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.
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.)
You may want to use this option if you are linking files with
an unusual binary format. You can also use -b to switch
formats explicitly (when linking object files of different
formats), by including -b input-format before each group of
object files in a particular format.
The default format is taken from the environment variable
"GNUTARGET".
You can also define the input format from a script, using the
command "TARGET";
-c MRI-commandfile
--mri-script=MRI-commandfile
For compatibility with linkers produced by MRI, ld accepts
script files written in an alternate, restricted command
language, described in the MRI Compatible Script Files
section of GNU ld documentation. Introduce MRI script files
with the option -c; use the -T option to run linker scripts
written in the general-purpose ld scripting language. If
MRI-cmdfile does not exist, ld looks for it in the
directories specified by any -L options.
-d
-dc
-dp These three options are equivalent; multiple forms are
supported for compatibility with other linkers. They assign
space to common symbols even if a relocatable output file is
specified (with -r). The script command
"FORCE_COMMON_ALLOCATION" has the same effect.
--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.
--enable-non-contiguous-regions
This option avoids generating an error if an input section
does not fit a matching output section. The linker tries to
allocate the input section to subseque nt matching output
sections, and generates an error only if no output section is
large enough. This is useful when several non-contiguous
memory regions are available and the input section does not
require a particular one. The order in which input sections
are evaluated does not change, for instance:
MEMORY {
MEM1 (rwx) : ORIGIN : 0x1000, LENGTH = 0x14
MEM2 (rwx) : ORIGIN : 0x1000, LENGTH = 0x40
MEM3 (rwx) : ORIGIN : 0x2000, LENGTH = 0x40
}
SECTIONS {
mem1 : { *(.data.*); } > MEM1
mem2 : { *(.data.*); } > MEM2
mem3 : { *(.data.*); } > MEM2
}
with input sections:
.data.1: size 8
.data.2: size 0x10
.data.3: size 4
results in .data.1 affected to mem1, and .data.2 and .data.3
affected to mem2, even though .data.3 would fit in mem3.
This option is incompatible with INSERT statements because it
changes the way input sections are mapped to output sections.
--enable-non-contiguous-regions-warnings
This option enables warnings when
"--enable-non-contiguous-regions" allows possibly unexpected
matches in sections mapping, potentially leading to silently
discarding a section instead of failing because it does not
fit any output region.
-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).
--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.
--export-dynamic-symbol=glob
When creating a dynamically linked executable, symbols
matching glob will be added to the dynamic symbol table. When
creating a shared library, references to symbols matching
glob will not be bound to the definitions within the shared
library. This option is a no-op when creating a shared
library and -Bsymbolic or --dynamic-list are not specified.
This option is only meaningful on ELF platforms which support
shared libraries.
--export-dynamic-symbol-list=file
Specify a --export-dynamic-symbol for each pattern in the
file. The format of the file is the same as the version node
without scope and node name. See VERSION for more
information.
-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.
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 the linker merges input .note.gnu.property sections
into one output .note.gnu.property section, some
properties are removed or updated. These actions are
reported in the link map. For example:
Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
This 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 0xc0010001 (0x1) to merge foo.o (0x1) and bar.o (0x1)
This 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.
--print-map-discarded
--no-print-map-discarded
Print (or do not print) the list of discarded and garbage
collected sections in the link map. Enabled by default.
-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.
--dependency-file=depfile
Write a dependency file to depfile. This file contains a
rule suitable for "make" describing the output file and all
the input files that were read to produce it. The output is
similar to the compiler's output with -M -MP. Note that
there is no option like the compiler's -MM, to exclude
"system files" (which is not a well-specified concept in the
linker, unlike "system headers" in the compiler). So the
output from --dependency-file is always specific to the exact
state of the installation where it was produced, and should
not be copied into distributed makefiles without careful
editing.
-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 one 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. 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.
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.
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.
"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.
cet-report=none
cet-report=warning
cet-report=error
Specify how to report the missing
GNU_PROPERTY_X86_FEATURE_1_IBT and
GNU_PROPERTY_X86_FEATURE_1_SHSTK properties in input
.note.gnu.property section. cet-report=none, which is
the default, will make the linker not report missing
properties in input files. cet-report=warning will make
the linker issue a warning for missing properties in
input files. cet-report=error will make the linker issue
an error for missing properties in input files. Note
that ibt will turn off the missing
GNU_PROPERTY_X86_FEATURE_1_IBT property report and shstk
will turn off the missing
GNU_PROPERTY_X86_FEATURE_1_SHSTK property report.
Supported for Linux/i386 and Linux/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.
unique
nounique
When generating a shared library or other dynamically
loadable ELF object mark it as one that should (by
default) only ever be loaded once, and only in the main
namespace (when using "dlmopen"). This is primarily used
to mark fundamental libraries such as libc, libpthread et
al which do not usually function correctly unless they
are the sole instances of themselves. This behaviour can
be overridden by the "dlmopen" caller and does not apply
to certain loading mechanisms (such as audit libraries).
lam-u48
Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U48 in
.note.gnu.property section to indicate compatibility with
Intel LAM_U48. Supported for Linux/x86_64.
lam-u57
Generate GNU_PROPERTY_X86_FEATURE_1_LAM_U57 in
.note.gnu.property section to indicate compatibility with
Intel LAM_U57. Supported for Linux/x86_64.
lam-u48-report=none
lam-u48-report=warning
lam-u48-report=error
Specify how to report the missing
GNU_PROPERTY_X86_FEATURE_1_LAM_U48 property in input
.note.gnu.property section. lam-u48-report=none, which
is the default, will make the linker not report missing
properties in input files. lam-u48-report=warning will
make the linker issue a warning for missing properties in
input files. lam-u48-report=error will make the linker
issue an error for missing properties in input files.
Supported for Linux/x86_64.
lam-u57-report=none
lam-u57-report=warning
lam-u57-report=error
Specify how to report the missing
GNU_PROPERTY_X86_FEATURE_1_LAM_U57 property in input
.note.gnu.property section. lam-u57-report=none, which
is the default, will make the linker not report missing
properties in input files. lam-u57-report=warning will
make the linker issue a warning for missing properties in
input files. lam-u57-report=error will make the linker
issue an error for missing properties in input files.
Supported for Linux/x86_64.
lam-report=none
lam-report=warning
lam-report=error
Specify how to report the missing
GNU_PROPERTY_X86_FEATURE_1_LAM_U48 and
GNU_PROPERTY_X86_FEATURE_1_LAM_U57 properties in input
.note.gnu.property section. lam-report=none, which is
the default, will make the linker not report missing
properties in input files. lam-report=warning will make
the linker issue a warning for missing properties in
input files. lam-report=error will make the linker issue
an error for missing properties in input files.
Supported for Linux/x86_64.
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.
unique-symbol
nounique-symbol
Avoid duplicated local symbol names in the symbol string
table. Append "."number"" to duplicated local symbol
names if unique-symbol is used. nounique-symbol is the
default.
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.
start-stop-visibility=value
Specify the ELF symbol visibility for synthesized
"__start_SECNAME" and "__stop_SECNAME" symbols. value
must be exactly default, internal, hidden, or protected.
If no -z start-stop-visibility option is given, protected
is used for compatibility with historical practice.
However, it's highly recommended to use -z
start-stop-visibility=hidden in new programs and shared
libraries so that these symbols are not exported between
shared objects, which is not usually what's intended.
text
notext
textoff
Report an error if DT_TEXTREL is set, i.e., if the
position-independent or shared object 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.
x86-64-baseline
x86-64-v2
x86-64-v3
x86-64-v4
Specify the x86-64 ISA level needed in .note.gnu.property
section. x86-64-baseline generates
"GNU_PROPERTY_X86_ISA_1_BASELINE". x86-64-v2 generates
"GNU_PROPERTY_X86_ISA_1_V2". x86-64-v3 generates
"GNU_PROPERTY_X86_ISA_1_V3". x86-64-v4 generates
"GNU_PROPERTY_X86_ISA_1_V4". Supported for Linux/i386
and Linux/x86_64.
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 will 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 is only meaningful on ELF platforms
which support shared libraries.
-Bsymbolic-functions
When creating a shared library, bind references to global
function symbols to the definition within the shared library,
if any. This option is only meaningful on ELF platforms
which support shared libraries.
--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.
--ctf-variables
--no-ctf-variables
The CTF debuginfo format supports a section which encodes the
names and types of variables found in the program which do
not appear in any symbol table. These variables clearly
cannot be looked up by address by conventional debuggers, so
the space used for their types and names is usually wasted:
the types are usually small but the names are often not.
--ctf-variables causes the generation of such a section. The
default behaviour can be restored with --no-ctf-variables.
--ctf-share-types=method
Adjust the method used to share types between translation
units in CTF.
share-unconflicted
Put all types that do not have ambiguous definitions into
the shared dictionary, where debuggers can easily access
them, even if they only occur in one translation unit.
This is the default.
share-duplicated
Put only types that occur in multiple translation units
into the shared dictionary: types with only one
definition go into per-translation-unit dictionaries.
Types with ambiguous definitions in multiple translation
units always go into per-translation-unit dictionaries.
This tends to make the CTF larger, but may reduce the
amount of CTF in the shared dictionary. For very large
projects this may speed up opening the CTF and save
memory in the CTF consumer at runtime.
--no-define-common
This option inhibits the assignment of addresses to common
symbols. The script command "INHIBIT_COMMON_ALLOCATION" has
the same effect.
The --no-define-common option allows decoupling the decision
to assign addresses to Common symbols from the choice of the
output file type; otherwise a 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.
--defsym=symbol=expression
Create a global symbol in the output file, containing the
absolute address given by expression. You may use this
option as many times as necessary to define multiple symbols
in the command line. A limited form of arithmetic is
supported for the expression in this context: you may give a
hexadecimal constant or the name of an existing symbol, or
use "+" and "-" to add or subtract hexadecimal constants or
symbols. If you need more elaborate expressions, consider
using the linker command language from a script. Note: there
should be no white space between symbol, the equals sign
("="), and expression.
The linker processes --defsym arguments and -T arguments in
order, placing --defsym before -T will define the symbol
before the linker script from -T is processed, while placing
--defsym after -T will define the symbol after the linker
script has been processed. This difference has consequences
for expressions within the linker script that use the
--defsym symbols, which order is correct will depend on what
you are trying to achieve.
--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.
As a GNU extension, ELF input sections marked with the
"SHF_GNU_RETAIN" flag will not be garbage collected.
--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.
--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. If mapfile is just the character "-"
then the map will be written to stdout.
Specifying a directory as mapfile causes the linker map to be
written as a file inside the directory. Normally name of the
file inside the directory is computed as the basename of the
output file with ".map" appended. If however the special
character "%" is used then this will be replaced by the full
path of the output file. Additionally if there are any
characters after the % symbol then ".map" will no longer be
appended.
-o foo.exe -Map=bar [Creates ./bar]
-o ../dir/foo.exe -Map=bar [Creates ./bar]
-o foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
-o ../dir2/foo.exe -Map=../dir [Creates ../dir/foo.exe.map]
-o foo.exe -Map=% [Creates ./foo.exe.map]
-o ../dir/foo.exe -Map=% [Creates ../dir/foo.exe.map]
-o foo.exe -Map=%.bar [Creates ./foo.exe.bar]
-o ../dir/foo.exe -Map=%.bar [Creates ../dir/foo.exe.bar]
-o ../dir2/foo.exe -Map=../dir/% [Creates ../dir/../dir2/foo.exe.map]
-o ../dir2/foo.exe -Map=../dir/%.bar [Creates ../dir/../dir2/foo.exe.bar]
It is an error to specify more than one "%" character.
If the map file already exists then it will be overwritten by
this operation.
--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.
--error-handling-script=scriptname
If this option is provided then the linker will invoke
scriptname whenever an error is encountered. Currently
however only two kinds of error are supported: missing
symbols and missing libraries. Two arguments will be passed
to script: the keyword "undefined-symbol" or `missing-lib"
and the name of the undefined symbol or missing library. The
intention is that the script will provide suggestions to the
user as to where the symbol or library might be found. After
the script has finished then the normal linker error message
will be displayed.
The availability of this option is controlled by a configure
time switch, so it may not be present in specific
implementations.
--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.
--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.
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 the feature is supported, the option
--no-relax will disable it.
On platforms where the feature is not supported, both --relax
and --no-relax are accepted, but ignored.
--retain-symbols-file=filename
Retain only the symbols listed in the file filename,
discarding all others. filename is simply a flat file, with
one symbol name per line. This option is especially useful
in environments (such as VxWorks) where a large global symbol
table is accumulated gradually, to conserve run-time memory.
--retain-symbols-file does not discard undefined symbols, or
symbols needed for relocations.
You may only specify --retain-symbols-file once in the
command line. It overrides -s and -S.
-rpath=dir
Add a directory to the runtime library search path. This is
used when linking an ELF executable with shared objects. All
-rpath arguments are concatenated and passed to the runtime
linker, which uses them to locate shared objects at runtime.
The -rpath option is also used when locating shared objects
which are needed by shared objects explicitly included in the
link; see the description of the -rpath-link option.
Searching -rpath in this way is only supported by native
linkers and cross linkers which have been configured with the
--with-sysroot 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 linker for a Linux system, if the file
/etc/ld.so.conf exists, the list of directories found in
that file. Note: the path to this file is prefixed with
the "sysroot" value, if that is defined, and then any
"prefix" string if the linker was configured with the
--prefix=<path> option.
9. For a native linker on a FreeBSD system, any directories
specified by the "_PATH_ELF_HINTS" macro defined in the
elf-hints.h header file.
10. Any directories specifed by a "SEARCH_DIR" command in the
linker script being used.
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.
--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.
--warn-textrel
Warn if the linker adds DT_TEXTREL to a position-independent
executable or 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.
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
--disable-high-entropy-va
Image is compatible with 64-bit address space layout
randomization (ASLR). This option is enabled by default for
64-bit PE images.
This option also implies --dynamicbase and
--enable-reloc-section.
--dynamicbase
--disable-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. This option is
enabled by default but can be disabled via the
--disable-dynamicbase option. This option also implies
--enable-reloc-section.
--forceinteg
--disable-forceinteg
Code integrity checks are enforced. This option is disabled
by default.
--nxcompat
--disable-nxcompat
The image is compatible with the Data Execution Prevention.
This feature was introduced with MS Windows XP SP2 for i386
PE targets. The option is enabled by default.
--no-isolation
--disable-no-isolation
Although the image understands isolation, do not isolate the
image. This option is disabled by default.
--no-seh
--disable-no-seh
The image does not use SEH. No SE handler may be called from
this image. This option is disabled by default.
--no-bind
--disable-no-bind
Do not bind this image. This option is disabled by default.
--wdmdriver
--disable-wdmdriver
The driver uses the MS Windows Driver Model. This option is
disabled by default.
--tsaware
--disable-tsaware
The image is Terminal Server aware. This option is disabled
by default.
--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.
--enable-reloc-section
--disable-reloc-section
Create the base relocation table, which is necessary if the
image is loaded at a different image base than specified in
the PE header. This option is enabled by default.
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.
--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.
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.
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.
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.
--compact-branches
--no-compact-branches
These options control the generation of compact instructions
by the linker in the PLT entries for MIPS R6.
For the pdp11-aout target, three variants of the output format
can be produced as selected by the following options. The
default variant for pdp11-aout is the --omagic option, whereas
for other targets --nmagic is the default. The --imagic option
is defined only for the pdp11-aout target, while the others are
described here as they apply to the pdp11-aout target.
-N
--omagic
Mark the output as "OMAGIC" (0407) in the a.out header to
indicate that the text segment is not to be write-protected
and shared. Since the text and data sections are both
readable and writable, the data section is allocated
immediately contiguous after the text segment. This is the
oldest format for PDP11 executable programs and is the
default for ld on PDP11 Unix systems from the beginning
through 2.11BSD.
-n
--nmagic
Mark the output as "NMAGIC" (0410) in the a.out header to
indicate that when the output file is executed, the text
portion will be read-only and shareable among all processes
executing the same file. This involves moving the data areas
up to the first possible 8K byte page boundary following the
end of the text. This option creates a pure executable
format.
-z
--imagic
Mark the output as "IMAGIC" (0411) in the a.out header to
indicate that when the output file is executed, the program
text and data areas will be loaded into separate address
spaces using the split instruction and data space feature of
the memory management unit in larger models of the PDP11.
This doubles the address space available to the program. The
text segment is again pure, write-protected, and shareable.
The only difference in the output format between this option
and the others, besides the magic number, is that both the
text and data sections start at location 0. The -z option
selected this format in 2.11BSD. This option creates a
separate executable format.
--no-omagic
Equivalent to --nmagic for pdp11-aout.
