GNU Info
(ld.info)Options
Command Line Options
====================
The linker supports a plethora of command-line options, but in actual
practice few of them are used in any particular context. For instance,
a frequent use of `ld' is to link standard Unix object files on a
standard, supported Unix system. On such a system, to link a file
`hello.o':
ld -o OUTPUT /lib/crt0.o hello.o -lc
This tells `ld' to produce a file called OUTPUT as the result of
linking the file `/lib/crt0.o' with `hello.o' and the library `libc.a',
which will come from the standard search directories. (See the
discussion of the `-l' option below.)
Some of the command-line options to `ld' may be specified at any
point in the command line. However, options which refer to files, such
as `-l' or `-T', cause the file to be read at the point at which the
option appears in the command line, relative to the object files and
other file options. Repeating non-file options with a different
argument will either have no further effect, or override prior
occurrences (those further to the left on the command line) of that
option. Options which may be meaningfully specified more than once are
noted in the descriptions below.
Non-option arguments are object files or archives which are to be
linked together. They may follow, precede, or be mixed in with
command-line options, except that an object file argument may not be
placed between an option and its argument.
Usually the linker is invoked with at least one object file, but you
can specify other forms of binary input files using `-l', `-R', and the
script command language. If _no_ binary input files at all are
specified, the linker does not produce any output, and issues the
message `No input files'.
If the linker 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 merely augments the main linker script; use the `-T'
option to replace the default linker script entirely. Note: Scripts.
For options whose names are a single letter, option arguments must
either follow the option letter without intervening whitespace, or be
given as separate arguments immediately following the option that
requires them.
For options whose names are multiple letters, either one dash or two
can precede the option name; for example, `-trace-symbol' and
`--trace-symbol' are equivalent. Note - there is one exception to this
rule. Multiple letter options that start with a lower case 'o' can
only be preceeded by two dashes. This is to reduce confusion with the
`-o' option. So for example `-omagic' sets the output file name to
`magic' whereas `--omagic' sets the NMAGIC flag on the output.
Arguments to multiple-letter options must either be separated from
the option name by an equals sign, or be given as separate arguments
immediately following the option that requires them. For example,
`--trace-symbol foo' and `--trace-symbol=foo' are equivalent. Unique
abbreviations of the names of multiple-letter options are accepted.
Note - if the linker is being invoked indirectly, via a compiler
driver (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
archive-library search path. *Note `ld' and the Intel 960 family:
i960, for details.
Future releases of `ld' may support similar functionality for
other architecture families.
`-b INPUT-FORMAT'
`--format=INPUT-FORMAT'
`ld' may be configured to support more than one kind of object
file. If your `ld' is configured this way, you can use the `-b'
option to specify the binary format for input object files that
follow this option on the command line. Even when `ld' is
configured to support alternative object formats, you don't
usually need to specify this, as `ld' should be configured to
expect as a default input format the most usual format on each
machine. INPUT-FORMAT is a text string, the name of a particular
format supported by the BFD libraries. (You can list the
available binary formats with `objdump -i'.) Note: BFD.
You may want to use this option if you are linking files with an
unusual binary format. You can also use `-b' to switch formats
explicitly (when linking object files of different formats), by
including `-b INPUT-FORMAT' before each group of object files in a
particular format.
The default format is taken from the environment variable
`GNUTARGET'. Note: Environment. You can also define the input
format from a script, using the command `TARGET'; see Note: Format
Commands.
`-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 Note: MRI Compatible Script Files. Introduce
MRI script files with the option `-c'; use the `-T' option to run
linker scripts written in the general-purpose `ld' scripting
language. If MRI-CMDFILE does not exist, `ld' looks for it in the
directories specified by any `-L' options.
`-d'
`-dc'
`-dp'
These three options are equivalent; multiple forms are supported
for compatibility with other linkers. They assign space to common
symbols even if a relocatable output file is specified (with
`-r'). The script command `FORCE_COMMON_ALLOCATION' has the same
effect. Note: Miscellaneous Commands.
`-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). Note: Entry Point, for a discussion of defaults
and other ways of specifying the entry point.
`-E'
`--export-dynamic'
When creating a dynamically linked executable, add all symbols to
the dynamic symbol table. The dynamic symbol table is the set of
symbols which are visible from dynamic objects at run time.
If you do not use this option, the dynamic symbol table will
normally contain only those symbols which are referenced by some
dynamic object mentioned in the link.
If you use `dlopen' to load a dynamic object which needs to refer
back to the symbols defined by the program, rather than some other
dynamic object, then you will probably need to use this option when
linking the program itself.
You can also use the version script to control what symbols should
be added to the dynamic symbol table if the output format supports
it. See the description of `--version-script' in Note: VERSION.
`-EB'
Link big-endian objects. This affects the default output format.
`-EL'
Link little-endian objects. This affects the default output
format.
`-f'
`--auxiliary NAME'
When creating an ELF shared object, set the internal DT_AUXILIARY
field to the specified name. This tells the dynamic linker that
the symbol table of the shared object should be used as an
auxiliary filter on the symbol table of the shared object NAME.
If you later link a program against this filter object, then, when
you run the program, the dynamic linker will see the DT_AUXILIARY
field. If the dynamic linker resolves any symbols from the filter
object, it will first check whether there is a definition in the
shared object NAME. If there is one, it will be used instead of
the definition in the filter object. The shared object NAME need
not exist. Thus the shared object NAME may be used to provide an
alternative implementation of certain functions, perhaps for
debugging or for machine specific performance.
This option may be specified more than once. The DT_AUXILIARY
entries will be created in the order in which they appear on the
command line.
`-F NAME'
`--filter NAME'
When creating an ELF shared object, set the internal DT_FILTER
field to the specified name. This tells the dynamic linker that
the symbol table of the shared object which is being created
should be used as a filter on the symbol table of the shared
object NAME.
If you later link a program against this filter object, then, when
you run the program, the dynamic linker will see the DT_FILTER
field. The dynamic linker will resolve symbols according to the
symbol table of the filter object as usual, but it will actually
link to the definitions found in the shared object NAME. Thus the
filter object can be used to select a subset of the symbols
provided by the object NAME.
Some older linkers used the `-F' option throughout a compilation
toolchain for specifying object-file format for both input and
output object files. The GNU linker uses other mechanisms for this
purpose: the `-b', `--format', `--oformat' options, the `TARGET'
command in linker scripts, and the `GNUTARGET' environment
variable. The GNU linker will ignore the `-F' option when not
creating an ELF shared object.
`-fini NAME'
When creating an ELF executable or shared object, call NAME when
the executable or shared object is unloaded, by setting DT_FINI to
the address of the function. By default, the linker uses `_fini'
as the function to call.
`-g'
Ignored. Provided for compatibility with other tools.
`-GVALUE'
`--gpsize=VALUE'
Set the maximum size of objects to be optimized using the GP
register to SIZE. This is only meaningful for object file formats
such as MIPS ECOFF which supports putting large and small objects
into different sections. This is ignored for other object file
formats.
`-hNAME'
`-soname=NAME'
When creating an ELF shared object, set the internal DT_SONAME
field to the specified name. When an executable is linked with a
shared object which has a DT_SONAME field, then when the
executable is run the dynamic linker will attempt to load the
shared object specified by the DT_SONAME field rather than the
using the file name given to the linker.
`-i'
Perform an incremental link (same as option `-r').
`-init NAME'
When creating an ELF executable or shared object, call NAME when
the executable or shared object is loaded, by setting DT_INIT to
the address of the function. By default, the linker uses `_init'
as the function to call.
`-lARCHIVE'
`--library=ARCHIVE'
Add archive file ARCHIVE to the list of files to link. This
option may be used any number of times. `ld' will search its
path-list for occurrences of `libARCHIVE.a' for every ARCHIVE
specified.
On systems which support shared libraries, `ld' may also search for
libraries with extensions other than `.a'. Specifically, on ELF
and SunOS systems, `ld' will search a directory for a library with
an extension of `.so' before searching for one with an extension of
`.a'. By convention, a `.so' extension indicates a shared library.
The linker will search an archive only once, at the location where
it is specified on the command line. If the archive defines a
symbol which was undefined in some object which appeared before
the archive on the command line, the linker will include the
appropriate file(s) from the archive. However, an undefined
symbol in an object appearing later on the command line will not
cause the linker to search the archive again.
See the `-(' option for a way to force the linker to search
archives multiple times.
You may list the same archive multiple times on the command line.
This type of archive searching is standard for Unix linkers.
However, if you are using `ld' on AIX, note that it is different
from the behaviour of the AIX linker.
`-LSEARCHDIR'
`--library-path=SEARCHDIR'
Add path SEARCHDIR to the list of paths that `ld' will search for
archive libraries and `ld' control scripts. You may use this
option any number of times. The directories are searched in the
order in which they are specified on the command line.
Directories specified on the command line are searched before the
default directories. All `-L' options apply to all `-l' options,
regardless of the order in which the options appear.
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. Note: Environment.
The paths can also be specified in a link script with the
`SEARCH_DIR' command. Directories specified this way are searched
at the point in which the linker script appears in the command
line.
`-mEMULATION'
Emulate the EMULATION linker. You can list the available
emulations with the `--verbose' or `-V' options.
If the `-m' option is not used, the emulation is taken from the
`LDEMULATION' environment variable, if that is defined.
Otherwise, the default emulation depends upon how the linker was
configured.
`-M'
`--print-map'
Print a link map to the standard output. A link map provides
information about the link, including the following:
* 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 page-align 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'
`--emit-relocs'
Leave relocation sections and contents in fully linked
exececutables. Post link analysis and optimization tools may need
this information in order to perform correct modifications of
executables. This results in larger executables.
This option is currently only supported on ELF platforms.
`-r'
`--relocateable'
Generate relocatable output--i.e., generate an output file that
can in turn serve as input to `ld'. This is often called "partial
linking". As a side effect, in environments that support standard
Unix magic numbers, this option also sets the output file's magic
number to `OMAGIC'. If this option is not specified, an absolute
file is produced. When linking C++ programs, this option _will
not_ resolve references to constructors; to do that, use `-Ur'.
When an input file does not have the same format as the output
file, partial linking is only supported if that input file does
not contain any relocations. Different output formats can have
further restrictions; for example some `a.out'-based formats do
not support partial linking with input files in other formats at
all.
This option does the same thing as `-i'.
`-R FILENAME'
`--just-symbols=FILENAME'
Read symbol names and their addresses from FILENAME, but do not
relocate it or include it in the output. This allows your output
file to refer symbolically to absolute locations of memory defined
in other programs. You may use this option more than once.
For compatibility with other ELF linkers, if the `-R' option is
followed by a directory name, rather than a file name, it is
treated as the `-rpath' option.
`-s'
`--strip-all'
Omit all symbol information from the output file.
`-S'
`--strip-debug'
Omit debugger symbol information (but not all symbols) from the
output file.
`-t'
`--trace'
Print the names of the input files as `ld' processes them.
`-T SCRIPTFILE'
`--script=SCRIPTFILE'
Use SCRIPTFILE as the linker script. This script replaces `ld''s
default linker script (rather than adding to it), so COMMANDFILE
must specify everything necessary to describe the output file.
Note: Scripts. 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'
`--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 symbol in your
link but don't know where the reference is coming from.
`-Y PATH'
Add PATH to the default library search path. This option exists
for Solaris compatibility.
`-z KEYWORD'
The recognized keywords are `initfirst', `interpose', `loadfltr',
`nodefaultlib', `nodelete', `nodlopen', `nodump', `now', `origin',
`combreloc', `nocombreloc' and `nocopyreloc'. The other keywords
are ignored for Solaris compatibility. `initfirst' marks the object
to be initialized first at runtime before any other objects.
`interpose' marks the object that its symbol table interposes
before all symbols but the primary executable. `loadfltr' marks
the object that its filtees be processed immediately at runtime.
`nodefaultlib' marks the object that the search for dependencies
of this object will ignore any default library search paths.
`nodelete' marks the object shouldn't be unloaded at runtime.
`nodlopen' marks the object not available to `dlopen'. `nodump'
marks the object can not be dumped by `dldump'. `now' marks the
object with the non-lazy runtime binding. `origin' marks the
object may contain $ORIGIN. `defs' disallows undefined symbols.
`combreloc' combines multiple reloc sections and sorts them to
make dynamic symbol lookup caching possible. `nocombreloc'
disables multiple reloc sections combining. `nocopyreloc'
disables production of copy relocs.
`-( ARCHIVES -)'
`--start-group ARCHIVES --end-group'
The ARCHIVES should be a list of archive files. They may be
either explicit file names, or `-l' options.
The specified archives are searched repeatedly until no new
undefined references are created. Normally, an archive is
searched only once in the order that it is specified on the
command line. If a symbol in that archive is needed to resolve an
undefined symbol referred to by an object in an archive that
appears later on the command line, the linker would not be able to
resolve that reference. By grouping the archives, they all be
searched repeatedly until all possible references are resolved.
Using this option has a significant performance cost. It is best
to use it only when there are unavoidable circular references
between two or more archives.
`-assert KEYWORD'
This option is ignored for SunOS compatibility.
`-Bdynamic'
`-dy'
`-call_shared'
Link against dynamic libraries. This is only meaningful on
platforms for which shared libraries are supported. This option
is normally the default on such platforms. The different variants
of this option are for compatibility with various systems. You
may use this option multiple times on the command line: it affects
library searching for `-l' options which follow it.
`-Bgroup'
Set the `DF_1_GROUP' flag in the `DT_FLAGS_1' entry in the dynamic
section. This causes the runtime linker to handle lookups in this
object and its dependencies to be performed only inside the group.
`--no-undefined' is implied. This option is only meaningful on ELF
platforms which support shared libraries.
`-Bstatic'
`-dn'
`-non_shared'
`-static'
Do not link against shared libraries. This is only meaningful on
platforms for which shared libraries are supported. The different
variants of this option are for compatibility with various
systems. You may use this option multiple times on the command
line: it affects library searching for `-l' options which follow
it.
`-Bsymbolic'
When creating a shared library, bind references to global symbols
to the definition within the shared library, if any. Normally, it
is possible for a program linked against a shared library to
override the definition within the shared library. This option is
only meaningful on ELF platforms which support shared libraries.
`--check-sections'
`--no-check-sections'
Asks the linker _not_ to check section addresses after they have
been assigned to see if there any overlaps. Normally the linker
will perform this check, and if it finds any overlaps it will
produce suitable error messages. The linker does know about, and
does make allowances for sections in overlays. The default
behaviour can be restored by using the command line switch
`--check-sections'.
`--cref'
Output a cross reference table. If a linker map file is being
generated, the cross reference table is printed to the map file.
Otherwise, it is printed on the standard output.
The format of the table is intentionally simple, so that it may be
easily processed by a script if necessary. The symbols are
printed out, sorted by name. For each symbol, a list of file
names is given. If the symbol is defined, the first file listed
is the location of the definition. The remaining files contain
references to the symbol.
`--no-define-common'
This option inhibits the assignment of addresses to common symbols.
The script command `INHIBIT_COMMON_ALLOCATION' has the same effect.
Note: Miscellaneous Commands.
The `--no-define-common' option allows decoupling the decision to
assign addresses to Common symbols from the choice of the output
file type; otherwise a non-Relocatable output type forces
assigning addresses to Common symbols. Using `--no-define-common'
allows Common symbols that are referenced from a shared library to
be assigned addresses only in the main program. This eliminates
the unused duplicate space in the shared library, and also
prevents any possible confusion over resolving to the wrong
duplicate when there are many dynamic modules with specialized
search paths for runtime symbol resolution.
`--defsym SYMBOL=EXPRESSION'
Create a global symbol in the output file, containing the absolute
address given by EXPRESSION. You may use this option as many
times as necessary to define multiple symbols in the command line.
A limited form of arithmetic is supported for the EXPRESSION in
this context: you may give a hexadecimal constant or the name of
an existing symbol, or use `+' and `-' to add or subtract
hexadecimal constants or symbols. If you need more elaborate
expressions, consider using the linker command language from a
script (Note: Assignment.).
_Note:_ there should be no white space between SYMBOL, the equals
sign ("<=>"), and EXPRESSION.
`--demangle[=STYLE]'
`--no-demangle'
These options control whether to demangle symbol names in error
messages and other output. When the linker is told to demangle,
it tries to present symbol names in a readable fashion: it strips
leading underscores if they are used by the object file format,
and converts C++ mangled symbol names into user readable names.
Different compilers have different mangling styles. The optional
demangling style argument can be used to choose an appropriate
demangling style for your compiler. The linker will demangle by
default unless the environment variable `COLLECT_NO_DEMANGLE' is
set. These options may be used to override the default.
`--dynamic-linker FILE'
Set the name of the dynamic linker. This is only meaningful when
generating dynamically linked ELF executables. The default dynamic
linker is normally correct; don't use this unless you know what
you are doing.
`--embedded-relocs'
This option is only meaningful when linking MIPS embedded PIC code,
generated by the -membedded-pic option to the GNU compiler and
assembler. It causes the linker to create a table which may be
used at runtime to relocate any data which was statically
initialized to pointer values. See the code in testsuite/ld-empic
for details.
`--fatal-warnings'
Treat all warnings as errors.
`--force-exe-suffix'
Make sure that an output file has a .exe suffix.
If a successfully built fully linked output file does not have a
`.exe' or `.dll' suffix, this option forces the linker to copy the
output file to one of the same name with a `.exe' suffix. This
option is useful when using unmodified Unix makefiles on a
Microsoft Windows host, since some versions of Windows won't run
an image unless it ends in a `.exe' suffix.
`--no-gc-sections'
`--gc-sections'
Enable garbage collection of unused input sections. It is ignored
on targets that do not support this option. This option is not
compatible with `-r', nor should it be used with dynamic linking.
The default behaviour (of not performing this garbage collection)
can be restored by specifying `--no-gc-sections' on the command
line.
`--help'
Print a summary of the command-line options on the standard output
and exit.
`--target-help'
Print a summary of all target specific options on the standard
output and exit.
`-Map MAPFILE'
Print a link map to the file MAPFILE. See the description of the
`-M' option, above.
`--no-keep-memory'
`ld' normally optimizes for speed over memory usage by caching the
symbol tables of input files in memory. This option tells `ld' to
instead optimize for memory usage, by rereading the symbol tables
as necessary. This may be required if `ld' runs out of memory
space while linking a large executable.
`--no-undefined'
`-z defs'
Normally when creating a non-symbolic shared library, undefined
symbols are allowed and left to be resolved by the runtime loader.
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 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.
`--no-warn-mismatch'
Normally `ld' will give an error if you try to link together input
files that are mismatched for some reason, perhaps because they
have been compiled for different processors or for different
endiannesses. This option tells `ld' that it should silently
permit such possible errors. This option should only be used with
care, in cases when you have taken some special action that
ensures that the linker errors are inappropriate.
`--no-whole-archive'
Turn off the effect of the `--whole-archive' option for subsequent
archive files.
`--noinhibit-exec'
Retain the executable output file whenever it is still usable.
Normally, the linker will not produce an output file if it
encounters errors during the link process; it exits without
writing an output file when it issues any error whatsoever.
`-nostdlib'
Only search library directories explicitly specified on the
command line. Library directories specified in linker scripts
(including linker scripts specified on the command line) are
ignored.
`--oformat OUTPUT-FORMAT'
`ld' may be configured to support more than one kind of object
file. If your `ld' is configured this way, you can use the
`--oformat' option to specify the binary format for the output
object file. Even when `ld' is configured to support alternative
object formats, you don't usually need to specify this, as `ld'
should be configured to produce as a default output format the most
usual format on each machine. OUTPUT-FORMAT is a text string, the
name of a particular format supported by the BFD libraries. (You
can list the available binary formats with `objdump -i'.) The
script command `OUTPUT_FORMAT' can also specify the output format,
but this option overrides it. Note: BFD.
`-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. Note: `ld' and the H8/300.
Note: `ld' and the Intel 960 family.
On some platforms, the `--relax' option performs global
optimizations that become possible when the linker resolves
addressing in the program, such as relaxing address modes and
synthesizing new instructions in the output object file.
On some platforms these link time global optimizations may make
symbolic debugging of the resulting executable impossible. This
is known to be the case for the Matsushita MN10200 and MN10300
family of processors.
On platforms where this is not supported, `--relax' is accepted,
but ignored.
`--retain-symbols-file FILENAME'
Retain _only_ the symbols listed in the file FILENAME, discarding
all others. FILENAME is simply a flat file, with one symbol name
per line. This option is especially useful in environments (such
as VxWorks) where a large global symbol table is accumulated
gradually, to conserve run-time memory.
`--retain-symbols-file' does _not_ discard undefined symbols, or
symbols needed for relocations.
You may only specify `--retain-symbols-file' once in the command
line. It overrides `-s' and `-S'.
`-rpath DIR'
Add a directory to the runtime library search path. This is used
when linking an ELF executable with shared objects. All `-rpath'
arguments are concatenated and passed to the runtime linker, which
uses them to locate shared objects at runtime. The `-rpath'
option is also used when locating shared objects which are needed
by shared objects explicitly included in the link; see the
description of the `-rpath-link' option. If `-rpath' is not used
when linking an ELF executable, the contents of the environment
variable `LD_RUN_PATH' will be used if it is defined.
The `-rpath' option may also be used on SunOS. By default, on
SunOS, the linker will form a runtime search patch out of all the
`-L' options it is given. If a `-rpath' option is used, the
runtime search path will be formed exclusively using the `-rpath'
options, ignoring the `-L' options. This can be useful when using
gcc, which adds many `-L' options which may be on NFS mounted
filesystems.
For compatibility with other ELF linkers, if the `-R' option is
followed by a directory name, rather than a file name, it is
treated as the `-rpath' option.
`-rpath-link DIR'
When using ELF or SunOS, one shared library may require another.
This happens when an `ld -shared' link includes a shared library
as one of the input files.
When the linker encounters such a dependency when doing a
non-shared, non-relocatable link, it will automatically try to
locate the required shared library and include it in the link, if
it is not included explicitly. In such a case, the `-rpath-link'
option specifies the first set of directories to search. The
`-rpath-link' option may specify a sequence of directory names
either by specifying a list of names separated by colons, or by
appearing multiple times.
This option should be used with caution as it overrides the search
path that may have been hard compiled into a shared library. In
such a case it is possible to use unintentionally a different
search path than the runtime linker would do.
The linker uses the following search paths to locate required
shared libraries.
1. Any directories specified by `-rpath-link' options.
2. Any directories specified by `-rpath' options. The difference
between `-rpath' and `-rpath-link' is that directories
specified by `-rpath' options are included in the executable
and used at runtime, whereas the `-rpath-link' option is only
effective at link time. It is for the native linker only.
3. On an ELF system, if the `-rpath' and `rpath-link' options
were not used, search the contents of the environment variable
`LD_RUN_PATH'. It is for the native linker only.
4. On SunOS, if the `-rpath' option was not used, search any
directories specified using `-L' options.
5. For a native linker, the contents of the environment variable
`LD_LIBRARY_PATH'.
6. For a native ELF linker, the directories in `DT_RUNPATH' or
`DT_RPATH' of a shared library are searched for shared
libraries needed by it. The `DT_RPATH' entries are ignored if
`DT_RUNPATH' entries exist.
7. The default directories, normally `/lib' and `/usr/lib'.
8. For a native linker on an ELF system, if the file
`/etc/ld.so.conf' exists, the list of directories found in
that file.
If the required shared library is not found, the linker will issue
a warning and continue with the link.
`-shared'
`-Bshareable'
Create a shared library. This is currently only supported on ELF,
XCOFF and SunOS platforms. On SunOS, the linker will
automatically create a shared library if the `-e' option is not
used and there are undefined symbols in the link.
`--sort-common'
This option tells `ld' to sort the common symbols by size when it
places them in the appropriate output sections. First come all
the one byte symbols, then all the two byte, then all the four
byte, and then everything else. This is to prevent gaps between
symbols due to alignment constraints.
`--split-by-file [SIZE]'
Similar to `--split-by-reloc' but creates a new output section for
each input file when SIZE is reached. SIZE defaults to a size of
1 if not given.
`--split-by-reloc [COUNT]'
Tries to creates extra sections in the output file so that no
single output section in the file contains more than COUNT
relocations. This is useful when generating huge relocatable
files for downloading into certain real time kernels with the COFF
object file format; since COFF cannot represent more than 65535
relocations in a single section. Note that this will fail to work
with object file formats which do not support arbitrary sections.
The linker will not split up individual input sections for
redistribution, so if a single input section contains more than
COUNT relocations one output section will contain that many
relocations. COUNT defaults to a value of 32768.
`--stats'
Compute and display statistics about the operation of the linker,
such as execution time and memory usage.
`--traditional-format'
For some targets, the output of `ld' is different in some ways from
the output of some existing linker. This switch requests `ld' to
use the traditional format instead.
For example, on SunOS, `ld' combines duplicate entries in the
symbol string table. This can reduce the size of an output file
with full debugging information by over 30 percent.
Unfortunately, the SunOS `dbx' program can not read the resulting
program (`gdb' has no trouble). The `--traditional-format' switch
tells `ld' to not combine duplicate entries.
`--section-start SECTIONNAME=ORG'
Locate a section in the output file at the absolute address given
by ORG. You may use this option as many times as necessary to
locate multiple sections in the command line. ORG must be a
single hexadecimal integer; for compatibility with other linkers,
you may omit the leading `0x' usually associated with hexadecimal
values. _Note:_ there should be no white space between
SECTIONNAME, the equals sign ("<=>"), and ORG.
`-Tbss ORG'
`-Tdata ORG'
`-Ttext ORG'
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.
`--dll-verbose'
`--verbose'
Display the version number for `ld' and list the linker emulations
supported. Display which input files can and cannot be opened.
Display the linker script being used by the linker.
`--version-script=VERSION-SCRIPTFILE'
Specify the name of a version script to the linker. This is
typically used when creating shared libraries to specify
additional information about the version heirarchy for the library
being created. This option is only meaningful on ELF platforms
which support shared libraries. Note: VERSION.
`--warn-common'
Warn when a common symbol is combined with another common symbol
or with a symbol definition. Unix linkers allow this somewhat
sloppy practice, but linkers on some other operating systems do
not. This option allows you to find potential problems from
combining global symbols. Unfortunately, some C libraries use
this practice, so you may get some warnings about symbols in the
libraries as well as in your programs.
There are three kinds of global symbols, illustrated here by C
examples:
`int i = 1;'
A definition, which goes in the initialized data section of
the output file.
`extern int i;'
An undefined reference, which does not allocate space. There
must be either a definition or a common symbol for the
variable somewhere.
`int i;'
A common symbol. If there are only (one or more) common
symbols for a variable, it goes in the uninitialized data
area of the output file. The linker merges multiple common
symbols for the same variable into a single symbol. If they
are of different sizes, it picks the largest size. The
linker turns a common symbol into a declaration, if there is
a definition of the same variable.
The `--warn-common' option can produce five kinds of warnings.
Each warning consists of a pair of lines: the first describes the
symbol just encountered, and the second describes the previous
symbol encountered with the same name. One or both of the two
symbols will be a common symbol.
1. Turning a common symbol into a reference, because there is
already a definition for the symbol.
FILE(SECTION): warning: common of `SYMBOL'
overridden by definition
FILE(SECTION): warning: defined here
2. Turning a common symbol into a reference, because a later
definition for the symbol is encountered. This is the same
as the previous case, except that the symbols are encountered
in a different order.
FILE(SECTION): warning: definition of `SYMBOL'
overriding common
FILE(SECTION): warning: common is here
3. Merging a common symbol with a previous same-sized common
symbol.
FILE(SECTION): warning: multiple common
of `SYMBOL'
FILE(SECTION): warning: previous common is here
4. Merging a common symbol with a previous larger common symbol.
FILE(SECTION): warning: common of `SYMBOL'
overridden by larger common
FILE(SECTION): warning: larger common is here
5. Merging a common symbol with a previous smaller common
symbol. This is the same as the previous case, except that
the symbols are encountered in a different order.
FILE(SECTION): warning: common of `SYMBOL'
overriding smaller common
FILE(SECTION): warning: smaller common is here
`--warn-constructors'
Warn if any global constructors are used. This is only useful for
a few object file formats. For formats like COFF or ELF, the
linker can not detect the use of global constructors.
`--warn-multiple-gp'
Warn if multiple global pointer values are required in the output
file. This is only meaningful for certain processors, such as the
Alpha. Specifically, some processors put large-valued constants
in a special section. A special register (the global pointer)
points into the middle of this section, so that constants can be
loaded efficiently via a base-register relative addressing mode.
Since the offset in 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.
`--warn-once'
Only warn once for each undefined symbol, rather than once per
module which refers to it.
`--warn-section-align'
Warn if the address of an output section is changed because of
alignment. Typically, the alignment will be set by an input
section. The address will only be changed if it not explicitly
specified; that is, if the `SECTIONS' command does not specify a
start address for the section (Note: SECTIONS).
`--whole-archive'
For each archive mentioned on the command line after the
`--whole-archive' option, include every object file in the archive
in the link, rather than searching the archive for the required
object files. This is normally used to turn an archive file into
a shared library, forcing every object to be included in the
resulting shared library. This option may be used more than once.
Two notes when using this option from gcc: First, gcc doesn't know
about this option, so you have to use `-Wl,-whole-archive'.
Second, don't forget to use `-Wl,-no-whole-archive' after your
list of archives, because gcc will add its own list of archives to
your link and you may not want this flag to affect those as well.
`--wrap SYMBOL'
Use a wrapper function for SYMBOL. Any undefined reference to
SYMBOL will be resolved to `__wrap_SYMBOL'. Any undefined
reference to `__real_SYMBOL' will be resolved to SYMBOL.
This can be used to provide a wrapper for a system function. The
wrapper function should be called `__wrap_SYMBOL'. If it wishes
to call the system function, it should call `__real_SYMBOL'.
Here is a trivial example:
void *
__wrap_malloc (int c)
{
printf ("malloc called with %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 `malloc' function.
You may wish to provide a `__real_malloc' function as well, so that
links without the `--wrap' option will succeed. If you do this,
you should not put the definition of `__real_malloc' in the same
file as `__wrap_malloc'; if you do, the assembler may resolve the
call before the linker has a chance to wrap it to `malloc'.
`--enable-new-dtags'
`--disable-new-dtags'
This linker can create the new dynamic tags in ELF. But the older
ELF systems may not understand them. If you specify
`--enable-new-dtags', the dynamic tags will be created as needed.
If you specify `--disable-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.
Options specific to i386 PE targets
-----------------------------------
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.
`--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 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.
`--enable-stdcall-fixup'
`--disable-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
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 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 anything else
unless this option is given. Note that the symbols `DllMain@12',
`DllEntryPoint@0', `DllMainCRTStartup@12', and `impure_ptr' will
not be automatically exported. Also, symbols imported from other
DLLs will not be re-exported, nor will symbols specifying the
DLL's internal layout such as those beginning with `_head_' or
ending with `_iname'. In addition, no symbols from `libgcc',
`libstd++', `libmingw32', or `crtX.o' will be exported. Symbols
whose names begin with `__rtti_' or `__builtin_' will not be
exported, to help with C++ DLLs. Finally, there is an extensive
list of cygwin-private symbols that are not exported (obviously,
this applies on when building DLLs for cygwin targets). These
cygwin-excludes are: `_cygwin_dll_entry@12',
`_cygwin_crt0_common@8', `_cygwin_noncygwin_dll_entry@12',
`_fmode', `_impure_ptr', `cygwin_attach_dll', `cygwin_premain0',
`cygwin_premain1', `cygwin_premain2', `cygwin_premain3', and
`environ'.
`--exclude-symbols SYMBOL,SYMBOL,...'
Specifies a list of symbols which should not be automatically
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 optionally 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 executables,
and 0x10000000 for dlls.
`--kill-at'
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 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.
`--out-implib FILE'
The linker will create the file FILE which will contain an import
lib corresponding to the DLL the linker is generating. This import
lib (which should be called `*.dll.a' or `*.a' may be used to link
clients against the generated DLL; this behavior makes it possible
to skip a separate `dlltool' import library creation step.
`--enable-auto-image-base'
Automatically choose the image base for DLLs, unless one is
specified using the `--image-base' argument. By using a hash
generated from the dllname to create unique image bases for each
DLL, in-memory collisions and relocations which can delay program
execution are avoided.
`--disable-auto-image-base'
Do not automatically generate a unique image base. If there is no
user-specified image base (`--image-base') then use the platform
default.
`--dll-search-prefix STRING'
When linking dynamically to a dll without an import library, i
search for `<string><basename>.dll' in preference to
`lib<basename>.dll'. This behavior allows easy distinction between
DLLs built for the various "subplatforms": native, cygwin, uwin,
pw, etc. For instance, cygwin DLLs typically use
`--dll-search-prefix=cyg'.
`--enable-auto-import'
Do sophisticated linking of `_symbol' to `__imp__symbol' for DATA
imports from DLLs, and create the necessary thunking symbols when
building the DLLs with those DATA exports. This generally will
'just work' - but sometimes you may see this message:
"variable '<var>' can't be auto-imported. Please read the
documentation for ld's `--enable-auto-import' for details."
This message occurs when some (sub)expression accesses an address
ultimately given by the sum of two constants (Win32 import tables
only allow one). Instances where this may occur include accesses
to member fields of struct variables imported from a DLL, as well
as using a constant index into an array variable imported from a
DLL. Any multiword variable (arrays, structs, long long, etc) may
trigger this error condition. However, regardless of the exact
data type of the offending exported variable, ld will always
detect it, issue the warning, and exit.
There are several ways to address this difficulty, regardless of
the data type of the exported variable:
One solution is to force one of the 'constants' to be a variable -
that is, unknown and un-optimizable at compile time. For arrays,
there are two possibilities: a) make the indexee (the array's
address) a variable, or b) make the 'constant' index a variable.
Thus:
extern type extern_array[];
extern_array[1] -->
{ volatile type *t=extern_array; t[1] }
or
extern type extern_array[];
extern_array[1] -->
{ volatile int t=1; extern_array[t] }
For structs (and most other multiword data types) the only option
is to make the struct itself (or the long long, or the ...)
variable:
extern struct s extern_struct;
extern_struct.field -->
{ volatile struct s *t=&extern_struct; t->field }
or
extern long long extern_ll;
extern_ll -->
{ volatile long long * local_ll=&extern_ll; *local_ll }
A second method of dealing with this difficulty is to abandon
'auto-import' for the offending symbol and mark it with
`__declspec(dllimport)'. However, in practice that requires using
compile-time #defines to indicate whether you are building a DLL,
building client code that will link to the DLL, or merely
building/linking to a static library. In making the choice
between the various methods of resolving the 'direct address with
constant offset' problem, you should consider typical real-world
usage:
Original:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d\n",arr[1]);
}
Solution 1:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
/* This workaround is for win32 and cygwin; do not "optimize" */
volatile int *parr = arr;
printf("%d\n",parr[1]);
}
Solution 2:
--foo.h
/* Note: auto-export is assumed (no __declspec(dllexport)) */
#if (defined(_WIN32) || defined(__CYGWIN__)) && \
!(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
#define FOO_IMPORT __declspec(dllimport)
#else
#define FOO_IMPORT
#endif
extern FOO_IMPORT int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d\n",arr[1]);
}
A third way to avoid this problem is to re-code your library to
use a functional interface rather than a data interface for the
offending variables (e.g. set_foo() and get_foo() accessor
functions).
`--disable-auto-import'
Do not attempt to do sophisticalted linking of `_symbol' to
`__imp__symbol' for DATA imports from DLLs.
`--enable-extra-pe-debug'
Show additional debug info related to auto-import symbol thunking.
`--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 optionally commit) to
be used as stack for this program. The default is 2Mb 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.
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