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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENVIRONMENT | SEE ALSO | COPYRIGHT | COLOPHON |
LD(1) GNU Development Tools LD(1)
ld - The GNU linker
ld [options] objfile ...
ld combines a number of object and archive files, relocates their
data and ties up symbol references. Usually the last step in
compiling a program is to run ld.
ld accepts Linker Command Language files written in a superset of
AT&T's Link Editor Command Language syntax, to provide explicit and
total control over the linking process.
This man page does not describe the command language; see the ld
entry in "info" for full details on the command language and on other
aspects of the GNU linker.
This version of ld uses the general purpose BFD libraries to operate
on object files. This allows ld to read, combine, and write object
files in many different formats---for example, COFF or "a.out".
Different formats may be linked together to produce any available
kind of object file.
Aside from its flexibility, the GNU linker is more helpful than other
linkers in providing diagnostic information. Many linkers abandon
execution immediately upon encountering an error; whenever possible,
ld continues executing, allowing you to identify other errors (or, in
some cases, to get an output file in spite of the error).
The GNU linker ld is meant to cover a broad range of situations, and
to be as compatible as possible with other linkers. As a result, you
have many choices to control its behavior.
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.
-A architecture
--architecture=architecture
In the current release of ld, this option is useful only for the
Intel 960 family of architectures. In that ld configuration, the
architecture argument identifies the particular architecture in
the 960 family, enabling some safeguards and modifying the
archive-library search path.
Future releases of ld may support similar functionality for other
architecture families.
-b input-format
--format=input-format
ld may be configured to support more than one kind of object
file. If your ld is configured this way, you can use the -b
option to specify the binary format for input object files that
follow this option on the command line. Even when ld is
configured to support alternative object formats, you don't
usually need to specify this, as ld should be configured to
expect as a default input format the most usual format on each
machine. input-format is a text string, the name of a particular
format supported by the BFD libraries. (You can list the
available binary formats with objdump -i.)
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.
-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.
-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 "=", then the "=" 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.
-n
--nmagic
Turn off page alignment of sections, and disable linking against
shared libraries. If the output format supports Unix style magic
numbers, mark the output as "NMAGIC".
-N
--omagic
Set the text and data sections to be readable and writable.
Also, do not page-align the data segment, and disable linking
against shared libraries. If the output format supports Unix
style magic numbers, mark the output as "OMAGIC". Note: Although
a writable text section is allowed for PE-COFF targets, it does
not conform to the format specification published by Microsoft.
--no-omagic
This option negates most of the effects of the -N option. It
sets the text section to be read-only, and forces the data
segment to be page-aligned. Note - this option does not enable
linking against shared libraries. Use -Bdynamic for this.
-o output
--output=output
Use output as the name for the program produced by ld; if this
option is not specified, the name a.out is used by default. The
script command "OUTPUT" can also specify the output file name.
-O level
If level is a numeric values greater than zero ld optimizes the
output. This might take significantly longer and therefore
probably should only be enabled for the final binary. At the
moment this option only affects ELF shared library generation.
Future releases of the linker may make more use of this option.
Also currently there is no difference in the linker's behaviour
for different non-zero values of this option. Again this may
change with future releases.
--push-state
The --push-state allows to preserve the current state of the
flags which govern the input file handling so that they can all
be restored with one corresponding --pop-state option.
The option which are covered are: -Bdynamic, -Bstatic, -dn, -dy,
-call_shared, -non_shared, -static, -N, -n, --whole-archive,
--no-whole-archive, -r, -Ur, --copy-dt-needed-entries,
--no-copy-dt-needed-entries, --as-needed, --no-as-needed, and -a.
One target for this option are specifications for pkg-config.
When used with the --libs option all possibly needed libraries
are listed and then possibly linked with all the time. It is
better to return something as follows:
-Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
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.
-t
--trace
Print the names of the input files as ld processes them.
-T scriptfile
--script=scriptfile
Use scriptfile as the linker script. This script replaces ld's
default linker script (rather than adding to it), so commandfile
must specify everything necessary to describe the output file.
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 effects 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:
combreloc
Combines multiple reloc sections and sorts them to make
dynamic symbol lookup caching possible.
common
Generate common symbols with the STT_COMMON type druing a
relocatable link.
defs
Disallows undefined symbols in object files. Undefined
symbols in shared libraries are still allowed.
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.
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
Marks the object that its symbol table interposes before all
symbols but the primary executable.
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
Marks the object that its filters be processed immediately
at runtime.
muldefs
Allows multiple definitions.
nocombreloc
Disables multiple reloc sections combining.
nocommon
Generate common symbols with the STT_OBJECT type druing a
relocatable link.
nocopyreloc
Disable linker generated .dynbss variables used in place of
variables defined in shared libraries. May result in dynamic
text relocations.
nodefaultlib
Marks the object that the search for dependencies of this
object will ignore any default library search paths.
nodelete
Marks the object shouldn't be unloaded at runtime.
nodlopen
Marks the object not available to "dlopen".
nodump
Marks the object can not be dumped by "dldump".
noexecstack
Marks the object as not requiring executable stack.
text
Treat DT_TEXTREL in shared object as error.
notext
Don't treat DT_TEXTREL in shared object as error.
textoff
Don't treat DT_TEXTREL in shared object as error.
norelro
Don't create an ELF "PT_GNU_RELRO" segment header in the
object.
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 linked to
using dlopen, instead of deferring function call resolution
to the point when the function is first called.
origin
Marks the object may contain $ORIGIN.
relro
Create an ELF "PT_GNU_RELRO" segment header in the object.
max-page-size=value
Set the emulation maximum page size to value.
common-page-size=value
Set the emulation common page size to value.
stack-size=value
Specify a stack size for in an ELF "PT_GNU_STACK" segment.
Specifying zero will override any default non-zero sized
"PT_GNU_STACK" segment creation.
bndplt
Always generate BND prefix in PLT entries. Supported for
Linux/x86_64.
noextern-protected-data
Don't treat protected data symbol as external when building
shared library. This option overrides linker backend
default. It can be used to workaround 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.
nodynamic-undefined-weak
Don't treat undefined weak symbols as dynamic when building
executable. This option overrides linker backend default.
It can be used to avoid dynamic relocations against undefined
weak symbols in executable. 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.
call-nop=prefix-addr
call-nop=prefix-nop
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=prefix-nop generates "0x90 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.
Other keywords are ignored for Solaris compatibility.
-( archives -)
--start-group archives --end-group
The archives should be a list of archive files. They may be
either explicit file names, or -l options.
The specified archives are searched repeatedly until no new
undefined references are created. Normally, an archive is
searched only once in the order that it is specified on the
command line. If a symbol in that archive is needed to resolve
an undefined symbol referred to by an object in an archive that
appears later on the command line, the linker would not be able
to resolve that reference. By grouping the archives, they all be
searched repeatedly until all possible references are resolved.
Using this option has a significant performance cost. It is best
to use it only when there are unavoidable circular references
between two or more archives.
--accept-unknown-input-arch
--no-accept-unknown-input-arch
Tells the linker to accept input files whose architecture cannot
be recognised. The assumption is that the user knows what they
are doing and deliberately wants to link in these unknown input
files. This was the default behaviour of the linker, before
release 2.14. The default behaviour from release 2.14 onwards is
to reject such input files, and so the
--accept-unknown-input-arch option has been added to restore the
old behaviour.
--as-needed
--no-as-needed
This option affects ELF DT_NEEDED tags for dynamic libraries
mentioned on the command line after the --as-needed option.
Normally the linker will add a DT_NEEDED tag for each dynamic
library mentioned on the command line, regardless of whether the
library is actually needed or not. --as-needed causes a
DT_NEEDED tag to only be emitted for a library that at that point
in the link satisfies a non-weak undefined symbol reference from
a regular object file or, if the library is not found in the
DT_NEEDED lists of other needed libraries, a non-weak undefined
symbol reference from another needed dynamic library. Object
files or libraries appearing on the command line after the
library in question do not affect whether the library is seen as
needed. This is similar to the rules for extraction of object
files from archives. --no-as-needed restores the default
behaviour.
--add-needed
--no-add-needed
These two options have been deprecated because of the similarity
of their names to the --as-needed and --no-as-needed options.
They have been replaced by --copy-dt-needed-entries and
--no-copy-dt-needed-entries.
-assert keyword
This option is ignored for SunOS compatibility.
-Bdynamic
-dy
-call_shared
Link against dynamic libraries. This is only meaningful on
platforms for which shared libraries are supported. This option
is normally the default on such platforms. The different
variants of this option are for compatibility with various
systems. You may use this option multiple times on the command
line: it affects library searching for -l options which follow
it.
-Bgroup
Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the
dynamic section. This causes the runtime linker to handle
lookups in this object and its dependencies to be performed only
inside the group. --unresolved-symbols=report-all is implied.
This option is only meaningful on ELF platforms which support
shared libraries.
-Bstatic
-dn
-non_shared
-static
Do not link against shared libraries. This is only meaningful on
platforms for which shared libraries are supported. The
different variants of this option are for compatibility with
various systems. You may use this option multiple times on the
command line: it affects library searching for -l options which
follow it. This option also implies
--unresolved-symbols=report-all. This option can be used with
-shared. Doing so means that a shared library is being created
but that all of the library's external references must be
resolved by pulling in entries from static libraries.
-Bsymbolic
When creating a shared library, bind references to global symbols
to the definition within the shared library, if any. Normally,
it is possible for a program linked against a shared library to
override the definition within the shared library. This option
can also be used with the --export-dynamic option, when creating
a position independent executable, to bind references to global
symbols to the definition within the executable. This option is
only meaningful on ELF platforms which support shared libraries
and position independent executables.
-Bsymbolic-functions
When creating a shared library, bind references to global
function symbols to the definition within the shared library, if
any. This option can also be used with the --export-dynamic
option, when creating a position independent executable, to bind
references to global function symbols to the definition within
the executable. This option is only meaningful on ELF platforms
which support shared libraries and position independent
executables.
--dynamic-list=dynamic-list-file
Specify the name of a dynamic list file to the linker. This is
typically used when creating shared libraries to specify a list
of global symbols whose references shouldn't be bound to the
definition within the shared library, or creating dynamically
linked executables to specify a list of symbols which should be
added to the symbol table in the executable. This option is only
meaningful on ELF platforms which support shared libraries.
The format of the dynamic list is the same as the version node
without scope and node name. See VERSION for more information.
--dynamic-list-data
Include all global data symbols to the dynamic list.
--dynamic-list-cpp-new
Provide the builtin dynamic list for C++ operator new and delete.
It is mainly useful for building shared libstdc++.
--dynamic-list-cpp-typeinfo
Provide the builtin dynamic list for C++ runtime type
identification.
--check-sections
--no-check-sections
Asks the linker not to check section addresses after they have
been assigned to see if there are any overlaps. Normally the
linker will perform this check, and if it finds any overlaps it
will produce suitable error messages. The linker does know
about, and does make allowances for sections in overlays. The
default behaviour can be restored by using the command line
switch --check-sections. Section overlap is not usually checked
for relocatable links. You can force checking in that case by
using the --check-sections option.
--copy-dt-needed-entries
--no-copy-dt-needed-entries
This option affects the treatment of dynamic libraries referred
to by DT_NEEDED tags inside ELF dynamic libraries mentioned on
the command line. Normally the linker won't add a DT_NEEDED tag
to the output binary for each library mentioned in a DT_NEEDED
tag in an input dynamic library. With --copy-dt-needed-entries
specified on the command line however any dynamic libraries that
follow it will have their DT_NEEDED entries added. The default
behaviour can be restored with --no-copy-dt-needed-entries.
This option also has an effect on the resolution of symbols in
dynamic libraries. With --copy-dt-needed-entries dynamic
libraries mentioned on the command line will be recursively
searched, following their DT_NEEDED tags to other libraries, in
order to resolve symbols required by the output binary. With the
default setting however the searching of dynamic libraries that
follow it will stop with the dynamic library itself. No
DT_NEEDED links will be traversed to resolve symbols.
--cref
Output a cross reference table. If a linker map file is being
generated, the cross reference table is printed to the map file.
Otherwise, it is printed on the standard output.
The format of the table is intentionally simple, so that it may
be easily processed by a script if necessary. The symbols are
printed out, sorted by name. For each symbol, a list of file
names is given. If the symbol is defined, the first file listed
is the location of the definition. If the symbol is defined as a
common value then any files where this happens appear next.
Finally any files that reference the symbol are listed.
--no-define-common
This option inhibits the assignment of addresses to common
symbols. The script command "INHIBIT_COMMON_ALLOCATION" has the
same effect.
The --no-define-common option allows decoupling the decision to
assign addresses to Common symbols from the choice of the output
file type; otherwise a non-Relocatable output type forces
assigning addresses to Common symbols. Using --no-define-common
allows Common symbols that are referenced from a shared library
to be assigned addresses only in the main program. This
eliminates the unused duplicate space in the shared library, and
also prevents any possible confusion over resolving to the wrong
duplicate when there are many dynamic modules with specialized
search paths for runtime symbol resolution.
--defsym=symbol=expression
Create a global symbol in the output file, containing the
absolute address given by expression. You may use this option as
many times as necessary to define multiple symbols in the command
line. A limited form of arithmetic is supported for the
expression in this context: you may give a hexadecimal constant
or the name of an existing symbol, or use "+" and "-" to add or
subtract hexadecimal constants or symbols. If you need more
elaborate expressions, consider using the linker command language
from a script. Note: there should be no white space between
symbol, the equals sign ("="), and expression.
--demangle[=style]
--no-demangle
These options control whether to demangle symbol names in error
messages and other output. When the linker is told to demangle,
it tries to present symbol names in a readable fashion: it strips
leading underscores if they are used by the object file format,
and converts C++ mangled symbol names into user readable names.
Different compilers have different mangling styles. The optional
demangling style argument can be used to choose an appropriate
demangling style for your compiler. The linker will demangle by
default unless the environment variable COLLECT_NO_DEMANGLE is
set. These options may be used to override the default.
-Ifile
--dynamic-linker=file
Set the name of the dynamic linker. This is only meaningful when
generating dynamically linked ELF executables. The default
dynamic linker is normally correct; don't use this unless you
know what you are doing.
--no-dynamic-linker
When producing an executable file, omit the request for a dynamic
linker to be used at load-time. This is only meaningful for ELF
executables that contain dynamic relocations, and usually
requires entry point code that is capable of processing these
relocations.
--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 and --undefined.
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 an --entry or --undefined option
or by a "ENTRY" command in the linker script.
--print-gc-sections
--no-print-gc-sections
List all sections removed by garbage collection. The listing is
printed on stderr. This option is only effective if garbage
collection has been enabled via the --gc-sections) option. The
default behaviour (of not listing the sections that are removed)
can be restored by specifying --no-print-gc-sections on the
command line.
--gc-keep-exported
When --gc-sections is enabled, this option prevents garbage
collection of unused input sections that contain global symbols
having default or protected visibility. This option is intended
to be used for executables where unreferenced sections would
otherwise be garbage collected regardless of the external
visibility of contained symbols. Note that this option has no
effect when linking shared objects since it is already the
default behaviour. This option is only supported for ELF format
targets.
--print-output-format
Print the name of the default output format (perhaps influenced
by other command-line options). This is the string that would
appear in an "OUTPUT_FORMAT" linker script command.
--print-memory-usage
Print used size, total size and used size of memory regions
created with the MEMORY command. This is useful on embedded
targets to have a quick view of amount of free memory. The
format of the output has one headline and one line per region.
It is both human readable and easily parsable by tools. Here is
an example of an output:
Memory region Used Size Region Size %age Used
ROM: 256 KB 1 MB 25.00%
RAM: 32 B 2 GB 0.00%
--help
Print a summary of the command-line options on the standard
output and exit.
--target-help
Print a summary of all target specific options on the standard
output and exit.
-Map=mapfile
Print a link map to the file mapfile. See the description of the
-M option, above.
--no-keep-memory
ld normally optimizes for speed over memory usage by caching the
symbol tables of input files in memory. This option tells ld to
instead optimize for memory usage, by rereading the symbol tables
as necessary. This may be required if ld runs out of memory
space while linking a large executable.
--no-undefined
-z defs
Report unresolved symbol references from regular object files.
This is done even if the linker is creating a non-symbolic shared
library. The switch --[no-]allow-shlib-undefined controls the
behaviour for reporting unresolved references found in shared
libraries being linked in.
--allow-multiple-definition
-z muldefs
Normally when a symbol is defined multiple times, the linker will
report a fatal error. These options allow multiple definitions
and the first definition will be used.
--allow-shlib-undefined
--no-allow-shlib-undefined
Allows or disallows undefined symbols in shared libraries. This
switch is similar to --no-undefined except that it determines the
behaviour when the undefined symbols are in a shared library
rather than a regular object file. It does not affect how
undefined symbols in regular object files are handled.
The default behaviour is to report errors for any undefined
symbols referenced in shared libraries if the linker is being
used to create an executable, but to allow them if the linker is
being used to create a shared library.
The reasons for allowing undefined symbol references in shared
libraries specified at link time are that:
· A shared library specified at link time may not be the same
as the one that is available at load time, so the symbol
might actually be resolvable at load time.
· There are some operating systems, eg BeOS and HPPA, where
undefined symbols in shared libraries are normal.
The BeOS kernel for example patches shared libraries at load
time to select whichever function is most appropriate for the
current architecture. This is used, for example, to
dynamically select an appropriate memset function.
--no-undefined-version
Normally when a symbol has an undefined version, the linker will
ignore it. This option disallows symbols with undefined version
and a fatal error will be issued instead.
--default-symver
Create and use a default symbol version (the soname) for
unversioned exported symbols.
--default-imported-symver
Create and use a default symbol version (the soname) for
unversioned imported symbols.
--no-warn-mismatch
Normally ld will give an error if you try to link together input
files that are mismatched for some reason, perhaps because they
have been compiled for different processors or for different
endiannesses. This option tells ld that it should silently
permit such possible errors. This option should only be used
with care, in cases when you have taken some special action that
ensures that the linker errors are inappropriate.
--no-warn-search-mismatch
Normally ld will give a warning if it finds an incompatible
library during a library search. This option silences the
warning.
--no-whole-archive
Turn off the effect of the --whole-archive option for subsequent
archive files.
--noinhibit-exec
Retain the executable output file whenever it is still usable.
Normally, the linker will not produce an output file if it
encounters errors during the link process; it exits without
writing an output file when it issues any error whatsoever.
-nostdlib
Only search library directories explicitly specified on the
command line. Library directories specified in linker scripts
(including linker scripts specified on the command line) are
ignored.
--oformat=output-format
ld may be configured to support more than one kind of object
file. If your ld is configured this way, you can use the
--oformat option to specify the binary format for the output
object file. Even when ld is configured to support alternative
object formats, you don't usually need to specify this, as ld
should be configured to produce as a default output format the
most usual format on each machine. output-format is a text
string, the name of a particular format supported by the BFD
libraries. (You can list the available binary formats with
objdump -i.) The script command "OUTPUT_FORMAT" can also specify
the output format, but this option overrides it.
--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 this is not supported, --relax is accepted,
but ignored.
On platforms where --relax is accepted the option --no-relax can
be used to disable the feature.
--retain-symbols-file=filename
Retain only the symbols listed in the file filename, discarding
all others. filename is simply a flat file, with one symbol name
per line. This option is especially useful in environments (such
as VxWorks) where a large global symbol table is accumulated
gradually, to conserve run-time memory.
--retain-symbols-file does not discard undefined symbols, or
symbols needed for relocations.
You may only specify --retain-symbols-file once in the command
line. It overrides -s and -S.
-rpath=dir
Add a directory to the runtime library search path. This is used
when linking an ELF executable with shared objects. All -rpath
arguments are concatenated and passed to the runtime linker,
which uses them to locate shared objects at runtime. The -rpath
option is also used when locating shared objects which are needed
by shared objects explicitly included in the link; see the
description of the -rpath-link option. If -rpath is not used
when linking an ELF executable, the contents of the environment
variable "LD_RUN_PATH" will be used if it is defined.
The -rpath option may also be used on SunOS. By default, on
SunOS, the linker will form a runtime search path out of all the
-L options it is given. If a -rpath option is used, the runtime
search path will be formed exclusively using the -rpath options,
ignoring the -L options. This can be useful when using gcc,
which adds many -L options which may be on NFS mounted file
systems.
For compatibility with other ELF linkers, if the -R option is
followed by a directory name, rather than a file name, it is
treated as the -rpath option.
-rpath-link=dir
When using ELF or SunOS, one shared library may require another.
This happens when an "ld -shared" link includes a shared library
as one of the input files.
When the linker encounters such a dependency when doing a non-
shared, non-relocatable link, it will automatically try to locate
the required shared library and include it in the link, if it is
not included explicitly. In such a case, the -rpath-link option
specifies the first set of directories to search. The
-rpath-link option may specify a sequence of directory names
either by specifying a list of names separated by colons, or by
appearing multiple times.
The tokens $ORIGIN and $LIB can appear in these search
directories. They will be replaced by the full path to the
directory containing the program or shared object in the case of
$ORIGIN and either lib - for 32-bit binaries - or lib64 - for
64-bit binaries - in the case of $LIB.
The alternative form of these tokens - ${ORIGIN} and ${LIB} can
also be used. The token $PLATFORM is not supported.
This option should be used with caution as it overrides the
search path that may have been hard compiled into a shared
library. In such a case it is possible to use unintentionally a
different search path than the runtime linker would do.
The linker uses the following search paths to locate required
shared libraries:
1. Any directories specified by -rpath-link options.
2. Any directories specified by -rpath options. The difference
between -rpath and -rpath-link is that directories specified
by -rpath options are included in the executable and used at
runtime, whereas the -rpath-link option is only effective at
link time. Searching -rpath in this way is only supported by
native linkers and cross linkers which have been configured
with the --with-sysroot option.
3. On an ELF system, for native linkers, if the -rpath and
-rpath-link options were not used, search the contents of the
environment variable "LD_RUN_PATH".
4. On SunOS, if the -rpath option was not used, search any
directories specified using -L options.
5. For a native linker, search the contents of the environment
variable "LD_LIBRARY_PATH".
6. For a native ELF linker, the directories in "DT_RUNPATH" or
"DT_RPATH" of a shared library are searched for shared
libraries needed by it. The "DT_RPATH" entries are ignored if
"DT_RUNPATH" entries exist.
7. The default directories, normally /lib and /usr/lib.
8. For a native linker on an ELF system, if the file
/etc/ld.so.conf exists, the list of directories found in that
file.
If the required shared library is not found, the linker will
issue a warning and continue with the link.
-shared
-Bshareable
Create a shared library. This is currently only supported on
ELF, XCOFF and SunOS platforms. On SunOS, the linker will
automatically create a shared library if the -e option is not
used and there are undefined symbols in the link.
--sort-common
--sort-common=ascending
--sort-common=descending
This option tells ld to sort the common symbols by alignment in
ascending or descending order when it places them in the
appropriate output sections. The symbol alignments considered
are sixteen-byte or larger, eight-byte, four-byte, two-byte, and
one-byte. This is to prevent gaps between symbols due to
alignment constraints. If no sorting order is specified, then
descending order is assumed.
--sort-section=name
This option will apply "SORT_BY_NAME" to all wildcard section
patterns in the linker script.
--sort-section=alignment
This option will apply "SORT_BY_ALIGNMENT" to all wildcard
section patterns in the linker script.
--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.
--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-shared-textrel
Warn if the linker adds a DT_TEXTREL to a shared object.
--warn-alternate-em
Warn if an object has alternate ELF machine code.
--warn-unresolved-symbols
If the linker is going to report an unresolved symbol (see the
option --unresolved-symbols) it will normally generate an error.
This option makes it generate a warning instead.
--error-unresolved-symbols
This restores the linker's default behaviour of generating errors
when it is reporting unresolved symbols.
--whole-archive
For each archive mentioned on the command line after the
--whole-archive option, include every object file in the archive
in the link, rather than searching the archive for the required
object files. This is normally used to turn an archive file into
a shared library, forcing every object to be included in the
resulting shared library. This option may be used more than
once.
Two notes when using this option from gcc: First, gcc doesn't
know about this option, so you have to use -Wl,-whole-archive.
Second, don't forget to use -Wl,-no-whole-archive after your list
of archives, because gcc will add its own list of archives to
your link and you may not want this flag to affect those as well.
--wrap=symbol
Use a wrapper function for symbol. Any undefined reference to
symbol will be resolved to "__wrap_symbol". Any undefined
reference to "__real_symbol" will be resolved to symbol.
This can be used to provide a wrapper for a system function. The
wrapper function should be called "__wrap_symbol". If it wishes
to call the system function, it should call "__real_symbol".
Here is a trivial example:
void *
__wrap_malloc (size_t c)
{
printf ("malloc called with %zu\n", c);
return __real_malloc (c);
}
If you link other code with this file using --wrap malloc, then
all calls to "malloc" will call the function "__wrap_malloc"
instead. The call to "__real_malloc" in "__wrap_malloc" will
call the real "malloc" function.
You may wish to provide a "__real_malloc" function as well, so
that links without the --wrap option will succeed. If you do
this, you should not put the definition of "__real_malloc" in the
same file as "__wrap_malloc"; if you do, the assembler may
resolve the call before the linker has a chance to wrap it to
"malloc".
--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 is
"sysv".
--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, and create the necessary thunking symbols when
building the import libraries with those DATA exports. 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). [This option is specific to the i386 PE targeted
port of the linker]
--disable-auto-import
Do not attempt to do sophisticated linking of "_symbol" to
"__imp__symbol" for DATA imports from DLLs. [This option is
specific to the i386 PE targeted port of the linker]
--enable-runtime-pseudo-reloc
If your code contains expressions described in
--enable-auto-import section, that is, DATA imports from DLL with
non-zero offset, this switch will create a vector of 'runtime
pseudo relocations' which can be used by runtime environment to
adjust references to such data in your client code. [This option
is specific to the i386 PE targeted port of the linker]
--disable-runtime-pseudo-reloc
Do not create pseudo relocations for non-zero offset DATA imports
from DLLs. [This option is specific to the i386 PE targeted port
of the linker]
--enable-extra-pe-debug
Show additional debug info related to auto-import symbol
thunking. [This option is specific to the i386 PE targeted port
of the linker]
--section-alignment
Sets the section alignment. Sections in memory will always begin
at addresses which are a multiple of this number. Defaults to
0x1000. [This option is specific to the i386 PE targeted port of
the linker]
--stack reserve
--stack reserve,commit
Specify the number of bytes of memory to reserve (and optionally
commit) to be used as stack for this program. The default is 2MB
reserved, 4K committed. [This option is specific to the i386 PE
targeted port of the linker]
--subsystem which
--subsystem which:major
--subsystem which:major.minor
Specifies the subsystem under which your program will execute.
The legal values for which are "native", "windows", "console",
"posix", and "xbox". You may optionally set the subsystem
version also. Numeric values are also accepted for which. [This
option is specific to the i386 PE targeted port of the linker]
The following options set flags in the "DllCharacteristics" field
of the PE file header: [These options are specific to PE targeted
ports of the linker]
--high-entropy-va
Image is compatible with 64-bit address space layout
randomization (ASLR).
--dynamicbase
The image base address may be relocated using address space
layout randomization (ASLR). This feature was introduced with MS
Windows Vista for i386 PE targets.
--forceinteg
Code integrity checks are enforced.
--nxcompat
The image is compatible with the Data Execution Prevention. This
feature was introduced with MS Windows XP SP2 for i386 PE
targets.
--no-isolation
Although the image understands isolation, do not isolate the
image.
--no-seh
The image does not use SEH. No SE handler may be called from this
image.
--no-bind
Do not bind this image.
--wdmdriver
The driver uses the MS Windows Driver Model.
--tsaware
The image is Terminal Server aware.
--insert-timestamp
--no-insert-timestamp
Insert a real timestamp into the image. This is the default
behaviour as it matches legacy code and it means that the image
will work with other, proprietary tools. The problem with this
default is that it will result in slightly different images being
produced each time the same sources are linked. The option
--no-insert-timestamp can be used to insert a zero value for the
timestamp, this ensuring that binaries produced from identical
sources will compare identically.
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.
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.
You can change the behaviour of ld with the environment variables
"GNUTARGET", "LDEMULATION" and "COLLECT_NO_DEMANGLE".
"GNUTARGET" determines the input-file object format if you don't use
-b (or its synonym --format). Its value should be one of the BFD
names for an input format. If there is no "GNUTARGET" in the
environment, ld uses the natural format of the target. If "GNUTARGET"
is set to "default" then BFD attempts to discover the input format by
examining binary input files; this method often succeeds, but there
are potential ambiguities, since there is no method of ensuring that
the magic number used to specify object-file formats is unique.
However, the configuration procedure for BFD on each system places
the conventional format for that system first in the search-list, so
ambiguities are resolved in favor of convention.
"LDEMULATION" determines the default emulation if you don't use the
-m option. The emulation can affect various aspects of linker
behaviour, particularly the default linker script. You can list the
available emulations with the --verbose or -V options. If the -m
option is not used, and the "LDEMULATION" environment variable is not
defined, the default emulation depends upon how the linker was
configured.
Normally, the linker will default to demangling symbols. However, if
"COLLECT_NO_DEMANGLE" is set in the environment, then it will default
to not demangling symbols. This environment variable is used in a
similar fashion by the "gcc" linker wrapper program. The default may
be overridden by the --demangle and --no-demangle options.
ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries
for binutils and ld.
Copyright (c) 1991-2017 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
"GNU Free Documentation License".
This page is part of the binutils (a collection of tools for working
with executable binaries) project. Information about the project can
be found at ⟨http://www.gnu.org/software/binutils/⟩. If you have a
bug report for this manual page, see
⟨http://sourceware.org/bugzilla/enter_bug.cgi?product=binutils⟩. This
page was obtained from the tarball binutils-2.28.tar.gz fetched from
⟨https://ftp.gnu.org/gnu/binutils/⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
binutils-2.28 2017-03-02 LD(1)
Pages that refer to this page: uselib(2), backtrace(3), dlopen(3), elf(5), ld.so(8)