Provided by: binutils-avr_2.23.1-2.1_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 ECOFF which supports 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, a
path 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.
-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.
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.
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 satisfies an undefined symbol reference from a regular object file or,
if the library is not found in the DT_NEEDED lists of other libraries linked up to
that point, an undefined symbol reference from another dynamic library.
--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. The remaining files contain references to the symbol.
--no-define-common
This option inhibits the assignment of addresses to common symbols. The script
command "INHIBIT_COMMON_ALLOCATION" has the same effect.
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 combinig 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, the 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 or shared object, it will set the address of the first
byte of the text 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 practise, 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 practise, 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 dynamic tags will be created
as needed. If you specify --disable-new-dtags, no new dynamic tags will be created.
By default, the new dynamic tags are not created. Note that those options are only
available for ELF systems.
--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 creation of ".note.gnu.build-id" ELF note 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]
--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
Automatically choose the image base for DLLs, unless one is specified using the
"--image-base" argument. By using a hash generated from the dllname to create unique
image bases for each DLL, in-memory collisions and relocations which can delay program
execution are avoided. [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 practise 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 is
the default. [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]
--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.
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.
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, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002,
2003, 2004, 2005, 2006, 2007, 2008, 2009 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".