ld.info: Options
2.1 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 cannot recognize the format of an object file, it will
assume that it is a linker script. A script specified in this way
augments the main linker script used for the link (either the default
linker script or the one specified by using '-T'). This feature permits
the linker to link against a file which appears to be an object or an
archive, but actually merely defines some symbol values, or uses 'INPUT'
or 'GROUP' to load other objects. Specifying a script in this way
merely augments the main linker script, with the extra commands placed
after the main script; use the '-T' option to replace the default linker
script entirely, but note the effect of the 'INSERT' command. 
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 preceded by two dashes. This is to reduce confusion with the '-o'
option. So for example '-omagic' sets the output file name to 'magic'
whereas '--omagic' sets the NMAGIC flag on the output.
Arguments to multiple-letter options must either be separated from
the option name by an equals sign, or be given as separate arguments
immediately following the option that requires them. For example,
'--trace-symbol foo' and '--trace-symbol=foo' are equivalent. Unique
abbreviations of the names of multiple-letter options are accepted.
Note--if the linker is being invoked indirectly, via a compiler
driver (e.g. 'gcc') then all the linker command-line options should be
prefixed by '-Wl,' (or whatever is appropriate for the particular
compiler driver) like this:
gcc -Wl,--start-group foo.o bar.o -Wl,--end-group
This is important, because otherwise the compiler driver program may
silently drop the linker options, resulting in a bad link. Confusion
may also arise when passing options that require values through a
driver, as the use of a space between option and argument acts as a
separator, and causes the driver to pass only the option to the linker
and the argument to the compiler. In this case, it is simplest to use
the joined forms of both single- and multiple-letter options, such as:
gcc foo.o bar.o -Wl,-eENTRY -Wl,-Map=a.map
Here is a table of the generic command-line switches accepted by the
GNU linker:
'@FILE'
Read command-line options from FILE. The options read are inserted
in place of the original @FILE option. If FILE does not exist, or
cannot be read, then the option will be treated literally, and not
removed.
Options in FILE are separated by whitespace. A whitespace
character may be included in an option by surrounding the entire
option in either single or double quotes. Any character (including
a backslash) may be included by prefixing the character to be
included with a backslash. The FILE may itself contain additional
@FILE options; any such options will be processed recursively.
'-a KEYWORD'
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.
'--audit AUDITLIB'
Adds AUDITLIB to the 'DT_AUDIT' entry of the dynamic section.
AUDITLIB is not checked for existence, nor will it use the
DT_SONAME specified in the library. If specified multiple times
'DT_AUDIT' will contain a colon separated list of audit interfaces
to use. If the linker finds an object with an audit entry while
searching for shared libraries, it will add a corresponding
'DT_DEPAUDIT' entry in the output file. This option is only
meaningful on ELF platforms supporting the rtld-audit interface.
'-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'.) 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'. Environment. You can also define the input
format from a script, using the command 'TARGET'; see 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 MRI Compatible Script Files MRI. 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.
Miscellaneous Commands.
'--depaudit AUDITLIB'
'-P AUDITLIB'
Adds AUDITLIB to the 'DT_DEPAUDIT' entry of the dynamic section.
AUDITLIB is not checked for existence, nor will it use the
DT_SONAME specified in the library. If specified multiple times
'DT_DEPAUDIT' will contain a colon separated list of audit
interfaces to use. This option is only meaningful on ELF platforms
supporting the rtld-audit interface. The -P option is provided for
Solaris compatibility.
'-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). Entry Point, for a discussion of defaults
and other ways of specifying the entry point.
'--exclude-libs LIB,LIB,...'
Specifies a list of archive libraries from which symbols should not
be automatically exported. The library names may be delimited by
commas or colons. Specifying '--exclude-libs ALL' excludes symbols
in all archive libraries from automatic export. This option is
available only for the i386 PE targeted port of the linker and for
ELF targeted ports. For i386 PE, symbols explicitly listed in a
.def file are still exported, regardless of this option. For ELF
targeted ports, symbols affected by this option will be treated as
hidden.
'--exclude-modules-for-implib MODULE,MODULE,...'
Specifies a list of object files or archive members, from which
symbols should not be automatically exported, but which should be
copied wholesale into the import library being generated during the
link. The module names may be delimited by commas or colons, and
must match exactly the filenames used by 'ld' to open the files;
for archive members, this is simply the member name, but for object
files the name listed must include and match precisely any path
used to specify the input file on the linker's command-line. This
option is available only for the i386 PE targeted port of the
linker. Symbols explicitly listed in a .def file are still
exported, regardless of this option.
'-E'
'--export-dynamic'
'--no-export-dynamic'
When creating a dynamically linked executable, using the '-E'
option or the '--export-dynamic' option causes the linker to 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 either of these options (or use the
'--no-export-dynamic' option to restore the default behavior), 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 dynamic list to control what symbols should be
added to the dynamic symbol table if the output format supports it.
See the description of '--dynamic-list'.
Note that this option is specific to ELF targeted ports. PE
targets support a similar function to export all symbols from a DLL
or EXE; see the description of '--export-all-symbols' below.
'-EB'
Link big-endian objects. This affects the default output format.
'-EL'
Link little-endian objects. This affects the default output
format.
'-f NAME'
'--auxiliary=NAME'
When creating an ELF shared object, set the internal DT_AUXILIARY
field to the specified name. This tells the dynamic linker that
the symbol table of the shared object should be used as an
auxiliary filter on the symbol table of the shared object NAME.
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.
'-G VALUE'
'--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 ELF that support putting large and small objects into
different sections. This is ignored for other object file formats.
'-h NAME'
'-soname=NAME'
When creating an ELF shared object, set the internal DT_SONAME
field to the specified name. When an executable is linked with a
shared object 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.
'-l NAMESPEC'
'--library=NAMESPEC'
Add the archive or object file specified by NAMESPEC to the list of
files to link. This option may be used any number of times. If
NAMESPEC is of the form ':FILENAME', 'ld' will search the library
path for a file called FILENAME, otherwise it will search the
library path for a file called 'libNAMESPEC.a'.
On systems which support shared libraries, 'ld' may also search for
files other than 'libNAMESPEC.a'. Specifically, on ELF and SunOS
systems, 'ld' will search a directory for a library called
'libNAMESPEC.so' before searching for one called 'libNAMESPEC.a'.
(By convention, a '.so' extension indicates a shared library.)
Note that this behavior does not apply to ':FILENAME', which always
specifies a file called FILENAME.
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.
'-L SEARCHDIR'
'--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. '-L' options
do not affect how 'ld' searches for a linker script unless '-T'
option is specified.
If SEARCHDIR begins with '=' or '$SYSROOT', then this prefix will
be replaced by the "sysroot prefix", controlled by the '--sysroot'
option, or specified when the linker is configured.
The default set of paths searched (without being specified with
'-L') depends on which emulation mode 'ld' is using, and in some
cases also on how it was configured. 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.
'-m EMULATION'
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 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.
* The values assigned to symbols.
Note - symbols whose values are computed by an expression
which involves a reference to a previous value of the same
symbol may not have correct result displayed in the link map.
This is because the linker discards intermediate results and
only retains the final value of an expression. Under such
circumstances the linker will display the final value enclosed
by square brackets. Thus for example a linker script
containing:
foo = 1
foo = foo * 4
foo = foo + 8
will produce the following output in the link map if the '-M'
option is used:
0x00000001 foo = 0x1
[0x0000000c] foo = (foo * 0x4)
[0x0000000c] foo = (foo + 0x8)
See Expressions for more information about expressions
in linker scripts.
* How GNU properties are merged.
When linker merges input .note.gnu.property sections into one
output .note.gnu.property section, some properties are removed
or updated, which are reported in the link map as
Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
It indicates that property 0xc0000002 is removed from output
when merging properties in 'foo.o', whose property 0xc0000002
value is 0x1, and 'bar.o', which doesn't have property
0xc0000002.
Updated property 0xc0000002 (0x1) to merge foo.o (0x1) and bar.o (0x1)
It indicates that property 0xc0010001 value is updated to 0x1
in output when merging properties in 'foo.o', whose 0xc0010001
property value is 0x1, and 'bar.o', whose 0xc0010001 property
value is 0x1.
'-n'
'--nmagic'
Turn off page alignment of sections, and disable linking against
shared libraries. If the output format supports Unix style magic
numbers, mark the output as 'NMAGIC'.
'-N'
'--omagic'
Set the text and data sections to be readable and writable. Also,
do not page-align the data segment, and disable linking against
shared libraries. If the output format supports Unix style magic
numbers, mark the output as 'OMAGIC'. Note: Although a writable
text section is allowed for PE-COFF targets, it does not conform to
the format specification published by Microsoft.
'--no-omagic'
This option negates most of the effects of the '-N' option. It
sets the text section to be read-only, and forces the data segment
to be page-aligned. Note - this option does not enable linking
against shared libraries. Use '-Bdynamic' for this.
'-o OUTPUT'
'--output=OUTPUT'
Use OUTPUT as the name for the program produced by 'ld'; if this
option is not specified, the name 'a.out' is used by default. The
script command 'OUTPUT' can also specify the output file name.
'-O LEVEL'
If LEVEL is a numeric values greater than zero 'ld' optimizes the
output. This might take significantly longer and therefore
probably should only be enabled for the final binary. At the
moment this option only affects ELF shared library generation.
Future releases of the linker may make more use of this option.
Also currently there is no difference in the linker's behaviour for
different non-zero values of this option. Again this may change
with future releases.
'-plugin NAME'
Involve a plugin in the linking process. The NAME parameter is the
absolute filename of the plugin. Usually this parameter is
automatically added by the complier, when using link time
optimization, but users can also add their own plugins if they so
wish.
Note that the location of the compiler originated plugins is
different from the place where the 'ar', 'nm' and 'ranlib' programs
search for their plugins. In order for those commands to make use
of a compiler based plugin it must first be copied into the
'${libdir}/bfd-plugins' directory. All gcc based linker plugins
are backward compatible, so it is sufficient to just copy in the
newest one.
'--push-state'
The '--push-state' allows to preserve the current state of the
flags which govern the input file handling so that they can all be
restored with one corresponding '--pop-state' option.
The option which are covered are: '-Bdynamic', '-Bstatic', '-dn',
'-dy', '-call_shared', '-non_shared', '-static', '-N', '-n',
'--whole-archive', '--no-whole-archive', '-r', '-Ur',
'--copy-dt-needed-entries', '--no-copy-dt-needed-entries',
'--as-needed', '--no-as-needed', and '-a'.
One target for this option are specifications for 'pkg-config'.
When used with the '--libs' option all possibly needed libraries
are listed and then possibly linked with all the time. It is
better to return something as follows:
-Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
'--pop-state'
Undoes the effect of -push-state, restores the previous values of
the flags governing input file handling.
'-q'
'--emit-relocs'
Leave relocation sections and contents in fully linked executables.
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.
'--force-dynamic'
Force the output file to have dynamic sections. This option is
specific to VxWorks targets.
'-r'
'--relocatable'
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.
'--strip-discarded'
'--no-strip-discarded'
Omit (or do not omit) global symbols defined in discarded sections.
Enabled by default.
'-t'
'--trace'
Print the names of the input files as 'ld' processes them. If '-t'
is given twice then members within archives are also printed. '-t'
output is useful to generate a list of all the object files and
scripts involved in linking, for example, when packaging files for
a linker bug report.
'-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.
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.
'-dT SCRIPTFILE'
'--default-script=SCRIPTFILE'
Use SCRIPTFILE as the default linker script. Scripts.
This option is similar to the '--script' option except that
processing of the script is delayed until after the rest of the
command line has been processed. This allows options placed after
the '--default-script' option on the command line to affect the
behaviour of the linker script, which can be important when the
linker command line cannot be directly controlled by the user. (eg
because the command line is being constructed by another tool, such
as 'gcc').
'-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.
If this option is being used to force additional modules to be
pulled into the link, and if it is an error for the symbol to
remain undefined, then the option '--require-defined' should be
used instead.
'--require-defined=SYMBOL'
Require that SYMBOL is defined in the output file. This option is
the same as option '--undefined' except that if SYMBOL is not
defined in the output file then the linker will issue an error and
exit. The same effect can be achieved in a linker script by using
'EXTERN', 'ASSERT' and 'DEFINED' together. This option can be used
multiple times to require additional symbols.
'-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.
'--orphan-handling=MODE'
Control how orphan sections are handled. An orphan section is one
not specifically mentioned in a linker script. Orphan
Sections.
MODE can have any of the following values:
'place'
Orphan sections are placed into a suitable output section
following the strategy described in Orphan Sections.
The option '--unique' also affects how sections are placed.
'discard'
All orphan sections are discarded, by placing them in the
'/DISCARD/' section (Output Section Discarding).
'warn'
The linker will place the orphan section as for 'place' and
also issue a warning.
'error'
The linker will exit with an error if any orphan section is
found.
The default if '--orphan-handling' is not given is 'place'.
'--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. (These symbols start with
system-specific local label prefixes, typically '.L' for ELF
systems or 'L' for traditional a.out systems.)
'-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:
'bndplt'
Always generate BND prefix in PLT entries. Supported for
Linux/x86_64.
'call-nop=prefix-addr'
'call-nop=suffix-nop'
'call-nop=prefix-BYTE'
'call-nop=suffix-BYTE'
Specify the 1-byte 'NOP' padding when transforming indirect
call to a locally defined function, foo, via its GOT slot.
'call-nop=prefix-addr' generates '0x67 call foo'.
'call-nop=suffix-nop' generates 'call foo 0x90'.
'call-nop=prefix-BYTE' generates 'BYTE call foo'.
'call-nop=suffix-BYTE' generates 'call foo BYTE'. Supported
for i386 and x86_64.
'combreloc'
'nocombreloc'
Combine multiple dynamic relocation sections and sort to
improve dynamic symbol lookup caching. Do not do this if
'nocombreloc'.
'common'
'nocommon'
Generate common symbols with STT_COMMON type during a
relocatable link. Use STT_OBJECT type if 'nocommon'.
'common-page-size=VALUE'
Set the page size most commonly used to VALUE. Memory image
layout will be optimized to minimize memory pages if the
system is using pages of this size.
'defs'
Report unresolved symbol references from regular object files.
This is done even if the linker is creating a non-symbolic
shared library. This option is the inverse of '-z undefs'.
'dynamic-undefined-weak'
'nodynamic-undefined-weak'
Make undefined weak symbols dynamic when building a dynamic
object, if they are referenced from a regular object file and
not forced local by symbol visibility or versioning. Do not
make them dynamic if 'nodynamic-undefined-weak'. If neither
option is given, a target may default to either option being
in force, or make some other selection of undefined weak
symbols dynamic. Not all targets support these options.
'execstack'
Marks the object as requiring executable stack.
'global'
This option is only meaningful when building a shared object.
It makes the symbols defined by this shared object available
for symbol resolution of subsequently loaded libraries.
'globalaudit'
This option is only meaningful when building a dynamic
executable. This option marks the executable as requiring
global auditing by setting the 'DF_1_GLOBAUDIT' bit in the
'DT_FLAGS_1' dynamic tag. Global auditing requires that any
auditing library defined via the '--depaudit' or '-P'
command-line options be run for all dynamic objects loaded by
the application.
'ibtplt'
Generate Intel Indirect Branch Tracking (IBT) enabled PLT
entries. Supported for Linux/i386 and Linux/x86_64.
'ibt'
Generate GNU_PROPERTY_X86_FEATURE_1_IBT in .note.gnu.property
section to indicate compatibility with IBT. This also implies
'ibtplt'. Supported for Linux/i386 and Linux/x86_64.
'initfirst'
This option is only meaningful when building a shared object.
It marks the object so that its runtime initialization will
occur before the runtime initialization of any other objects
brought into the process at the same time. Similarly the
runtime finalization of the object will occur after the
runtime finalization of any other objects.
'interpose'
Specify that the dynamic loader should modify its symbol
search order so that symbols in this shared library interpose
all other shared libraries not so marked.
'lazy'
When generating an executable or shared library, mark it to
tell the dynamic linker to defer function call resolution to
the point when the function is called (lazy binding), rather
than at load time. Lazy binding is the default.
'loadfltr'
Specify that the object's filters be processed immediately at
runtime.
'max-page-size=VALUE'
Set the maximum memory page size supported to VALUE.
'muldefs'
Allow multiple definitions.
'nocopyreloc'
Disable linker generated .dynbss variables used in place of
variables defined in shared libraries. May result in dynamic
text relocations.
'nodefaultlib'
Specify that the dynamic loader search for dependencies of
this object should ignore any default library search paths.
'nodelete'
Specify that the object shouldn't be unloaded at runtime.
'nodlopen'
Specify that the object is not available to 'dlopen'.
'nodump'
Specify that the object can not be dumped by 'dldump'.
'noexecstack'
Marks the object as not requiring executable stack.
'noextern-protected-data'
Don't treat protected data symbols as external when building a
shared library. This option overrides the linker backend
default. It can be used to work around incorrect relocations
against protected data symbols generated by compiler. Updates
on protected data symbols by another module aren't visible to
the resulting shared library. Supported for i386 and x86-64.
'noreloc-overflow'
Disable relocation overflow check. This can be used to
disable relocation overflow check if there will be no dynamic
relocation overflow at run-time. Supported for x86_64.
'now'
When generating an executable or shared library, mark it to
tell the dynamic linker to resolve all symbols when the
program is started, or when the shared library is loaded by
dlopen, instead of deferring function call resolution to the
point when the function is first called.
'origin'
Specify that the object requires '$ORIGIN' handling in paths.
'relro'
'norelro'
Create an ELF 'PT_GNU_RELRO' segment header in the object.
This specifies a memory segment that should be made read-only
after relocation, if supported. Specifying 'common-page-size'
smaller than the system page size will render this protection
ineffective. Don't create an ELF 'PT_GNU_RELRO' segment if
'norelro'.
'separate-code'
'noseparate-code'
Create separate code 'PT_LOAD' segment header in the object.
This specifies a memory segment that should contain only
instructions and must be in wholly disjoint pages from any
other data. Don't create separate code 'PT_LOAD' segment if
'noseparate-code' is used.
'shstk'
Generate GNU_PROPERTY_X86_FEATURE_1_SHSTK in
.note.gnu.property section to indicate compatibility with
Intel Shadow Stack. Supported for Linux/i386 and
Linux/x86_64.
'stack-size=VALUE'
Specify a stack size for an ELF 'PT_GNU_STACK' segment.
Specifying zero will override any default non-zero sized
'PT_GNU_STACK' segment creation.
'text'
'notext'
'textoff'
Report an error if DT_TEXTREL is set, i.e., if the binary has
dynamic relocations in read-only sections. Don't report an
error if 'notext' or 'textoff'.
'undefs'
Do not report unresolved symbol references from regular object
files, either when creating an executable, or when creating a
shared library. This option is the inverse of '-z defs'.
Other keywords are ignored for Solaris compatibility.
'-( ARCHIVES -)'
'--start-group ARCHIVES --end-group'
The ARCHIVES should be a list of archive files. They may be either
explicit file names, or '-l' options.
The specified archives are searched repeatedly until no new
undefined references are created. Normally, an archive is searched
only once in the order that it is specified on the command line.
If a symbol in that archive is needed to resolve an undefined
symbol referred to by an object in an archive that appears later on
the command line, the linker would not be able to resolve that
reference. By grouping the archives, they all be searched
repeatedly until all possible references are resolved.
Using this option has a significant performance cost. It is best
to use it only when there are unavoidable circular references
between two or more archives.
'--accept-unknown-input-arch'
'--no-accept-unknown-input-arch'
Tells the linker to accept input files whose architecture cannot be
recognised. The assumption is that the user knows what they are
doing and deliberately wants to link in these unknown input files.
This was the default behaviour of the linker, before release 2.14.
The default behaviour from release 2.14 onwards is to reject such
input files, and so the '--accept-unknown-input-arch' option has
been added to restore the old behaviour.
'--as-needed'
'--no-as-needed'
This option affects ELF DT_NEEDED tags for dynamic libraries
mentioned on the command line after the '--as-needed' option.
Normally the linker will add a DT_NEEDED tag for each dynamic
library mentioned on the command line, regardless of whether the
library is actually needed or not. '--as-needed' causes a
DT_NEEDED tag to only be emitted for a library that _at that point
in the link_ satisfies a non-weak undefined symbol reference from a
regular object file or, if the library is not found in the
DT_NEEDED lists of other needed libraries, a non-weak undefined
symbol reference from another needed dynamic library. Object files
or libraries appearing on the command line _after_ the library in
question do not affect whether the library is seen as needed. This
is similar to the rules for extraction of object files from
archives. '--no-as-needed' restores the default behaviour.
'--add-needed'
'--no-add-needed'
These two options have been deprecated because of the similarity of
their names to the '--as-needed' and '--no-as-needed' options.
They have been replaced by '--copy-dt-needed-entries' and
'--no-copy-dt-needed-entries'.
'-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.
'--unresolved-symbols=report-all' 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. This
option also implies '--unresolved-symbols=report-all'. This option
can be used with '-shared'. Doing so means that a shared library
is being created but that all of the library's external references
must be resolved by pulling in entries from static libraries.
'-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 can
also be used with the '--export-dynamic' option, when creating a
position independent executable, to bind references to global
symbols to the definition within the executable. This option is
only meaningful on ELF platforms which support shared libraries and
position independent executables.
'-Bsymbolic-functions'
When creating a shared library, bind references to global function
symbols to the definition within the shared library, if any. This
option can also be used with the '--export-dynamic' option, when
creating a position independent executable, to bind references to
global function symbols to the definition within the executable.
This option is only meaningful on ELF platforms which support
shared libraries and position independent executables.
'--dynamic-list=DYNAMIC-LIST-FILE'
Specify the name of a dynamic list file to the linker. This is
typically used when creating shared libraries to specify a list of
global symbols whose references shouldn't be bound to the
definition within the shared library, or creating dynamically
linked executables to specify a list of symbols which should be
added to the symbol table in the executable. This option is only
meaningful on ELF platforms which support shared libraries.
The format of the dynamic list is the same as the version node
without scope and node name. See VERSION for more
information.
'--dynamic-list-data'
Include all global data symbols to the dynamic list.
'--dynamic-list-cpp-new'
Provide the builtin dynamic list for C++ operator new and delete.
It is mainly useful for building shared libstdc++.
'--dynamic-list-cpp-typeinfo'
Provide the builtin dynamic list for C++ runtime type
identification.
'--check-sections'
'--no-check-sections'
Asks the linker _not_ to check section addresses after they have
been assigned to see if there are 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'. Section overlap is not usually checked for
relocatable links. You can force checking in that case by using
the '--check-sections' option.
'--copy-dt-needed-entries'
'--no-copy-dt-needed-entries'
This option affects the treatment of dynamic libraries referred to
by DT_NEEDED tags _inside_ ELF dynamic libraries mentioned on the
command line. Normally the linker won't add a DT_NEEDED tag to the
output binary for each library mentioned in a DT_NEEDED tag in an
input dynamic library. With '--copy-dt-needed-entries' specified
on the command line however any dynamic libraries that follow it
will have their DT_NEEDED entries added. The default behaviour can
be restored with '--no-copy-dt-needed-entries'.
This option also has an effect on the resolution of symbols in
dynamic libraries. With '--copy-dt-needed-entries' dynamic
libraries mentioned on the command line will be recursively
searched, following their DT_NEEDED tags to other libraries, in
order to resolve symbols required by the output binary. With the
default setting however the searching of dynamic libraries that
follow it will stop with the dynamic library itself. No DT_NEEDED
links will be traversed to resolve symbols.
'--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. If the symbol is defined as a common
value then any files where this happens appear next. Finally any
files that reference the symbol are listed.
'--no-define-common'
This option inhibits the assignment of addresses to common symbols.
The script command 'INHIBIT_COMMON_ALLOCATION' has the same effect.
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.
'--force-group-allocation'
This option causes the linker to place section group members like
normal input sections, and to delete the section groups. This is
the default behaviour for a final link but this option can be used
to change the behaviour of a relocatable link ('-r'). The script
command 'FORCE_GROUP_ALLOCATION' has the same effect.
Miscellaneous Commands.
'--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 (
Assignments). _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.
'-IFILE'
'--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.
'--no-dynamic-linker'
When producing an executable file, omit the request for a dynamic
linker to be used at load-time. This is only meaningful for ELF
executables that contain dynamic relocations, and usually requires
entry point code that is capable of processing these relocations.
'--embedded-relocs'
This option is similar to the '--emit-relocs' option except that
the relocs are stored in a target specific section. This option is
only supported by the 'BFIN', 'CR16' and _M68K_ targets.
'--disable-multiple-abs-defs'
Do not allow multiple definitions with symbols included in filename
invoked by -R or -just-symbols
'--fatal-warnings'
'--no-fatal-warnings'
Treat all warnings as errors. The default behaviour can be
restored with the option '--no-fatal-warnings'.
'--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.
'--gc-sections'
'--no-gc-sections'
Enable garbage collection of unused input sections. It is ignored
on targets that do not support this option. The default behaviour
(of not performing this garbage collection) can be restored by
specifying '--no-gc-sections' on the command line. Note that
garbage collection for COFF and PE format targets is supported, but
the implementation is currently considered to be experimental.
'--gc-sections' decides which input sections are used by examining
symbols and relocations. The section containing the entry symbol
and all sections containing symbols undefined on the command-line
will be kept, as will sections containing symbols referenced by
dynamic objects. Note that when building shared libraries, the
linker must assume that any visible symbol is referenced. Once
this initial set of sections has been determined, the linker
recursively marks as used any section referenced by their
relocations. See '--entry', '--undefined', and
'--gc-keep-exported'.
This option can be set when doing a partial link (enabled with
option '-r'). In this case the root of symbols kept must be
explicitly specified either by one of the options '--entry',
'--undefined', or '--gc-keep-exported' or by a 'ENTRY' command in
the linker script.
'--print-gc-sections'
'--no-print-gc-sections'
List all sections removed by garbage collection. The listing is
printed on stderr. This option is only effective if garbage
collection has been enabled via the '--gc-sections') option. The
default behaviour (of not listing the sections that are removed)
can be restored by specifying '--no-print-gc-sections' on the
command line.
'--gc-keep-exported'
When '--gc-sections' is enabled, this option prevents garbage
collection of unused input sections that contain global symbols
having default or protected visibility. This option is intended to
be used for executables where unreferenced sections would otherwise
be garbage collected regardless of the external visibility of
contained symbols. Note that this option has no effect when
linking shared objects since it is already the default behaviour.
This option is only supported for ELF format targets.
'--print-output-format'
Print the name of the default output format (perhaps influenced by
other command-line options). This is the string that would appear
in an 'OUTPUT_FORMAT' linker script command (File
Commands).
'--print-memory-usage'
Print used size, total size and used size of memory regions created
with the MEMORY command. This is useful on embedded
targets to have a quick view of amount of free memory. The format
of the output has one headline and one line per region. It is both
human readable and easily parsable by tools. Here is an example of
an output:
Memory region Used Size Region Size %age Used
ROM: 256 KB 1 MB 25.00%
RAM: 32 B 2 GB 0.00%
'--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'
Report unresolved symbol references from regular object files.
This is done even if the linker is creating a non-symbolic shared
library. The switch '--[no-]allow-shlib-undefined' controls the
behaviour for reporting unresolved references found in shared
libraries being linked in.
The effects of this option can be reverted by using '-z undefs'.
'--allow-multiple-definition'
'-z muldefs'
Normally when a symbol is defined multiple times, the linker will
report a fatal error. These options allow multiple definitions and
the first definition will be used.
'--allow-shlib-undefined'
'--no-allow-shlib-undefined'
Allows or disallows undefined symbols in shared libraries. This
switch is similar to '--no-undefined' except that it determines the
behaviour when the undefined symbols are in a shared library rather
than a regular object file. It does not affect how undefined
symbols in regular object files are handled.
The default behaviour is to report errors for any undefined symbols
referenced in shared libraries if the linker is being used to
create an executable, but to allow them if the linker is being used
to create a shared library.
The reasons for allowing undefined symbol references in shared
libraries specified at link time are that:
* A shared library specified at link time may not be the same as
the one that is available at load time, so the symbol might
actually be resolvable at load time.
* There are some operating systems, eg BeOS and HPPA, where
undefined symbols in shared libraries are normal.
The BeOS kernel for example patches shared libraries at load
time to select whichever function is most appropriate for the
current architecture. This is used, for example, to
dynamically select an appropriate memset function.
'--no-undefined-version'
Normally when a symbol has an undefined version, the linker will
ignore it. This option disallows symbols with undefined version
and a fatal error will be issued instead.
'--default-symver'
Create and use a default symbol version (the soname) for
unversioned exported symbols.
'--default-imported-symver'
Create and use a default symbol version (the soname) for
unversioned imported 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-warn-search-mismatch'
Normally 'ld' will give a warning if it finds an incompatible
library during a library search. This option silences the warning.
'--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. BFD.
'--out-implib FILE'
Create an import library in FILE corresponding to the executable
the linker is generating (eg. a DLL or ELF program). This import
library (which should be called '*.dll.a' or '*.a' for DLLs) may be
used to link clients against the generated executable; this
behaviour makes it possible to skip a separate import library
creation step (eg. 'dlltool' for DLLs). This option is only
available for the i386 PE and ELF targetted ports of the linker.
'-pie'
'--pic-executable'
Create a position independent executable. This is currently only
supported on ELF platforms. Position independent executables are
similar to shared libraries in that they are relocated by the
dynamic linker to the virtual address the OS chooses for them
(which can vary between invocations). Like normal dynamically
linked executables they can be executed and symbols defined in the
executable cannot be overridden by shared libraries.
'-qmagic'
This option is ignored for Linux compatibility.
'-Qy'
This option is ignored for SVR4 compatibility.
'--relax'
'--no-relax'
An option with machine dependent effects. This option is only
supported on a few targets. 'ld' and the H8/300 H8/300.
DONTPRINTYET 'ld' and Xtensa Processors Xtensa. *Note'ld' and the
DONTPRINTYET DONTPRINTYET 'ld' and Xtensa Processors Xtensa. 'ld' and the
68HC11 and 68HC12 M68HC11/68HC12. *Note'ld' and the Altera Nios
DONTPRINTYET DONTPRINTYET DONTPRINTYET 'ld' and Xtensa Processors Xtensa. 'ld' and the
68HC11 and 68HC12 M68HC11/68HC12. 'ld' and the Altera Nios
II Nios II. *Note'ld' and PowerPC 32-bit ELF Support: PowerPC
DONTPRINTYET DONTPRINTYET DONTPRINTYET 'ld' and Xtensa Processors Xtensa. 'ld' and the
68HC11 and 68HC12 M68HC11/68HC12. 'ld' and the Altera Nios
II Nios II. 'ld' and PowerPC 32-bit ELF Support PowerPC
ELF32.
On some platforms the '--relax' option performs target specific,
global optimizations that become possible when the linker resolves
addressing in the program, such as relaxing address modes,
synthesizing new instructions, selecting shorter version of current
instructions, and combining constant values.
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.
On platforms where '--relax' is accepted the option '--no-relax'
can be used to disable the feature.
'--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 path 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 file
systems.
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.
The tokens $ORIGIN and $LIB can appear in these search directories.
They will be replaced by the full path to the directory containing
the program or shared object in the case of $ORIGIN and either
'lib' - for 32-bit binaries - or 'lib64' - for 64-bit binaries - in
the case of $LIB.
The alternative form of these tokens - ${ORIGIN} and ${LIB} can
also be used. The token $PLATFORM is not supported.
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. Searching '-rpath' in this way is
only supported by native linkers and cross linkers which have
been configured with the '--with-sysroot' option.
3. On an ELF system, for native linkers, if the '-rpath' and
'-rpath-link' options were not used, search the contents of
the environment variable 'LD_RUN_PATH'.
4. On SunOS, if the '-rpath' option was not used, search any
directories specified using '-L' options.
5. For a native linker, search 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'
'--sort-common=ascending'
'--sort-common=descending'
This option tells 'ld' to sort the common symbols by alignment in
ascending or descending order when it places them in the
appropriate output sections. The symbol alignments considered are
sixteen-byte or larger, eight-byte, four-byte, two-byte, and
one-byte. This is to prevent gaps between symbols due to alignment
constraints. If no sorting order is specified, then descending
order is assumed.
'--sort-section=name'
This option will apply 'SORT_BY_NAME' to all wildcard section
patterns in the linker script.
'--sort-section=alignment'
This option will apply 'SORT_BY_ALIGNMENT' to all wildcard section
patterns in the linker script.
'--spare-dynamic-tags=COUNT'
This option specifies the number of empty slots to leave in the
.dynamic section of ELF shared objects. Empty slots may be needed
by post processing tools, such as the prelinker. The default is 5.
'--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.
'--sysroot=DIRECTORY'
Use DIRECTORY as the location of the sysroot, overriding the
configure-time default. This option is only supported by linkers
that were configured using '--with-sysroot'.
'--task-link'
This is used by COFF/PE based targets to create a task-linked
object file where all of the global symbols have been converted to
statics.
'--traditional-format'
For some targets, the output of 'ld' is different in some ways from
the output of some existing linker. This switch requests 'ld' to
use the traditional format instead.
For example, on SunOS, 'ld' combines duplicate entries in the
symbol string table. This can reduce the size of an output file
with full debugging information by over 30 percent. Unfortunately,
the SunOS 'dbx' program can not read the resulting program ('gdb'
has no trouble). The '--traditional-format' switch tells 'ld' to
not combine duplicate entries.
'--section-start=SECTIONNAME=ORG'
Locate a section in the output file at the absolute address given
by ORG. You may use this option as many times as necessary to
locate multiple sections in the command line. ORG must be a single
hexadecimal integer; for compatibility with other linkers, you may
omit the leading '0x' usually associated with hexadecimal values.
_Note:_ there should be no white space between SECTIONNAME, the
equals sign ("<=>"), and ORG.
'-Tbss=ORG'
'-Tdata=ORG'
'-Ttext=ORG'
Same as '--section-start', with '.bss', '.data' or '.text' as the
SECTIONNAME.
'-Ttext-segment=ORG'
When creating an ELF executable, it will set the address of the
first byte of the text segment.
'-Trodata-segment=ORG'
When creating an ELF executable or shared object for a target where
the read-only data is in its own segment separate from the
executable text, it will set the address of the first byte of the
read-only data segment.
'-Tldata-segment=ORG'
When creating an ELF executable or shared object for x86-64 medium
memory model, it will set the address of the first byte of the
ldata segment.
'--unresolved-symbols=METHOD'
Determine how to handle unresolved symbols. There are four
possible values for 'method':
'ignore-all'
Do not report any unresolved symbols.
'report-all'
Report all unresolved symbols. This is the default.
'ignore-in-object-files'
Report unresolved symbols that are contained in shared
libraries, but ignore them if they come from regular object
files.
'ignore-in-shared-libs'
Report unresolved symbols that come from regular object files,
but ignore them if they come from shared libraries. This can
be useful when creating a dynamic binary and it is known that
all the shared libraries that it should be referencing are
included on the linker's command line.
The behaviour for shared libraries on their own can also be
controlled by the '--[no-]allow-shlib-undefined' option.
Normally the linker will generate an error message for each
reported unresolved symbol but the option
'--warn-unresolved-symbols' can change this to a warning.
'--dll-verbose'
'--verbose[=NUMBER]'
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. If the
optional NUMBER argument > 1, plugin symbol status will also be
displayed.
'--version-script=VERSION-SCRIPTFILE'
Specify the name of a version script to the linker. This is
typically used when creating shared libraries to specify additional
information about the version hierarchy for the library being
created. This option is only fully supported on ELF platforms
which support shared libraries; see VERSION. It is
partially supported on PE platforms, which can use version scripts
to filter symbol visibility in auto-export mode: any symbols marked
'local' in the version script will not be exported. WIN32.
'--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 (SECTIONS).
'--warn-shared-textrel'
Warn if the linker adds a DT_TEXTREL to a shared object.
'--warn-alternate-em'
Warn if an object has alternate ELF machine code.
'--warn-unresolved-symbols'
If the linker is going to report an unresolved symbol (see the
option '--unresolved-symbols') it will normally generate an error.
This option makes it generate a warning instead.
'--error-unresolved-symbols'
This restores the linker's default behaviour of generating errors
when it is reporting unresolved symbols.
'--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 (size_t c)
{
printf ("malloc called with %zu\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'.
Only undefined references are replaced by the linker. So,
translation unit internal references to SYMBOL are not resolved to
'__wrap_SYMBOL'. In the next example, the call to 'f' in 'g' is
not resolved to '__wrap_f'.
int
f (void)
{
return 123;
}
int
g (void)
{
return f();
}
'--eh-frame-hdr'
'--no-eh-frame-hdr'
Request ('--eh-frame-hdr') or suppress ('--no-eh-frame-hdr') the
creation of '.eh_frame_hdr' section and ELF 'PT_GNU_EH_FRAME'
segment header.
'--no-ld-generated-unwind-info'
Request creation of '.eh_frame' unwind info for linker generated
code sections like PLT. This option is on by default if linker
generated unwind info is supported.
'--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 new dynamic tags will be created as
needed and older dynamic tags will be omitted. 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.
'--hash-size=NUMBER'
Set the default size of the linker's hash tables to a prime number
close to NUMBER. Increasing this value can reduce the length of
time it takes the linker to perform its tasks, at the expense of
increasing the linker's memory requirements. Similarly reducing
this value can reduce the memory requirements at the expense of
speed.
'--hash-style=STYLE'
Set the type of linker's hash table(s). STYLE can be either 'sysv'
for classic ELF '.hash' section, 'gnu' for new style GNU
'.gnu.hash' section or 'both' for both the classic ELF '.hash' and
new style GNU '.gnu.hash' hash tables. The default depends upon
how the linker was configured, but for most Linux based systems it
will be 'both'.
'--compress-debug-sections=none'
'--compress-debug-sections=zlib'
'--compress-debug-sections=zlib-gnu'
'--compress-debug-sections=zlib-gabi'
On ELF platforms, these options control how DWARF debug sections
are compressed using zlib.
'--compress-debug-sections=none' doesn't compress DWARF debug
sections. '--compress-debug-sections=zlib-gnu' compresses DWARF
debug sections and renames them to begin with '.zdebug' instead of
'.debug'. '--compress-debug-sections=zlib-gabi' also compresses
DWARF debug sections, but rather than renaming them it sets the
SHF_COMPRESSED flag in the sections' headers.
The '--compress-debug-sections=zlib' option is an alias for
'--compress-debug-sections=zlib-gabi'.
Note that this option overrides any compression in input debug
sections, so if a binary is linked with
'--compress-debug-sections=none' for example, then any compressed
debug sections in input files will be uncompressed before they are
copied into the output binary.
The default compression behaviour varies depending upon the target
involved and the configure options used to build the toolchain.
The default can be determined by examining the output from the
linker's '--help' option.
'--reduce-memory-overheads'
This option reduces memory requirements at ld runtime, at the
expense of linking speed. This was introduced to select the old
O(n^2) algorithm for link map file generation, rather than the new
O(n) algorithm which uses about 40% more memory for symbol storage.
Another effect of the switch is to set the default hash table size
to 1021, which again saves memory at the cost of lengthening the
linker's run time. This is not done however if the '--hash-size'
switch has been used.
The '--reduce-memory-overheads' switch may be also be used to
enable other tradeoffs in future versions of the linker.
'--build-id'
'--build-id=STYLE'
Request the creation of a '.note.gnu.build-id' ELF note section or
a '.buildid' COFF section. The contents of the note are unique
bits identifying this linked file. STYLE can be 'uuid' to use 128
random bits, 'sha1' to use a 160-bit SHA1 hash on the normative
parts of the output contents, 'md5' to use a 128-bit MD5 hash on
the normative parts of the output contents, or '0xHEXSTRING' to use
a chosen bit string specified as an even number of hexadecimal
digits ('-' and ':' characters between digit pairs are ignored).
If STYLE is omitted, 'sha1' is used.
The 'md5' and 'sha1' styles produces an identifier that is always
the same in an identical output file, but will be unique among all
nonidentical output files. It is not intended to be compared as a
checksum for the file's contents. A linked file may be changed
later by other tools, but the build ID bit string identifying the
original linked file does not change.
Passing 'none' for STYLE disables the setting from any '--build-id'
options earlier on the command line.
2.1.1 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. [This option is specific
to the i386 PE targeted port of the linker]
'--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'.
[This is an i386 PE specific option]
'--dll'
Create a DLL instead of a regular executable. You may also use
'-shared' or specify a 'LIBRARY' in a given '.def' file. [This
option is specific to the i386 PE targeted port of the linker]
'--enable-long-section-names'
'--disable-long-section-names'
The PE variants of the COFF object format add an extension that
permits the use of section names longer than eight characters, the
normal limit for COFF. By default, these names are only allowed in
object files, as fully-linked executable images do not carry the
COFF string table required to support the longer names. As a GNU
extension, it is possible to allow their use in executable images
as well, or to (probably pointlessly!) disallow it in object
files, by using these two options. Executable images generated
with these long section names are slightly non-standard, carrying
as they do a string table, and may generate confusing output when
examined with non-GNU PE-aware tools, such as file viewers and
dumpers. However, GDB relies on the use of PE long section names
to find Dwarf-2 debug information sections in an executable image
at runtime, and so if neither option is specified on the
command-line, 'ld' will enable long section names, overriding the
default and technically correct behaviour, when it finds the
presence of debug information while linking an executable image and
not stripping symbols. [This option is valid for all PE targeted
ports of the linker]
'--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. [This option is specific
to the i386 PE targeted port of the linker]
'--leading-underscore'
'--no-leading-underscore'
For most targets default symbol-prefix is an underscore and is
defined in target's description. By this option it is possible to
disable/enable the default underscore symbol-prefix.
'--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'. [This option is specific to the i386 PE targeted port
of the linker]
'--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.
[This option is specific to the i386 PE targeted port of the
linker]
'--exclude-all-symbols'
Specifies no symbols should be automatically exported. [This
option is specific to the i386 PE targeted port of the linker]
'--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. [This option is specific to the i386 PE targeted port of
the linker]
'--heap RESERVE'
'--heap RESERVE,COMMIT'
Specify the number of bytes of memory to reserve (and optionally
commit) to be used as heap for this program. The default is 1MB
reserved, 4K committed. [This option is specific to the i386 PE
targeted port of the linker]
'--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. [This option is specific to the i386 PE
targeted port of the linker]
'--kill-at'
If given, the stdcall suffixes (@NN) will be stripped from symbols
before they are exported. [This option is specific to the i386 PE
targeted port of the linker]
'--large-address-aware'
If given, the appropriate bit in the "Characteristics" field of the
COFF header is set to indicate that this executable supports
virtual addresses greater than 2 gigabytes. This should be used in
conjunction with the /3GB or /USERVA=VALUE megabytes switch in the
"[operating systems]" section of the BOOT.INI. Otherwise, this bit
has no effect. [This option is specific to PE targeted ports of
the linker]
'--disable-large-address-aware'
Reverts the effect of a previous '--large-address-aware' option.
This is useful if '--large-address-aware' is always set by the
compiler driver (e.g. Cygwin gcc) and the executable does not
support virtual addresses greater than 2 gigabytes. [This option
is specific to PE targeted ports of the linker]
'--major-image-version VALUE'
Sets the major number of the "image version". Defaults to 1.
[This option is specific to the i386 PE targeted port of the
linker]
'--major-os-version VALUE'
Sets the major number of the "os version". Defaults to 4. [This
option is specific to the i386 PE targeted port of the linker]
'--major-subsystem-version VALUE'
Sets the major number of the "subsystem version". Defaults to 4.
[This option is specific to the i386 PE targeted port of the
linker]
'--minor-image-version VALUE'
Sets the minor number of the "image version". Defaults to 0.
[This option is specific to the i386 PE targeted port of the
linker]
'--minor-os-version VALUE'
Sets the minor number of the "os version". Defaults to 0. [This
option is specific to the i386 PE targeted port of the linker]
'--minor-subsystem-version VALUE'
Sets the minor number of the "subsystem version". Defaults to 0.
[This option is specific to the i386 PE targeted port of the
linker]
'--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. [This option is
specific to the i386 PE targeted port of the linker]
'--enable-auto-image-base'
'--enable-auto-image-base=VALUE'
Automatically choose the image base for DLLs, optionally starting
with base VALUE, 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. [This
option is specific to the i386 PE targeted port of the linker]
'--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. [This option is specific to the i386 PE targeted port of
the linker]
'--dll-search-prefix STRING'
When linking dynamically to a dll without an import library, search
for '<string><basename>.dll' in preference to 'lib<basename>.dll'.
This behaviour 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'.
[This option is specific to the i386 PE targeted port of the
linker]
'--enable-auto-import'
Do sophisticated linking of '_symbol' to '__imp__symbol' for DATA
imports from DLLs, thus making it possible to bypass the dllimport
mechanism on the user side and to reference unmangled symbol names.
[This option is specific to the i386 PE targeted port of the
linker]
The following remarks pertain to the original implementation of the
feature and are obsolete nowadays for Cygwin and MinGW targets.
Note: Use of the 'auto-import' extension will cause the text
section of the image file to be made writable. This does not
conform to the PE-COFF format specification published by Microsoft.
Note - use of the 'auto-import' extension will also cause read only
data which would normally be placed into the .rdata section to be
placed into the .data section instead. This is in order to work
around a problem with consts that is described here:
http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
Using 'auto-import' 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 way is to use -enable-runtime-pseudo-reloc switch. This leaves
the task of adjusting references in your client code for runtime
environment, so this method works only when runtime environment
supports this feature.
A second 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 third 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 fourth 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 sophisticated linking of '_symbol' to
'__imp__symbol' for DATA imports from DLLs. [This option is
specific to the i386 PE targeted port of the linker]
'--enable-runtime-pseudo-reloc'
If your code contains expressions described in -enable-auto-import
section, that is, DATA imports from DLL with non-zero offset, this
switch will create a vector of 'runtime pseudo relocations' which
can be used by runtime environment to adjust references to such
data in your client code. [This option is specific to the i386 PE
targeted port of the linker]
'--disable-runtime-pseudo-reloc'
Do not create pseudo relocations for non-zero offset DATA imports
from DLLs. [This option is specific to the i386 PE targeted port
of the linker]
'--enable-extra-pe-debug'
Show additional debug info related to auto-import symbol thunking.
[This option is specific to the i386 PE targeted port of the
linker]
'--section-alignment'
Sets the section alignment. Sections in memory will always begin
at addresses which are a multiple of this number. Defaults to
0x1000. [This option is specific to the i386 PE targeted port of
the linker]
'--stack RESERVE'
'--stack RESERVE,COMMIT'
Specify the number of bytes of memory to reserve (and optionally
commit) to be used as stack for this program. The default is 2MB
reserved, 4K committed. [This option is specific to the i386 PE
targeted port of the linker]
'--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', 'posix',
and 'xbox'. You may optionally set the subsystem version also.
Numeric values are also accepted for WHICH. [This option is
specific to the i386 PE targeted port of the linker]
The following options set flags in the 'DllCharacteristics' field
of the PE file header: [These options are specific to PE targeted
ports of the linker]
'--high-entropy-va'
Image is compatible with 64-bit address space layout randomization
(ASLR).
'--dynamicbase'
The image base address may be relocated using address space layout
randomization (ASLR). This feature was introduced with MS Windows
Vista for i386 PE targets.
'--forceinteg'
Code integrity checks are enforced.
'--nxcompat'
The image is compatible with the Data Execution Prevention. This
feature was introduced with MS Windows XP SP2 for i386 PE targets.
'--no-isolation'
Although the image understands isolation, do not isolate the image.
'--no-seh'
The image does not use SEH. No SE handler may be called from this
image.
'--no-bind'
Do not bind this image.
'--wdmdriver'
The driver uses the MS Windows Driver Model.
'--tsaware'
The image is Terminal Server aware.
'--insert-timestamp'
'--no-insert-timestamp'
Insert a real timestamp into the image. This is the default
behaviour as it matches legacy code and it means that the image
will work with other, proprietary tools. The problem with this
default is that it will result in slightly different images being
produced each time the same sources are linked. The option
'--no-insert-timestamp' can be used to insert a zero value for the
timestamp, this ensuring that binaries produced from identical
sources will compare identically.
2.1.2 Options specific to C6X uClinux targets
---------------------------------------------
The C6X uClinux target uses a binary format called DSBT to support
shared libraries. Each shared library in the system needs to have a
unique index; all executables use an index of 0.
'--dsbt-size SIZE'
This option sets the number of entries in the DSBT of the current
executable or shared library to SIZE. The default is to create a
table with 64 entries.
'--dsbt-index INDEX'
This option sets the DSBT index of the current executable or shared
library to INDEX. The default is 0, which is appropriate for
generating executables. If a shared library is generated with a
DSBT index of 0, the 'R_C6000_DSBT_INDEX' relocs are copied into
the output file.
The '--no-merge-exidx-entries' switch disables the merging of
adjacent exidx entries in frame unwind info.
2.1.3 Options specific to C-SKY targets
---------------------------------------
'--branch-stub'
This option enables linker branch relaxation by inserting branch
stub sections when needed to extend the range of branches. This
option is usually not required since C-SKY supports branch and call
instructions that can access the full memory range and branch
relaxation is normally handled by the compiler or assembler.
'--stub-group-size=N'
This option allows finer control of linker branch stub creation.
It sets the maximum size of a group of input sections that can be
handled by one stub section. A negative value of N locates stub
sections after their branches, while a positive value allows stub
sections to appear either before or after the branches. Values of
'1' or '-1' indicate that the linker should choose suitable
defaults.
2.1.4 Options specific to Motorola 68HC11 and 68HC12 targets
------------------------------------------------------------
The 68HC11 and 68HC12 linkers support specific options to control the
memory bank switching mapping and trampoline code generation.
'--no-trampoline'
This option disables the generation of trampoline. By default a
trampoline is generated for each far function which is called using
a 'jsr' instruction (this happens when a pointer to a far function
is taken).
'--bank-window NAME'
This option indicates to the linker the name of the memory region
in the 'MEMORY' specification that describes the memory bank
window. The definition of such region is then used by the linker
to compute paging and addresses within the memory window.
2.1.5 Options specific to Motorola 68K target
---------------------------------------------
The following options are supported to control handling of GOT
generation when linking for 68K targets.
'--got=TYPE'
This option tells the linker which GOT generation scheme to use.
TYPE should be one of 'single', 'negative', 'multigot' or 'target'.
For more information refer to the Info entry for 'ld'.
2.1.6 Options specific to MIPS targets
--------------------------------------
The following options are supported to control microMIPS instruction
generation and branch relocation checks for ISA mode transitions when
linking for MIPS targets.
'--insn32'
'--no-insn32'
These options control the choice of microMIPS instructions used in
code generated by the linker, such as that in the PLT or lazy
binding stubs, or in relaxation. If '--insn32' is used, then the
linker only uses 32-bit instruction encodings. By default or if
'--no-insn32' is used, all instruction encodings are used,
including 16-bit ones where possible.
'--ignore-branch-isa'
'--no-ignore-branch-isa'
These options control branch relocation checks for invalid ISA mode
transitions. If '--ignore-branch-isa' is used, then the linker
accepts any branch relocations and any ISA mode transition required
is lost in relocation calculation, except for some cases of 'BAL'
instructions which meet relaxation conditions and are converted to
equivalent 'JALX' instructions as the associated relocation is
calculated. By default or if '--no-ignore-branch-isa' is used a
check is made causing the loss of an ISA mode transition to produce
an error.
Info Catalog
ld.info: Invocation
ld.info: Environment