ld - Using LD, the GNU linker
ld [options] objfile ...
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", 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 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.
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. Note
that specifying a script in this way merely augments the
main linker script; use the -T option to replace the
default linker script entirely.
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
preceeded 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,--startgroup foo.o bar.o -Wl,--endgroup
This is important, because otherwise the compiler driver
program may silently drop the linker options, resulting in
a bad link.
Here is a table of the generic command line switches
accepted by the GNU linker:
-akeyword
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.
-Aarchitecture
--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 archivelibrary
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 obj-
dump -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.
-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).
-E
--export-dynamic
When creating a dynamically linked executable, 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 this option, 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 version script to control what
symbols should be added to the dynamic symbol table if
the output format supports it. See the description of
--version-script in @ref{VERSION}.
-EB Link big-endian objects. This affects the default
output format.
-EL Link little-endian objects. This affects the default
output format.
-f
--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.
-Gvalue
--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 ECOFF which supports
putting large and small objects into different sections.
This is ignored for other object file formats.
-hname
-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.
-larchive
--library=archive
Add archive file archive to the list of files to link.
This option may be used any number of times. ld will
search its path-list for occurrences of "libarchive.a"
for every archive specified.
On systems which support shared libraries, ld may also
search for libraries with extensions other than ".a".
Specifically, on ELF and SunOS systems, ld will search
a directory for a library with an extension of ".so"
before searching for one with an extension of ".a".
By convention, a ".so" extension indicates a shared
library.
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.
-Lsearchdir
--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.
If searchdir begins with "=", then the "=" will be
replaced by the sysroot prefix, a path 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.
-memulation
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 and symbols 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.
-n
--nmagic
Turn off page alignment of sections, and mark the output
as "NMAGIC" if possible.
-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".
--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.
-q
--emit-relocs
Leave relocation sections and contents in fully linked
exececutables. 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.
-r
--relocateable
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 script-
file does not exist in the current directory, "ld"
looks for it in the directories specified by any preceding
-L options. Multiple -T options accumulate.
-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.
-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.
--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. For most targets,
this is all local symbols whose names begin with L.
-Z Produce 'Standard' executables, disables Writable XOR
Executable features of resulting binaries.
-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 "initfirst", "interpose",
"loadfltr", "nodefaultlib", "nodelete", "nodlopen",
"nodump", "now", "origin", "combreloc", "nocombreloc"
and "nocopyreloc". The other keywords are ignored for
Solaris compatibility. "initfirst" marks the object to
be initialized first at runtime before any other
objects. "interpose" marks the object that its symbol
table interposes before all symbols but the primary
executable. "loadfltr" marks the object that its filtees
be processed immediately at runtime. "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". "now" marks the object
with the non-lazy runtime binding. "origin" marks the
object may contain $ORIGIN. "defs" disallows undefined
symbols. "muldefs" allows multiple definitions.
"combreloc" combines multiple reloc sections and sorts
them to make dynamic symbol lookup caching possible.
"nocombreloc" disables multiple reloc sections
combining. "nocopyreloc" disables production of copy
relocs.
-( 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.
-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. --no-undefined
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.
-Bsymbolic
When creating a shared library, bind references to
global symbols to the definition within the shared
library, if any. Normally, it is possible for a program
linked against a shared library to override the
definition within the shared library. This option is
only meaningful on ELF platforms which support shared
libraries.
--check-sections
--no-check-sections
Asks the linker not to check section addresses after
they have been assigned to see if there 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.
--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. The remaining files contain
references to the symbol.
--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 nonRelocatable
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.
--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.
--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 which may be used at runtime
to relocate any data which was statically initialized
to pointer values. See the code in testsuite/ld-empic
for details.
--fatal-warnings
Treat all warnings as errors.
--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.
--no-gc-sections
--gc-sections
Enable garbage collection of unused input sections.
It is ignored on targets that do not support this
option. This option is not compatible with -r, nor
should it be used with dynamic linking. The default
behaviour (of not performing this garbage collection)
can be restored by specifying --no-gc-sections on the
command line.
--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
Normally when creating a non-symbolic shared library,
undefined symbols are allowed and left to be resolved
by the runtime loader. This option disallows such
undefined symbols if they come from regular object
files. The switch --no-allow-shlib-undefined controls
the behaviour for shared objects being linked into the
shared library.
--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
Allow (the default) or disallow undefined symbols in
shared objects. The setting of this switch overrides
--no-undefined where shared objects are concerned.
Thus if --no-undefined is set but
--no-allow-shlib-undefined is not, the net result will
be that undefined symbols in regular object files will
trigger an error, but undefined symbols in shared
objects will be ignored.
The reason that --allow-shlib-undefined is the default
is that the shared object being specified at link time
may not be the same one that is available at load
time, so the symbols might actually be resolvable at
load time. Plus there are some systems, (eg BeOS)
where undefined symbols in shared libraries is normal
since the kernel patches them at load time to select
which function is most appropriate for the current
architecture. eg. to dynamically select an appropriate
memset function. Apparently it is also normal for
HPPA shared libraries to have undefined symbols.
--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.
--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-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.
-qmagic
This option is ignored for Linux compatibility.
-Qy This option is ignored for SVR4 compatibility.
--relax
An option with machine dependent effects. This option
is only supported on a few targets.
On some platforms, the --relax option performs global
optimizations that become possible when the linker
resolves addressing in the program, such as relaxing
address modes and synthesizing new instructions in the
output object file.
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.
--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 patch 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 filesystems.
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. It is for the native linker only.
3. On an ELF system, if the -rpath and "rpath-link"
options were not used, search the contents of the
environment variable "LD_RUN_PATH". It is for the
native linker only.
4. On SunOS, if the -rpath option was not used,
search any directories specified using -L options.
5. For a native linker, 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
This option tells ld to sort the common symbols by
size when it places them in the appropriate output
sections. First come all the one byte symbols, then
all the two byte, then all the four byte, and then
everything else. This is to prevent gaps between symbols
due to alignment constraints.
--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.
--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.
--dll-verbose
--verbose
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.
--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 meaningful on ELF platforms which support
shared libraries.
--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 baseregister
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.
--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 (int c)
{
printf ("malloc called with %ld0, 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".
--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 dynamic tags will
be created as needed. If you specify --dis-
able-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.
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.
|
