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ld(1) ld(1)
ld
NAME
ld - the GNU linker
SYNOPSIS
ld [-EgiMSstVvXx] [-o output] objfile ...
[-A architecture] [-b input-format]
[-Bstatic] [-Bdynamic] [-Bsymbolic]
[-c commandfile] [--cref] [-d|-dc|-dp]
[-defsym symbol=expression] [-dll] [-e entry]
[-embedded-relocs] [-export-dynamic] [-f name]
[--auxiliary name] [-F name] [--filter name]
[-format input-format] [-G size] [-h name]
[-soname name] [--help] [-l ar] [-L searchdir]
[-Map mapfile] [-m emulation] [-n|-N]
[--noinhibit-exec] [--no-keep-memory] [--oformat output-format]
[-R filename] [--relax] [-r|-Ur]
[--rpath directory] [--rpath--link directory]
[--shared] [--sort-common] [--split-by-reloc count]
[--split-by-file] [-T commandfile] [-Ttext textorg]
[-Tdata dataorg] [-Tbss bssorg] [-u sym]
[--verbose] [--version] [--warn-common] [--warn-constructors]
[--warn-multiple-gp] [--warn-once] [--warn-section-align]
[--whole-archive] [--no-whole-archive] [--wrap symbol]
DESCRIPTION
The ld(1) utility combines a number of object and archive files, relocates
their data and ties up symbol references. Often, the last step in building
a new compiled program to run is a call to ld(1).
The ld(1) utility accepts Linker Command Language files to provide
explicit and total control over the linking process. This topic does not
describe the command language; see the ld(1) entry in info or the manual
ld: the GNU linker, for full details on the command language and on other
aspects of the GNU linker.
This version of ld(1) uses the general purpose BFD libraries to operate on
object files. This allows ld(1) to read, combine, and write object files
in many different formats, for example, COFF or a.out. Different formats
can be linked together to produce any available kind of object file. You
can use objdump -i to get a list of formats supported on various
architectures; see objdump(1).
In addition to being flexible, 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(1)
continues executing, which allows you to identify other errors (or, in
some cases, to get an output file in spite of the error).
The GNU linker ld(1) 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 through the command line and through
environment variables.
OPTIONS
The command-line options to ld(1) can be specified in any order, and can
be repeated at will. Usually, repeating an option with a different
argument will either have no further effect, or it will override the prior
occurrences (those further to the left on the command line) of an option.
The exceptions that can meaningfully be used more than once are -A, -b (or
its synonym -format), -defsym, -L, -l, -R, and -u.
The list of object files to be linked together, shown as objfile, can
follow, precede, or be mixed in with command-line options, except that an
objfile argument cannot be placed between an option flag and its argument.
Usually, the linker is invoked with at least one object file. Other forms
of binary input files can also be specified with -l, -R, and the script
command language, however. If no binary input files are specified, the
linker does not produce any output, and it issues the message "No input
files."
Option arguments must either follow the option letter without intervening
white space, or be given as separate arguments immediately following the
option that requires them.
-A architecture
In the current release of ld(1), this option is useful only for the
Intel 960 family of architectures. In that ld(1) configuration, the
architecture argument is one of the two-letter names identifying
members of the 960 family. The option specifies the desired output
target, and warns of any incompatible instructions in the input files.
It also modifies the linker's search strategy for archive libraries,
to support the use of libraries specific to each particular
architecture, by including in the search loop names suffixed with the
string identifying the architecture.
For example, if your ld(1) command line included -ACA and -ltry, the
linker would look (in its built-in search paths and in any paths you
specify with -L) for a library with the names
try
libtry.a tryca libtryca.a
The first two possibilities would be considered in any event; the last
two are due to the use of -ACA.
Future releases of ld(1) might support similar functionality for other
architecture families.
You can meaningfully use -A more than once on a command line if an
architecture family allows combination of target architectures. Each
use will add another pair of name variants to search for when -
l specifies a library.
--architecture=architecture
Equivalent to -A.
-b input-format
Specify the binary format for input object files that follow this
option on the command line. You do not usually need to specify this
because ld(1) is configured to expect as a default input format the
most usual format on each computer. input-format is a text string, the
name of a particular format supported by the BFD libraries. Using -
format input-format has the same effect, as does the script command
TARGET.
You might 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.
-Bstatic
Do not link against shared libraries. This is only meaningful on
platforms for which shared libraries are supported.
-Bdynamic
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.
-Bsymbolic
When creating a shared library, bind references to global symbols to
the definitions within the shared library, if there are any. Normally,
it is possible for a program linked against a shared library to
override the definition within the shared library. This option is only
meaningful on ELF platforms which support shared libraries.
-c commandfile
Directs ld(1) to read link commands from the file commandfile. These
commands will completely override the ld(1)default link format (rather
than adding to it); commandfile must specify everything necessary to
describe the target format.
You can also include a script of link commands directly in the command
line by bracketing it between { and } characters.
This is not a way to extend the command line, that is, to bypass the
command line-length limitation imposed by ARG_MAX. The script
here describes link commands in built-in language, MRI. The -c option
is also known as --mri-script.
--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.
-d, -dc, -dp
These three options are equivalent; multiple forms are supported for
compatibility with other linkers. Use any of them to make ld(1) assign
space to common symbols even if a relocatable output file is specified
(-r). The script command FORCE_COMMON_ALLOCATION has the same effect.
-defsym symbol-expression
Create a global symbol in the output file, containing the absolute
address given by expression. You can 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 can 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.
-dll
Link with a dynamic-link library (DLL). Note that the entire option
must be spelled out completely, due to a conflict with the -d option.
-e entry
Use entry as the explicit symbol for beginning execution of your
program rather than using the default entry point.
-embedded-relocs
This option is only meaningful when linking MIPS embedded PIC code,
generated by the -membedded-pic option to the GNU compiler and
assembler. It causes the linker to create a table that can be used at
run time to relocate any data that was statically initialized to
pointer values.
-E, --export-dynamic
When creating an ELF file, add all symbols to the dynamic-symbol
table. Normally, the dynamic-symbol table contains only symbols that
are used by a dynamic object. This option is needed for some uses of
dlopen(3).
-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.
-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 should be used as a filter on the symbol
table of the shared object name.
--format input-format
Synonym for -b input-format.
-g
Accepted, but ignored; this is provided for compatibility with other
tools.
-G size
Set the maximum size of objects to be optimized using the GP register
to size under MIPS ECOFF. 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 that has a DT_SONAME field, and 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.
--help
Print a summary of the command-line options on the standard output and
exit. This option and --version begin with two dashes instead of one
for compatibility with other GNU programs. The other options start
with only one dash for compatibility with other linkers.
-i
Perform an incremental link (same as option -r).
-l ar
Add an archive file ar to the list of files to link. This option can
be used any number of times. The ld(1) utility will search its path
list for occurrences of libar.a for every ar specified.
-L searchdir
This command adds path searchdir to the list of paths that ld(1) will
search for archive libraries. You can use this option any number of
times.
The default set of paths searched (without being specified with -L)
depends on which emulation mode ld(1) is using, and in some cases, how
it was configured. The paths can also be specified in a link script
with the SEARCH_DIR command.
-M
Print (to the standard output file) a link map—diagnostic information
about where symbols are mapped by ld(1), and information on global
common storage allocation.
-Map mapfile
Print to the file mapfile a link map—diagnostic information about
where symbols are mapped by ld(1), and information on global common
storage allocation.
-m emulation
Emulate the emulation linker. You can list the available emulations
with the --verbose or -V options. This option overrides the compiled-
in default, which is the system for which you configured ld(1).
--mri=script=MRI-commandfile
Equivalent to -c.
-N
Specifies readable and writeable text and data sections. If the output
format supports traditional magic numbers, the output is marked as
OMAGIC.
When you use the -N option, the linker does not page-align the data
segment.
-n
Sets the text segment to be read only, and NMAGIC is written, if
possible.
-noinhibit-exec
Normally, the linker will not produce an output file if it encounters
errors during the link process. With this flag, you can specify that
you want the output file retained even after non-fatal errors. In some
versions of gcc(1) and g++(1), this option is always passed to the
linker, but not with Interix.
-no-keep-memory
The linker normally optimizes for speed over memory usage by caching
the symbol tables of input files in memory. This option tells the
linker to optimize for memory usage instead by rereading the symbol
tables as necessary. This might be required if the linker runs out of
memory space while linking a large executable.
-o output
output is a name for the program produced by ld(1); 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.
-oformat output-format
Specify the binary format for the output object file. You do not
usually need to specify this, as ld(1) is configured to produce as a
default output format the most usual format on each computer. output-
format is a text string, the name of a particular format supported by
the BFD libraries. The script command OUTPUT_FORMAT can also specify
the output format, but this option overrides it.
-R 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.
-r
Generates relocatable output; that is, generates an output file that
can, in turn, serve as input to ld(1). This is often called partial
linking. As a side effect, in environments that support traditional
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; -Ur is an alternative.
This option does the same as -i.
-relax
An option with computer-dependent effects. Currently this option is
only supported on the H8/300.
On some platforms, you can use this option to perform global
optimizations that become possible when the linker resolves addressing
in your program, such as relaxing address modes and synthesizing new
instructions in the output object file.
On platforms where this is not supported, -relax is accepted, but has
no effect.
-rpath directory
Add a directory to the run-time library search path. This is used when
linking an ELF executable with shared objects. All -rpath arguments
are concatenated and passed to the run-time linker, which uses them to
locate shared objects at run time. The -rpath option is also used when
locating shared objects that 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 can also be used on SunOS. By default, on SunOS, the
linker will form a run-time search patch out of all of the -L options
it is given. If a -rpath option is used, the run-time search path will
be formed exclusively using the -rpath options, ignoring the -
L options. This can be helpful when using gcc, which adds many -
L options that might be on NFS mounted file systems.
-rpath-link directory
When using ELF or SunOS, one shared library might require another.
This happens when an ld -shared(1) link includes a shared library as
one of the input files.
If the linker encounters such a dependency when doing a non-shared,
non-relocateable 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 can
specify a sequence of directory names, either by specifying a list of
names separated by colons, or by appearing multiple times.
If the required shared library is not found, the linker will issue a
warning and continue with the link.
-S
Omits debugger symbol information (but not all symbols) from the
output file.
-s
Omits all symbol information from the output file.
-shared
Create a shared library. This is currently only supported on ELF and
SunOS platforms (on SunOS, it is not required because the linker
automatically creates a shared library when there are undefined
symbols and the -e option is not used).
-sort-common
Normally, when ld(1) places the global common symbols in the
appropriate output sections, it sorts them by size, starting with the
one-byte symbols, followed by the two-byte symbols, then the four-byte
symbols, and then everything else. This prevent gaps between symbols
that result from alignment constraints. This option disables that
sorting.
-split-by-reloc count
Tries to create 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 relocatables for downloading into
certain real-time kernels with the COFF object-file format because
COFF cannot represent more than 65535 relocations in a single section.
Note that this will fail to work with object-file formats that 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.
-split-by-file
Similar to -split-by-reloc but creates a new output section for each
input file.
-Tbss org
-Tdata org
-Ttext org
Use org as the starting address for the bss, data, or text segment of
the output file. The org argument is a hexadecimal integer that
specifies an address relative to the image base, not an absolute
address.
-T commandfile
Equivalent to -c commandfile; supported for compatibility with other
tools. The language used for -T is the default language, rather than
MRI. The -T option is also known as --script.
-t
Prints names of input files as ld(1) processes them.
-u sym
Forces sym to be entered in the output file as an undefined symbol.
This might, for example, trigger linking of additional modules from
standard libraries. -u can be repeated with different option arguments
to enter additional undefined symbols.
-Ur
For anything other than C++ programs, this option is equivalent to -r:
it generates relocatable output; that is, an output file that can, in
turn, serve as input to ld(1). When linking C++ programs, -Ur will
resolve references to constructors, unlike -r.
--verbose
Display the version number for ld(1) and list the supported
emulations. Display which input files can and can not be opened.
-v
Display the version number for ld(1).
-V
Display the version number and the supported emulations for ld(1).
--version
Display the version number for ld(1) and exit.
-warn-common
Warn when a common symbol is combined with another common symbol or
with a symbol definition. Traditional linkers allow this somewhat
inefficient practice, but other linkers may not not. This option
allows you to find potential problems from combining global symbols.
-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
cannot detect the use of global constructors.
-warn-multiple-gp
Warn if the output file requires multiple global-pointer values. This
option is meaningful only for certain processors, such as those that
are Alpha-based.
-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 be changed only if it not explicitly specified; that
is, if the SECTIONS command does not specify a start address for the
section.
--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.
--no-whole-archive
Turn off the effect of the --whole-archive option for archives that
appear later on the command line.
--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.
-X
Delete all temporary local symbols. For most targets, this includes
all local symbols whose names begin with L.
-x
Delete all local symbols.
ENVIRONMENT
You can change the behavior of ld(1) with the environment variable
GNUTARGET.
GNUTARGET determines the input-file object format if you do not 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(1) uses the
natural format of the host. If GNUTARGET is set to default, BFD attempts
to discover the input format by examining binary input files. This method
often succeeds, but there are potential ambiguities because there is no
method of ensuring that the magic number used to flag object-file formats
is unique. The configuration procedure for BFD on each system, however,
places the conventional format for that system first in the search-list,
so ambiguities are resolved in favor of convention.
COPYING
Copyright (c) 1991, 1992 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the entire
resulting derived work is distributed under the terms of a permission
notice identical to this one.
Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be included in translations
approved by the Free Software Foundation instead of in the original
English.
SEE ALSO
liblock(1)
objdump(1)
ld(1) and binutils entries in info
ld: the GNU linker, Steve Chamberlain and Roland Pesch; The GNU Binary
Utilities, Roland H. Pesch.