LD(1) GNU Development Tools LD(1)
NAME
ld - The GNU linker
SYNOPSIS
ld [options] objfile ...
DESCRIPTION
ld combines a number of object and archive files, relocates their data and ties up symbol references. Usually the last step in compiling a
program is to run ld.
ld accepts Linker Command Language files written in a superset of AT&T's Link Editor Command Language syntax, to provide explicit and total
control over the linking process.
This man page does not describe the command language; see the ld entry in "info" for full details on the command language and on other
aspects of the GNU linker.
This version of ld uses the general purpose BFD libraries to operate on object files. This allows ld to read, combine, and write object
files in many different formats---for example, COFF or "a.out". Different formats may be linked together to produce any available kind of
object file.
Aside from its flexibility, the GNU linker is more helpful than other linkers in providing diagnostic information. Many linkers abandon
execution immediately upon encountering an error; whenever possible, ld continues executing, allowing you to identify other errors (or, in
some cases, to get an output file in spite of the error).
The GNU linker ld is meant to cover a broad range of situations, and to be as compatible as possible with other linkers. As a result, you
have many choices to control its behavior.
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.
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.
-A architecture
--architecture=architecture
In the current release of ld, this option is useful only for the Intel 960 family of architectures. In that ld configuration, the
architecture argument identifies the particular architecture in the 960 family, enabling some safeguards and modifying the archive-
library search path.
Future releases of ld may support similar functionality for other architecture families.
-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.)
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".
You can also define the input format from a script, using the command "TARGET";
-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 the MRI Compatible Script Files section of GNU ld documentation. 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.
--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.
-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).
--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.
-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 the 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.
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.
-M
--print-map
Print a link map to the standard output. A link map provides information about the link, including the following:
o Where object files are mapped into memory.
o How common symbols are allocated.
o All archive members included in the link, with a mention of the symbol which caused the archive member to be brought in.
o 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 for more information about expressions in linker scripts.
-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.
-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 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.
-T scriptfile
--script=scriptfile
Use scriptfile as the linker script. This script replaces ld's default linker script (rather than adding to it), so commandfile must
specify everything necessary to describe the output file. 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.
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 anything other than C++ programs, this option is equivalent to -r: it generates relocatable output---i.e., an output file that can
in turn serve as input to ld. When linking C++ programs, -Ur does resolve references to constructors, unlike -r. 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.
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.
"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.
-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:
bndplt
Always generate BND prefix in PLT entries. Supported for Linux/x86_64.
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.
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.
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.
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.
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.
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.
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.
text
notext
textoff
Report an error if DT_TEXTREL is set, i.e., if the binary 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.
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 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.
--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 can also be
used with the --export-dynamic option, when creating a position independent executable, to bind references to global symbols to the
definition within the executable. This option is only meaningful on ELF platforms which support shared libraries and position
independent executables.
-Bsymbolic-functions
When creating a shared library, bind references to global function symbols to the definition within the shared library, if any. This
option can also be used with the --export-dynamic option, when creating a position independent executable, to bind references to global
function symbols to the definition within the executable. This option is only meaningful on ELF platforms which support shared
libraries and position independent executables.
--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 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.
--no-define-common
This option inhibits the assignment of addresses to common symbols. The script command "INHIBIT_COMMON_ALLOCATION" has the same
effect.
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.
--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. Note: there
should be no white space between symbol, the equals sign ("="), and expression.
--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.
--fatal-warnings
--no-fatal-warnings
Treat all warnings as errors. The default behaviour can be restored with the option --no-fatal-warnings.
--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 and
--undefined.
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 an --entry or --undefined option or by a "ENTRY" command in the linker script.
--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.
--print-memory-usage
Print used size, total size and used size of memory regions created with the MEMORY 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.
--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:
o 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.
o 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.
--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.
--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.
-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.
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 this is not supported, --relax is accepted, but ignored.
On platforms where --relax is accepted the option --no-relax can be used to disable the feature.
--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. 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. The default directories, normally /lib and /usr/lib.
8. For a native linker on an ELF system, if the file /etc/ld.so.conf exists, the list of directories found in that file.
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. 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.
--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-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-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.
--warn-shared-textrel
Warn if the linker adds a DT_TEXTREL to a 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
", 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".
--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.
--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 is "sysv".
--compress-debug-sections=none
--compress-debug-sections=zlib
--compress-debug-sections=zlib-gnu
--compress-debug-sections=zlib-gabi
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.
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.
--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.
The i386 PE linker supports the -shared option, which causes the output to be a dynamically linked library (DLL) instead of a normal
executable. You should name the output "*.dll" when you use this option. In addition, the linker fully supports the standard "*.def"
files, which may be specified on the linker command line like an object file (in fact, it should precede archives it exports symbols from,
to ensure that they get linked in, just like a normal object file).
In addition to the options common to all targets, the i386 PE linker support additional command line options that are specific to the i386
PE target. Options that take values may be separated from their values by either a space or an equals sign.
--add-stdcall-alias
If given, symbols with a stdcall suffix (@nn) will be exported as-is and also with the suffix stripped. [This option is specific to
the i386 PE targeted port of the linker]
--base-file file
Use file as the name of a file in which to save the base addresses of all the relocations needed for generating DLLs with dlltool.
[This is an i386 PE specific option]
--dll
Create a DLL instead of a regular executable. You may also use -shared or specify a "LIBRARY" in a given ".def" file. [This option is
specific to the i386 PE targeted port of the linker]
--enable-long-section-names
--disable-long-section-names
The PE variants of the COFF object format add an extension that permits the use of section names longer than eight characters, the
normal limit for COFF. By default, these names are only allowed in object files, as fully-linked executable images do not carry the
COFF string table required to support the longer names. As a GNU extension, it is possible to allow their use in executable images as
well, or to (probably pointlessly!) disallow it in object files, by using these two options. Executable images generated with these
long section names are slightly non-standard, carrying as they do a string table, and may generate confusing output when examined with
non-GNU PE-aware tools, such as file viewers and dumpers. However, GDB relies on the use of PE long section names to find Dwarf-2
debug information sections in an executable image at runtime, and so if neither option is specified on the command-line, ld will enable
long section names, overriding the default and technically correct behaviour, when it finds the presence of debug information while
linking an executable image and not stripping symbols. [This option is valid for all PE targeted ports of the linker]
--enable-stdcall-fixup
--disable-stdcall-fixup
If the link finds a symbol that it cannot resolve, it will attempt to do "fuzzy linking" by looking for another defined symbol that
differs only in the format of the symbol name (cdecl vs stdcall) and will resolve that symbol by linking to the match. For example,
the undefined symbol "_foo" might be linked to the function "_foo@12", or the undefined symbol "_bar@16" might be linked to the
function "_bar". When the linker does this, it prints a warning, since it normally should have failed to link, but sometimes import
libraries generated from third-party dlls may need this feature to be usable. If you specify --enable-stdcall-fixup, this feature is
fully enabled and warnings are not printed. If you specify --disable-stdcall-fixup, this feature is disabled and such mismatches are
considered to be errors. [This option is specific to the i386 PE targeted port of the linker]
--leading-underscore
--no-leading-underscore
For most targets default symbol-prefix is an underscore and is defined in target's description. By this option it is possible to
disable/enable the default underscore symbol-prefix.
--export-all-symbols
If given, all global symbols in the objects used to build a DLL will be exported by the DLL. Note that this is the default if there
otherwise wouldn't be any exported symbols. When symbols are explicitly exported via DEF files or implicitly exported via function
attributes, the default is to not export anything else unless this option is given. Note that the symbols "DllMain@12",
"DllEntryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will not be automatically exported. Also, symbols imported from other DLLs
will not be re-exported, nor will symbols specifying the DLL's internal layout such as those beginning with "_head_" or ending with
"_iname". In addition, no symbols from "libgcc", "libstd++", "libmingw32", or "crtX.o" will be exported. Symbols whose names begin
with "__rtti_" or "__builtin_" will not be exported, to help with C++ DLLs. Finally, there is an extensive list of cygwin-private
symbols that are not exported (obviously, this applies on when building DLLs for cygwin targets). These cygwin-excludes are:
"_cygwin_dll_entry@12", "_cygwin_crt0_common@8", "_cygwin_noncygwin_dll_entry@12", "_fmode", "_impure_ptr", "cygwin_attach_dll",
"cygwin_premain0", "cygwin_premain1", "cygwin_premain2", "cygwin_premain3", and "environ". [This option is specific to the i386 PE
targeted port of the linker]
--exclude-symbols symbol,symbol,...
Specifies a list of symbols which should not be automatically exported. The symbol names may be delimited by commas or colons. [This
option is specific to the i386 PE targeted port of the linker]
--exclude-all-symbols
Specifies no symbols should be automatically exported. [This option is specific to the i386 PE targeted port of the linker]
--file-alignment
Specify the file alignment. Sections in the file will always begin at file offsets which are multiples of this number. This defaults
to 512. [This option is specific to the i386 PE targeted port of the linker]
--heap reserve
--heap reserve,commit
Specify the number of bytes of memory to reserve (and optionally commit) to be used as heap for this program. The default is 1MB
reserved, 4K committed. [This option is specific to the i386 PE targeted port of the linker]
--image-base value
Use value as the base address of your program or dll. This is the lowest memory location that will be used when your program or dll is
loaded. To reduce the need to relocate and improve performance of your dlls, each should have a unique base address and not overlap
any other dlls. The default is 0x400000 for executables, and 0x10000000 for dlls. [This option is specific to the i386 PE targeted
port of the linker]
--kill-at
If given, the stdcall suffixes (@nn) will be stripped from symbols before they are exported. [This option is specific to the i386 PE
targeted port of the linker]
--large-address-aware
If given, the appropriate bit in the "Characteristics" field of the COFF header is set to indicate that this executable supports
virtual addresses greater than 2 gigabytes. This should be used in conjunction with the /3GB or /USERVA=value megabytes switch in the
"[operating systems]" section of the BOOT.INI. Otherwise, this bit has no effect. [This option is specific to PE targeted ports of
the linker]
--disable-large-address-aware
Reverts the effect of a previous --large-address-aware option. This is useful if --large-address-aware is always set by the compiler
driver (e.g. Cygwin gcc) and the executable does not support virtual addresses greater than 2 gigabytes. [This option is specific to
PE targeted ports of the linker]
--major-image-version value
Sets the major number of the "image version". Defaults to 1. [This option is specific to the i386 PE targeted port of the linker]
--major-os-version value
Sets the major number of the "os version". Defaults to 4. [This option is specific to the i386 PE targeted port of the linker]
--major-subsystem-version value
Sets the major number of the "subsystem version". Defaults to 4. [This option is specific to the i386 PE targeted port of the linker]
--minor-image-version value
Sets the minor number of the "image version". Defaults to 0. [This option is specific to the i386 PE targeted port of the linker]
--minor-os-version value
Sets the minor number of the "os version". Defaults to 0. [This option is specific to the i386 PE targeted port of the linker]
--minor-subsystem-version value
Sets the minor number of the "subsystem version". Defaults to 0. [This option is specific to the i386 PE targeted port of the linker]
--output-def file
The linker will create the file file which will contain a DEF file corresponding to the DLL the linker is generating. This DEF file
(which should be called "*.def") may be used to create an import library with "dlltool" or may be used as a reference to automatically
or implicitly exported symbols. [This option is specific to the i386 PE targeted port of the linker]
--enable-auto-image-base
--enable-auto-image-base=value
Automatically choose the image base for DLLs, optionally starting with base value, unless one is specified using the "--image-base"
argument. By using a hash generated from the dllname to create unique image bases for each DLL, in-memory collisions and relocations
which can delay program execution are avoided. [This option is specific to the i386 PE targeted port of the linker]
--disable-auto-image-base
Do not automatically generate a unique image base. If there is no user-specified image base ("--image-base") then use the platform
default. [This option is specific to the i386 PE targeted port of the linker]
--dll-search-prefix string
When linking dynamically to a dll without an import library, search for "<string><basename>.dll" in preference to "lib<basename>.dll".
This behaviour allows easy distinction between DLLs built for the various "subplatforms": native, cygwin, uwin, pw, etc. For instance,
cygwin DLLs typically use "--dll-search-prefix=cyg". [This option is specific to the i386 PE targeted port of the linker]
--enable-auto-import
Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA imports from DLLs, and create the necessary thunking symbols when
building the import libraries with those DATA exports. Note: Use of the 'auto-import' extension will cause the text section of the
image file to be made writable. This does not conform to the PE-COFF format specification published by Microsoft.
Note - use of the 'auto-import' extension will also cause read only data which would normally be placed into the .rdata section to be
placed into the .data section instead. This is in order to work around a problem with consts that is described here:
http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
Using 'auto-import' generally will 'just work' -- but sometimes you may see this message:
"variable '<var>' can't be auto-imported. Please read the documentation for ld's "--enable-auto-import" for details."
This message occurs when some (sub)expression accesses an address ultimately given by the sum of two constants (Win32 import tables
only allow one). Instances where this may occur include accesses to member fields of struct variables imported from a DLL, as well as
using a constant index into an array variable imported from a DLL. Any multiword variable (arrays, structs, long long, etc) may
trigger this error condition. However, regardless of the exact data type of the offending exported variable, ld will always detect it,
issue the warning, and exit.
There are several ways to address this difficulty, regardless of the data type of the exported variable:
One way is to use --enable-runtime-pseudo-reloc switch. This leaves the task of adjusting references in your client code for runtime
environment, so this method works only when runtime environment supports this feature.
A second solution is to force one of the 'constants' to be a variable -- that is, unknown and un-optimizable at compile time. For
arrays, there are two possibilities: a) make the indexee (the array's address) a variable, or b) make the 'constant' index a variable.
Thus:
extern type extern_array[];
extern_array[1] -->
{ volatile type *t=extern_array; t[1] }
or
extern type extern_array[];
extern_array[1] -->
{ volatile int t=1; extern_array[t] }
For structs (and most other multiword data types) the only option is to make the struct itself (or the long long, or the ...) variable:
extern struct s extern_struct;
extern_struct.field -->
{ volatile struct s *t=&extern_struct; t->field }
or
extern long long extern_ll;
extern_ll -->
{ volatile long long * local_ll=&extern_ll; *local_ll }
A third method of dealing with this difficulty is to abandon 'auto-import' for the offending symbol and mark it with
"__declspec(dllimport)". However, in practice that requires using compile-time #defines to indicate whether you are building a DLL,
building client code that will link to the DLL, or merely building/linking to a static library. In making the choice between the
various methods of resolving the 'direct address with constant offset' problem, you should consider typical real-world usage:
Original:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d
",arr[1]);
}
Solution 1:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
/* This workaround is for win32 and cygwin; do not "optimize" */
volatile int *parr = arr;
printf("%d
",parr[1]);
}
Solution 2:
--foo.h
/* Note: auto-export is assumed (no __declspec(dllexport)) */
#if (defined(_WIN32) || defined(__CYGWIN__)) &&
!(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
#define FOO_IMPORT __declspec(dllimport)
#else
#define FOO_IMPORT
#endif
extern FOO_IMPORT int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d
",arr[1]);
}
A fourth way to avoid this problem is to re-code your library to use a functional interface rather than a data interface for the
offending variables (e.g. set_foo() and get_foo() accessor functions). [This option is specific to the i386 PE targeted port of the
linker]
--disable-auto-import
Do not attempt to do sophisticated linking of "_symbol" to "__imp__symbol" for DATA imports from DLLs. [This option is specific to the
i386 PE targeted port of the linker]
--enable-runtime-pseudo-reloc
If your code contains expressions described in --enable-auto-import section, that is, DATA imports from DLL with non-zero offset, this
switch will create a vector of 'runtime pseudo relocations' which can be used by runtime environment to adjust references to such data
in your client code. [This option is specific to the i386 PE targeted port of the linker]
--disable-runtime-pseudo-reloc
Do not create pseudo relocations for non-zero offset DATA imports from DLLs. [This option is specific to the i386 PE targeted port of
the linker]
--enable-extra-pe-debug
Show additional debug info related to auto-import symbol thunking. [This option is specific to the i386 PE targeted port of the
linker]
--section-alignment
Sets the section alignment. Sections in memory will always begin at addresses which are a multiple of this number. Defaults to
0x1000. [This option is specific to the i386 PE targeted port of the linker]
--stack reserve
--stack reserve,commit
Specify the number of bytes of memory to reserve (and optionally commit) to be used as stack for this program. The default is 2MB
reserved, 4K committed. [This option is specific to the i386 PE targeted port of the linker]
--subsystem which
--subsystem which:major
--subsystem which:major.minor
Specifies the subsystem under which your program will execute. The legal values for which are "native", "windows", "console", "posix",
and "xbox". You may optionally set the subsystem version also. Numeric values are also accepted for which. [This option is specific
to the i386 PE targeted port of the linker]
The following options set flags in the "DllCharacteristics" field of the PE file header: [These options are specific to PE targeted
ports of the linker]
--high-entropy-va
Image is compatible with 64-bit address space layout randomization (ASLR).
--dynamicbase
The image base address may be relocated using address space layout randomization (ASLR). This feature was introduced with MS Windows
Vista for i386 PE targets.
--forceinteg
Code integrity checks are enforced.
--nxcompat
The image is compatible with the Data Execution Prevention. This feature was introduced with MS Windows XP SP2 for i386 PE targets.
--no-isolation
Although the image understands isolation, do not isolate the image.
--no-seh
The image does not use SEH. No SE handler may be called from this image.
--no-bind
Do not bind this image.
--wdmdriver
The driver uses the MS Windows Driver Model.
--tsaware
The image is Terminal Server aware.
--insert-timestamp
--no-insert-timestamp
Insert a real timestamp into the image. This is the default behaviour as it matches legacy code and it means that the image will work
with other, proprietary tools. The problem with this default is that it will result in slightly different images being produced each
time the same sources are linked. The option --no-insert-timestamp can be used to insert a zero value for the timestamp, this ensuring
that binaries produced from identical sources will compare identically.
The C6X uClinux target uses a binary format called DSBT to support shared libraries. Each shared library in the system needs to have a
unique index; all executables use an index of 0.
--dsbt-size size
This option sets the number of entries in the DSBT of the current executable or shared library to size. The default is to create a
table with 64 entries.
--dsbt-index index
This option sets the DSBT index of the current executable or shared library to index. The default is 0, which is appropriate for
generating executables. If a shared library is generated with a DSBT index of 0, the "R_C6000_DSBT_INDEX" relocs are copied into the
output file.
The --no-merge-exidx-entries switch disables the merging of adjacent exidx entries in frame unwind info.
The 68HC11 and 68HC12 linkers support specific options to control the memory bank switching mapping and trampoline code generation.
--no-trampoline
This option disables the generation of trampoline. By default a trampoline is generated for each far function which is called using a
"jsr" instruction (this happens when a pointer to a far function is taken).
--bank-window name
This option indicates to the linker the name of the memory region in the MEMORY specification that describes the memory bank window.
The definition of such region is then used by the linker to compute paging and addresses within the memory window.
The following options are supported to control handling of GOT generation when linking for 68K targets.
--got=type
This option tells the linker which GOT generation scheme to use. type should be one of single, negative, multigot or target. For more
information refer to the Info entry for ld.
The following options are supported to control microMIPS instruction generation and branch relocation checks for ISA mode transitions when
linking for MIPS targets.
--insn32
--no-insn32
These 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.
--ignore-branch-isa
--no-ignore-branch-isa
These 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.
ENVIRONMENT
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. 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.
SEE ALSO
ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries for binutils and ld.
COPYRIGHT
Copyright (c) 1991-2018 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".
binutils-2.30-system 2018-05-16 LD(1)