ld - Using LD, the GNU linker
SYNOPSIS
ld [ options ] objfile...
DESCRIPTION
`ld' combines a number of object and archive files, relo
cates 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 pro
cess.
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 encounter
ing 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 partic
ular 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 I<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 stan
dard search directories. (See the discussion of the -l
option below.)
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 com
mand 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 com
mand line) of that option. Options which may be meaning
fully specified more than once are noted in the descrip
tions 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 can not 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 should only be used
to augment the main linker script; if you want to use some
command that logically can only appear once, such as the
`SECTIONS' or `MEMORY' command, you must replace the
default linker script using the -T option.
For options whose names are a single letter, option argu
ments must either follow the option letter without inter
vening whitespace, or be given as separate arguments imme
diately 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 pre
ceeded 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.
rated 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 (eg gcc) then all the linker command line
options should be prefixed by -Wl, (or whatever is appro
priate 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 equiva
lent to -Bstatic, and the other two keywords are func
tionally 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 fam
ily, enabling some safeguards and modifying the
archive-library search path.
Future releases of `ld' may support similar function
ality 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
(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 particu
lar format.
The default format is taken from the environment vari
able `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 Com
patible 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 gen
eral-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 com
mand `FORCE_COMMON_ALLOCATION' has the same effect.
`-e entry'
`--entry=entry'
Use entry as the explicit symbol for beginning execu
tion 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'
When creating a dynamically linked executable, add all
symbols to the dynamic symbol table. The dynamic sym
bol 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 pro
gram, rather than some other dynamic object, then you
will probably need to use this option when linking the
program itself.
`-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 defini
tion 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, per
haps for debugging or for machine specific perfor
mance.
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'
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 fil
ter 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 actu
ally 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 for
mat 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' envi
ronment 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 sec
tions. 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 exe
cutable 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
`-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 exten
sion of `.so' before searching for one with an exten
sion of `.a'. By convention, a `.so' extension indi
cates 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 sym
bol 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
are specified on the command line. Directories speci
fied 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.
The default set of paths searched (without being spec
ified with -L) depends on which emulation mode `ld' is
using, and in some cases also on how it was config
ured.
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 avail
able 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 and symbols 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.
`-n'
`--nmagic'
Turn off page alignment of sections, and mark the out
put as `NMAGIC' if possible.
`-N'
`--omagic'
Set the text and data sections to be readable and
If the output format supports Unix style magic num
bers, mark the output as `OMAGIC'.
`-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.
`-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 construc
tors; to do that, use -Ur.
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 pro
grams. 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.
`--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. You must use
this option if you want to use a command which can
only appear once in a linker script, such as the `SEC
TIONS' or `MEMORY' command. 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.
`-u symbol'
`--undefined=symbol'
Force symbol to be entered in the output file as an
undefined symbol. Doing this may, for example, trig
ger 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 out
put---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.
Creates a separate output section for every input sec
tion 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.
`-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 sym
bol 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' and `nocombre
loc'. The other keywords are ignored for Solaris com
patibility. `initfirst' marks the object to be ini
tialized first at runtime before any other objects.
`interpose' marks the object that its symbol table
cutable. `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 unde
fined symbols. `combreloc' combines multiple reloc
sections and sorts them to make dynamic symbol lookup
caching possible. `nocombreloc' disables multiple
reloc sections combining.
`-( 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.
`-assert keyword'
This option is ignored for SunOS compatibility.
`-Bdynamic'
`-dy'
`-call_shared'
Link against dynamic libraries. This is only meaning
ful on platforms for which shared libraries are sup
ported. 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 fol
low it.
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-unde
fined' 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 fol
low 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 pro
gram 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 mes
sages. 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 neces
sary. The symbols are printed out, sorted by name.
For each symbol, a list of file names is given. If
location of the definition. The remaining files con
tain references to the symbol.
`--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 mul
tiple 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 con
verts 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 exe
cutables. The default dynamic linker is normally cor
rect; 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 run
time to relocate any data which was statically ini
tialized to pointer values. See the code in test
suite/ld-empic for details.
`--fatal-warnings'
Treat all warnings as errors.
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. These options disallows such
undefined symbols.
`--allow-shlib-undefined'
Allow undefined symbols in shared objects even when
--no-undefined is set. The net result will be that
undefined symbols in regular objects will still
objects will be ignored. The implementation of
no_undefined makes the assumption that the runtime
linker will choke on undefined symbols. However there
is at least one system (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. I.E. dynam
ically select an appropriate memset function. Appar
ently it is also normal for HPPA shared libraries to
have undefined symbols.
`--no-warn-mismatch'
Normally `ld' will give an error if you try to link
together input files that are mismatched for some rea
son, perhaps because they have been compiled for dif
ferent 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 out
put file if it encounters errors during the link pro
cess; it exits without writing an output file when it
issues any error whatsoever.
`--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.
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 exe
cutable impossible. This is known to be the case for
the Matsushita MN10200 and MN10300 family of proces
sors.
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 grad
ually, to conserve run-time memory.
--retain-symbols-file does not discard undefined sym
bols, 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 concate
nated 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 envi
ronment 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
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 IR'
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 direc
tories to search. The `-rpath-link' option may spec
ify 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 over
rides 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 run
time, 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 environ
ment variable `LD_LIBRARY_PATH'.
`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 sup
ported 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 bytes, then all the four bytes, and then
everything else. This is to prevent gaps between sym
bols 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 gen
erating 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 relo
cations one output section will contain that many
relocations. count defaults to a value of 32768.
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 for
mat 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' pro
gram 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 inte
ger; for compatibility with other linkers, you may
omit the leading 0x usually associated with hexadeci
mal values. Note: there should be no white space
between sectionname, the equals sign (``=''), and org.
`-Tbss org'
`-Tdata org'
`-Ttext org'
Use org as the starting address for---respec
tively---the `bss', `data', or the `text' segment of
the output file. org must be a single hexadecimal
integer; for compatibility with other linkers, you may
omit the leading 0x usually associated with hexadeci
mal values.
`--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 if using a default builtin script.
`--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
heirarchy for the library being created. This option
is only meaningful on ELF platforms which support
`--warn-common'
Warn when a common symbol is combined with another
common symbol or with a symbol definition. Unix link
ers 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 sym
bols 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.
I<file>(I<section>): warning: common of `I<symbol>'
overridden by definition
I<file>(I<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.
overriding common
I<file>(I<section>): warning: common is here
3. Merging a common symbol with a previous same-sized
common symbol.
I<file>(I<section>): warning: multiple common
of `I<symbol>'
I<file>(I<section>): warning: previous common is here
4. Merging a common symbol with a previous larger
common symbol.
I<file>(I<section>): warning: common of `I<symbol>'
overridden by larger common
I<file>(I<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.
I<file>(I<section>): warning: common of `I<symbol>'
overriding smaller common
I<file>(I<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 for
mats 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 con
stants can be loaded efficiently via a base-register
relative addressing mode. Since the offset in base-
register relative mode is fixed and relatively small
(e.g., 16 bits), this limits the maximum size of the
constant pool. Thus, in large programs, it is often
necessary to use multiple global pointer values in
order to be able to address all possible constants.
This option causes a warning to be issued whenever
this case occurs.
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 ref
erence 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 %ld\n", c);
return __real_malloc (c);
}
If you link other code with this file using `--wrap
malloc', then all calls to `malloc' will call the
function `__wrap_malloc' instead. The call to
`__real_malloc' in `__wrap_malloc' will call the real
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 defi
nition 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 out
put `*.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 sym
bols from, to ensure that they get linked in, just like a
normal object file).
In addition to the options common to all targets, the i386
PE linker support additional command line options that are
specific to the i386 PE target. Options that take values
may be separated from their values by either a space or an
equals sign.
`--add-stdcall-alias'
If given, symbols with a stdcall suffix (@nn) will be
exported as-is and also with the suffix stripped.
`--base-file file'
Use file as the name of a file in which to save the
base addresses of all the relocations needed for gen
erating DLLs with dlltool.
`--dll'
Create a DLL instead of a regular executable. You may
also use `-shared' or specify a `LIBRARY' in a given
`.def' file.
`--enable-stdcall-fixup'
If the link finds a symbol that it cannot resolve, it
will attempt to do "fuzzy linking" by looking for
another defined symbol that differs only in the format
of the symbol name (cdecl vs stdcall) and will resolve
that symbol by linking to the match. For example, the
undefined symbol `_foo' might be linked to the func
tion `_foo@12', or the undefined symbol `_bar@16'
might be linked to the function `_bar'. When the
linker does this, it prints a warning, since it nor
mally should have failed to link, but sometimes import
libraries generated from third-party dlls may need
this feature to be usable. If you specify
`--enable-stdcall-fixup', this feature is fully
enabled and warnings are not printed. If you specify
`--disable-stdcall-fixup', this feature is disabled
and such mismatches are considered to be errors.
`--export-all-symbols'
If given, all global symbols in the objects used to
build a DLL will be exported by the DLL. Note that
this is the default if there otherwise wouldn't be any
exported symbols. When symbols are explicitly
exported via DEF files or implicitly exported via
function attributes, the default is to not export any
thing else unless this option is given. Note that the
symbols `DllMain@12', `DllEntryPoint@0', and
`impure_ptr' will not be automatically exported.
`--exclude-symbols symbol,symbol,...'
Specifies a list of symbols which should not be auto
matically exported. The symbol names may be delimited
by commas or colons.
`--file-alignment'
Specify the file alignment. Sections in the file will
always begin at file offsets which are multiples of
this number. This defaults to 512.
`--heap reserve'
`--heap reserve,commit'
Specify the amount of memory to reserve (and option
ally commit) to be used as heap for this program. The
default is 1Mb reserved, 4K committed.
`--image-base value'
Use value as the base address of your program or dll.
This is the lowest memory location that will be used
when your program or dll is loaded. To reduce the
need to relocate and improve performance of your dlls,
each should have a unique base address and not overlap
any other dlls. The default is 0x400000 for executa
bles, and 0x10000000 for dlls.
If given, the stdcall suffixes (@nn) will be stripped
from symbols before they are exported.
`--major-image-version value'
Sets the major number of the "image version".
Defaults to 1.
`--major-os-version value'
Sets the major number of the "os version". Defaults
to 4.
`--major-subsystem-version value'
Sets the major number of the "subsystem version".
Defaults to 4.
`--minor-image-version value'
Sets the minor number of the "image version".
Defaults to 0.
`--minor-os-version value'
Sets the minor number of the "os version". Defaults
to 0.
`--minor-subsystem-version value'
Sets the minor number of the "subsystem version".
Defaults to 0.
`--output-def file'
The linker will create the file file which will con
tain a DEF file corresponding to the DLL the linker is
generating. This DEF file (which should be called
`*.def') may be used to create an import library with
`dlltool' or may be used as a reference to automati
cally or implicitly exported symbols.
`--section-alignment'
Sets the section alignment. Sections in memory will
always begin at addresses which are a multiple of this
number. Defaults to 0x1000.
`--stack reserve'
`--stack reserve,commit'
Specify the amount of memory to reserve (and option
ally commit) to be used as stack for this program.
The default is 32Mb reserved, 4K committed.
`--subsystem which'
`--subsystem which:major'
`--subsystem which:major.minor'
Specifies the subsystem under which your program will
`windows', `console', and `posix'. You may optionally
set the subsystem version also.
ENVIRONMENT
You can change the behavior of `ld' with the environment
variables `GNUTARGET', `LDEMULATION', and `COL
LECT_NO_DEMANGLE'.
`GNUTARGET' determines the input-file object format if you
don't use -b (or its synonym --format). Its value should
be one of the BFD names for an input format. If there is
no `GNUTARGET' in the environment, `ld' uses the natural
format of the target. If `GNUTARGET' is set to `default'
then BFD attempts to discover the input format by examin
ing binary input files; this method often succeeds, but
there are potential ambiguities, since there is no method
of ensuring that the magic number used to specify object-
file formats is unique. However, the configuration proce
dure for BFD on each system places the conventional format
for that system first in the search-list, so ambiguities
are resolved in favor of convention.
`LDEMULATION' determines the default emulation if you
don't use the -m option. The emulation can affect various
aspects of linker behaviour, particularly the default
linker script. You can list the available emulations with
the --verbose or -V options. If the -m option is not
used, and the `LDEMULATION' environment variable is not
defined, the default emulation depends upon how the linker
was configured.
Normally, the linker will default to demangling symbols.
However, if `COLLECT_NO_DEMANGLE' is set in the environ
ment, then it will default to not demangling symbols.
This environment variable is used in a similar fashion by
the `gcc' linker wrapper program. The default may be
overridden by the --demangle and --no-demangle options.
SEE ALSO
ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the
Info entries for binutils and ld.
COPYRIGHT
Copyright (c) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000
Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify
this document under the terms of the GNU Free Documenta
tion License, Version 1.1 or any later version published
by the Free Software Foundation; with no Invariant Sec
tions, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section
entitled "GNU Free Documentation License".
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