Provided by: binutils-avr_2.25+Atmel3.5.0-2_amd64 
NAME
ld - The GNU linker
SYNOPSIS
ld [options] objfile ...
DESCRIPTION
ld combines a number of object and archive files, relocates their data and ties up symbol references.
Usually the last step in compiling a program is to run ld.
ld accepts Linker Command Language files written in a superset of AT&T's Link Editor Command Language
syntax, to provide explicit and total control over the linking process.
This man page does not describe the command language; see the ld entry in "info" for full details on the
command language and on other aspects of the GNU linker.
This version of ld uses the general purpose BFD libraries to operate on object files. This allows ld to
read, combine, and write object files in many different formats---for example, COFF or "a.out".
Different formats may be linked together to produce any available kind of object file.
Aside from its flexibility, the GNU linker is more helpful than other linkers in providing diagnostic
information. Many linkers abandon execution immediately upon encountering an error; whenever possible,
ld continues executing, allowing you to identify other errors (or, in some cases, to get an output file
in spite of the error).
The GNU linker ld is meant to cover a broad range of situations, and to be as compatible as possible with
other linkers. As a result, you have many choices to control its behavior.
OPTIONS
The linker supports a plethora of 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.
-Ur For anything other than C++ programs, this option is equivalent to -r: it generates relocatable
output---i.e., an output file that can in turn serve as input to ld. When linking C++ programs, -Ur
does resolve references to constructors, unlike -r. It does not work to use -Ur on files that were
themselves linked with -Ur; once the constructor table has been built, it cannot be added to. Use
-Ur only for the last partial link, and -r for the others.
--unique[=SECTION]
Creates a separate output section for every input section matching SECTION, or if the optional
wildcard SECTION argument is missing, for every orphan input section. An orphan section is one not
specifically mentioned in a linker script. You may use this option multiple times on the command
line; It prevents the normal merging of input sections with the same name, overriding output section
assignments in a linker script.
-v
--version
-V Display the version number for ld. The -V option also lists the supported emulations.
-x
--discard-all
Delete all local symbols.
-X
--discard-locals
Delete all temporary local symbols. (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.
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.
nocopyreloc
Disables production of copy relocs.
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.
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.
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 is only meaningful on ELF platforms which
support shared libraries.
-Bsymbolic-functions
When creating a shared library, bind references to global function symbols to the definition within
the shared library, if any. This option is only meaningful on ELF platforms which support shared
libraries.
--dynamic-list=dynamic-list-file
Specify the name of a dynamic list file to the linker. This is typically used when creating shared
libraries to specify a list of global symbols whose references shouldn't be bound to the definition
within the shared library, or creating dynamically linked executables to specify a list of symbols
which should be added to the symbol table in the executable. This option is only meaningful on ELF
platforms which support shared libraries.
The format of the dynamic list is the same as the version node without scope and node name. See
VERSION for more information.
--dynamic-list-data
Include all global data symbols to the dynamic list.
--dynamic-list-cpp-new
Provide the builtin dynamic list for C++ operator new and delete. It is mainly useful for building
shared libstdc++.
--dynamic-list-cpp-typeinfo
Provide the builtin dynamic list for C++ runtime type identification.
--check-sections
--no-check-sections
Asks the linker not to check section addresses after they have been assigned to see if there are any
overlaps. Normally the linker will perform this check, and if it finds any overlaps it will produce
suitable error messages. The linker does know about, and does make allowances for sections in
overlays. The default behaviour can be restored by using the command line switch --check-sections.
Section overlap is not usually checked for relocatable links. You can force checking in that case by
using the --check-sections option.
--copy-dt-needed-entries
--no-copy-dt-needed-entries
This option affects the treatment of dynamic libraries referred to by DT_NEEDED tags inside ELF
dynamic libraries mentioned on the command line. Normally the linker won't add a DT_NEEDED tag to
the output binary for each library mentioned in a DT_NEEDED tag in an input dynamic library. With
--copy-dt-needed-entries specified on the command line however any dynamic libraries that follow it
will have their DT_NEEDED entries added. The default behaviour can be restored with
--no-copy-dt-needed-entries.
This option also has an effect on the resolution of symbols in dynamic libraries. With
--copy-dt-needed-entries dynamic libraries mentioned on the command line will be recursively
searched, following their DT_NEEDED tags to other libraries, in order to resolve symbols required by
the output binary. With the default setting however the searching of dynamic libraries that follow
it will stop with the dynamic library itself. No DT_NEEDED links will be traversed to resolve
symbols.
--cref
Output a cross reference table. If a linker map file is being generated, the cross reference table
is printed to the map file. Otherwise, it is printed on the standard output.
The format of the table is intentionally simple, so that it may be easily processed by a script if
necessary. The symbols are printed out, sorted by name. For each symbol, a list of file names is
given. If the symbol is defined, the first file listed is the location of the definition. If the
symbol is defined as a common value then any files where this happens appear next. Finally any files
that reference the symbol are listed.
--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.
--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.
--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.
--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.
--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.
-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 patch out of all the -L options it is given. If a -rpath option is used, the runtime search
path will be formed exclusively using the -rpath options, ignoring the -L options. This can be
useful when using gcc, which adds many -L options which may be on NFS mounted 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.
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
Request 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".
--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 ".build-id" 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]
--out-implib file
The linker will create the file file which will contain an import lib corresponding to the DLL the
linker is generating. This import lib (which should be called "*.dll.a" or "*.a" may be used to link
clients against the generated DLL; this behaviour makes it possible to skip a separate "dlltool"
import library creation step. [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 tiem 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 indentical 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 entires 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 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.
ENVIRONMENT
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.
SEE ALSO
ar(1), nm(1), objcopy(1), objdump(1), readelf(1) and the Info entries for binutils and ld.
COPYRIGHT
Copyright (c) 1991-2014 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".
binutils-2.25 2014-12-23 LD(1)