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ld.txt
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ld.txt
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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 "=", then the "=" 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:
· Where object files are mapped into memory.
· How common symbols are allocated.
· All archive members included in the link, with a mention of the symbol which caused the archive member to be brought in.
· The values assigned to symbols.
Note - symbols whose values are computed by an expression which involves a reference to a previous value of the same symbol may not have correct
result displayed in the link map. This is because the linker discards intermediate results and only retains the final value of an expression. Under
such circumstances the linker will display the final value enclosed by square brackets. Thus for example a linker script containing:
foo = 1
foo = foo * 4
foo = foo + 8
will produce the following output in the link map if the -M option is used:
0x00000001 foo = 0x1
[0x0000000c] foo = (foo * 0x4)
[0x0000000c] foo = (foo + 0x8)
See Expressions 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.
--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
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.
-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 effects 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:
combreloc
Combines multiple reloc sections and sorts them to make dynamic symbol lookup caching possible.
defs
Disallows undefined symbols in object files. Undefined symbols in shared libraries are still allowed.
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.
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
Marks the object that its symbol table interposes before all symbols but the primary executable.
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
Marks the object that its filters be processed immediately at runtime.
muldefs
Allows multiple definitions.
nocombreloc
Disables multiple reloc sections combining.
nocopyreloc
Disable linker generated .dynbss variables used in place of variables defined in shared libraries. May result in dynamic text relocations.
nodefaultlib
Marks the object that the search for dependencies of this object will ignore any default library search paths.
nodelete
Marks the object shouldn't be unloaded at runtime.
nodlopen
Marks the object not available to "dlopen".
nodump
Marks the object can not be dumped by "dldump".
noexecstack
Marks the object as not requiring executable stack.
text
Treat DT_TEXTREL in shared object as error.
notext
Don't treat DT_TEXTREL in shared object as error.
textoff
Don't treat DT_TEXTREL in shared object as error.
norelro
Don't create an ELF "PT_GNU_RELRO" segment header in the object.
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 linked to using dlopen, instead of deferring function call resolution to the point when the function is first called.
origin
Marks the object may contain $ORIGIN.
relro
Create an ELF "PT_GNU_RELRO" segment header in the object.
max-page-size=value
Set the emulation maximum page size to value.
common-page-size=value
Set the emulation common page size to value.
stack-size=value
Specify a stack size for in an ELF "PT_GNU_STACK" segment. Specifying zero will override any default non-zero sized "PT_GNU_STACK" segment creation.
bndplt
Always generate BND prefix in PLT entries. Supported for Linux/x86_64.
noextern-protected-data
Don't treat protected data symbol as external when building shared library. This option overrides linker backend default. It can be used to
workaround 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.
call-nop=prefix-addr
call-nop=prefix-nop
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=prefix-nop generates "0x90 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.
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.
--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.
--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.
--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.
--allow-multiple-definition
-z muldefs
Normally when a symbol is defined multiple times, the linker will report a fatal error. These options allow multiple definitions and the first definition
will be used.
--allow-shlib-undefined
--no-allow-shlib-undefined
Allows or disallows undefined symbols in shared libraries. This switch is similar to --no-undefined except that it determines the behaviour when the
undefined symbols are in a shared library rather than a regular object file. It does not affect how undefined symbols in regular object files are
handled.
The default behaviour is to report errors for any undefined symbols referenced in shared libraries if the linker is being used to create an executable,
but to allow them if the linker is being used to create a shared library.
The reasons for allowing undefined symbol references in shared libraries specified at link time are that:
· A shared library specified at link time may not be the same as the one that is available at load time, so the symbol might actually be resolvable at
load time.
· There are some operating systems, eg BeOS and HPPA, where undefined symbols in shared libraries are normal.
The BeOS kernel for example patches shared libraries at load time to select whichever function is most appropriate for the current architecture.
This is used, for example, to dynamically select an appropriate memset function.
--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.
-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.
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.
--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.
--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