Temporary local symbols (typically those that start with ‘.L’) will not be included in the output. Disabled by default.

-n ¶

--nmagic

Turn off page alignment of sections, and disable linking against shared libraries. If the output format supports Unix style magic numbers, mark the output as NMAGIC.

-N ¶

--omagic

Set the text and data sections to be readable and writable. Also, do not page-align the data segment, and disable linking against shared libraries. If the output format supports Unix style magic numbers, mark the output as OMAGIC. Note: Although a writable text section is allowed for PE-COFF targets, it does not conform to the format specification published by Microsoft.

--no-omagic ¶

This option negates most of the effects of the -N option. It sets the text section to be read-only, and forces the data segment to be page-aligned. Note - this option does not enable linking against shared libraries. Use -Bdynamic for this.

-o output ¶

--output=output

Use output as the name for the program produced by ld; if this option is not specified, the name a.out is used by default. The script command OUTPUT can also specify the output file name.

--dependency-file=depfile ¶

Write a dependency file to depfile. This file contains a rule suitable for make describing the output file and all the input files that were read to produce it. The output is similar to the compiler’s output with ‘-M -MP’ (see Options Controlling the Preprocessor in Using the GNU Compiler Collection). Note that there is no option like the compiler’s ‘-MM’, to exclude “system files” (which is not a well-specified concept in the linker, unlike “system headers” in the compiler). So the output from ‘--dependency-file’ is always specific to the exact state of the installation where it was produced, and should not be copied into distributed makefiles without careful editing.

-O level ¶

If level is a numeric values greater than zero ld optimizes the output. This might take significantly longer and therefore probably should only be enabled for the final binary. At the moment this option only affects ELF shared library generation. Future releases of the linker may make more use of this option. Also currently there is no difference in the linker’s behaviour for different non-zero values of this option. Again this may change with future releases.

-plugin name ¶

Involve a plugin in the linking process. The name parameter is the absolute filename of the plugin. Usually this parameter is automatically added by the complier, when using link time optimization, but users can also add their own plugins if they so wish.

Note that the location of the compiler originated plugins is different from the place where the ar, nm and ranlib programs search for their plugins. In order for those commands to make use of a compiler based plugin it must first be copied into the ${libdir}/bfd-plugins directory. All gcc based linker plugins are backward compatible, so it is sufficient to just copy in the newest one.

--push-state ¶

The --push-state allows one to preserve the current state of the flags which govern the input file handling so that they can all be restored with one corresponding --pop-state option.

The option which are covered are: -Bdynamic, -Bstatic, -dn, -dy, -call_shared, -non_shared, -static, -N, -n, --whole-archive, --no-whole-archive, -r, -Ur, --copy-dt-needed-entries, --no-copy-dt-needed-entries, --as-needed, --no-as-needed, and -a.

One target for this option are specifications for pkg-config. When used with the --libs option all possibly needed libraries are listed and then possibly linked with all the time. It is better to return something as follows:

-Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state

--pop-state ¶

Undoes the effect of –push-state, restores the previous values of the flags governing input file handling.

-q ¶

--emit-relocs

Leave relocation sections and contents in fully linked executables. Post link analysis and optimization tools may need this information in order to perform correct modifications of executables. This results in larger executables.

This option is currently only supported on ELF platforms.

--force-dynamic ¶

Force the output file to have dynamic sections. This option is specific to VxWorks targets.

-r ¶

--relocatable

Generate relocatable output—i.e., generate an output file that can in turn serve as input to ld. This is often called partial linking. As a side effect, in environments that support standard Unix magic numbers, this option also sets the output file’s magic number to OMAGIC. If this option is not specified, an absolute file is produced. When linking C++ programs, this option will not resolve references to constructors; to do that, use ‘-Ur’.

When an input file does not have the same format as the output file, partial linking is only supported if that input file does not contain any relocations. Different output formats can have further restrictions; for example some a.out-based formats do not support partial linking with input files in other formats at all.

This option does the same thing as ‘-i’.

-R filename ¶

--just-symbols=filename

Read symbol names and their addresses from filename, but do not relocate it or include it in the output. This allows your output file to refer symbolically to absolute locations of memory defined in other programs. You may use this option more than once.

For compatibility with other ELF linkers, if the -R option is followed by a directory name, rather than a file name, it is treated as the -rpath option.

-s ¶

--strip-all

Omit all symbol information from the output file.

-S ¶

--strip-debug

Omit debugger symbol information (but not all symbols) from the output file.

--strip-discarded ¶

--no-strip-discarded

Omit (or do not omit) global symbols defined in discarded sections. Enabled by default.

-t ¶

--trace

Print the names of the input files as ld processes them. If ‘-t’ is given twice then members within archives are also printed. ‘-t’ output is useful to generate a list of all the object files and scripts involved in linking, for example, when packaging files for a linker bug report.

-T scriptfile ¶

--script=scriptfile

Use scriptfile as the linker script. This script replaces ld’s default linker script (rather than adding to it), unless the script contains INSERT, so commandfile must specify everything necessary to describe the output file. See Linker Scripts. If scriptfile does not exist in the current directory, ld looks for it in the directories specified by any preceding ‘-L’ options. Multiple ‘-T’ options accumulate.

-dT scriptfile ¶

--default-script=scriptfile

Use scriptfile as the default linker script. See Linker Scripts.

This option is similar to the --script option except that processing of the script is delayed until after the rest of the command line has been processed. This allows options placed after the --default-script option on the command line to affect the behaviour of the linker script, which can be important when the linker command line cannot be directly controlled by the user. (eg because the command line is being constructed by another tool, such as ‘gcc’).

-u symbol ¶

--undefined=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. This option is equivalent to the EXTERN linker script command.

If this option is being used to force additional modules to be pulled into the link, and if it is an error for the symbol to remain undefined, then the option --require-defined should be used instead.

--require-defined=symbol ¶

Require that symbol is defined in the output file. This option is the same as option --undefined except that if symbol is not defined in the output file then the linker will issue an error and exit. The same effect can be achieved in a linker script by using EXTERN, ASSERT and DEFINED together. This option can be used multiple times to require additional symbols.

-Ur ¶

For programs that do not use constructors or destructors, or for ELF based systems this option is equivalent to -r: it generates relocatable output—i.e., an output file that can in turn serve as input to ld. For other binaries however the -Ur option is similar to -r but it also resolves references to constructors and destructors.

For those systems where -r and -Ur behave differently, it does not work to use -Ur on files that were themselves linked with -Ur; once the constructor table has been built, it cannot be added to. Use -Ur only for the last partial link, and -r for the others.

--orphan-handling=MODE ¶

Control how orphan sections are handled. An orphan section is one not specifically mentioned in a linker script. See Orphan Sections.

MODE can have any of the following values:

place

Orphan sections are placed into a suitable output section following the strategy described in Orphan Sections. The option ‘--unique’ also affects how sections are placed.

discard

All orphan sections are discarded, by placing them in the ‘/DISCARD/’ section (see Output Section Discarding).

warn

The linker will place the orphan section as for place and also issue a warning.

error

The linker will exit with an error if any orphan section is found.

The default if ‘--orphan-handling’ is not given is place.

--unique[=SECTION] ¶

Creates a separate output section for every input section matching SECTION, or if the optional wildcard SECTION argument is missing, for every orphan input section. An orphan section is one not specifically mentioned in a linker script. You may use this option multiple times on the command line; It prevents the normal merging of input sections with the same name, overriding output section assignments in a linker script.

-v ¶

--version

-V

Display the version number for ld. The -V option also lists the supported emulations. See also the description of the --enable-linker-version in Command-line Options which can be used to insert the linker version string into a binary.

-x ¶

--discard-all

Delete all local symbols.

-X ¶

--discard-locals

Delete all temporary local symbols. (These symbols start with system-specific local label prefixes, typically ‘.L’ for ELF systems or ‘L’ for traditional a.out systems.)

-y symbol ¶

--trace-symbol=symbol

Print the name of each linked file in which symbol appears. This option may be given any number of times. On many systems it is necessary to prepend an underscore.

This option is useful when you have an undefined symbol in your link but don’t know where the reference is coming from.

-Y path ¶

Add path to the default library search path. This option exists for Solaris compatibility.

-z keyword ¶

The recognized keywords are:

‘call-nop=prefix-addr’

‘call-nop=suffix-nop’

‘call-nop=prefix-byte’

‘call-nop=suffix-byte’

Specify the 1-byte NOP padding when transforming indirect call to a locally defined function, foo, via its GOT slot. call-nop=prefix-addr generates 0x67 call foo. call-nop=suffix-nop generates call foo 0x90. call-nop=prefix-byte generates byte call foo. call-nop=suffix-byte generates call foo byte. Supported for i386 and x86_64.

‘cet-report=none’

‘cet-report=warning’

‘cet-report=error’

Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_IBT and GNU_PROPERTY_X86_FEATURE_1_SHSTK properties in input .note.gnu.property section. cet-report=none, which is the default, will make the linker not report missing properties in input files. cet-report=warning will make the linker issue a warning for missing properties in input files. cet-report=error will make the linker issue an error for missing properties in input files. Note that ibt will turn off the missing GNU_PROPERTY_X86_FEATURE_1_IBT property report and shstk will turn off the missing GNU_PROPERTY_X86_FEATURE_1_SHSTK property report. Supported for Linux/i386 and Linux/x86_64.

‘combreloc’

‘nocombreloc’

Combine multiple dynamic relocation sections and sort to improve dynamic symbol lookup caching. Do not do this if ‘nocombreloc’.

‘common’

‘nocommon’

Generate common symbols with STT_COMMON type during a relocatable link. Use STT_OBJECT type if ‘nocommon’.

‘common-page-size=value’

Set the page size most commonly used to value. Memory image layout will be optimized to minimize memory pages if the system is using pages of this size.

‘defs’

Report unresolved symbol references from regular object files. This is done even if the linker is creating a non-symbolic shared library. This option is the inverse of ‘-z undefs’.

‘dynamic-undefined-weak’

‘nodynamic-undefined-weak’

Make undefined weak symbols dynamic when building a dynamic object, if they are referenced from a regular object file and not forced local by symbol visibility or versioning. Do not make them dynamic if ‘nodynamic-undefined-weak’. If neither option is given, a target may default to either option being in force, or make some other selection of undefined weak symbols dynamic. Not all targets support these options.

‘execstack’

Marks the object as requiring executable stack.

‘global’

This option is only meaningful when building a shared object. It makes the symbols defined by this shared object available for symbol resolution of subsequently loaded libraries.

‘globalaudit’

This option is only meaningful when building a dynamic executable. This option marks the executable as requiring global auditing by setting the DF_1_GLOBAUDIT bit in the DT_FLAGS_1 dynamic tag. Global auditing requires that any auditing library defined via the --depaudit or -P command-line options be run for all dynamic objects loaded by the application.

‘ibtplt’

Generate Intel Indirect Branch Tracking (IBT) enabled PLT entries. Supported for Linux/i386 and Linux/x86_64.

‘ibt’

Generate GNU_PROPERTY_X86_FEATURE_1_IBT in .note.gnu.property section to indicate compatibility with IBT. This also implies ibtplt. Supported for Linux/i386 and Linux/x86_64.

‘indirect-extern-access’

‘noindirect-extern-access’

Generate GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS in .note.gnu.property section to indicate that object file requires canonical function pointers and cannot be used with copy relocation. This option also implies noextern-protected-data and nocopyreloc. Supported for i386 and x86-64.

noindirect-extern-access removes GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS from .note.gnu.property section.

‘initfirst’

This option is only meaningful when building a shared object. It marks the object so that its runtime initialization will occur before the runtime initialization of any other objects brought into the process at the same time. Similarly the runtime finalization of the object will occur after the runtime finalization of any other objects.

‘interpose’

Specify that the dynamic loader should modify its symbol search order so that symbols in this shared library interpose all other shared libraries not so marked.

‘unique’

‘nounique’

When generating a shared library or other dynamically loadable ELF object mark it as one that should (by default) only ever be loaded once, and only in the main namespace (when using dlmopen). This is primarily used to mark fundamental libraries such as libc, libpthread et al which do not usually function correctly unless they are the sole instances of themselves. This behaviour can be overridden by the dlmopen caller and does not apply to certain loading mechanisms (such as audit libraries).

‘lam-u48’

Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U48 in .note.gnu.property section to indicate compatibility with Intel LAM_U48. Supported for Linux/x86_64.

‘lam-u57’

Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U57 in .note.gnu.property section to indicate compatibility with Intel LAM_U57. Supported for Linux/x86_64.

‘lam-u48-report=none’

‘lam-u48-report=warning’

‘lam-u48-report=error’

Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U48 property in input .note.gnu.property section. lam-u48-report=none, which is the default, will make the linker not report missing properties in input files. lam-u48-report=warning will make the linker issue a warning for missing properties in input files. lam-u48-report=error will make the linker issue an error for missing properties in input files. Supported for Linux/x86_64.

‘lam-u57-report=none’

‘lam-u57-report=warning’

‘lam-u57-report=error’

Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U57 property in input .note.gnu.property section. lam-u57-report=none, which is the default, will make the linker not report missing properties in input files. lam-u57-report=warning will make the linker issue a warning for missing properties in input files. lam-u57-report=error will make the linker issue an error for missing properties in input files. Supported for Linux/x86_64.

‘lam-report=none’

‘lam-report=warning’

‘lam-report=error’

Specify how to report the missing GNU_PROPERTY_X86_FEATURE_1_LAM_U48 and GNU_PROPERTY_X86_FEATURE_1_LAM_U57 properties in input .note.gnu.property section. lam-report=none, which is the default, will make the linker not report missing properties in input files. lam-report=warning will make the linker issue a warning for missing properties in input files. lam-report=error will make the linker issue an error for missing properties in input files. Supported for Linux/x86_64.

‘lazy’

When generating an executable or shared library, mark it to tell the dynamic linker to defer function call resolution to the point when the function is called (lazy binding), rather than at load time. Lazy binding is the default.

‘loadfltr’

Specify that the object’s filters be processed immediately at runtime.

‘max-page-size=value’

Set the maximum memory page size supported to value.

‘mark-plt’

‘nomark-plt’

Mark PLT entries with dynamic tags, DT_X86_64_PLT, DT_X86_64_PLTSZ and DT_X86_64_PLTENT. Since this option stores a non-zero value in the r_addend field of R_X86_64_JUMP_SLOT relocations, the resulting executables and shared libraries are incompatible with dynamic linkers, such as those in older versions of glibc without the change to ignore r_addend in R_X86_64_GLOB_DAT and R_X86_64_JUMP_SLOT relocations, which don’t ignore the r_addend field of R_X86_64_JUMP_SLOT relocations. Supported for x86_64.

‘muldefs’

Allow multiple definitions.

‘nocopyreloc’

Disable linker generated .dynbss variables used in place of variables defined in shared libraries. May result in dynamic text relocations.

‘nodefaultlib’

Specify that the dynamic loader search for dependencies of this object should ignore any default library search paths.

‘nodelete’

Specify that the object shouldn’t be unloaded at runtime.

‘nodlopen’

Specify that the object is not available to dlopen.

‘nodump’

Specify that the object can not be dumped by dldump.

‘noexecstack’

Marks the object as not requiring executable stack.

‘noextern-protected-data’

Don’t treat protected data symbols as external when building a shared library. This option overrides the linker backend default. It can be used to work around incorrect relocations against protected data symbols generated by compiler. Updates on protected data symbols by another module aren’t visible to the resulting shared library. Supported for i386 and x86-64.

‘noreloc-overflow’

Disable relocation overflow check. This can be used to disable relocation overflow check if there will be no dynamic relocation overflow at run-time. Supported for x86_64.

‘now’

When generating an executable or shared library, mark it to tell the dynamic linker to resolve all symbols when the program is started, or when the shared library is loaded by dlopen, instead of deferring function call resolution to the point when the function is first called.

‘origin’

Specify that the object requires ‘$ORIGIN’ handling in paths.

‘pack-relative-relocs’

‘nopack-relative-relocs’

Generate compact relative relocation in position-independent executable and shared library. It adds DT_RELR, DT_RELRSZ and DT_RELRENT entries to the dynamic section. It is ignored when building position-dependent executable and relocatable output. nopack-relative-relocs is the default, which disables compact relative relocation. When linked against the GNU C Library, a GLIBC_ABI_DT_RELR symbol version dependency on the shared C Library is added to the output. Supported for i386 and x86-64.

‘relro’

‘norelro’

Create an ELF PT_GNU_RELRO segment header in the object. This specifies a memory segment that should be made read-only after relocation, if supported. Specifying ‘common-page-size’ smaller than the system page size will render this protection ineffective. Don’t create an ELF PT_GNU_RELRO segment if ‘norelro’.

‘report-relative-reloc’

Report dynamic relative relocations generated by linker. Supported for Linux/i386 and Linux/x86_64.

‘sectionheader’

‘nosectionheader’

Generate section header. Don’t generate section header if ‘nosectionheader’ is used. sectionheader is the default.

‘separate-code’

‘noseparate-code’

Create separate code PT_LOAD segment header in the object. This specifies a memory segment that should contain only instructions and must be in wholly disjoint pages from any other data. Don’t create separate code PT_LOAD segment if ‘noseparate-code’ is used.

‘shstk’

Generate GNU_PROPERTY_X86_FEATURE_1_SHSTK in .note.gnu.property section to indicate compatibility with Intel Shadow Stack. Supported for Linux/i386 and Linux/x86_64.

‘stack-size=value’

Specify a stack size for an ELF PT_GNU_STACK segment. Specifying zero will override any default non-zero sized PT_GNU_STACK segment creation.

‘start-stop-gc’ ¶

‘nostart-stop-gc’

When ‘--gc-sections’ is in effect, a reference from a retained section to __start_SECNAME or __stop_SECNAME causes all input sections named SECNAME to also be retained, if SECNAME is representable as a C identifier and either __start_SECNAME or __stop_SECNAME is synthesized by the linker. ‘-z start-stop-gc’ disables this effect, allowing sections to be garbage collected as if the special synthesized symbols were not defined. ‘-z start-stop-gc’ has no effect on a definition of __start_SECNAME or __stop_SECNAME in an object file or linker script. Such a definition will prevent the linker providing a synthesized __start_SECNAME or __stop_SECNAME respectively, and therefore the special treatment by garbage collection for those references.

‘start-stop-visibility=value’ ¶

Specify the ELF symbol visibility for synthesized __start_SECNAME and __stop_SECNAME symbols (see Input Section Example). value must be exactly ‘default’, ‘internal’, ‘hidden’, or ‘protected’. If no ‘-z start-stop-visibility’ option is given, ‘protected’ is used for compatibility with historical practice. However, it’s highly recommended to use ‘-z start-stop-visibility=hidden’ in new programs and shared libraries so that these symbols are not exported between shared objects, which is not usually what’s intended.

‘text’

‘notext’

‘textoff’

Report an error if DT_TEXTREL is set, i.e., if the position-independent or shared object has dynamic relocations in read-only sections. Don’t report an error if ‘notext’ or ‘textoff’.

‘undefs’

Do not report unresolved symbol references from regular object files, either when creating an executable, or when creating a shared library. This option is the inverse of ‘-z defs’.

‘unique-symbol’

‘nounique-symbol’

Avoid duplicated local symbol names in the symbol string table. Append ".number" to duplicated local symbol names if ‘unique-symbol’ is used. nounique-symbol is the default.

‘x86-64-baseline’

‘x86-64-v2’

‘x86-64-v3’

‘x86-64-v4’

Specify the x86-64 ISA level needed in .note.gnu.property section. x86-64-baseline generates GNU_PROPERTY_X86_ISA_1_BASELINE. x86-64-v2 generates GNU_PROPERTY_X86_ISA_1_V2. x86-64-v3 generates GNU_PROPERTY_X86_ISA_1_V3. x86-64-v4 generates GNU_PROPERTY_X86_ISA_1_V4. Supported for Linux/i386 and Linux/x86_64.

Other keywords are ignored for Solaris compatibility.

-( archives -) ¶

--start-group archives --end-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.

--accept-unknown-input-arch ¶

--no-accept-unknown-input-arch

Tells the linker to accept input files whose architecture cannot be recognised. The assumption is that the user knows what they are doing and deliberately wants to link in these unknown input files. This was the default behaviour of the linker, before release 2.14. The default behaviour from release 2.14 onwards is to reject such input files, and so the ‘--accept-unknown-input-arch’ option has been added to restore the old behaviour.

--as-needed ¶

--no-as-needed

This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the --as-needed option. Normally the linker will add a DT_NEEDED tag for each dynamic library mentioned on the command line, regardless of whether the library is actually needed or not. --as-needed causes a DT_NEEDED tag to only be emitted for a library that at that point in the link satisfies a non-weak undefined symbol reference from a regular object file or, if the library is not found in the DT_NEEDED lists of other needed libraries, a non-weak undefined symbol reference from another needed dynamic library. Object files or libraries appearing on the command line after the library in question do not affect whether the library is seen as needed. This is similar to the rules for extraction of object files from archives. --no-as-needed restores the default behaviour.

Note: On Linux based systems the --as-needed option also has an affect on the behaviour of the --rpath and --rpath-link options. See the description of --rpath-link for more details.

--add-needed ¶

--no-add-needed

These two options have been deprecated because of the similarity of their names to the --as-needed and --no-as-needed options. They have been replaced by --copy-dt-needed-entries and --no-copy-dt-needed-entries.

-assert keyword ¶

This option is ignored for SunOS compatibility.

-Bdynamic ¶

-dy

-call_shared

Link against dynamic libraries. This is only meaningful on platforms for which shared libraries are supported. This option is normally the default on such platforms. The different variants of this option are for compatibility with various systems. You may use this option multiple times on the command line: it affects library searching for -l options which follow it.

-Bgroup ¶

Set the DF_1_GROUP flag in the DT_FLAGS_1 entry in the dynamic section. This causes the runtime linker to handle lookups in this object and its dependencies to be performed only inside the group. --unresolved-symbols=report-all is implied. This option is only meaningful on ELF platforms which support shared libraries.

-Bstatic ¶

-dn

-non_shared

-static

Do not link against shared libraries. This is only meaningful on platforms for which shared libraries are supported. The different variants of this option are for compatibility with various systems. You may use this option multiple times on the command line: it affects library searching for -l options which follow it. This option also implies --unresolved-symbols=report-all. This option can be used with -shared. Doing so means that a shared library is being created but that all of the library’s external references must be resolved by pulling in entries from static libraries.

-Bsymbolic ¶

When creating a shared library, bind references to global symbols to the definition within the shared library, if any. Normally, it is possible for a program linked against a shared library to override the definition within the shared library. This option is only meaningful on ELF platforms which support shared libraries.

-Bsymbolic-functions ¶

When creating a shared library, bind references to global function symbols to the definition within the shared library, if any. This option is only meaningful on ELF platforms which support shared libraries.

-Bno-symbolic ¶

This option can cancel previously specified ‘-Bsymbolic’ and ‘-Bsymbolic-functions’.

--dynamic-list=dynamic-list-file ¶

Specify the name of a dynamic list file to the linker. This is typically used when creating shared libraries to specify a list of global symbols whose references shouldn’t be bound to the definition within the shared library, or creating dynamically linked executables to specify a list of symbols which should be added to the symbol table in the executable. This option is only meaningful on ELF platforms which support shared libraries.

The format of the dynamic list is the same as the version node without scope and node name. See VERSION Command for more information.

--dynamic-list-data ¶

Include all global data symbols to the dynamic list.

--dynamic-list-cpp-new ¶

Provide the builtin dynamic list for C++ operator new and delete. It is mainly useful for building shared libstdc++.

--dynamic-list-cpp-typeinfo ¶

Provide the builtin dynamic list for C++ runtime type identification.

--check-sections ¶

--no-check-sections

Asks the linker not to check section addresses after they have been assigned to see if there are any overlaps. Normally the linker will perform this check, and if it finds any overlaps it will produce suitable error messages. The linker does know about, and does make allowances for sections in overlays. The default behaviour can be restored by using the command-line switch --check-sections. Section overlap is not usually checked for relocatable links. You can force checking in that case by using the --check-sections option.

--copy-dt-needed-entries ¶

--no-copy-dt-needed-entries

This option affects the treatment of dynamic libraries referred to by DT_NEEDED tags inside ELF dynamic libraries mentioned on the command line. Normally the linker won’t add a DT_NEEDED tag to the output binary for each library mentioned in a DT_NEEDED tag in an input dynamic library. With --copy-dt-needed-entries specified on the command line however any dynamic libraries that follow it will have their DT_NEEDED entries added. The default behaviour can be restored with --no-copy-dt-needed-entries.

This option also has an effect on the resolution of symbols in dynamic libraries. With --copy-dt-needed-entries dynamic libraries mentioned on the command line will be recursively searched, following their DT_NEEDED tags to other libraries, in order to resolve symbols required by the output binary. With the default setting however the searching of dynamic libraries that follow it will stop with the dynamic library itself. No DT_NEEDED links will be traversed to resolve symbols.

--cref ¶

Output a 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 intentionally simple, so that it may be easily processed by a script 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. If the symbol is defined as a common value then any files where this happens appear next. Finally any files that reference the symbol are listed.

--ctf-variables ¶

--no-ctf-variables

The CTF debuginfo format supports a section which encodes the names and types of variables found in the program which do not appear in any symbol table. These variables clearly cannot be looked up by address by conventional debuggers, so the space used for their types and names is usually wasted: the types are usually small but the names are often not. --ctf-variables causes the generation of such a section. The default behaviour can be restored with --no-ctf-variables.

--ctf-share-types=method ¶

Adjust the method used to share types between translation units in CTF.

‘share-unconflicted’

Put all types that do not have ambiguous definitions into the shared dictionary, where debuggers can easily access them, even if they only occur in one translation unit. This is the default.

‘share-duplicated’

Put only types that occur in multiple translation units into the shared dictionary: types with only one definition go into per-translation-unit dictionaries. Types with ambiguous definitions in multiple translation units always go into per-translation-unit dictionaries. This tends to make the CTF larger, but may reduce the amount of CTF in the shared dictionary. For very large projects this may speed up opening the CTF and save memory in the CTF consumer at runtime.

--no-define-common ¶

This option inhibits the assignment of addresses to common symbols. The script command INHIBIT_COMMON_ALLOCATION has the same effect. See Other Linker Script Commands.

The ‘--no-define-common’ option allows decoupling the decision to assign addresses to Common symbols from the choice of the output file type; otherwise a non-Relocatable output type forces assigning addresses to Common symbols. Using ‘--no-define-common’ allows Common symbols that are referenced from a shared library to be assigned addresses only in the main program. This eliminates the unused duplicate space in the shared library, and also prevents any possible confusion over resolving to the wrong duplicate when there are many dynamic modules with specialized search paths for runtime symbol resolution.

--force-group-allocation ¶

This option causes the linker to place section group members like normal input sections, and to delete the section groups. This is the default behaviour for a final link but this option can be used to change the behaviour of a relocatable link (‘-r’). The script command FORCE_GROUP_ALLOCATION has the same effect. See Other Linker Script Commands.

--defsym=symbol=expression ¶

Create a global symbol in the output file, containing the absolute address given by expression. 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 expression 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. If you need more elaborate expressions, consider using the linker command language from a script (see Assigning Values to Symbols). Note: there should be no white space between symbol, the equals sign (“=”), and expression.

The linker processes ‘--defsym’ arguments and ‘-T’ arguments in order, placing ‘--defsym’ before ‘-T’ will define the symbol before the linker script from ‘-T’ is processed, while placing ‘--defsym’ after ‘-T’ will define the symbol after the linker script has been processed. This difference has consequences for expressions within the linker script that use the ‘--defsym’ symbols, which order is correct will depend on what you are trying to achieve.

--demangle[=style] ¶

--no-demangle

These options control whether to demangle symbol names in error messages and other output. When the linker is told to demangle, it tries to present symbol names in a readable fashion: it strips leading underscores if they are used by the object file format, and converts C++ mangled symbol names into user readable names. Different compilers have different mangling styles. The optional demangling style argument can be used to choose an appropriate demangling style for your compiler. The linker will demangle by default unless the environment variable ‘COLLECT_NO_DEMANGLE’ is set. These options may be used to override the default.

-Ifile ¶

--dynamic-linker=file

Set the name of the dynamic linker. This is only meaningful when generating dynamically linked ELF executables. The default dynamic linker is normally correct; don’t use this unless you know what you are doing.

--no-dynamic-linker ¶

When producing an executable file, omit the request for a dynamic linker to be used at load-time. This is only meaningful for ELF executables that contain dynamic relocations, and usually requires entry point code that is capable of processing these relocations.

--embedded-relocs ¶

This option is similar to the --emit-relocs option except that the relocs are stored in a target-specific section. This option is only supported by the ‘BFIN’, ‘CR16’ and M68K targets.

--disable-multiple-abs-defs ¶

Do not allow multiple definitions with symbols included in filename invoked by -R or –just-symbols

--fatal-warnings ¶

--no-fatal-warnings

Treat all warnings as errors. The default behaviour can be restored with the option --no-fatal-warnings.

-w ¶

--no-warnings

Do not display any warning or error messages. This overrides --fatal-warnings if it has been enabled. This option can be used when it is known that the output binary will not work, but there is still a need to create it.

--force-exe-suffix ¶

Make sure that an output file has a .exe suffix.

If a successfully built fully linked output file does not have a .exe or .dll suffix, this option forces the linker to copy the output file to one of the same name with a .exe suffix. This option is useful when using unmodified Unix makefiles on a Microsoft Windows host, since some versions of Windows won’t run an image unless it ends in a .exe suffix.

--gc-sections ¶

--no-gc-sections

Enable garbage collection of unused input sections. It is ignored on targets that do not support this option. The default behaviour (of not performing this garbage collection) can be restored by specifying ‘--no-gc-sections’ on the command line. Note that garbage collection for COFF and PE format targets is supported, but the implementation is currently considered to be experimental.

‘--gc-sections’ decides which input sections are used by examining symbols and relocations. The section containing the entry symbol and all sections containing symbols undefined on the command-line will be kept, as will sections containing symbols referenced by dynamic objects. Note that when building shared libraries, the linker must assume that any visible symbol is referenced. Once this initial set of sections has been determined, the linker recursively marks as used any section referenced by their relocations. See ‘--entry’, ‘--undefined’, and ‘--gc-keep-exported’.

This option can be set when doing a partial link (enabled with option ‘-r’). In this case the root of symbols kept must be explicitly specified either by one of the options ‘--entry’, ‘--undefined’, or ‘--gc-keep-exported’ or by a ENTRY command in the linker script.

As a GNU extension, ELF input sections marked with the SHF_GNU_RETAIN flag will not be garbage collected.

--print-gc-sections ¶

--no-print-gc-sections

List all sections removed by garbage collection. The listing is printed on stderr. This option is only effective if garbage collection has been enabled via the ‘--gc-sections’) option. The default behaviour (of not listing the sections that are removed) can be restored by specifying ‘--no-print-gc-sections’ on the command line.

--gc-keep-exported ¶

When ‘--gc-sections’ is enabled, this option prevents garbage collection of unused input sections that contain global symbols having default or protected visibility. This option is intended to be used for executables where unreferenced sections would otherwise be garbage collected regardless of the external visibility of contained symbols. Note that this option has no effect when linking shared objects since it is already the default behaviour. This option is only supported for ELF format targets.

--print-output-format ¶

Print the name of the default output format (perhaps influenced by other command-line options). This is the string that would appear in an OUTPUT_FORMAT linker script command (see Commands Dealing with Files).

--print-memory-usage ¶

Print used size, total size and used size of memory regions created with the MEMORY Command command. This is useful on embedded targets to have a quick view of amount of free memory. The format of the output has one headline and one line per region. It is both human readable and easily parsable by tools. Here is an example of an output:

Memory region         Used Size  Region Size  %age Used
             ROM:        256 KB         1 MB     25.00%
             RAM:          32 B         2 GB      0.00%

--help ¶

Print a summary of the command-line options on the standard output and exit.

--target-help ¶

Print a summary of all target-specific options on the standard output and exit.

-Map=mapfile ¶

Print a link map to the file mapfile. See the description of the -M option, above. If mapfile is just the character - then the map will be written to stdout.

Specifying a directory as mapfile causes the linker map to be written as a file inside the directory. Normally name of the file inside the directory is computed as the basename of the output file with .map appended. If however the special character % is used then this will be replaced by the full path of the output file. Additionally if there are any characters after the % symbol then .map will no longer be appended.

 -o foo.exe -Map=bar                  [Creates ./bar]
 -o ../dir/foo.exe -Map=bar           [Creates ./bar]
 -o foo.exe -Map=../dir               [Creates ../dir/foo.exe.map]
 -o ../dir2/foo.exe -Map=../dir       [Creates ../dir/foo.exe.map]
 -o foo.exe -Map=%                    [Creates ./foo.exe.map]
 -o ../dir/foo.exe -Map=%             [Creates ../dir/foo.exe.map]
 -o foo.exe -Map=%.bar                [Creates ./foo.exe.bar]
 -o ../dir/foo.exe -Map=%.bar         [Creates ../dir/foo.exe.bar]
 -o ../dir2/foo.exe -Map=../dir/%     [Creates ../dir/../dir2/foo.exe.map]
 -o ../dir2/foo.exe -Map=../dir/%.bar [Creates ../dir/../dir2/foo.exe.bar]

It is an error to specify more than one % character.

If the map file already exists then it will be overwritten by this operation.

--no-keep-memory ¶

ld normally optimizes for speed over memory usage by caching the symbol tables of input files in memory. This option tells ld to instead optimize for memory usage, by rereading the symbol tables as necessary. This may be required if ld runs out of memory space while linking a large executable.

--no-undefined ¶

-z defs

Report unresolved symbol references from regular object files. This is done even if the linker is creating a non-symbolic shared library. The switch --[no-]allow-shlib-undefined controls the behaviour for reporting unresolved references found in shared libraries being linked in.

The effects of this option can be reverted by using -z undefs.

--allow-multiple-definition ¶

-z muldefs

Normally when a symbol is defined multiple times, the linker will report a fatal error. These options allow multiple definitions and the first definition will be used.

--allow-shlib-undefined ¶

--no-allow-shlib-undefined

Allows or disallows undefined symbols in shared libraries. This switch is similar to --no-undefined except that it determines the behaviour when the undefined symbols are in a shared library rather than a regular object file. It does not affect how undefined symbols in regular object files are handled.

The default behaviour is to report errors for any undefined symbols referenced in shared libraries if the linker is being used to create an executable, but to allow them if the linker is being used to create a shared library.

The reasons for allowing undefined symbol references in shared libraries specified at link time are that:

• A shared library specified at link time may not be the same as the one that is available at load time, so the symbol might actually be resolvable at load time.
• There are some operating systems, eg BeOS and HPPA, where undefined symbols in shared libraries are normal.

  The BeOS kernel for example patches shared libraries at load time to select whichever function is most appropriate for the current architecture. This is used, for example, to dynamically select an appropriate memset function.

--error-handling-script=scriptname ¶

If this option is provided then the linker will invoke scriptname whenever an error is encountered. Currently however only two kinds of error are supported: missing symbols and missing libraries. Two arguments will be passed to script: the keyword “undefined-symbol” or ‘missing-lib” and the name of the undefined symbol or missing library. The intention is that the script will provide suggestions to the user as to where the symbol or library might be found. After the script has finished then the normal linker error message will be displayed.

The availability of this option is controlled by a configure time switch, so it may not be present in specific implementations.

--no-undefined-version ¶

Normally when a symbol has an undefined version, the linker will ignore it. This option disallows symbols with undefined version and a fatal error will be issued instead.

--default-symver ¶

Create and use a default symbol version (the soname) for unversioned exported symbols.

--default-imported-symver ¶

Create and use a default symbol version (the soname) for unversioned imported symbols.

--no-warn-mismatch ¶

Normally 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 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.

--no-warn-search-mismatch ¶

Normally ld will give a warning if it finds an incompatible library during a library search. This option silences the warning.

--no-whole-archive ¶

Turn off the effect of the --whole-archive option for subsequent archive files.

--noinhibit-exec ¶

Retain the executable output file whenever it is still usable. Normally, the linker will not produce an output file if it encounters errors during the link process; it exits without writing an output file when it issues any error whatsoever.

-nostdlib ¶

Only search library directories explicitly specified on the command line. Library directories specified in linker scripts (including linker scripts specified on the command line) are ignored.

--oformat=output-format ¶

ld may be configured to support more than one kind of object file. If your ld is configured this way, you can use the ‘--oformat’ option to specify the binary format for the output object file. Even when ld is configured to support alternative object formats, you don’t usually need to specify this, as ld should be configured to produce as a default output format the most usual format on each machine. output-format is a text string, the name of a particular format supported by the BFD libraries. (You can list the available binary formats with ‘objdump -i’.) The script command OUTPUT_FORMAT can also specify the output format, but this option overrides it. See BFD.

--out-implib file ¶

Create an import library in file corresponding to the executable the linker is generating (eg. a DLL or ELF program). This import library (which should be called *.dll.a or *.a for DLLs) may be used to link clients against the generated executable; this behaviour makes it possible to skip a separate import library creation step (eg. dlltool for DLLs). This option is only available for the i386 PE and ELF targetted ports of the linker.

-pie ¶

--pic-executable

Create a position independent executable. This is currently only supported on ELF platforms. Position independent executables are similar to shared libraries in that they are relocated by the dynamic linker to the virtual address the OS chooses for them (which can vary between invocations). Like normal dynamically linked executables they can be executed and symbols defined in the executable cannot be overridden by shared libraries.

-no-pie ¶

Create a position dependent executable. This is the default.

-qmagic ¶

This option is ignored for Linux compatibility.

-Qy ¶

This option is ignored for SVR4 compatibility.

--relax ¶

--no-relax

An option with machine dependent effects. This option is only supported on a few targets. See ld and the H8/300. See ld and Xtensa Processors. See ld and the 68HC11 and 68HC12. See ld and the Altera Nios II. See ld and PowerPC 32-bit ELF Support.

On some platforms the --relax option performs target specific, global optimizations that become possible when the linker resolves addressing in the program, such as relaxing address modes, synthesizing new instructions, selecting shorter version of current instructions, and combining constant values.

On some platforms these link time global optimizations may make symbolic debugging of the resulting executable impossible. This is known to be the case for the Matsushita MN10200 and MN10300 family of processors.

On platforms where the feature is supported, the option --no-relax will disable it.

On platforms where the feature is not supported, both --relax and --no-relax are accepted, but ignored.

--retain-symbols-file=filename ¶

Retain only the symbols listed in the file filename, discarding all others. filename is simply a flat file, with one symbol name per line. This option is especially useful in environments (such as VxWorks) 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’.

-rpath=dir ¶

Add a directory to the runtime library search path. This is used when linking an ELF executable with shared objects. All -rpath arguments are concatenated and passed to the runtime linker, which uses them to locate shared objects at runtime.

The -rpath option is also used when locating shared objects which are needed by shared objects explicitly included in the link; see the description of the -rpath-link option. Searching -rpath in this way is only supported by native linkers and cross linkers which have been configured with the --with-sysroot option.

If -rpath is not used when linking an ELF executable, the contents of the environment variable LD_RUN_PATH will be used if it is defined.

The -rpath option may also be used on SunOS. By default, on SunOS, the linker will form a runtime search path out of all the -L options it is given. If a -rpath option is used, the runtime search path will be formed exclusively using the -rpath options, ignoring the -L options. This can be useful when using gcc, which adds many -L options which may be on NFS mounted file systems.

For compatibility with other ELF linkers, if the -R option is followed by a directory name, rather than a file name, it is treated as the -rpath option.

-rpath-link=dir ¶

When using ELF or SunOS, one shared library may require another. This happens when an ld -shared link includes a shared library as one of the input files.

When the linker encounters such a dependency when doing a non-shared, non-relocatable link, it will automatically try to locate the required shared library and include it in the link, if it is not included explicitly. In such a case, the -rpath-link option specifies the first set of directories to search. The -rpath-link option may specify a sequence of directory names either by specifying a list of names separated by colons, or by appearing multiple times.

The tokens $ORIGIN and $LIB can appear in these search directories. They will be replaced by the full path to the directory containing the program or shared object in the case of $ORIGIN and either ‘lib’ - for 32-bit binaries - or ‘lib64’ - for 64-bit binaries - in the case of $LIB.

The alternative form of these tokens - ${ORIGIN} and ${LIB} can also be used. The token $PLATFORM is not supported.

This option should be used with caution as it overrides the search path that may have been hard compiled into a shared library. In such a case it is possible to use unintentionally a different search path than the runtime linker would do.

The linker uses the following search paths to locate required shared libraries:

1. Any directories specified by -rpath-link options.
2. Any directories specified by -rpath options. The difference between -rpath and -rpath-link is that directories specified by -rpath options are included in the executable and used at runtime, whereas the -rpath-link option is only effective at link time. Searching -rpath in this way is only supported by native linkers and cross linkers which have been configured with the --with-sysroot option.
3. On an ELF system, for native linkers, if the -rpath and -rpath-link options were not used, search the contents of the environment variable LD_RUN_PATH.
4. On SunOS, if the -rpath option was not used, search any directories specified using -L options.
5. For a native linker, search the contents of the environment variable LD_LIBRARY_PATH.
6. For a native ELF linker, the directories in DT_RUNPATH or DT_RPATH of a shared library are searched for shared libraries needed by it. The DT_RPATH entries are ignored if DT_RUNPATH entries exist.
7. For a linker for a Linux system, if the file /etc/ld.so.conf exists, the list of directories found in that file. Note: the path to this file is prefixed with the sysroot value, if that is defined, and then any prefix string if the linker was configured with the --prefix=<path> option.
8. For a native linker on a FreeBSD system, any directories specified by the _PATH_ELF_HINTS macro defined in the elf-hints.h header file.
9. Any directories specified by a SEARCH_DIR command in a linker script given on the command line, including scripts specified by -T (but not -dT).
10. The default directories, normally /lib and /usr/lib.
11. Any directories specified by a plugin LDPT_SET_EXTRA_LIBRARY_PATH.
12. Any directories specified by a SEARCH_DIR command in a default linker script.

Note however on Linux based systems there is an additional caveat: If the --as-needed option is active and a shared library is located which would normally satisfy the search and this library does not have DT_NEEDED tag for libc.so and there is a shared library later on in the set of search directories which also satisfies the search and this second shared library does have a DT_NEEDED tag for libc.so then the second library will be selected instead of the first.

If the required shared library is not found, the linker will issue a warning and continue with the link.

-shared ¶

-Bshareable

Create a shared library. This is currently only supported on ELF, XCOFF and SunOS platforms. On SunOS, the linker will automatically create a shared library if the -e option is not used and there are undefined symbols in the link.

--sort-common ¶

--sort-common=ascending

--sort-common=descending

This option tells ld to sort the common symbols by alignment in ascending or descending order when it places them in the appropriate output sections. The symbol alignments considered are sixteen-byte or larger, eight-byte, four-byte, two-byte, and one-byte. This is to prevent gaps between symbols due to alignment constraints. If no sorting order is specified, then descending order is assumed.

--sort-section=name ¶

This option will apply SORT_BY_NAME to all wildcard section patterns in the linker script.

--sort-section=alignment ¶

This option will apply SORT_BY_ALIGNMENT to all wildcard section patterns in the linker script.

--spare-dynamic-tags=count ¶

This option specifies the number of empty slots to leave in the .dynamic section of ELF shared objects. Empty slots may be needed by post processing tools, such as the prelinker. The default is 5.

--split-by-file[=size] ¶

Similar to --split-by-reloc but creates a new output section for each input file when size is reached. size defaults to a size of 1 if not given.

--split-by-reloc[=count] ¶

Tries to creates extra sections in the output file so that no single output section in the file contains more than count relocations. This is useful when generating huge relocatable files for downloading into certain real time kernels with the COFF object file format; since COFF cannot represent more than 65535 relocations in a single section. Note that this will fail to work with object file formats which do not support arbitrary sections. The linker will not split up individual input sections for redistribution, so if a single input section contains more than count relocations one output section will contain that many relocations. count defaults to a value of 32768.

--stats ¶

Compute and display statistics about the operation of the linker, such as execution time and memory usage.

--sysroot=directory ¶

Use directory as the location of the sysroot, overriding the configure-time default. This option is only supported by linkers that were configured using --with-sysroot.

--task-link ¶

This is used by COFF/PE based targets to create a task-linked object file where all of the global symbols have been converted to statics.

--traditional-format ¶

For some targets, the output of ld is different in some ways from the output of some existing linker. This switch requests ld to use the traditional format instead.

For example, on SunOS, ld combines duplicate entries in the symbol string table. This can reduce the size of an output file with full debugging information by over 30 percent. Unfortunately, the SunOS dbx program can not read the resulting program (gdb has no trouble). The ‘--traditional-format’ switch tells ld to not combine duplicate entries.

--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’ usually associated with hexadecimal values. Note: there should be no white space between sectionname, the equals sign (“=”), and org.

-Tbss=org ¶

-Tdata=org

-Ttext=org

Same as --section-start, with .bss, .data or .text as the sectionname.

-Ttext-segment=org ¶

When creating an ELF executable, it will set the address of the first byte of the text segment.

-Trodata-segment=org ¶

When creating an ELF executable or shared object for a target where the read-only data is in its own segment separate from the executable text, it will set the address of the first byte of the read-only data segment.

-Tldata-segment=org ¶

When creating an ELF executable or shared object for x86-64 medium memory model, it will set the address of the first byte of the ldata segment.

--unresolved-symbols=method ¶

Determine how to handle unresolved symbols. There are four possible values for ‘method’:

‘ignore-all’

Do not report any unresolved symbols.

‘report-all’

Report all unresolved symbols. This is the default.

‘ignore-in-object-files’

Report unresolved symbols that are contained in shared libraries, but ignore them if they come from regular object files.

‘ignore-in-shared-libs’

Report unresolved symbols that come from regular object files, but ignore them if they come from shared libraries. This can be useful when creating a dynamic binary and it is known that all the shared libraries that it should be referencing are included on the linker’s command line.

The behaviour for shared libraries on their own can also be controlled by the --[no-]allow-shlib-undefined option.

Normally the linker will generate an error message for each reported unresolved symbol but the option --warn-unresolved-symbols can change this to a warning.

--dll-verbose ¶

--verbose[=NUMBER]

Display the version number for ld and list the linker emulations supported. Display which input files can and cannot be opened. Display the linker script being used by the linker. If the optional NUMBER argument > 1, plugin symbol status will also be displayed.

--version-script=version-scriptfile ¶

Specify the name of a version script to the linker. This is typically used when creating shared libraries to specify additional information about the version hierarchy for the library being created. This option is only fully supported on ELF platforms which support shared libraries; see VERSION Command. It is partially supported on PE platforms, which can use version scripts to filter symbol visibility in auto-export mode: any symbols marked ‘local’ in the version script will not be exported. See ld and WIN32 (cygwin/mingw).

--warn-common ¶

Warn when a common symbol is combined with another common symbol or with a symbol definition. Unix linkers allow this somewhat sloppy practice, but linkers on some other operating systems do not. This option allows you to find potential problems from combining global symbols. Unfortunately, some C libraries use this practice, so you may get some warnings about symbols in the libraries as well as in your programs.

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.

1. 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
   

2. 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
   

3. 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
   

4. 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
   

5. 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
   

--warn-constructors ¶

Warn if any global constructors are used. This is only useful for a few object file formats. For formats like COFF or ELF, the linker can not detect the use of global constructors.

--warn-execstack ¶

--warn-execstack-objects

--no-warn-execstack

On ELF platforms the linker may generate warning messages if it is asked to create an output file that contains an executable stack. There are three possible states:

1. Do not generate any warnings.
2. Always generate warnings, even if the executable stack is requested via the -z execstack command line option.
3. Only generate a warning if an object file requests an executable stack, but not if the -z execstack option is used.

The default state depends upon how the linker was configured when it was built. The --no-warn-execstack option always puts the linker into the no-warnings state. The --warn-execstack option puts the linker into the warn-always state. The --warn-execstack-objects option puts the linker into the warn-for-object-files-only state.

Note: ELF format input files can specify that they need an executable stack by having a .note.GNU-stack section with the executable bit set in its section flags. They can specify that they do not need an executable stack by having the same section, but without the executable flag bit set. If an input file does not have a .note.GNU-stack section then the default behaviour is target specific. For some targets, then absence of such a section implies that an executable stack is required. This is often a problem for hand crafted assembler files.

--error-execstack ¶

--no-error-execstack

If the linker is going to generate a warning message about an executable stack then the --error-execstack option will instead change that warning into an error. Note - this option does not change the linker’s execstack warning generation state. Use --warn-execstack or --warn-execstack-objects to set a specific warning state.

The --no-error-execstack option will restore the default behaviour of generating warning messages.

--warn-multiple-gp ¶

Warn if multiple global pointer values are required in the output file. This is only meaningful for certain processors, such as the Alpha. Specifically, some processors put large-valued constants in a special section. A special register (the global pointer) points into the middle of this section, so that constants can be loaded efficiently via a base-register relative addressing mode. Since the offset in base-register relative mode is fixed and relatively small (e.g., 16 bits), this limits the maximum size of the constant pool. Thus, in large programs, it is often necessary to use multiple global pointer values in order to be able to address all possible constants. This option causes a warning to be issued whenever this case occurs.

--warn-once ¶

Only warn once for each undefined symbol, rather than once per module which refers to it.

--warn-rwx-segments ¶

--no-warn-rwx-segments

Warn if the linker creates a loadable, non-zero sized segment that has all three of the read, write and execute permission flags set. Such a segment represents a potential security vulnerability. In addition warnings will be generated if a thread local storage segment is created with the execute permission flag set, regardless of whether or not it has the read and/or write flags set.

These warnings are enabled by default. They can be disabled via the --no-warn-rwx-segments option and re-enabled via the --warn-rwx-segments option.

--error-rwx-segments ¶

--no-error-rwx-segments

If the linker is going to generate a warning message about an executable, writeable segment, or an executable TLS segment, then the --error-rwx-segments option will turn this warning into an error instead. The --no-error-rwx-segments option will restore the default behaviour of just generating a warning message.

Note - the --error-rwx-segments option does not by itself turn on warnings about these segments. These warnings are either enabled by default, if the linker was configured that way, or via the --warn-rwx-segments command line option.

--warn-section-align ¶

Warn if the address of an output section is changed because of alignment. Typically, the alignment will be set by an input section. The address will only be changed if it not explicitly specified; that is, if the SECTIONS command does not specify a start address for the section (see SECTIONS Command).

--warn-textrel ¶

Warn if the linker adds DT_TEXTREL to a position-independent executable or shared object.

--warn-alternate-em ¶

Warn if an object has alternate ELF machine code.

--warn-unresolved-symbols ¶

If the linker is going to report an unresolved symbol (see the option --unresolved-symbols) it will normally generate an error. This option makes it generate a warning instead.

--error-unresolved-symbols ¶

This restores the linker’s default behaviour of generating errors when it is reporting unresolved symbols.

--whole-archive ¶

For each archive mentioned on the command line after the --whole-archive option, include every object file in the archive in the link, rather than searching the archive for the required object files. This is normally used to turn an archive file into a shared library, forcing every object to be included in the resulting shared library. This option may be used more than once.

Two notes when using this option from gcc: First, gcc doesn’t know about this option, so you have to use -Wl,-whole-archive. Second, don’t forget to use -Wl,-no-whole-archive after your list of archives, because gcc will add its own list of archives to your link and you may not want this flag to affect those as well.

--wrap=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 (size_t c)
{
  printf ("malloc called with %zu\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.

Only undefined references are replaced by the linker. So, translation unit internal references to symbol are not resolved to __wrap_symbol. In the next example, the call to f in g is not resolved to __wrap_f.

int
f (void)
{
  return 123;
}

int
g (void)
{
  return f();
}

--eh-frame-hdr ¶

--no-eh-frame-hdr

Request (--eh-frame-hdr) or suppress (--no-eh-frame-hdr) the creation of .eh_frame_hdr section and ELF PT_GNU_EH_FRAME segment header.

--no-ld-generated-unwind-info ¶

Request creation of .eh_frame unwind info for linker generated code sections like PLT. This option is on by default if linker generated unwind info is supported. This option also controls the generation of .sframe stack trace info for linker generated code sections like PLT.

--enable-new-dtags ¶

--disable-new-dtags

This linker can create the new dynamic tags in ELF. But the older ELF systems may not understand them. If you specify --enable-new-dtags, the new dynamic tags will be created as needed and older dynamic tags will be omitted. If you specify --disable-new-dtags, no new dynamic tags will be created. By default, the new dynamic tags are not created. Note that those options are only available for ELF systems.

--hash-size=number ¶

Set the default size of the linker’s hash tables to a prime number close to number. Increasing this value can reduce the length of time it takes the linker to perform its tasks, at the expense of increasing the linker’s memory requirements. Similarly reducing this value can reduce the memory requirements at the expense of speed.

--hash-style=style ¶

Set the type of linker’s hash table(s). style can be either sysv for classic ELF .hash section, gnu for new style GNU .gnu.hash section or both for both the classic ELF .hash and new style GNU .gnu.hash hash tables. The default depends upon how the linker was configured, but for most Linux based systems it will be both.

--compress-debug-sections=none ¶

--compress-debug-sections=zlib

--compress-debug-sections=zlib-gnu

--compress-debug-sections=zlib-gabi

--compress-debug-sections=zstd

On ELF platforms, these options control how DWARF debug sections are compressed using zlib.

--compress-debug-sections=none doesn’t compress DWARF debug sections. --compress-debug-sections=zlib-gnu compresses DWARF debug sections and renames them to begin with ‘.zdebug’ instead of ‘.debug’. --compress-debug-sections=zlib-gabi also compresses DWARF debug sections, but rather than renaming them it sets the SHF_COMPRESSED flag in the sections’ headers.

The --compress-debug-sections=zlib option is an alias for --compress-debug-sections=zlib-gabi.

--compress-debug-sections=zstd compresses DWARF debug sections using zstd.

Note that this option overrides any compression in input debug sections, so if a binary is linked with --compress-debug-sections=none for example, then any compressed debug sections in input files will be uncompressed before they are copied into the output binary.

The default compression behaviour varies depending upon the target involved and the configure options used to build the toolchain. The default can be determined by examining the output from the linker’s --help option.

--reduce-memory-overheads ¶

This option reduces memory requirements at ld runtime, at the expense of linking speed. This was introduced to select the old O(n^2) algorithm for link map file generation, rather than the new O(n) algorithm which uses about 40% more memory for symbol storage.

Another effect of the switch is to set the default hash table size to 1021, which again saves memory at the cost of lengthening the linker’s run time. This is not done however if the --hash-size switch has been used.

The --reduce-memory-overheads switch may be also be used to enable other tradeoffs in future versions of the linker.

--max-cache-size=size ¶

ld normally caches the relocation information and symbol tables of input files in memory with the unlimited size. This option sets the maximum cache size to size.

--build-id ¶

--build-id=style

Request the creation of a .note.gnu.build-id ELF note section or a .buildid COFF section. The contents of the note are unique bits identifying this linked file. style can be uuid to use 128 random bits, sha1 to use a 160-bit SHA1 hash on the normative parts of the output contents, md5 to use a 128-bit MD5 hash on the normative parts of the output contents, or 0xhexstring to use a chosen bit string specified as an even number of hexadecimal digits (- and : characters between digit pairs are ignored). If style is omitted, sha1 is used.

The md5 and sha1 styles produces an identifier that is always the same in an identical output file, but will be unique among all nonidentical output files. It is not intended to be compared as a checksum for the file’s contents. A linked file may be changed later by other tools, but the build ID bit string identifying the original linked file does not change.

Passing none for style disables the setting from any --build-id options earlier on the command line.

--package-metadata=JSON ¶

Request the creation of a .note.package ELF note section. The contents of the note are in JSON format, as per the package metadata specification. For more information see: https://systemd.io/ELF_PACKAGE_METADATA/ If the JSON argument is missing/empty then this will disable the creation of the metadata note, if one had been enabled by an earlier occurrence of the –package-metadata option. If the linker has been built with libjansson, then the JSON string will be validated.

• Options Specific to i386 PE Targets
• Options specific to C6X uClinux targets
• Options specific to C-SKY targets
• Options specific to Motorola 68HC11 and 68HC12 targets
• Options specific to Motorola 68K target
• Options specific to MIPS targets
• Options specific to PDP11 targets

2.2 Environment Variables ¶

You can change the behaviour of ld with the environment variables GNUTARGET, LDEMULATION and COLLECT_NO_DEMANGLE.

GNUTARGET determines the input-file object format if you don’t use ‘-b’ (or its synonym ‘--format’). Its value should be one of the BFD names for an input format (see BFD). If there is no GNUTARGET in the environment, ld uses the natural format of the target. If GNUTARGET is set to default then BFD attempts to discover the input format by examining binary input files; this method often succeeds, but there are potential ambiguities, since there is no method of ensuring that the magic number used to specify object-file formats is unique. However, the configuration procedure for BFD on each system places the conventional format for that system first in the search-list, so ambiguities are resolved in favor of convention.

LDEMULATION determines the default emulation if you don’t use the ‘-m’ option. The emulation can affect various aspects of linker behaviour, particularly the default linker script. You can list the available emulations with the ‘--verbose’ or ‘-V’ options. If the ‘-m’ option is not used, and the LDEMULATION environment variable is not defined, the default emulation depends upon how the linker was configured.

Normally, the linker will default to demangling symbols. However, if COLLECT_NO_DEMANGLE is set in the environment, then it will default to not demangling symbols. This environment variable is used in a similar fashion by the gcc linker wrapper program. The default may be overridden by the ‘--demangle’ and ‘--no-demangle’ options.

3.1 Basic Linker Script Concepts ¶

We need to define some basic concepts and vocabulary in order to describe the linker script language.

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 object file format. Each file is called an object file. The output file is often called an executable, but for our purposes we will also call it an object file. Each object file has, among other things, a list of sections. We sometimes refer to a section in an input file as 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 means 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). A section which is neither loadable nor allocatable typically contains some sort of debugging information.

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 data section is loaded into ROM, and then copied into RAM when the program starts up (this technique is often used to initialize global variables in a ROM based system). In this case the ROM address would be the LMA, and the RAM address would be the VMA.

You can see the sections in an object file by using the 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 you compile a C or C++ program into an object file, you will get a defined symbol 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.

You can see the symbols in an object file by using the nm program, or by using the objdump program with the ‘-t’ option.

3.2 Linker Script Format ¶

Linker scripts are text files.

You write a linker script as a series of commands. Each command is either a keyword, possibly followed by arguments, or an assignment to a symbol. You may separate commands using semicolons. Whitespace is generally ignored.

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, you may put the file name in double quotes. There is no way to use a double quote character in a file name.

You may include comments in linker scripts just as in C, delimited by ‘/*’ and ‘*/’. As in C, comments are syntactically equivalent to whitespace.

3.3 Simple Linker Script Example ¶

Many linker scripts are fairly simple.

The simplest possible linker script has just one command: ‘SECTIONS’. You use the ‘SECTIONS’ command to describe the memory layout of the output file.

The ‘SECTIONS’ command is a powerful command. Here we will describe a simple use of it. Let’s assume your program consists only of code, initialized data, and uninitialized data. These will be in the ‘.text’, ‘.data’, and ‘.bss’ sections, respectively. Let’s assume further that these are the only sections which appear in your input files.

For this example, let’s say that the code should be loaded at address 0x10000, and that the data should start at address 0x8000000. Here is a linker script which will do that:

SECTIONS
{
  . = 0x10000;
  .text : { *(.text) }
  . = 0x8000000;
  .data : { *(.data) }
  .bss : { *(.bss) }
}

You write the ‘SECTIONS’ command as the keyword ‘SECTIONS’, followed by a series of symbol assignments and output section descriptions enclosed in curly braces.

The first line inside the ‘SECTIONS’ command of the above example sets the value of the special symbol ‘.’, which is the location counter. If you do not specify the address of an output section in some other way (other ways are described later), the address is set from the current value of the location counter. The location counter is then incremented by the size of the output section. At the start of the ‘SECTIONS’ command, the location counter has the value ‘0’.

The second line defines an output section, ‘.text’. The colon is required syntax which may be ignored for now. Within the curly braces after the output section name, you list the names of the input sections which should be placed into this output section. The ‘*’ is a wildcard which matches any file name. The expression ‘*(.text)’ means all ‘.text’ input sections in all input files.

Since the location counter is ‘0x10000’ when the output section ‘.text’ is defined, the linker will set the address of the ‘.text’ section in the output file to be ‘0x10000’.

The remaining lines define the ‘.data’ and ‘.bss’ sections in the output file. The linker will place the ‘.data’ output section at address ‘0x8000000’. After the linker places the ‘.data’ output section, the value of the location counter will be ‘0x8000000’ plus the size of the ‘.data’ output section. The effect is that the linker will place the ‘.bss’ output section immediately after the ‘.data’ output section in memory.

The linker will ensure that each output section has the required alignment, by increasing the location counter if necessary. In this example, the specified addresses for the ‘.text’ and ‘.data’ sections will probably satisfy any alignment constraints, but the linker may have to create a small gap between the ‘.data’ and ‘.bss’ sections.

That’s it! That’s a simple and complete linker script.

3.4 Simple Linker Script Commands ¶

In this section we describe the simple linker script commands.

• Setting the Entry Point
• Commands Dealing with Files
• Commands Dealing with Object File Formats
• Assign alias names to memory regions
• Other Linker Script Commands

ENTRY(symbol)

REGION_ALIAS(alias, region)

INCLUDE linkcmds.memory

SECTIONS
  {
    .text :
      {
        *(.text)
      } > REGION_TEXT
    .rodata :
      {
        *(.rodata)
        rodata_end = .;
      } > REGION_RODATA
    .data : AT (rodata_end)
      {
        data_start = .;
        *(.data)
      } > REGION_DATA
    data_size = SIZEOF(.data);
    data_load_start = LOADADDR(.data);
    .bss :
      {
        *(.bss)
      } > REGION_BSS
  }

#include <string.h>

extern char data_start [];
extern char data_size [];
extern char data_load_start [];

void copy_data(void)
{
  if (data_start != data_load_start)
    {
      memcpy(data_start, data_load_start, (size_t) data_size);
    }
}

3.5 Assigning Values to Symbols ¶

You may assign a value to a symbol in a linker script. This will define the symbol and place it into the symbol table with a global scope.

• Simple Assignments
• HIDDEN
• PROVIDE
• PROVIDE_HIDDEN
• Source Code Reference

floating_point = 0;
SECTIONS
{
  .text :
    {
      *(.text)
      _etext = .;
    }
  _bdata = (. + 3) & ~ 3;
  .data : { *(.data) }
}

HIDDEN(floating_point = 0);
SECTIONS
{
  .text :
    {
      *(.text)
      HIDDEN(_etext = .);
    }
  HIDDEN(_bdata = (. + 3) & ~ 3);
  .data : { *(.data) }
}

SECTIONS
{
  .text :
    {
      *(.text)
      _etext = .;
      PROVIDE(etext = .);
    }
}

  extern int foo;

  _foo = 1000;

  int foo = 1000;

  foo = 1;

  int * a = & foo;

  foo = 1000;

  start_of_ROM   = .ROM;
  end_of_ROM     = .ROM + sizeof (.ROM);
  start_of_FLASH = .FLASH;

  extern char start_of_ROM, end_of_ROM, start_of_FLASH;

  memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);

  extern char start_of_ROM[], end_of_ROM[], start_of_FLASH[];

  memcpy (start_of_FLASH, start_of_ROM, end_of_ROM - start_of_ROM);

3.6 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 of be one of the following:

• an ENTRY command (see Entry command)
• a symbol assignment (see 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 you can use those commands at meaningful points in the layout of the output file.

Output section descriptions and overlay descriptions are described below.

If you do not use a SECTIONS command in your 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.

• Output Section Description
• Output Section Name
• Output Section Address
• Input Section Description
• Output Section Data
• Output Section Keywords
• Output Section Discarding
• Output Section Attributes
• Overlay Description

section [address] [(type)] :
  [AT(lma)]
  [ALIGN(section_align) | ALIGN_WITH_INPUT]
  [SUBALIGN(subsection_align)]
  [constraint]
  {
    output-section-command
    output-section-command
    ...
  } [>region] [AT>lma_region] [:phdr :phdr ...] [=fillexp] [,]

.text . : { *(.text) }

.text : { *(.text) }

.text ALIGN(0x10) : { *(.text) }

*(.text)

EXCLUDE_FILE (*crtend.o *otherfile.o) *(.ctors)

*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)

*(.text .rdata)
*(.text) *(.rdata)

*(EXCLUDE_FILE (*somefile.o) .text .rdata)

*(EXCLUDE_FILE (*somefile.o) .text EXCLUDE_FILE (*somefile.o) .rdata)

EXCLUDE_FILE (*somefile.o) *(.text .rdata)

data.o(.data)

SECTIONS {
  .text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) }
  .text2 :  { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) }
}

data.o

.data : { *(.data) }
.data1 : { data.o(.data) }

  *(REVERSE(.text* .init*))

  *(REVERSE(.text*))
  *(REVERSE(.init*))

  *(SORT_BY_NAME(EXCLUDE_FILE(foo) .text*))

  *(EXCLUDE_FILE(foo) SORT_BY_NAME(.text*))

SECTIONS {
  .text : { *(.text) }
  .DATA : { [A-Z]*(.data) }
  .data : { *(.data) }
  .bss : { *(.bss) }
}

.bss { *(.bss) *(COMMON) }

SECTIONS {
  outputa 0x10000 :
    {
    all.o
    foo.o (.input1)
    }

  outputb :
    {
    foo.o (.input2)
    foo1.o (.input1)
    }

  outputc :
    {
    *(.input1)
    *(.input2)
    }
}

BYTE(1)
LONG(addr)

  ASCIZ "This is 16 bytes"

SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } } 

SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } } 

FILL(0x90909090)

.foo : { *(.foo) }

section [address] [(type)] :
  [AT(lma)]
  [ALIGN(section_align) | ALIGN_WITH_INPUT]
  [SUBALIGN(subsection_align)]
  [constraint]
  {
    output-section-command
    output-section-command
    ...
  } [>region] [AT>lma_region] [:phdr :phdr ...] [=fillexp]

SECTIONS {
  ROM 0 (NOLOAD) : { ... }
  ...
}

SECTIONS
  {
  .text 0x1000 : { *(.text) _etext = . ; }
  .mdata 0x2000 :
    AT ( ADDR (.text) + SIZEOF (.text) )
    { _data = . ; *(.data); _edata = . ;  }
  .bss 0x3000 :
    { _bstart = . ;  *(.bss) *(COMMON) ; _bend = . ;}
}

extern char _etext, _data, _edata, _bstart, _bend;
char *src = &_etext;
char *dst = &_data;

/* ROM has data at end of text; copy it.  */
while (dst < &_edata)
  *dst++ = *src++;

/* Zero bss.  */
for (dst = &_bstart; dst< &_bend; dst++)
  *dst = 0;

MEMORY { rom : ORIGIN = 0x1000, LENGTH = 0x1000 }
SECTIONS { ROM : { *(.text) } >rom }

PHDRS { text PT_LOAD ; }
SECTIONS { .text : { *(.text) } :text }

Fill Value     Fill Pattern
0x90           90 90 90 90
0x0090         00 90 00 90
144            00 00 00 90

SECTIONS { .text : { *(.text) } =0x90909090 }

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] [,]

  OVERLAY 0x1000 : AT (0x4000)
   {
     .text0 { o1/*.o(.text) }
     .text1 { o2/*.o(.text) }
   }

  extern char __load_start_text1, __load_stop_text1;
  memcpy ((char *) 0x1000, &__load_start_text1,
          &__load_stop_text1 - &__load_start_text1);

  .text0 0x1000 : AT (0x4000) { o1/*.o(.text) }
  PROVIDE (__load_start_text0 = LOADADDR (.text0));
  PROVIDE (__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0));
  .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) { o2/*.o(.text) }
  PROVIDE (__load_start_text1 = LOADADDR (.text1));
  PROVIDE (__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1));
  . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));

3.7 MEMORY Command ¶

The linker’s default configuration permits allocation of all available memory. You can override this by using the MEMORY command.

The MEMORY command describes the location and size of blocks of memory in the target. You can use it to describe which memory regions may be used by the linker, and which memory regions it must avoid. You can then assign sections 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.

A linker script may contain many uses of the MEMORY command, however, all memory blocks defined are treated as if they were specified inside a single MEMORY command. The syntax for MEMORY 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 within the MEMORY command. However you can add later alias names to existing memory regions with the Assign alias names to memory regions command.

The attr string is an optional list of attributes that specify whether to use a particular memory region for an input section which is not explicitly mapped in the linker script. As described in SECTIONS Command, if you do not specify an output section for some input section, the linker will create an output section with the same name as the input section. If you define region attributes, the linker will use them to select the memory region for the output section that it creates.

The attr string must consist only of the following characters:

‘R’

Read-only section

‘W’

Read/write section

‘X’

Executable section

‘A’

Allocatable section

‘I’

Initialized section

‘L’

Same as ‘I’

‘!’

Invert the sense of any of the attributes that follow

If an unmapped section matches any of the listed attributes other than ‘!’, it will be placed in the memory region. The ‘!’ attribute reverses the test for the characters that follow, so that an unmapped section will be placed in the memory region only if it does not match any of the attributes listed afterwards. Thus an attribute string of ‘RW!X’ will match any unmapped section that has either or both of the ‘R’ and ‘W’ attributes, but only as long as the section does not also have the ‘X’ attribute.

The origin is an numerical expression for the start address of the memory region. The expression must evaluate to a constant and it cannot involve any symbols. 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 be numerical only and must evaluate to a constant. 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 256 kilobytes, and the other starting at ‘0x40000000’ for four megabytes. 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 = 256K
    ram (!rx) : org = 0x40000000, l = 4M
  }

Once you define a memory region, you can direct the linker to place specific output sections into that memory region by using the ‘>region’ output section attribute. For example, if you have a memory region named ‘mem’, you would use ‘>mem’ in the output section definition. See Output Section Region. 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.

It is possible to access the origin and length of a memory in an expression via the ORIGIN(memory) and LENGTH(memory) functions:

  _fstack = ORIGIN(ram) + LENGTH(ram) - 4;

3.8 PHDRS Command ¶

The ELF object file format uses program headers, also knows as segments. The program headers describe how the program should be loaded into memory. You can print them out by using the objdump program with the ‘-p’ option.

When you run an ELF program on a native ELF system, the system loader reads the program headers in order to figure out how to load the program. This will only work if the program headers are set correctly. This manual does not describe the details of how the system loader interprets program headers; for more information, see the ELF ABI.

The linker will create reasonable program headers by default. However, in some cases, you may need to specify the program headers more precisely. You may use the PHDRS command for this purpose. When the linker sees the PHDRS command in the linker script, it will not create any program headers other than the ones specified.

The linker only pays attention to the PHDRS command when generating an ELF output file. In other cases, the linker will simply ignore PHDRS.

This is the syntax of the PHDRS command. The words PHDRS, FILEHDR, AT, and FLAGS are keywords.

PHDRS
{
  name type [ FILEHDR ] [ PHDRS ] [ AT ( address ) ]
        [ FLAGS ( flags ) ] ;
}

The name is used only for reference in the SECTIONS command of the linker script. It is not put into the output file. Program header names are stored in a separate name space, and will not conflict with symbol names, file names, or section names. Each program header must have a distinct name. The headers are processed in order and it is usual for them to map to sections in ascending load address order.

Certain program header types describe segments of memory which the system loader will load from the file. In the linker script, you specify the contents of these segments by placing allocatable output sections in the segments. You use the ‘:phdr’ output section attribute to place a section in a particular segment. See Output Section Phdr.

It is normal to put certain sections in more than one segment. This merely implies that one segment of memory contains another. You may repeat ‘:phdr’, using it once for each segment which should contain the section.

If you place a section in one or more segments using ‘:phdr’, then the linker will place all subsequent allocatable sections which do not specify ‘:phdr’ in the same segments. This is for convenience, since generally a whole set of contiguous sections will be placed in a single segment. You can use :NONE to override the default segment and tell the linker to not put the section in any segment at all.

You may use the FILEHDR and PHDRS keywords after the program header type to further describe the contents of the segment. The FILEHDR keyword means that the segment should include the ELF file header. The PHDRS keyword means that the segment should include the ELF program headers themselves. If applied to a loadable segment (PT_LOAD), all prior loadable segments must have one of these keywords.

The type may be one of the following. The numbers indicate the value of the keyword.

PT_NULL (0)

Indicates an unused program header.

PT_LOAD (1)

Indicates that this program header describes a segment to be loaded from the file.

PT_DYNAMIC (2)

Indicates a segment where dynamic linking information can be found.

PT_INTERP (3)

Indicates a segment where the name of the program interpreter may be found.

PT_NOTE (4)

Indicates a segment holding note information.

PT_SHLIB (5)

A reserved program header type, defined but not specified by the ELF ABI.

PT_PHDR (6)

Indicates a segment where the program headers may be found.

PT_TLS (7)

Indicates a segment containing thread local storage.

expression

An expression giving the numeric type of the program header. This may be used for types not defined above.

You can specify that a segment should be loaded at a particular address in memory by using an AT expression. This is identical to the AT command used as an output section attribute (see Output Section LMA). The AT command for a program header overrides the output section attribute.

The linker will normally set the segment flags based on the sections which comprise the segment. You may use the FLAGS keyword to explicitly specify the segment flags. The value of flags must be an integer. It is used to set the p_flags field of the program header.

Here is an example of PHDRS. This shows a typical set of program headers used on a native ELF system.

PHDRS
{
  headers PT_PHDR PHDRS ;
  interp PT_INTERP ;
  text PT_LOAD FILEHDR PHDRS ;
  data PT_LOAD ;
  dynamic PT_DYNAMIC ;
}

SECTIONS
{
  . = SIZEOF_HEADERS;
  .interp : { *(.interp) } :text :interp
  .text : { *(.text) } :text
  .rodata : { *(.rodata) } /* defaults to :text */
  ...
  . = . + 0x1000; /* move to a new page in memory */
  .data : { *(.data) } :data
  .dynamic : { *(.dynamic) } :data :dynamic
  ...
}

3.9 VERSION Command ¶

The linker supports symbol versions when using ELF. Symbol versions are only useful when using shared libraries. The dynamic linker can use symbol versions to select a specific version of a function when it runs a program that may have been linked against an earlier version of the shared library.

You can include a version script directly in the main linker script, or you can supply the version script as an implicit linker script. You can also use the ‘--version-script’ linker option.

The syntax of the VERSION command is simply

VERSION { version-script-commands }

The format of the version script commands is identical to that used by Sun’s linker in Solaris 2.5. The version script defines a tree of version nodes. You specify the node names and interdependencies in the version script. You can specify which symbols are bound to which version nodes, and you can reduce a specified set of symbols to local scope so that they are not globally visible outside of the shared library.

The easiest way to demonstrate the version script language is with a few examples.

VERS_1.1 {
	 global:
		 foo1;
	 local:
		 old*;
		 original*;
		 new*;
};

VERS_1.2 {
		 foo2;
} VERS_1.1;

VERS_2.0 {
		 bar1; bar2;
	 extern "C++" {
		 ns::*;
		 "f(int, double)";
	 };
} VERS_1.2;

This example version script defines three version nodes. The first version node defined is ‘VERS_1.1’; it has no other dependencies. The script binds the symbol ‘foo1’ to ‘VERS_1.1’. It reduces a number of symbols to local scope so that they are not visible outside of the shared library; this is done using wildcard patterns, so that any symbol whose name begins with ‘old’, ‘original’, or ‘new’ is matched. The wildcard patterns available are the same as those used in the shell when matching filenames (also known as “globbing”). However, if you specify the symbol name inside double quotes, then the name is treated as literal, rather than as a glob pattern.

Next, the version script defines node ‘VERS_1.2’. This node depends upon ‘VERS_1.1’. The script binds the symbol ‘foo2’ to the version node ‘VERS_1.2’.

Finally, the version script defines node ‘VERS_2.0’. This node depends upon ‘VERS_1.2’. The scripts binds the symbols ‘bar1’ and ‘bar2’ are bound to the version node ‘VERS_2.0’.

When the linker finds a symbol defined in a library which is not specifically bound to a version node, it will effectively bind it to an unspecified base version of the library. You can bind all otherwise unspecified symbols to a given version node by using ‘global: *;’ somewhere in the version script. Note that it’s slightly crazy to use wildcards in a global spec except on the last version node. Global wildcards elsewhere run the risk of accidentally adding symbols to the set exported for an old version. That’s wrong since older versions ought to have a fixed set of symbols.

The names of the version nodes have no specific meaning other than what they might suggest to the person reading them. The ‘2.0’ version could just as well have appeared in between ‘1.1’ and ‘1.2’. However, this would be a confusing way to write a version script.

Node name can be omitted, provided it is the only version node in the version script. Such version script doesn’t assign any versions to symbols, only selects which symbols will be globally visible out and which won’t.

{ global: foo; bar; local: *; };

When you link an application against a shared library that has versioned symbols, the application itself knows which version of each symbol it requires, and it also knows which version nodes it needs from each shared library it is linked against. Thus at runtime, the dynamic loader can make a quick check to make sure that the libraries you have linked against do in fact supply all of the version nodes that the application will need to resolve all of the dynamic symbols. In this way it is possible for the dynamic linker to know with certainty that all external symbols that it needs will be resolvable without having to search for each symbol reference.

The symbol versioning is in effect a much more sophisticated way of doing minor version checking that SunOS does. The fundamental problem that is being addressed here is that typically references to external functions are bound on an as-needed basis, and are not all bound when the application starts up. If a shared library is out of date, a required interface may be missing; when the application tries to use that interface, it may suddenly and unexpectedly fail. With symbol versioning, the user will get a warning when they start their program if the libraries being used with the application are too old.

There are several GNU extensions to Sun’s versioning approach. The first of these is the ability to bind a symbol to a version node in the source file where the symbol is defined instead of in the versioning script. This was done mainly to reduce the burden on the library maintainer. You can do this by putting something like:

__asm__(".symver original_foo,foo@VERS_1.1");

in the C source file. This renames the function ‘original_foo’ to be an alias for ‘foo’ bound to the version node ‘VERS_1.1’. The ‘local:’ directive can be used to prevent the symbol ‘original_foo’ from being exported. A ‘.symver’ directive takes precedence over a version script.

The second GNU extension is to allow multiple versions of the same function to appear in a given shared library. In this way you can make an incompatible change to an interface without increasing the major version number of the shared library, while still allowing applications linked against the old interface to continue to function.

To do this, you must use multiple ‘.symver’ directives in the source file. Here is an example:

__asm__(".symver original_foo,foo@");
__asm__(".symver old_foo,foo@VERS_1.1");
__asm__(".symver old_foo1,foo@VERS_1.2");
__asm__(".symver new_foo,foo@@VERS_2.0");

In this example, ‘foo@’ represents the symbol ‘foo’ bound to the unspecified base version of the symbol. The source file that contains this example would define 4 C functions: ‘original_foo’, ‘old_foo’, ‘old_foo1’, and ‘new_foo’.

When you have multiple definitions of a given symbol, there needs to be some way to specify a default version to which external references to this symbol will be bound. You can do this with the ‘foo@@VERS_2.0’ type of ‘.symver’ directive. You can only declare one version of a symbol as the default in this manner; otherwise you would effectively have multiple definitions of the same symbol.

If you wish to bind a reference to a specific version of the symbol within the shared library, you can use the aliases of convenience (i.e., ‘old_foo’), or you can use the ‘.symver’ directive to specifically bind to an external version of the function in question.

You can also specify the language in the version script:

VERSION extern "lang" { version-script-commands }

The supported ‘lang’s are ‘C’, ‘C++’, and ‘Java’. The linker will iterate over the list of symbols at the link time and demangle them according to ‘lang’ before matching them to the patterns specified in ‘version-script-commands’. The default ‘lang’ is ‘C’.

Demangled names may contains spaces and other special characters. As described above, you can use a glob pattern to match demangled names, or you can use a double-quoted string to match the string exactly. In the latter case, be aware that minor differences (such as differing whitespace) between the version script and the demangler output will cause a mismatch. As the exact string generated by the demangler might change in the future, even if the mangled name does not, you should check that all of your version directives are behaving as you expect when you upgrade.

3.10 Expressions in Linker Scripts ¶

The syntax for expressions in the linker script language is identical to that of C expressions, except that whitespace is required in some places to resolve syntactic ambiguities. All expressions are evaluated as integers. All expressions are evaluated in the same size, which is 32 bits if both the host and target are 32 bits, and is otherwise 64 bits.

You can use and set symbol values in expressions.

The linker defines several special purpose builtin functions for use in expressions.

• Constants
• Symbolic Constants
• Symbol Names
• Orphan Sections
• The Location Counter
• Operators
• Evaluation
• The Section of an Expression
• Builtin Functions

_fourk_1 = 4K;
_fourk_2 = 4096;
_fourk_3 = 0x1000;
_fourk_4 = 10000o;

  .text ALIGN (CONSTANT (MAXPAGESIZE)) : { *(.text) }

"SECTION" = 9;
"with a space" = "also with a space" + 10;

SECTIONS
{
  output :
    {
      file1(.text)
      . = . + 1000;
      file2(.text)
      . += 1000;
      file3(.text)
    } = 0x12345678;
}

SECTIONS
{
    . = 0x100
    .text: {
      *(.text)
      . = 0x200
    }
    . = 0x500
    .data: {
      *(.data)
      . += 0x600
    }
}

SECTIONS
{
    start_of_text = . ;
    .text: { *(.text) }
    end_of_text = . ;

    start_of_data = . ;
    .data: { *(.data) }
    end_of_data = . ;
}

SECTIONS
{
    start_of_text = . ;
    .text: { *(.text) }
    end_of_text = . ;

    start_of_data = . ;
    .rodata: { *(.rodata) }
    .data: { *(.data) }
    end_of_data = . ;
}

SECTIONS
{
    start_of_text = . ;
    .text: { *(.text) }
    end_of_text = . ;

    . = . ;
    start_of_data = . ;
    .data: { *(.data) }
    end_of_data = . ;
}

precedence      associativity   Operators                           Notes
(highest)
1               left            !  -  ~                             (1)
2               left            *  /  %
3               left            +  -
4               left            >>  <<
5               left            >  <  <=  >=
6               left            ==  !=
7               left            &
8               left            ^
9               left            |
10              left            &&
11              left            ||
12              right           ? :
13              right           +=  -=  *=  /=  <<=  >>=  &=  |= ^= (2)
(lowest)

SECTIONS
  {
    .text 9+this_isnt_constant :
      { *(.text) }
  }

SECTIONS
  {
    . = 0x100;
    __executable_start = 0x100;
    .data :
    {
      . = 0x10;
      __data_start = 0x10;
      *(.data)
    }
    ...
  }

SECTIONS
  {
    .data : { *(.data) _edata = ABSOLUTE(.); }
  }

3.11 Implicit Linker Scripts ¶

If you specify a linker input file which the linker can not recognize as an object file or an archive file, it will try to read the file as a linker script. If the file can not be parsed as a linker script, the linker will report an error.

An implicit linker script will not replace the default linker script.

Typically an implicit linker script would contain only symbol assignments, or the INPUT, GROUP, or VERSION commands.

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. This can affect archive searching.

4.1 Static Library Dependencies Plugin ¶

Originally, static libraries were contained in an archive file consisting just of a collection of relocatable object files. Later they evolved to optionally include a symbol table, to assist in finding the needed objects within a library. There their evolution ended, and dynamic libraries rose to ascendance.

One useful feature of dynamic libraries was that, more than just collecting multiple objects into a single file, they also included a list of their dependencies, such that one could specify just the name of a single dynamic library at link time, and all of its dependencies would be implicitly referenced as well. But static libraries lacked this feature, so if a link invocation was switched from using dynamic libraries to static libraries, the link command would usually fail unless it was rewritten to explicitly list the dependencies of the static library.

The GNU ar utility now supports a --record-libdeps option to embed dependency lists into static libraries as well, and the libdep plugin may be used to read this dependency information at link time. The dependency information is stored as a single string, carrying -l and -L arguments as they would normally appear in a linker command line. As such, the information can be written with any text utility and stored into any archive, even if GNU ar is not being used to create the archive. The information is stored in an archive member named ‘__.LIBDEP’.

For example, given a library libssl.a that depends on another library libcrypto.a which may be found in /usr/local/lib, the ‘__.LIBDEP’ member of libssl.a would contain

-L/usr/local/lib -lcrypto

6.1 ld and the H8/300 ¶

For the H8/300, ld can perform these global optimizations when you specify the ‘--relax’ command-line option.

relaxing address modes ¶

ld finds all jsr and jmp instructions whose targets are within eight bits, and turns them into eight-bit program-counter relative bsr and bra instructions, respectively.

synthesizing instructions ¶

ld finds all mov.b instructions which use the sixteen-bit absolute address form, but refer to the top page of memory, and changes them to use the eight-bit address form. (That is: the linker turns ‘mov.b @aa:16’ into ‘mov.b @aa:8’ whenever the address aa is in the top page of memory).

ld finds all mov instructions which use the register indirect with 32-bit displacement addressing mode, but use a small displacement inside 16-bit displacement range, and changes them to use the 16-bit displacement form. (That is: the linker turns ‘mov.b @d:32,ERx’ into ‘mov.b @d:16,ERx’ whenever the displacement d is in the 16 bit signed integer range. Only implemented in ELF-format ld).

bit manipulation instructions

ld finds all bit manipulation instructions like band, bclr, biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor which use 32 bit and 16 bit absolute address form, but refer to the top page of memory, and changes them to use the 8 bit address form. (That is: the linker turns ‘bset #xx:3,@aa:32’ into ‘bset #xx:3,@aa:8’ whenever the address aa is in the top page of memory).

system control instructions

ld finds all ldc.w, stc.w instructions which use the 32 bit absolute address form, but refer to the top page of memory, and changes them to use 16 bit address form. (That is: the linker turns ‘ldc.w @aa:32,ccr’ into ‘ldc.w @aa:16,ccr’ whenever the address aa is in the top page of memory).

6.2 ld and the Motorola 68HC11 and 68HC12 families ¶

• Linker Relaxation
• Trampoline Generation

6.3 ld and the ARM family ¶

For the ARM, ld will generate code stubs to allow functions calls between ARM and Thumb code. These stubs only work with code that has been compiled and assembled with the ‘-mthumb-interwork’ command line option. If it is necessary to link with old ARM object files or libraries, which have not been compiled with the -mthumb-interwork option then the ‘--support-old-code’ command-line switch should be given to the linker. This will make it generate larger stub functions which will work with non-interworking aware ARM code. Note, however, the linker does not support generating stubs for function calls to non-interworking aware Thumb code.

The ‘--thumb-entry’ switch is a duplicate of the generic ‘--entry’ switch, in that it sets the program’s starting address. But it also sets the bottom bit of the address, so that it can be branched to using a BX instruction, and the program will start executing in Thumb mode straight away.

The ‘--use-nul-prefixed-import-tables’ switch is specifying, that the import tables idata4 and idata5 have to be generated with a zero element prefix for import libraries. This is the old style to generate import tables. By default this option is turned off.

The ‘--be8’ switch instructs ld to generate BE8 format executables. This option is only valid when linking big-endian objects - ie ones which have been assembled with the -EB option. The resulting image will contain big-endian data and little-endian code.

The ‘R_ARM_TARGET1’ relocation is typically used for entries in the ‘.init_array’ section. It is interpreted as either ‘R_ARM_REL32’ or ‘R_ARM_ABS32’, depending on the target. The ‘--target1-rel’ and ‘--target1-abs’ switches override the default.

The ‘--target2=type’ switch overrides the default definition of the ‘R_ARM_TARGET2’ relocation. Valid values for ‘type’, their meanings, and target defaults are as follows:

‘rel’

‘R_ARM_REL32’ (arm*-*-elf, arm*-*-eabi)

‘abs’

‘R_ARM_ABS32’

‘got-rel’

‘R_ARM_GOT_PREL’ (arm*-*-linux, arm*-*-*bsd)

The ‘R_ARM_V4BX’ relocation (defined by the ARM AAELF specification) enables objects compiled for the ARMv4 architecture to be interworking-safe when linked with other objects compiled for ARMv4t, but also allows pure ARMv4 binaries to be built from the same ARMv4 objects.

In the latter case, the switch --fix-v4bx must be passed to the linker, which causes v4t BX rM instructions to be rewritten as MOV PC,rM, since v4 processors do not have a BX instruction.

In the former case, the switch should not be used, and ‘R_ARM_V4BX’ relocations are ignored.

Replace BX rM instructions identified by ‘R_ARM_V4BX’ relocations with a branch to the following veneer:

TST rM, #1
MOVEQ PC, rM
BX Rn

This allows generation of libraries/applications that work on ARMv4 cores and are still interworking safe. Note that the above veneer clobbers the condition flags, so may cause incorrect program behavior in rare cases.

The ‘--use-blx’ switch enables the linker to use ARM/Thumb BLX instructions (available on ARMv5t and above) in various situations. Currently it is used to perform calls via the PLT from Thumb code using BLX rather than using BX and a mode-switching stub before each PLT entry. This should lead to such calls executing slightly faster.

The ‘--vfp11-denorm-fix’ switch enables a link-time workaround for a bug in certain VFP11 coprocessor hardware, which sometimes allows instructions with denorm operands (which must be handled by support code) to have those operands overwritten by subsequent instructions before the support code can read the intended values.

The bug may be avoided in scalar mode if you allow at least one intervening instruction between a VFP11 instruction which uses a register and another instruction which writes to the same register, or at least two intervening instructions if vector mode is in use. The bug only affects full-compliance floating-point mode: you do not need this workaround if you are using "runfast" mode. Please contact ARM for further details.

If you know you are using buggy VFP11 hardware, you can enable this workaround by specifying the linker option ‘--vfp-denorm-fix=scalar’ if you are using the VFP11 scalar mode only, or ‘--vfp-denorm-fix=vector’ if you are using vector mode (the latter also works for scalar code). The default is ‘--vfp-denorm-fix=none’.

If the workaround is enabled, instructions are scanned for potentially-troublesome sequences, and a veneer is created for each such sequence which may trigger the erratum. The veneer consists of the first instruction of the sequence and a branch back to the subsequent instruction. The original instruction is then replaced with a branch to the veneer. The extra cycles required to call and return from the veneer are sufficient to avoid the erratum in both the scalar and vector cases.

The ‘--fix-arm1176’ switch enables a link-time workaround for an erratum in certain ARM1176 processors. The workaround is enabled by default if you are targeting ARM v6 (excluding ARM v6T2) or earlier. It can be disabled unconditionally by specifying ‘--no-fix-arm1176’.

Further information is available in the “ARM1176JZ-S and ARM1176JZF-S Programmer Advice Notice” available on the ARM documentation website at: http://infocenter.arm.com/.

The ‘--fix-stm32l4xx-629360’ switch enables a link-time workaround for a bug in the bus matrix / memory controller for some of the STM32 Cortex-M4 based products (STM32L4xx). When accessing off-chip memory via the affected bus for bus reads of 9 words or more, the bus can generate corrupt data and/or abort. These are only core-initiated accesses (not DMA), and might affect any access: integer loads such as LDM, POP and floating-point loads such as VLDM, VPOP. Stores are not affected.

The bug can be avoided by splitting memory accesses into the necessary chunks to keep bus reads below 8 words.

The workaround is not enabled by default, this is equivalent to use ‘--fix-stm32l4xx-629360=none’. If you know you are using buggy STM32L4xx hardware, you can enable the workaround by specifying the linker option ‘--fix-stm32l4xx-629360’, or the equivalent ‘--fix-stm32l4xx-629360=default’.

If the workaround is enabled, instructions are scanned for potentially-troublesome sequences, and a veneer is created for each such sequence which may trigger the erratum. The veneer consists in a replacement sequence emulating the behaviour of the original one and a branch back to the subsequent instruction. The original instruction is then replaced with a branch to the veneer.

The workaround does not always preserve the memory access order for the LDMDB instruction, when the instruction loads the PC.

The workaround is not able to handle problematic instructions when they are in the middle of an IT block, since a branch is not allowed there. In that case, the linker reports a warning and no replacement occurs.

The workaround is not able to replace problematic instructions with a PC-relative branch instruction if the ‘.text’ section is too large. In that case, when the branch that replaces the original code cannot be encoded, the linker reports a warning and no replacement occurs.

The --no-enum-size-warning switch prevents the linker from warning when linking object files that specify incompatible EABI enumeration size attributes. For example, with this switch enabled, linking of an object file using 32-bit enumeration values with another using enumeration values fitted into the smallest possible space will not be diagnosed.

The --no-wchar-size-warning switch prevents the linker from warning when linking object files that specify incompatible EABI wchar_t size attributes. For example, with this switch enabled, linking of an object file using 32-bit wchar_t values with another using 16-bit wchar_t values will not be diagnosed.

The ‘--pic-veneer’ switch makes the linker use PIC sequences for ARM/Thumb interworking veneers, even if the rest of the binary is not PIC. This avoids problems on uClinux targets where ‘--emit-relocs’ is used to generate relocatable binaries.

The linker will automatically generate and insert small sequences of code into a linked ARM ELF executable whenever an attempt is made to perform a function call to a symbol that is too far away. The placement of these sequences of instructions - called stubs - is controlled by the command-line option --stub-group-size=N. The placement is important because a poor choice can create a need for duplicate stubs, increasing the code size. The linker will try to group stubs together in order to reduce interruptions to the flow of code, but it needs guidance as to how big these groups should be and where they should be placed.

The value of ‘N’, the parameter to the --stub-group-size= option controls where the stub groups are placed. If it is negative then all stubs are placed after the first branch that needs them. If it is positive then the stubs can be placed either before or after the branches that need them. If the value of ‘N’ is 1 (either +1 or -1) then the linker will choose exactly where to place groups of stubs, using its built in heuristics. A value of ‘N’ greater than 1 (or smaller than -1) tells the linker that a single group of stubs can service at most ‘N’ bytes from the input sections.

The default, if --stub-group-size= is not specified, is ‘N = +1’.

Farcalls stubs insertion is fully supported for the ARM-EABI target only, because it relies on object files properties not present otherwise.

The ‘--fix-cortex-a8’ switch enables a link-time workaround for an erratum in certain Cortex-A8 processors. The workaround is enabled by default if you are targeting the ARM v7-A architecture profile. It can be enabled otherwise by specifying ‘--fix-cortex-a8’, or disabled unconditionally by specifying ‘--no-fix-cortex-a8’.

The erratum only affects Thumb-2 code. Please contact ARM for further details.

The ‘--fix-cortex-a53-835769’ switch enables a link-time workaround for erratum 835769 present on certain early revisions of Cortex-A53 processors. The workaround is disabled by default. It can be enabled by specifying ‘--fix-cortex-a53-835769’, or disabled unconditionally by specifying ‘--no-fix-cortex-a53-835769’.

Please contact ARM for further details.

The ‘--no-merge-exidx-entries’ switch disables the merging of adjacent exidx entries in debuginfo.

The ‘--long-plt’ option enables the use of 16 byte PLT entries which support up to 4Gb of code. The default is to use 12 byte PLT entries which only support 512Mb of code.

The ‘--no-apply-dynamic-relocs’ option makes AArch64 linker do not apply link-time values for dynamic relocations.

All SG veneers are placed in the special output section .gnu.sgstubs. Its start address must be set, either with the command-line option ‘--section-start’ or in a linker script, to indicate where to place these veneers in memory.

The ‘--cmse-implib’ option requests that the import libraries specified by the ‘--out-implib’ and ‘--in-implib’ options are secure gateway import libraries, suitable for linking a non-secure executable against secure code as per ARMv8-M Security Extensions.

The ‘--in-implib=file’ specifies an input import library whose symbols must keep the same address in the executable being produced. A warning is given if no ‘--out-implib’ is given but new symbols have been introduced in the executable that should be listed in its import library. Otherwise, if ‘--out-implib’ is specified, the symbols are added to the output import library. A warning is also given if some symbols present in the input import library have disappeared from the executable. This option is only effective for Secure Gateway import libraries, ie. when ‘--cmse-implib’ is specified.

6.4 ld and HPPA 32-bit ELF Support ¶

When generating a shared library, ld will by default generate import stubs suitable for use with a single sub-space application. The ‘--multi-subspace’ switch causes ld to generate export stubs, and different (larger) import stubs suitable for use with multiple sub-spaces.

Long branch stubs and import/export stubs are placed by ld in stub sections located between groups of input sections. ‘--stub-group-size’ specifies the maximum size of a group of input sections handled by one stub section. Since branch offsets are signed, a stub section may serve two groups of input sections, one group before the stub section, and one group after it. However, when using conditional branches that require stubs, it may be better (for branch prediction) that stub sections only serve one group of input sections. A negative value for ‘N’ chooses this scheme, ensuring that branches to stubs always use a negative offset. Two special values of ‘N’ are recognized, ‘1’ and ‘-1’. These both instruct ld to automatically size input section groups for the branch types detected, with the same behaviour regarding stub placement as other positive or negative values of ‘N’ respectively.

Note that ‘--stub-group-size’ does not split input sections. A single input section larger than the group size specified will of course create a larger group (of one section). If input sections are too large, it may not be possible for a branch to reach its stub.

6.5 ld and the Motorola 68K family ¶

The ‘--got=type’ option lets you choose the GOT generation scheme. The choices are ‘single’, ‘negative’, ‘multigot’ and ‘target’. When ‘target’ is selected the linker chooses the default GOT generation scheme for the current target. ‘single’ tells the linker to generate a single GOT with entries only at non-negative offsets. ‘negative’ instructs the linker to generate a single GOT with entries at both negative and positive offsets. Not all environments support such GOTs. ‘multigot’ allows the linker to generate several GOTs in the output file. All GOT references from a single input object file access the same GOT, but references from different input object files might access different GOTs. Not all environments support such GOTs.

6.6 ld and the MIPS family ¶

The ‘--insn32’ and ‘--no-insn32’ options control the choice of microMIPS instructions used in code generated by the linker, such as that in the PLT or lazy binding stubs, or in relaxation. If ‘--insn32’ is used, then the linker only uses 32-bit instruction encodings. By default or if ‘--no-insn32’ is used, all instruction encodings are used, including 16-bit ones where possible.

The ‘--ignore-branch-isa’ and ‘--no-ignore-branch-isa’ options control branch relocation checks for invalid ISA mode transitions. If ‘--ignore-branch-isa’ is used, then the linker accepts any branch relocations and any ISA mode transition required is lost in relocation calculation, except for some cases of BAL instructions which meet relaxation conditions and are converted to equivalent JALX instructions as the associated relocation is calculated. By default or if ‘--no-ignore-branch-isa’ is used a check is made causing the loss of an ISA mode transition to produce an error.

6.7 ld and MMIX ¶

For MMIX, there is a choice of generating ELF object files or mmo object files when linking. The simulator mmix understands the mmo format. The binutils objcopy utility can translate between the two formats.

There is one special section, the ‘.MMIX.reg_contents’ section. Contents in this section is assumed to correspond to that of global registers, and symbols referring to it are translated to special symbols, equal to registers. In a final link, the start address of the ‘.MMIX.reg_contents’ section corresponds to the first allocated global register multiplied by 8. Register $255 is not included in this section; it is always set to the program entry, which is at the symbol Main for mmo files.

Global symbols with the prefix __.MMIX.start., for example __.MMIX.start..text and __.MMIX.start..data are special. The default linker script uses these to set the default start address of a section.

Initial and trailing multiples of zero-valued 32-bit words in a section, are left out from an mmo file.

6.8 ld and MSP430 ¶

For the MSP430 it is possible to select the MPU architecture. The flag ‘-m [mpu type]’ will select an appropriate linker script for selected MPU type. (To get a list of known MPUs just pass ‘-m help’ option to the linker).

The linker will recognize some extra sections which are MSP430 specific:

‘.vectors’

Defines a portion of ROM where interrupt vectors located.

‘.bootloader’

Defines the bootloader portion of the ROM (if applicable). Any code in this section will be uploaded to the MPU.

‘.infomem’

Defines an information memory section (if applicable). Any code in this section will be uploaded to the MPU.

‘.infomemnobits’

This is the same as the ‘.infomem’ section except that any code in this section will not be uploaded to the MPU.

‘.noinit’

Denotes a portion of RAM located above ‘.bss’ section.

The last two sections are used by gcc.

--code-region=[either,lower,upper,none] ¶

This will transform .text* sections to [either,lower,upper].text* sections. The argument passed to GCC for -mcode-region is propagated to the linker using this option.

--data-region=[either,lower,upper,none] ¶

This will transform .data*, .bss* and .rodata* sections to [either,lower,upper].[data,bss,rodata]* sections. The argument passed to GCC for -mdata-region is propagated to the linker using this option.

--disable-sec-transformation ¶

Prevent the transformation of sections as specified by the --code-region and --data-region options. This is useful if you are compiling and linking using a single call to the GCC wrapper, and want to compile the source files using -m[code,data]-region but not transform the sections for prebuilt libraries and objects.

6.9 ld and NDS32 ¶

For NDS32, there are some options to select relaxation behavior. The linker relaxes objects according to these options.

‘--m[no-]fp-as-gp’

Disable/enable fp-as-gp relaxation.

‘--mexport-symbols=FILE’

Exporting symbols and their address into FILE as linker script.

‘--m[no-]ex9’

Disable/enable link-time EX9 relaxation.

‘--mexport-ex9=FILE’

Export the EX9 table after linking.

‘--mimport-ex9=FILE’

Import the Ex9 table for EX9 relaxation.

‘--mupdate-ex9’

Update the existing EX9 table.

‘--mex9-limit=NUM’

Maximum number of entries in the ex9 table.

‘--mex9-loop-aware’

Avoid generating the EX9 instruction inside the loop.

‘--m[no-]ifc’

Disable/enable the link-time IFC optimization.

‘--mifc-loop-aware’

Avoid generating the IFC instruction inside the loop.

6.10 ld and the Altera Nios II ¶

Call and immediate jump instructions on Nios II processors are limited to transferring control to addresses in the same 256MB memory segment, which may result in ld giving ‘relocation truncated to fit’ errors with very large programs. The command-line option --relax enables the generation of trampolines that can access the entire 32-bit address space for calls outside the normal call and jmpi address range. These trampolines are inserted at section boundaries, so may not themselves be reachable if an input section and its associated call trampolines are larger than 256MB.

The --relax option is enabled by default unless -r is also specified. You can disable trampoline generation by using the --no-relax linker option. You can also disable this optimization locally by using the ‘set .noat’ directive in assembly-language source files, as the linker-inserted trampolines use the at register as a temporary.

Note that the linker --relax option is independent of assembler relaxation options, and that using the GNU assembler’s -relax-all option interferes with the linker’s more selective call instruction relaxation.

6.11 ld and PowerPC 32-bit ELF Support ¶

Branches on PowerPC processors are limited to a signed 26-bit displacement, which may result in ld giving ‘relocation truncated to fit’ errors with very large programs. ‘--relax’ enables the generation of trampolines that can access the entire 32-bit address space. These trampolines are inserted at section boundaries, so may not themselves be reachable if an input section exceeds 33M in size. You may combine ‘-r’ and ‘--relax’ to add trampolines in a partial link. In that case both branches to undefined symbols and inter-section branches are also considered potentially out of range, and trampolines inserted.

--bss-plt ¶

Current PowerPC GCC accepts a ‘-msecure-plt’ option that generates code capable of using a newer PLT and GOT layout that has the security advantage of no executable section ever needing to be writable and no writable section ever being executable. PowerPC ld will generate this layout, including stubs to access the PLT, if all input files (including startup and static libraries) were compiled with ‘-msecure-plt’. ‘--bss-plt’ forces the old BSS PLT (and GOT layout) which can give slightly better performance.

--secure-plt ¶

ld will use the new PLT and GOT layout if it is linking new ‘-fpic’ or ‘-fPIC’ code, but does not do so automatically when linking non-PIC code. This option requests the new PLT and GOT layout. A warning will be given if some object file requires the old style BSS PLT.

--sdata-got ¶

The new secure PLT and GOT are placed differently relative to other sections compared to older BSS PLT and GOT placement. The location of .plt must change because the new secure PLT is an initialized section while the old PLT is uninitialized. The reason for the .got change is more subtle: The new placement allows .got to be read-only in applications linked with ‘-z relro -z now’. However, this placement means that .sdata cannot always be used in shared libraries, because the PowerPC ABI accesses .sdata in shared libraries from the GOT pointer. ‘--sdata-got’ forces the old GOT placement. PowerPC GCC doesn’t use .sdata in shared libraries, so this option is really only useful for other compilers that may do so.

--emit-stub-syms ¶

This option causes ld to label linker stubs with a local symbol that encodes the stub type and destination.

--no-tls-optimize ¶

PowerPC ld normally performs some optimization of code sequences used to access Thread-Local Storage. Use this option to disable the optimization.

6.12 ld and PowerPC64 64-bit ELF Support ¶