NAME
ld - Using LD, the GNU linker
SYNOPSIS
ld [ options ] objfile...
DESCRIPTION
ld combines a number of object and archive files, relocates their data and ties up symbol
references. Usually the last step in compiling a program is to run ld.
ld accepts Linker Command Language files written in a superset of AT&T's Link Editor
Command Language syntax, to provide explicit and total control over the linking process.
This man page does not describe the command language; see the ld entry in info, 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.
OPTIONS
The linker supports a plethora of commandline 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 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 standard search
directories. (See the discussion of the -l option below.)
Some of the commandline 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 nonfile 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.
Nonoption arguments are object files or archives which are to be linked together. They may
follow, precede, or be mixed in with commandline 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 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, -tracesymbol and tracesymbol 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 multipleletter 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, tracesymbol foo and tracesymbol=foo are equivalent. Unique
abbreviations of the names of multipleletter 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 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 inputformat
format=inputformat
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. inputformat is
a text string, the name of a particular format supported by the BFD libraries. (You can list
the available binary formats with objdump -i.)
You may want to use this option if you are linking files with an unusual binary format.
You can also use -b to switch formats explicitly (when linking object files of different
formats), by including -b inputformat 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 MRIcommandfile
mriscript=MRIcommandfile
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 generalpurpose ld scripting language. If
MRIcmdfile 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
exportdynamic
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.
-EB
Link bigendian objects. This affects the default output format.
-EL
Link littleendian 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
objectfile 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 pathlist 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
librarypath=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.
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
printmap
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 output as NMAGIC if possible.
-N
omagic
Set the text and data sections to be readable and writable. Also, do not pagealign the
data segment. If the output format supports Unix style magic numbers, 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
emitrelocs
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 constructors; to do that,
use -Ur.
This option does the same thing as -i.
-R filename
justsymbols=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
stripall
Omit all symbol information from the output file.
-S
stripdebug
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 SECTIONS 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, 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
discardall
Delete all local symbols.
-X
discardlocals
Delete all temporary local symbols. For most targets, this is all local symbols whose
names begin with L.
-y symbol
tracesymbol=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 and origin. 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 nonlazy runtime binding.
origin marks the object may contain $ORIGIN. defs disallows undefined
symbols.
-( archives -)
startgroup archives endgroup
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 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. noundefined 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.
checksections
nochecksections
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 checksections.
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.
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]
nodemangle
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.
dynamiclinker 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.
embeddedrelocs
This option is only meaningful when linking MIPS embedded PIC code, generated by the
-membeddedpic 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/ldempic for details.
forceexesuffix
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.
nogcsections
gcsections
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 nogcsections on the command line.
help
Print a summary of the commandline options on the standard output and exit.
targethelp
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.
nokeepmemory
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.
noundefined
-z defs
Normally when creating a nonsymbolic shared library, undefined symbols are allowed
and left to be resolved by the runtime loader. These options disallow such undefined
symbols.
allowshlibundefined
Allow undefined symbols in shared objects even when --noundefined is set. The net
result will be that undefined symbols in regular objects will still trigger an error, but
undefined symbols in shared 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. dynamically select an
appropriate memset function. Apparently it is also normal for HPPA shared libraries to
have undefined symbols.
nowarnmismatch
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.
nowholearchive
Turn off the effect of the wholearchive option for subsequent archive files.
noinhibitexec
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.
oformat outputformat
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. outputformat 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.
retainsymbolsfile 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 runtime memory.
retainsymbolsfile does not discard undefined symbols, or symbols needed for
relocations.
You may only specify retainsymbolsfile 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 -rpathlink 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.
-rpathlink 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 nonshared,
nonrelocatable 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 -rpathlink option
specifies the first set of directories to search. The -rpathlink 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 -rpathlink options.
2. Any directories specified by -rpath options. The difference between -rpath and
-rpathlink is that directories specified by -rpath options are included in the
executable and used at runtime, whereas the -rpathlink 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.
sortcommon
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
symbols due to alignment constraints.
splitbyfile [size]
Similar to splitbyreloc but creates a new output section for each input file when size
is reached. size defaults to a size of 1 if not given.
splitbyreloc [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.
traditionalformat
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 traditionalformat switch tells ld to not combine duplicate entries.
sectionstart 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
Use org as the starting address for---respectively---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 hexadecimal
values.
dllverbose
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.
versionscript=versionscriptfile
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
shared libraries.
warncommon
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 warncommon 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.
I<file>(I<section>): warning: definition of `I<symbol>'
overriding common
I<file>(I<section>): warning: common is here
3. Merging a common symbol with a previous samesized 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
warnconstructors
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.
warnmultiplegp
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
largevalued 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
baseregister 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.
warnonce
Only warn once for each undefined symbol, rather than once per module which refers to
it.
warnsectionalign
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.
wholearchive
For each archive mentioned on the command line after the wholearchive 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,-wholearchive. Second, don't forget to use
-Wl,-nowholearchive 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 %ldn", 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.
enablenewdtags
disablenewdtags
This linker can create the new dynamic tags in ELF. But the older ELF systems may not
understand them. If you specify enablenewdtags, the dynamic tags will be created as
needed. If you specify disablenewdtags, 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.
addstdcallalias
If given, symbols with a stdcall suffix (@nn) will be exported asis and also with the suffix
stripped.
basefile file
Use file as the name of a file in which to save the base addresses of all the relocations
needed for generating DLLs with dlltool.
dll
Create a DLL instead of a regular executable. You may also use -shared or specify a
LIBRARY in a given .def file.
enablestdcallfixup
disablestdcallfixup
If the link finds a symbol that it cannot resolve, it will attempt to do ``fuzzy linking'' by
looking for another defined symbol that differs only in the format of the symbol name
(cdecl vs stdcall) and will resolve that symbol by linking to the match. For example, the
undefined symbol _foo might be linked to the function _foo@12, or the undefined
symbol _bar@16 might be linked to the function _bar. When the linker does this, it
prints a warning, since it normally should have failed to link, but sometimes import
libraries generated from thirdparty dlls may need this feature to be usable. If you specify
enablestdcallfixup, this feature is fully enabled and warnings are not printed. If you
specify disablestdcallfixup, this feature is disabled and such mismatches are
considered to be errors.
exportallsymbols
If given, all global symbols in the objects used to build a DLL will be exported by the DLL.
Note that this is the default if there otherwise wouldn't be any exported symbols. When
symbols are explicitly exported via DEF files or implicitly exported via function attributes,
the default is to not export anything else unless this option is given. Note that the symbols
DllMain@12, DllEntryPoint@0, and impure_ptr will not be automatically
exported.
excludesymbols symbol,symbol,...
Specifies a list of symbols which should not be automatically exported. The symbol
names may be delimited by commas or colons.
filealignment
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 optionally commit) to be used as heap for
this program. The default is 1Mb reserved, 4K committed.
imagebase value
Use value as the base address of your program or dll. This is the lowest memory location
that will be used when your program or dll is loaded. To reduce the need to relocate and
improve performance of your dlls, each should have a unique base address and not
overlap any other dlls. The default is 0x400000 for executables, and 0x10000000 for dlls.
killat
If given, the stdcall suffixes (@nn) will be stripped from symbols before they are
exported.
majorimageversion value
Sets the major number of the ``image version''. Defaults to 1.
majorosversion value
Sets the major number of the ``os version''. Defaults to 4.
majorsubsystemversion value
Sets the major number of the ``subsystem version''. Defaults to 4.
minorimageversion value
Sets the minor number of the ``image version''. Defaults to 0.
minorosversion value
Sets the minor number of the ``os version''. Defaults to 0.
minorsubsystemversion value
Sets the minor number of the ``subsystem version''. Defaults to 0.
outputdef file
The linker will create the file file which will contain a DEF file corresponding to the DLL
the linker is generating. This DEF file (which should be called *.def) may be used to
create an import library with dlltool or may be used as a reference to automatically
or implicitly exported symbols.
sectionalignment
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 optionally 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 execute. The legal values for
which are native, 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 COLLECT_NO_DEMANGLE.
GNUTARGET determines the inputfile object format if you don't use -b (or its synonym
format). Its value should be one of the BFD names for an input format. If there is no
GNUTARGET in the environment, ld uses the natural format of the target. If GNUTARGET is
set to default then BFD attempts to discover the input format by examining binary input
files; this method often succeeds, but there are potential ambiguities, since there is no method
of ensuring that the magic number used to specify objectfile formats is unique. However,
the configuration procedure for BFD on each system places the conventional format for that
system first in the searchlist, so ambiguities are resolved in favor of convention.
LDEMULATION determines the default emulation if you don't use the -m option. The
emulation can affect various aspects of linker behaviour, particularly the default linker script.
You can list the available emulations with the verbose or -V options. If the -m option is
not used, and the LDEMULATION environment variable is not defined, the default emulation
depends upon how the linker was configured.
Normally, the linker will default to demangling symbols. However, if
COLLECT_NO_DEMANGLE is set in the environment, then it will default to not demangling
symbols. This environment variable is used in a similar fashion by the gcc linker wrapper
program. The default may be overridden by the demangle and nodemangle 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 Documentation License, Version 1.1 or any later version published by the Free
Software Foundation; with no Invariant Sections, with no FrontCover Texts, and with no
BackCover Texts. A copy of the license is included in the section entitled ``GNU Free
Documentation License''.