LD(1) GNU Development Tools LD(1)
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.
-b input-format
--format=input-format
ld may be configured to support more than one kind of object file.
If your ld is configured this way, you can use the -b option to
specify the binary format for input object files that follow this
option on the command line. Even when ld is configured to support
alternative object formats, you don't usually need to specify this,
as ld should be configured to expect as a default input format the
most usual format on each machine. input-format is a text string,
the name of a particular format supported by the BFD libraries.
(You can list the available binary formats with objdump -i.)
You may want to use this option if you are linking files with an
unusual binary format. You can also use -b to switch formats
explicitly (when linking object files of different formats), by
including -b input-format before each group of object files in a
particular format.
The default format is taken from the environment variable
"GNUTARGET".
You can also define the input format from a script, using the
command "TARGET";
-c MRI-commandfile
--mri-script=MRI-commandfile
For compatibility with linkers produced by MRI, ld accepts script
files written in an alternate, restricted command language,
described in the MRI Compatible Script Files section of GNU ld
documentation. Introduce MRI script files with the option -c; use
the -T option to run linker scripts written in the general-purpose
ld scripting language. If MRI-cmdfile does not exist, ld looks for
it in the directories specified by any -L options.
-d
-dc
-dp These three options are equivalent; multiple forms are supported
for compatibility with other linkers. They assign space to common
symbols even if a relocatable output file is specified (with -r).
The script command "FORCE_COMMON_ALLOCATION" has the same effect.
--depaudit AUDITLIB
-P AUDITLIB
Adds AUDITLIB to the "DT_DEPAUDIT" entry of the dynamic section.
AUDITLIB is not checked for existence, nor will it use the
DT_SONAME specified in the library. If specified multiple times
"DT_DEPAUDIT" will contain a colon separated list of audit
interfaces to use. This option is only meaningful on ELF platforms
supporting the rtld-audit interface. The -P option is provided for
Solaris compatibility.
--enable-non-contiguous-regions
This option avoids generating an error if an input section does not
fit a matching output section. The linker tries to allocate the
input section to subseque nt matching output sections, and
generates an error only if no output section is large enough. This
is useful when several non-contiguous memory regions are available
and the input section does not require a particular one. The order
in which input sections are evaluated does not change, for
instance:
MEMORY {
MEM1 (rwx) : ORIGIN : 0x1000, LENGTH = 0x14
MEM2 (rwx) : ORIGIN : 0x1000, LENGTH = 0x40
MEM3 (rwx) : ORIGIN : 0x2000, LENGTH = 0x40
}
SECTIONS {
mem1 : { *(.data.*); } > MEM1
mem2 : { *(.data.*); } > MEM2
mem3 : { *(.data.*); } > MEM2
}
with input sections:
.data.1: size 8
.data.2: size 0x10
.data.3: size 4
results in .data.1 affected to mem1, and .data.2 and .data.3
affected to mem2, even though .data.3 would fit in mem3.
This option is incompatible with INSERT statements because it
changes the way input sections are mapped to output sections.
--enable-non-contiguous-regions-warnings
This option enables warnings when "--enable-non-contiguous-regions"
allows possibly unexpected matches in sections mapping, potentially
leading to silently discarding a section instead of failing because
it does not fit any output region.
-e entry
--entry=entry
Use entry as the explicit symbol for beginning execution of your
program, rather than the default entry point. If there is no
symbol named entry, the linker will try to parse entry as a number,
and use that as the entry address (the number will be interpreted
in base 10; you may use a leading 0x for base 16, or a leading 0
for base 8).
--exclude-libs lib,lib,...
Specifies a list of archive libraries from which symbols should not
be automatically exported. The library names may be delimited by
commas or colons. Specifying "--exclude-libs ALL" excludes symbols
in all archive libraries from automatic export. This option is
available only for the i386 PE targeted port of the linker and for
ELF targeted ports. For i386 PE, symbols explicitly listed in a
.def file are still exported, regardless of this option. For ELF
targeted ports, symbols affected by this option will be treated as
hidden.
--exclude-modules-for-implib module,module,...
Specifies a list of object files or archive members, from which
symbols should not be automatically exported, but which should be
copied wholesale into the import library being generated during the
link. The module names may be delimited by commas or colons, and
must match exactly the filenames used by ld to open the files; for
archive members, this is simply the member name, but for object
files the name listed must include and match precisely any path
used to specify the input file on the linker's command-line. This
option is available only for the i386 PE targeted port of the
linker. Symbols explicitly listed in a .def file are still
exported, regardless of this option.
-E
--export-dynamic
--no-export-dynamic
When creating a dynamically linked executable, using the -E option
or the --export-dynamic option causes the linker to add all symbols
to the dynamic symbol table. The dynamic symbol table is the set
of symbols which are visible from dynamic objects at run time.
If you do not use either of these options (or use the
--no-export-dynamic option to restore the default behavior), the
dynamic symbol table will normally contain only those symbols which
are referenced by some dynamic object mentioned in the link.
If you use "dlopen" to load a dynamic object which needs to refer
back to the symbols defined by the program, rather than some other
dynamic object, then you will probably need to use this option when
linking the program itself.
You can also use the dynamic list to control what symbols should be
added to the dynamic symbol table if the output format supports it.
See the description of --dynamic-list.
Note that this option is specific to ELF targeted ports. PE
targets support a similar function to export all symbols from a DLL
or EXE; see the description of --export-all-symbols below.
--export-dynamic-symbol=glob
When creating a dynamically linked executable, symbols matching
glob will be added to the dynamic symbol table. When creating a
shared library, references to symbols matching glob will not be
bound to the definitions within the shared library. This option is
a no-op when creating a shared library and -Bsymbolic or
--dynamic-list are not specified. This option is only meaningful on
ELF platforms which support shared libraries.
--export-dynamic-symbol-list=file
Specify a --export-dynamic-symbol for each pattern in the file.
The format of the file is the same as the version node without
scope and node name. See VERSION for more information.
-EB Link big-endian objects. This affects the default output format.
-EL Link little-endian objects. This affects the default output
format.
-f name
--auxiliary=name
When creating an ELF shared object, set the internal DT_AUXILIARY
field to the specified name. This tells the dynamic linker that
the symbol table of the shared object should be used as an
auxiliary filter on the symbol table of the shared object name.
If you later link a program against this filter object, then, when
you run the program, the dynamic linker will see the DT_AUXILIARY
field. If the dynamic linker resolves any symbols from the filter
object, it will first check whether there is a definition in the
shared object name. If there is one, it will be used instead of
the definition in the filter object. The shared object name need
not exist. Thus the shared object name may be used to provide an
alternative implementation of certain functions, perhaps for
debugging or for machine-specific performance.
This option may be specified more than once. The DT_AUXILIARY
entries will be created in the order in which they appear on the
command line.
-F name
--filter=name
When creating an ELF shared object, set the internal DT_FILTER
field to the specified name. This tells the dynamic linker that
the symbol table of the shared object which is being created should
be used as a filter on the symbol table of the shared object name.
If you later link a program against this filter object, then, when
you run the program, the dynamic linker will see the DT_FILTER
field. The dynamic linker will resolve symbols according to the
symbol table of the filter object as usual, but it will actually
link to the definitions found in the shared object name. Thus the
filter object can be used to select a subset of the symbols
provided by the object name.
Some older linkers used the -F option throughout a compilation
toolchain for specifying object-file format for both input and
output object files. The GNU linker uses other mechanisms for this
purpose: the -b, --format, --oformat options, the "TARGET" command
in linker scripts, and the "GNUTARGET" environment variable. The
GNU linker will ignore the -F option when not creating an ELF
shared object.
-fini=name
When creating an ELF executable or shared object, call NAME when
the executable or shared object is unloaded, by setting DT_FINI to
the address of the function. By default, the linker uses "_fini"
as the function to call.
-g Ignored. Provided for compatibility with other tools.
-G value
--gpsize=value
Set the maximum size of objects to be optimized using the GP
register to size. This is only meaningful for object file formats
such as MIPS ELF that support putting large and small objects into
different sections. This is ignored for other object file formats.
-h name
-soname=name
When creating an ELF shared object, set the internal DT_SONAME
field to the specified name. When an executable is linked with a
shared object which has a DT_SONAME field, then when the executable
is run the dynamic linker will attempt to load the shared object
specified by the DT_SONAME field rather than the using the file
name given to the linker.
-i Perform an incremental link (same as option -r).
-init=name
When creating an ELF executable or shared object, call NAME when
the executable or shared object is loaded, by setting DT_INIT to
the address of the function. By default, the linker uses "_init"
as the function to call.
-l namespec
--library=namespec
Add the archive or object file specified by namespec to the list of
files to link. This option may be used any number of times. If
namespec is of the form :filename, ld will search the library path
for a file called filename, otherwise it will search the library
path for a file called libnamespec.a.
On systems which support shared libraries, ld may also search for
files other than libnamespec.a. Specifically, on ELF and SunOS
systems, ld will search a directory for a library called
libnamespec.so before searching for one called libnamespec.a. (By
convention, a ".so" extension indicates a shared library.) Note
that this behavior does not apply to :filename, which always
specifies a file called filename.
The linker will search an archive only once, at the location where
it is specified on the command line. If the archive defines a
symbol which was undefined in some object which appeared before the
archive on the command line, the linker will include the
appropriate file(s) from the archive. However, an undefined symbol
in an object appearing later on the command line will not cause the
linker to search the archive again.
See the -( option for a way to force the linker to search archives
multiple times.
You may list the same archive multiple times on the command line.
This type of archive searching is standard for Unix linkers.
However, if you are using ld on AIX, note that it is different from
the behaviour of the AIX linker.
-L searchdir
--library-path=searchdir
Add path searchdir to the list of paths that ld will search for
archive libraries and ld control scripts. You may use this option
any number of times. The directories are searched in the order in
which they are specified on the command line. Directories
specified on the command line are searched before the default
directories. All -L options apply to all -l options, regardless of
the order in which the options appear. -L options do not affect
how ld searches for a linker script unless -T option is specified.
If searchdir begins with "=" or $SYSROOT, then this prefix will be
replaced by the sysroot prefix, controlled by the --sysroot option,
or specified when the linker is configured.
The default set of paths searched (without being specified with -L)
depends on which emulation mode ld is using, and in some cases also
on how it was configured.
The paths can also be specified in a link script with the
"SEARCH_DIR" command. Directories specified this way are searched
at the point in which the linker script appears in the command
line.
-m emulation
Emulate the emulation linker. You can list the available
emulations with the --verbose or -V options.
If the -m option is not used, the emulation is taken from the
"LDEMULATION" environment variable, if that is defined.
Otherwise, the default emulation depends upon how the linker was
configured.
-M
--print-map
Print a link map to the standard output. A link map provides
information about the link, including the following:
o Where object files are mapped into memory.
o How common symbols are allocated.
o All archive members included in the link, with a mention of the
symbol which caused the archive member to be brought in.
o 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.
o How GNU properties are merged.
When the linker merges input .note.gnu.property sections into
one output .note.gnu.property section, some properties are
removed or updated. These actions are reported in the link
map. For example:
Removed property 0xc0000002 to merge foo.o (0x1) and bar.o (not found)
This indicates that property 0xc0000002 is removed from output
when merging properties in foo.o, whose property 0xc0000002
value is 0x1, and bar.o, which doesn't have property
0xc0000002.
Updated property 0xc0010001 (0x1) to merge foo.o (0x1) and bar.o (0x1)
This indicates that property 0xc0010001 value is updated to 0x1
in output when merging properties in foo.o, whose 0xc0010001
property value is 0x1, and bar.o, whose 0xc0010001 property
value is 0x1.
--print-map-discarded
--no-print-map-discarded
Print (or do not print) the list of discarded and garbage collected
sections in the link map. Enabled by default.
-n
--nmagic
Turn off page alignment of sections, and disable linking against
shared libraries. If the output format supports Unix style magic
numbers, mark the output as "NMAGIC".
-N
--omagic
Set the text and data sections to be readable and writable. Also,
do not page-align the data segment, and disable linking against
shared libraries. If the output format supports Unix style magic
numbers, mark the output as "OMAGIC". Note: Although a writable
text section is allowed for PE-COFF targets, it does not conform to
the format specification published by Microsoft.
--no-omagic
This option negates most of the effects of the -N option. It sets
the text section to be read-only, and forces the data segment to be
page-aligned. Note - this option does not enable linking against
shared libraries. Use -Bdynamic for this.
-o output
--output=output
Use output as the name for the program produced by ld; if this
option is not specified, the name a.out is used by default. The
script command "OUTPUT" can also specify the output file name.
--dependency-file=depfile
Write a dependency file to depfile. This file contains a rule
suitable for "make" describing the output file and all the input
files that were read to produce it. The output is similar to the
compiler's output with -M -MP. Note that there is no option like
the compiler's -MM, to exclude "system files" (which is not a well-
specified concept in the linker, unlike "system headers" in the
compiler). So the output from --dependency-file is always specific
to the exact state of the installation where it was produced, and
should not be copied into distributed makefiles without careful
editing.
-O level
If level is a numeric values greater than zero ld optimizes the
output. This might take significantly longer and therefore
probably should only be enabled for the final binary. At the
moment this option only affects ELF shared library generation.
Future releases of the linker may make more use of this option.
Also currently there is no difference in the linker's behaviour for
different non-zero values of this option. Again this may change
with future releases.
-plugin name
Involve a plugin in the linking process. The name parameter is the
absolute filename of the plugin. Usually this parameter is
automatically added by the complier, when using link time
optimization, but users can also add their own plugins if they so
wish.
Note that the location of the compiler originated plugins is
different from the place where the ar, nm and ranlib programs
search for their plugins. In order for those commands to make use
of a compiler based plugin it must first be copied into the
${libdir}/bfd-plugins directory. All gcc based linker plugins are
backward compatible, so it is sufficient to just copy in the newest
one.
--push-state
The --push-state allows to preserve the current state of the flags
which govern the input file handling so that they can all be
restored with one corresponding --pop-state option.
The option which are covered are: -Bdynamic, -Bstatic, -dn, -dy,
-call_shared, -non_shared, -static, -N, -n, --whole-archive,
--no-whole-archive, -r, -Ur, --copy-dt-needed-entries,
--no-copy-dt-needed-entries, --as-needed, --no-as-needed, and -a.
One target for this option are specifications for pkg-config. When
used with the --libs option all possibly needed libraries are
listed and then possibly linked with all the time. It is better to
return something as follows:
-Wl,--push-state,--as-needed -libone -libtwo -Wl,--pop-state
--pop-state
Undoes the effect of --push-state, restores the previous values of
the flags governing input file handling.
-q
--emit-relocs
Leave relocation sections and contents in fully linked executables.
Post link analysis and optimization tools may need this information
in order to perform correct modifications of executables. This
results in larger executables.
This option is currently only supported on ELF platforms.
--force-dynamic
Force the output file to have dynamic sections. This option is
specific to VxWorks targets.
-r
--relocatable
Generate relocatable output---i.e., generate an output file that
can in turn serve as input to ld. This is often called partial
linking. As a side effect, in environments that support standard
Unix magic numbers, this option also sets the output file's magic
number to "OMAGIC". If this option is not specified, an absolute
file is produced. When linking C++ programs, this option will not
resolve references to constructors; to do that, use -Ur.
When an input file does not have the same format as the output
file, partial linking is only supported if that input file does not
contain any relocations. Different output formats can have further
restrictions; for example some "a.out"-based formats do not support
partial linking with input files in other formats at all.
This option does the same thing as -i.
-R filename
--just-symbols=filename
Read symbol names and their addresses from filename, but do not
relocate it or include it in the output. This allows your output
file to refer symbolically to absolute locations of memory defined
in other programs. You may use this option more than once.
For compatibility with other ELF linkers, if the -R option is
followed by a directory name, rather than a file name, it is
treated as the -rpath option.
-s
--strip-all
Omit all symbol information from the output file.
-S
--strip-debug
Omit debugger symbol information (but not all symbols) from the
output file.
--strip-discarded
--no-strip-discarded
Omit (or do not omit) global symbols defined in discarded sections.
Enabled by default.
-t
--trace
Print the names of the input files as ld processes them. If -t is
given twice then members within archives are also printed. -t
output is useful to generate a list of all the object files and
scripts involved in linking, for example, when packaging files for
a linker bug report.
-T scriptfile
--script=scriptfile
Use scriptfile as the linker script. This script replaces ld's
default linker script (rather than adding to it), so commandfile
must specify everything necessary to describe the output file.
If scriptfile does not exist in the current directory, "ld" looks
for it in the directories specified by any preceding -L options.
Multiple -T options accumulate.
-dT scriptfile
--default-script=scriptfile
Use scriptfile as the default linker script.
This option is similar to the --script option except that
processing of the script is delayed until after the rest of the
command line has been processed. This allows options placed after
the --default-script option on the command line to affect the
behaviour of the linker script, which can be important when the
linker command line cannot be directly controlled by the user. (eg
because the command line is being constructed by another tool, such
as gcc).
-u symbol
--undefined=symbol
Force symbol to be entered in the output file as an undefined
symbol. Doing this may, for example, trigger linking of additional
modules from standard libraries. -u may be repeated with different
option arguments to enter additional undefined symbols. This
option is equivalent to the "EXTERN" linker script command.
If this option is being used to force additional modules to be
pulled into the link, and if it is an error for the symbol to
remain undefined, then the option --require-defined should be used
instead.
--require-defined=symbol
Require that symbol is defined in the output file. This option is
the same as option --undefined except that if symbol is not defined
in the output file then the linker will issue an error and exit.
The same effect can be achieved in a linker script by using
"EXTERN", "ASSERT" and "DEFINED" together. This option can be used
multiple times to require additional symbols.
-Ur For anything other than C++ programs, this option is equivalent to
-r: it generates relocatable output---i.e., an output file that can
in turn serve as input to ld. When linking C++ programs, -Ur does
resolve references to constructors, unlike -r. It does not work to
use -Ur on files that were themselves linked with -Ur; once the
constructor table has been built, it cannot be added to. Use -Ur
only for the last partial link, and -r for the others.
--orphan-handling=MODE
Control how orphan sections are handled. An orphan section is one
not specifically mentioned in a linker script.
MODE can have any of the following values:
"place"
Orphan sections are placed into a suitable output section
following the strategy described in Orphan Sections. The
option --unique also affects how sections are placed.
"discard"
All orphan sections are discarded, by placing them in the
/DISCARD/ section.
"warn"
The linker will place the orphan section as for "place" and
also issue a warning.
"error"
The linker will exit with an error if any orphan section is
found.
The default if --orphan-handling is not given is "place".
--unique[=SECTION]
Creates a separate output section for every input section matching
SECTION, or if the optional wildcard SECTION argument is missing,
for every orphan input section. An orphan section is one not
specifically mentioned in a linker script. You may use this option
multiple times on the command line; It prevents the normal merging
of input sections with the same name, overriding output section
assignments in a linker script.
-v
--version
-V Display the version number for ld. The -V option also lists the
supported emulations.
-x
--discard-all
Delete all local symbols.
-X
--discard-locals
Delete all temporary local symbols. (These symbols start with
system-specific local label prefixes, typically .L for ELF systems
or L for traditional a.out systems.)
-y symbol
--trace-symbol=symbol
Print the name of each linked file in which symbol appears. This
option may be given any number of times. On many systems it is
necessary to prepend an underscore.
This option is useful when you have an undefined symbol in your
link but don't know where the reference is coming from.
-Y path
Add path to the default library search path. This option exists
for Solaris compatibility.
-z keyword
The recognized keywords are:
bndplt
Always generate BND prefix in PLT entries. Supported for
Linux/x86_64.
call-nop=prefix-addr
call-nop=suffix-nop
call-nop=prefix-byte
call-nop=suffix-byte
Specify the 1-byte "NOP" padding when transforming indirect
call to a locally defined function, foo, via its GOT slot.
call-nop=prefix-addr generates "0x67 call foo".
call-nop=suffix-nop generates "call foo 0x90".
call-nop=prefix-byte generates "byte call foo".
call-nop=suffix-byte generates "call foo byte". Supported for
i386 and x86_64.
cet-report=none
cet-report=warning
cet-report=error
Specify how to report the missing
GNU_PROPERTY_X86_FEATURE_1_IBT and
GNU_PROPERTY_X86_FEATURE_1_SHSTK properties in input
.note.gnu.property section. cet-report=none, which is the
default, will make the linker not report missing properties in
input files. cet-report=warning will make the linker issue a
warning for missing properties in input files.
cet-report=error will make the linker issue an error for
missing properties in input files. Note that ibt will turn off
the missing GNU_PROPERTY_X86_FEATURE_1_IBT property report and
shstk will turn off the missing
GNU_PROPERTY_X86_FEATURE_1_SHSTK property report. Supported
for Linux/i386 and Linux/x86_64.
combreloc
nocombreloc
Combine multiple dynamic relocation sections and sort to
improve dynamic symbol lookup caching. Do not do this if
nocombreloc.
common
nocommon
Generate common symbols with STT_COMMON type during a
relocatable link. Use STT_OBJECT type if nocommon.
common-page-size=value
Set the page size most commonly used to value. Memory image
layout will be optimized to minimize memory pages if the system
is using pages of this size.
defs
Report unresolved symbol references from regular object files.
This is done even if the linker is creating a non-symbolic
shared library. This option is the inverse of -z undefs.
dynamic-undefined-weak
nodynamic-undefined-weak
Make undefined weak symbols dynamic when building a dynamic
object, if they are referenced from a regular object file and
not forced local by symbol visibility or versioning. Do not
make them dynamic if nodynamic-undefined-weak. If neither
option is given, a target may default to either option being in
force, or make some other selection of undefined weak symbols
dynamic. Not all targets support these options.
execstack
Marks the object as requiring executable stack.
global
This option is only meaningful when building a shared object.
It makes the symbols defined by this shared object available
for symbol resolution of subsequently loaded libraries.
globalaudit
This option is only meaningful when building a dynamic
executable. This option marks the executable as requiring
global auditing by setting the "DF_1_GLOBAUDIT" bit in the
"DT_FLAGS_1" dynamic tag. Global auditing requires that any
auditing library defined via the --depaudit or -P command-line
options be run for all dynamic objects loaded by the
application.
ibtplt
Generate Intel Indirect Branch Tracking (IBT) enabled PLT
entries. Supported for Linux/i386 and Linux/x86_64.
ibt Generate GNU_PROPERTY_X86_FEATURE_1_IBT in .note.gnu.property
section to indicate compatibility with IBT. This also implies
ibtplt. Supported for Linux/i386 and Linux/x86_64.
initfirst
This option is only meaningful when building a shared object.
It marks the object so that its runtime initialization will
occur before the runtime initialization of any other objects
brought into the process at the same time. Similarly the
runtime finalization of the object will occur after the runtime
finalization of any other objects.
interpose
Specify that the dynamic loader should modify its symbol search
order so that symbols in this shared library interpose all
other shared libraries not so marked.
lazy
When generating an executable or shared library, mark it to
tell the dynamic linker to defer function call resolution to
the point when the function is called (lazy binding), rather
than at load time. Lazy binding is the default.
loadfltr
Specify that the object's filters be processed immediately at
runtime.
max-page-size=value
Set the maximum memory page size supported to value.
muldefs
Allow multiple definitions.
nocopyreloc
Disable linker generated .dynbss variables used in place of
variables defined in shared libraries. May result in dynamic
text relocations.
nodefaultlib
Specify that the dynamic loader search for dependencies of this
object should ignore any default library search paths.
nodelete
Specify that the object shouldn't be unloaded at runtime.
nodlopen
Specify that the object is not available to "dlopen".
nodump
Specify that the object can not be dumped by "dldump".
noexecstack
Marks the object as not requiring executable stack.
noextern-protected-data
Don't treat protected data symbols as external when building a
shared library. This option overrides the linker backend
default. It can be used to work around incorrect relocations
against protected data symbols generated by compiler. Updates
on protected data symbols by another module aren't visible to
the resulting shared library. Supported for i386 and x86-64.
noreloc-overflow
Disable relocation overflow check. This can be used to disable
relocation overflow check if there will be no dynamic
relocation overflow at run-time. Supported for x86_64.
now When generating an executable or shared library, mark it to
tell the dynamic linker to resolve all symbols when the program
is started, or when the shared library is loaded by dlopen,
instead of deferring function call resolution to the point when
the function is first called.
origin
Specify that the object requires $ORIGIN handling in paths.
relro
norelro
Create an ELF "PT_GNU_RELRO" segment header in the object.
This specifies a memory segment that should be made read-only
after relocation, if supported. Specifying common-page-size
smaller than the system page size will render this protection
ineffective. Don't create an ELF "PT_GNU_RELRO" segment if
norelro.
separate-code
noseparate-code
Create separate code "PT_LOAD" segment header in the object.
This specifies a memory segment that should contain only
instructions and must be in wholly disjoint pages from any
other data. Don't create separate code "PT_LOAD" segment if
noseparate-code is used.
shstk
Generate GNU_PROPERTY_X86_FEATURE_1_SHSTK in .note.gnu.property
section to indicate compatibility with Intel Shadow Stack.
Supported for Linux/i386 and Linux/x86_64.
stack-size=value
Specify a stack size for an ELF "PT_GNU_STACK" segment.
Specifying zero will override any default non-zero sized
"PT_GNU_STACK" segment creation.
start-stop-visibility=value
Specify the ELF symbol visibility for synthesized
"__start_SECNAME" and "__stop_SECNAME" symbols. value must be
exactly default, internal, hidden, or protected. If no -z
start-stop-visibility option is given, protected is used for
compatibility with historical practice. However, it's highly
recommended to use -z start-stop-visibility=hidden in new
programs and shared libraries so that these symbols are not
exported between shared objects, which is not usually what's
intended.
text
notext
textoff
Report an error if DT_TEXTREL is set, i.e., if the position-
independent or shared object has dynamic relocations in read-
only sections. Don't report an error if notext or textoff.
undefs
Do not report unresolved symbol references from regular object
files, either when creating an executable, or when creating a
shared library. This option is the inverse of -z defs.
Other keywords are ignored for Solaris compatibility.
-( archives -)
--start-group archives --end-group
The archives should be a list of archive files. They may be either
explicit file names, or -l options.
The specified archives are searched repeatedly until no new
undefined references are created. Normally, an archive is searched
only once in the order that it is specified on the command line.
If a symbol in that archive is needed to resolve an undefined
symbol referred to by an object in an archive that appears later on
the command line, the linker would not be able to resolve that
reference. By grouping the archives, they will all be searched
repeatedly until all possible references are resolved.
Using this option has a significant performance cost. It is best
to use it only when there are unavoidable circular references
between two or more archives.
--accept-unknown-input-arch
--no-accept-unknown-input-arch
Tells the linker to accept input files whose architecture cannot be
recognised. The assumption is that the user knows what they are
doing and deliberately wants to link in these unknown input files.
This was the default behaviour of the linker, before release 2.14.
The default behaviour from release 2.14 onwards is to reject such
input files, and so the --accept-unknown-input-arch option has been
added to restore the old behaviour.
--as-needed
--no-as-needed
This option affects ELF DT_NEEDED tags for dynamic libraries
mentioned on the command line after the --as-needed option.
Normally the linker will add a DT_NEEDED tag for each dynamic
library mentioned on the command line, regardless of whether the
library is actually needed or not. --as-needed causes a DT_NEEDED
tag to only be emitted for a library that at that point in the link
satisfies a non-weak undefined symbol reference from a regular
object file or, if the library is not found in the DT_NEEDED lists
of other needed libraries, a non-weak undefined symbol reference
from another needed dynamic library. Object files or libraries
appearing on the command line after the library in question do not
affect whether the library is seen as needed. This is similar to
the rules for extraction of object files from archives.
--no-as-needed restores the default behaviour.
--add-needed
--no-add-needed
These two options have been deprecated because of the similarity of
their names to the --as-needed and --no-as-needed options. They
have been replaced by --copy-dt-needed-entries and
--no-copy-dt-needed-entries.
-assert keyword
This option is ignored for SunOS compatibility.
-Bdynamic
-dy
-call_shared
Link against dynamic libraries. This is only meaningful on
platforms for which shared libraries are supported. This option is
normally the default on such platforms. The different variants of
this option are for compatibility with various systems. You may
use this option multiple times on the command line: it affects
library searching for -l options which follow it.
-Bgroup
Set the "DF_1_GROUP" flag in the "DT_FLAGS_1" entry in the dynamic
section. This causes the runtime linker to handle lookups in this
object and its dependencies to be performed only inside the group.
--unresolved-symbols=report-all is implied. This option is only
meaningful on ELF platforms which support shared libraries.
-Bstatic
-dn
-non_shared
-static
Do not link against shared libraries. This is only meaningful on
platforms for which shared libraries are supported. The different
variants of this option are for compatibility with various systems.
You may use this option multiple times on the command line: it
affects library searching for -l options which follow it. This
option also implies --unresolved-symbols=report-all. This option
can be used with -shared. Doing so means that a shared library is
being created but that all of the library's external references
must be resolved by pulling in entries from static libraries.
-Bsymbolic
When creating a shared library, bind references to global symbols
to the definition within the shared library, if any. Normally, it
is possible for a program linked against a shared library to
override the definition within the shared library. This option is
only meaningful on ELF platforms which support shared libraries.
-Bsymbolic-functions
When creating a shared library, bind references to global function
symbols to the definition within the shared library, if any. This
option is only meaningful on ELF platforms which support shared
libraries.
--dynamic-list=dynamic-list-file
Specify the name of a dynamic list file to the linker. This is
typically used when creating shared libraries to specify a list of
global symbols whose references shouldn't be bound to the
definition within the shared library, or creating dynamically
linked executables to specify a list of symbols which should be
added to the symbol table in the executable. This option is only
meaningful on ELF platforms which support shared libraries.
The format of the dynamic list is the same as the version node
without scope and node name. See VERSION for more information.
--dynamic-list-data
Include all global data symbols to the dynamic list.
--dynamic-list-cpp-new
Provide the builtin dynamic list for C++ operator new and delete.
It is mainly useful for building shared libstdc++.
--dynamic-list-cpp-typeinfo
Provide the builtin dynamic list for C++ runtime type
identification.
--check-sections
--no-check-sections
Asks the linker not to check section addresses after they have been
assigned to see if there are any overlaps. Normally the linker
will perform this check, and if it finds any overlaps it will
produce suitable error messages. The linker does know about, and
does make allowances for sections in overlays. The default
behaviour can be restored by using the command-line switch
--check-sections. Section overlap is not usually checked for
relocatable links. You can force checking in that case by using
the --check-sections option.
--copy-dt-needed-entries
--no-copy-dt-needed-entries
This option affects the treatment of dynamic libraries referred to
by DT_NEEDED tags inside ELF dynamic libraries mentioned on the
command line. Normally the linker won't add a DT_NEEDED tag to the
output binary for each library mentioned in a DT_NEEDED tag in an
input dynamic library. With --copy-dt-needed-entries specified on
the command line however any dynamic libraries that follow it will
have their DT_NEEDED entries added. The default behaviour can be
restored with --no-copy-dt-needed-entries.
This option also has an effect on the resolution of symbols in
dynamic libraries. With --copy-dt-needed-entries dynamic libraries
mentioned on the command line will be recursively searched,
following their DT_NEEDED tags to other libraries, in order to
resolve symbols required by the output binary. With the default
setting however the searching of dynamic libraries that follow it
will stop with the dynamic library itself. No DT_NEEDED links will
be traversed to resolve symbols.
--cref
Output a cross reference table. If a linker map file is being
generated, the cross reference table is printed to the map file.
Otherwise, it is printed on the standard output.
The format of the table is intentionally simple, so that it may be
easily processed by a script if necessary. The symbols are printed
out, sorted by name. For each symbol, a list of file names is
given. If the symbol is defined, the first file listed is the
location of the definition. If the symbol is defined as a common
value then any files where this happens appear next. Finally any
files that reference the symbol are listed.
--no-define-common
This option inhibits the assignment of addresses to common symbols.
The script command "INHIBIT_COMMON_ALLOCATION" has the same effect.
The --no-define-common option allows decoupling the decision to
assign addresses to Common symbols from the choice of the output
file type; otherwise a non-Relocatable output type forces assigning
addresses to Common symbols. Using --no-define-common allows
Common symbols that are referenced from a shared library to be
assigned addresses only in the main program. This eliminates the
unused duplicate space in the shared library, and also prevents any
possible confusion over resolving to the wrong duplicate when there
are many dynamic modules with specialized search paths for runtime
symbol resolution.
--force-group-allocation
This option causes the linker to place section group members like
normal input sections, and to delete the section groups. This is
the default behaviour for a final link but this option can be used
to change the behaviour of a relocatable link (-r). The script
command "FORCE_GROUP_ALLOCATION" has the same effect.
--defsym=symbol=expression
Create a global symbol in the output file, containing the absolute
address given by expression. You may use this option as many times
as necessary to define multiple symbols in the command line. A
limited form of arithmetic is supported for the expression in this
context: you may give a hexadecimal constant or the name of an
existing symbol, or use "+" and "-" to add or subtract hexadecimal
constants or symbols. If you need more elaborate expressions,
consider using the linker command language from a script. Note:
there should be no white space between symbol, the equals sign
("="), and expression.
--demangle[=style]
--no-demangle
These options control whether to demangle symbol names in error
messages and other output. When the linker is told to demangle, it
tries to present symbol names in a readable fashion: it strips
leading underscores if they are used by the object file format, and
converts C++ mangled symbol names into user readable names.
Different compilers have different mangling styles. The optional
demangling style argument can be used to choose an appropriate
demangling style for your compiler. The linker will demangle by
default unless the environment variable COLLECT_NO_DEMANGLE is set.
These options may be used to override the default.
-Ifile
--dynamic-linker=file
Set the name of the dynamic linker. This is only meaningful when
generating dynamically linked ELF executables. The default dynamic
linker is normally correct; don't use this unless you know what you
are doing.
--no-dynamic-linker
When producing an executable file, omit the request for a dynamic
linker to be used at load-time. This is only meaningful for ELF
executables that contain dynamic relocations, and usually requires
entry point code that is capable of processing these relocations.
--embedded-relocs
This option is similar to the --emit-relocs option except that the
relocs are stored in a target-specific section. This option is
only supported by the BFIN, CR16 and M68K targets.
--disable-multiple-abs-defs
Do not allow multiple definitions with symbols included in filename
invoked by -R or --just-symbols
--fatal-warnings
--no-fatal-warnings
Treat all warnings as errors. The default behaviour can be
restored with the option --no-fatal-warnings.
--force-exe-suffix
Make sure that an output file has a .exe suffix.
If a successfully built fully linked output file does not have a
".exe" or ".dll" suffix, this option forces the linker to copy the
output file to one of the same name with a ".exe" suffix. This
option is useful when using unmodified Unix makefiles on a
Microsoft Windows host, since some versions of Windows won't run an
image unless it ends in a ".exe" suffix.
--gc-sections
--no-gc-sections
Enable garbage collection of unused input sections. It is ignored
on targets that do not support this option. The default behaviour
(of not performing this garbage collection) can be restored by
specifying --no-gc-sections on the command line. Note that garbage
collection for COFF and PE format targets is supported, but the
implementation is currently considered to be experimental.
--gc-sections decides which input sections are used by examining
symbols and relocations. The section containing the entry symbol
and all sections containing symbols undefined on the command-line
will be kept, as will sections containing symbols referenced by
dynamic objects. Note that when building shared libraries, the
linker must assume that any visible symbol is referenced. Once
this initial set of sections has been determined, the linker
recursively marks as used any section referenced by their
relocations. See --entry, --undefined, and --gc-keep-exported.
This option can be set when doing a partial link (enabled with
option -r). In this case the root of symbols kept must be
explicitly specified either by one of the options --entry,
--undefined, or --gc-keep-exported or by a "ENTRY" command in the
linker script.
--print-gc-sections
--no-print-gc-sections
List all sections removed by garbage collection. The listing is
printed on stderr. This option is only effective if garbage
collection has been enabled via the --gc-sections) option. The
default behaviour (of not listing the sections that are removed)
can be restored by specifying --no-print-gc-sections on the command
line.
--gc-keep-exported
When --gc-sections is enabled, this option prevents garbage
collection of unused input sections that contain global symbols
having default or protected visibility. This option is intended to
be used for executables where unreferenced sections would otherwise
be garbage collected regardless of the external visibility of
contained symbols. Note that this option has no effect when
linking shared objects since it is already the default behaviour.
This option is only supported for ELF format targets.
--print-output-format
Print the name of the default output format (perhaps influenced by
other command-line options). This is the string that would appear
in an "OUTPUT_FORMAT" linker script command.
--print-memory-usage
Print used size, total size and used size of memory regions created
with the MEMORY command. This is useful on embedded targets to
have a quick view of amount of free memory. The format of the
output has one headline and one line per region. It is both human
readable and easily parsable by tools. Here is an example of an
output:
Memory region Used Size Region Size %age Used
ROM: 256 KB 1 MB 25.00%
RAM: 32 B 2 GB 0.00%
--help
Print a summary of the command-line options on the standard output
and exit.
--target-help
Print a summary of all target-specific options on the standard
output and exit.
-Map=mapfile
Print a link map to the file mapfile. See the description of the
-M option, above. Specifying a directory as mapfile causes the
linker map to be written into a file inside the directory. The
name of the file is based upon the output filename with ".map"
appended.
--no-keep-memory
ld normally optimizes for speed over memory usage by caching the
symbol tables of input files in memory. This option tells ld to
instead optimize for memory usage, by rereading the symbol tables
as necessary. This may be required if ld runs out of memory space
while linking a large executable.
--no-undefined
-z defs
Report unresolved symbol references from regular object files.
This is done even if the linker is creating a non-symbolic shared
library. The switch --[no-]allow-shlib-undefined controls the
behaviour for reporting unresolved references found in shared
libraries being linked in.
The effects of this option can be reverted by using "-z undefs".
--allow-multiple-definition
-z muldefs
Normally when a symbol is defined multiple times, the linker will
report a fatal error. These options allow multiple definitions and
the first definition will be used.
--allow-shlib-undefined
--no-allow-shlib-undefined
Allows or disallows undefined symbols in shared libraries. This
switch is similar to --no-undefined except that it determines the
behaviour when the undefined symbols are in a shared library rather
than a regular object file. It does not affect how undefined
symbols in regular object files are handled.
The default behaviour is to report errors for any undefined symbols
referenced in shared libraries if the linker is being used to
create an executable, but to allow them if the linker is being used
to create a shared library.
The reasons for allowing undefined symbol references in shared
libraries specified at link time are that:
o 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.
o There are some operating systems, eg BeOS and HPPA, where
undefined symbols in shared libraries are normal.
The BeOS kernel for example patches shared libraries at load
time to select whichever function is most appropriate for the
current architecture. This is used, for example, to
dynamically select an appropriate memset function.
--no-undefined-version
Normally when a symbol has an undefined version, the linker will
ignore it. This option disallows symbols with undefined version and
a fatal error will be issued instead.
--default-symver
Create and use a default symbol version (the soname) for
unversioned exported symbols.
--default-imported-symver
Create and use a default symbol version (the soname) for
unversioned imported symbols.
--no-warn-mismatch
Normally ld will give an error if you try to link together input
files that are mismatched for some reason, perhaps because they
have been compiled for different processors or for different
endiannesses. This option tells ld that it should silently permit
such possible errors. This option should only be used with care,
in cases when you have taken some special action that ensures that
the linker errors are inappropriate.
--no-warn-search-mismatch
Normally ld will give a warning if it finds an incompatible library
during a library search. This option silences the warning.
--no-whole-archive
Turn off the effect of the --whole-archive option for subsequent
archive files.
--noinhibit-exec
Retain the executable output file whenever it is still usable.
Normally, the linker will not produce an output file if it
encounters errors during the link process; it exits without writing
an output file when it issues any error whatsoever.
-nostdlib
Only search library directories explicitly specified on the command
line. Library directories specified in linker scripts (including
linker scripts specified on the command line) are ignored.
--oformat=output-format
ld may be configured to support more than one kind of object file.
If your ld is configured this way, you can use the --oformat option
to specify the binary format for the output object file. Even when
ld is configured to support alternative object formats, you don't
usually need to specify this, as ld should be configured to produce
as a default output format the most usual format on each machine.
output-format is a text string, the name of a particular format
supported by the BFD libraries. (You can list the available binary
formats with objdump -i.) The script command "OUTPUT_FORMAT" can
also specify the output format, but this option overrides it.
--out-implib file
Create an import library in file corresponding to the executable
the linker is generating (eg. a DLL or ELF program). This import
library (which should be called "*.dll.a" or "*.a" for DLLs) may be
used to link clients against the generated executable; this
behaviour makes it possible to skip a separate import library
creation step (eg. "dlltool" for DLLs). This option is only
available for the i386 PE and ELF targetted ports of the linker.
-pie
--pic-executable
Create a position independent executable. This is currently only
supported on ELF platforms. Position independent executables are
similar to shared libraries in that they are relocated by the
dynamic linker to the virtual address the OS chooses for them
(which can vary between invocations). Like normal dynamically
linked executables they can be executed and symbols defined in the
executable cannot be overridden by shared libraries.
-qmagic
This option is ignored for Linux compatibility.
-Qy This option is ignored for SVR4 compatibility.
--relax
--no-relax
An option with machine dependent effects. This option is only
supported on a few targets.
On some platforms the --relax option performs target-specific,
global optimizations that become possible when the linker resolves
addressing in the program, such as relaxing address modes,
synthesizing new instructions, selecting shorter version of current
instructions, and combining constant values.
On some platforms these link time global optimizations may make
symbolic debugging of the resulting executable impossible. This is
known to be the case for the Matsushita MN10200 and MN10300 family
of processors.
On platforms where this is not supported, --relax is accepted, but
ignored.
On platforms where --relax is accepted the option --no-relax can be
used to disable the feature.
--retain-symbols-file=filename
Retain only the symbols listed in the file filename, discarding all
others. filename is simply a flat file, with one symbol name per
line. This option is especially useful in environments (such as
VxWorks) where a large global symbol table is accumulated
gradually, to conserve run-time memory.
--retain-symbols-file does not discard undefined symbols, or
symbols needed for relocations.
You may only specify --retain-symbols-file once in the command
line. It overrides -s and -S.
-rpath=dir
Add a directory to the runtime library search path. This is used
when linking an ELF executable with shared objects. All -rpath
arguments are concatenated and passed to the runtime linker, which
uses them to locate shared objects at runtime.
The -rpath option is also used when locating shared objects which
are needed by shared objects explicitly included in the link; see
the description of the -rpath-link option. Searching -rpath in
this way is only supported by native linkers and cross linkers
which have been configured with the --with-sysroot option.
If -rpath is not used when linking an ELF executable, the contents
of the environment variable "LD_RUN_PATH" will be used if it is
defined.
The -rpath option may also be used on SunOS. By default, on SunOS,
the linker will form a runtime search path out of all the -L
options it is given. If a -rpath option is used, the runtime
search path will be formed exclusively using the -rpath options,
ignoring the -L options. This can be useful when using gcc, which
adds many -L options which may be on NFS mounted file systems.
For compatibility with other ELF linkers, if the -R option is
followed by a directory name, rather than a file name, it is
treated as the -rpath option.
-rpath-link=dir
When using ELF or SunOS, one shared library may require another.
This happens when an "ld -shared" link includes a shared library as
one of the input files.
When the linker encounters such a dependency when doing a non-
shared, non-relocatable link, it will automatically try to locate
the required shared library and include it in the link, if it is
not included explicitly. In such a case, the -rpath-link option
specifies the first set of directories to search. The -rpath-link
option may specify a sequence of directory names either by
specifying a list of names separated by colons, or by appearing
multiple times.
The tokens $ORIGIN and $LIB can appear in these search directories.
They will be replaced by the full path to the directory containing
the program or shared object in the case of $ORIGIN and either lib
- for 32-bit binaries - or lib64 - for 64-bit binaries - in the
case of $LIB.
The alternative form of these tokens - ${ORIGIN} and ${LIB} can
also be used. The token $PLATFORM is not supported.
This option should be used with caution as it overrides the search
path that may have been hard compiled into a shared library. In
such a case it is possible to use unintentionally a different
search path than the runtime linker would do.
The linker uses the following search paths to locate required
shared libraries:
1. Any directories specified by -rpath-link options.
2. Any directories specified by -rpath options. The difference
between -rpath and -rpath-link is that directories specified by
-rpath options are included in the executable and used at
runtime, whereas the -rpath-link option is only effective at
link time. Searching -rpath in this way is only supported by
native linkers and cross linkers which have been configured
with the --with-sysroot option.
3. On an ELF system, for native linkers, if the -rpath and
-rpath-link options were not used, search the contents of the
environment variable "LD_RUN_PATH".
4. On SunOS, if the -rpath option was not used, search any
directories specified using -L options.
5. For a native linker, search the contents of the environment
variable "LD_LIBRARY_PATH".
6. For a native ELF linker, the directories in "DT_RUNPATH" or
"DT_RPATH" of a shared library are searched for shared
libraries needed by it. The "DT_RPATH" entries are ignored if
"DT_RUNPATH" entries exist.
7. The default directories, normally /lib and /usr/lib.
8. For a linker for a Linux system, if the file /etc/ld.so.conf
exists, the list of directories found in that file. Note: the
path to this file is prefixed with the "sysroot" value, if that
is defined, and then any "prefix" string if the linker was
configured with the --prefix=<path> option.
9. For a native linker on a FreeBSD system, any directories
specified by the "_PATH_ELF_HINTS" macro defined in the
elf-hints.h header file.
10. Any directories specifed by a "SEARCH_DIR" command in the
linker script being used.
If the required shared library is not found, the linker will issue
a warning and continue with the link.
-shared
-Bshareable
Create a shared library. This is currently only supported on ELF,
XCOFF and SunOS platforms. On SunOS, the linker will automatically
create a shared library if the -e option is not used and there are
undefined symbols in the link.
--sort-common
--sort-common=ascending
--sort-common=descending
This option tells ld to sort the common symbols by alignment in
ascending or descending order when it places them in the
appropriate output sections. The symbol alignments considered are
sixteen-byte or larger, eight-byte, four-byte, two-byte, and one-
byte. This is to prevent gaps between symbols due to alignment
constraints. If no sorting order is specified, then descending
order is assumed.
--sort-section=name
This option will apply "SORT_BY_NAME" to all wildcard section
patterns in the linker script.
--sort-section=alignment
This option will apply "SORT_BY_ALIGNMENT" to all wildcard section
patterns in the linker script.
--spare-dynamic-tags=count
This option specifies the number of empty slots to leave in the
.dynamic section of ELF shared objects. Empty slots may be needed
by post processing tools, such as the prelinker. The default is 5.
--split-by-file[=size]
Similar to --split-by-reloc but creates a new output section for
each input file when size is reached. size defaults to a size of 1
if not given.
--split-by-reloc[=count]
Tries to creates extra sections in the output file so that no
single output section in the file contains more than count
relocations. This is useful when generating huge relocatable files
for downloading into certain real time kernels with the COFF object
file format; since COFF cannot represent more than 65535
relocations in a single section. Note that this will fail to work
with object file formats which do not support arbitrary sections.
The linker will not split up individual input sections for
redistribution, so if a single input section contains more than
count relocations one output section will contain that many
relocations. count defaults to a value of 32768.
--stats
Compute and display statistics about the operation of the linker,
such as execution time and memory usage.
--sysroot=directory
Use directory as the location of the sysroot, overriding the
configure-time default. This option is only supported by linkers
that were configured using --with-sysroot.
--task-link
This is used by COFF/PE based targets to create a task-linked
object file where all of the global symbols have been converted to
statics.
--traditional-format
For some targets, the output of ld is different in some ways from
the output of some existing linker. This switch requests ld to use
the traditional format instead.
For example, on SunOS, ld combines duplicate entries in the symbol
string table. This can reduce the size of an output file with full
debugging information by over 30 percent. Unfortunately, the SunOS
"dbx" program can not read the resulting program ("gdb" has no
trouble). The --traditional-format switch tells ld to not combine
duplicate entries.
--section-start=sectionname=org
Locate a section in the output file at the absolute address given
by org. You may use this option as many times as necessary to
locate multiple sections in the command line. org must be a single
hexadecimal integer; for compatibility with other linkers, you may
omit the leading 0x usually associated with hexadecimal values.
Note: there should be no white space between sectionname, the
equals sign ("="), and org.
-Tbss=org
-Tdata=org
-Ttext=org
Same as --section-start, with ".bss", ".data" or ".text" as the
sectionname.
-Ttext-segment=org
When creating an ELF executable, it will set the address of the
first byte of the text segment.
-Trodata-segment=org
When creating an ELF executable or shared object for a target where
the read-only data is in its own segment separate from the
executable text, it will set the address of the first byte of the
read-only data segment.
-Tldata-segment=org
When creating an ELF executable or shared object for x86-64 medium
memory model, it will set the address of the first byte of the
ldata segment.
--unresolved-symbols=method
Determine how to handle unresolved symbols. There are four
possible values for method:
ignore-all
Do not report any unresolved symbols.
report-all
Report all unresolved symbols. This is the default.
ignore-in-object-files
Report unresolved symbols that are contained in shared
libraries, but ignore them if they come from regular object
files.
ignore-in-shared-libs
Report unresolved symbols that come from regular object files,
but ignore them if they come from shared libraries. This can
be useful when creating a dynamic binary and it is known that
all the shared libraries that it should be referencing are
included on the linker's command line.
The behaviour for shared libraries on their own can also be
controlled by the --[no-]allow-shlib-undefined option.
Normally the linker will generate an error message for each
reported unresolved symbol but the option --warn-unresolved-symbols
can change this to a warning.
--dll-verbose
--verbose[=NUMBER]
Display the version number for ld and list the linker emulations
supported. Display which input files can and cannot be opened.
Display the linker script being used by the linker. If the optional
NUMBER argument > 1, plugin symbol status will also be displayed.
--version-script=version-scriptfile
Specify the name of a version script to the linker. This is
typically used when creating shared libraries to specify additional
information about the version hierarchy for the library being
created. This option is only fully supported on ELF platforms
which support shared libraries; see VERSION. It is partially
supported on PE platforms, which can use version scripts to filter
symbol visibility in auto-export mode: any symbols marked local in
the version script will not be exported.
--warn-common
Warn when a common symbol is combined with another common symbol or
with a symbol definition. Unix linkers allow this somewhat sloppy
practice, but linkers on some other operating systems do not. This
option allows you to find potential problems from combining global
symbols. Unfortunately, some C libraries use this practice, so you
may get some warnings about symbols in the libraries as well as in
your programs.
There are three kinds of global symbols, illustrated here by C
examples:
int i = 1;
A definition, which goes in the initialized data section of the
output file.
extern int i;
An undefined reference, which does not allocate space. There
must be either a definition or a common symbol for the variable
somewhere.
int i;
A common symbol. If there are only (one or more) common
symbols for a variable, it goes in the uninitialized data area
of the output file. The linker merges multiple common symbols
for the same variable into a single symbol. If they are of
different sizes, it picks the largest size. The linker turns a
common symbol into a declaration, if there is a definition of
the same variable.
The --warn-common option can produce five kinds of warnings. Each
warning consists of a pair of lines: the first describes the symbol
just encountered, and the second describes the previous symbol
encountered with the same name. One or both of the two symbols
will be a common symbol.
1. Turning a common symbol into a reference, because there is
already a definition for the symbol.
<file>(<section>): warning: common of `<symbol>'
overridden by definition
<file>(<section>): warning: defined here
2. Turning a common symbol into a reference, because a later
definition for the symbol is encountered. This is the same as
the previous case, except that the symbols are encountered in a
different order.
<file>(<section>): warning: definition of `<symbol>'
overriding common
<file>(<section>): warning: common is here
3. Merging a common symbol with a previous same-sized common
symbol.
<file>(<section>): warning: multiple common
of `<symbol>'
<file>(<section>): warning: previous common is here
4. Merging a common symbol with a previous larger common symbol.
<file>(<section>): warning: common of `<symbol>'
overridden by larger common
<file>(<section>): warning: larger common is here
5. Merging a common symbol with a previous smaller common symbol.
This is the same as the previous case, except that the symbols
are encountered in a different order.
<file>(<section>): warning: common of `<symbol>'
overriding smaller common
<file>(<section>): warning: smaller common is here
--warn-constructors
Warn if any global constructors are used. This is only useful for
a few object file formats. For formats like COFF or ELF, the
linker can not detect the use of global constructors.
--warn-multiple-gp
Warn if multiple global pointer values are required in the output
file. This is only meaningful for certain processors, such as the
Alpha. Specifically, some processors put large-valued constants in
a special section. A special register (the global pointer) points
into the middle of this section, so that constants can be loaded
efficiently via a base-register relative addressing mode. Since
the offset in base-register relative mode is fixed and relatively
small (e.g., 16 bits), this limits the maximum size of the constant
pool. Thus, in large programs, it is often necessary to use
multiple global pointer values in order to be able to address all
possible constants. This option causes a warning to be issued
whenever this case occurs.
--warn-once
Only warn once for each undefined symbol, rather than once per
module which refers to it.
--warn-section-align
Warn if the address of an output section is changed because of
alignment. Typically, the alignment will be set by an input
section. The address will only be changed if it not explicitly
specified; that is, if the "SECTIONS" command does not specify a
start address for the section.
--warn-textrel
Warn if the linker adds DT_TEXTREL to a position-independent
executable or shared object.
--warn-alternate-em
Warn if an object has alternate ELF machine code.
--warn-unresolved-symbols
If the linker is going to report an unresolved symbol (see the
option --unresolved-symbols) it will normally generate an error.
This option makes it generate a warning instead.
--error-unresolved-symbols
This restores the linker's default behaviour of generating errors
when it is reporting unresolved symbols.
--whole-archive
For each archive mentioned on the command line after the
--whole-archive option, include every object file in the archive in
the link, rather than searching the archive for the required object
files. This is normally used to turn an archive file into a shared
library, forcing every object to be included in the resulting
shared library. This option may be used more than once.
Two notes when using this option from gcc: First, gcc doesn't know
about this option, so you have to use -Wl,-whole-archive. Second,
don't forget to use -Wl,-no-whole-archive after your list of
archives, because gcc will add its own list of archives to your
link and you may not want this flag to affect those as well.
--wrap=symbol
Use a wrapper function for symbol. Any undefined reference to
symbol will be resolved to "__wrap_symbol". Any undefined
reference to "__real_symbol" will be resolved to symbol.
This can be used to provide a wrapper for a system function. The
wrapper function should be called "__wrap_symbol". If it wishes to
call the system function, it should call "__real_symbol".
Here is a trivial example:
void *
__wrap_malloc (size_t c)
{
printf ("malloc called with %zu\n", c);
return __real_malloc (c);
}
If you link other code with this file using --wrap malloc, then all
calls to "malloc" will call the function "__wrap_malloc" instead.
The call to "__real_malloc" in "__wrap_malloc" will call the real
"malloc" function.
You may wish to provide a "__real_malloc" function as well, so that
links without the --wrap option will succeed. If you do this, you
should not put the definition of "__real_malloc" in the same file
as "__wrap_malloc"; if you do, the assembler may resolve the call
before the linker has a chance to wrap it to "malloc".
Only undefined references are replaced by the linker. So,
translation unit internal references to symbol are not resolved to
"__wrap_symbol". In the next example, the call to "f" in "g" is
not resolved to "__wrap_f".
int
f (void)
{
return 123;
}
int
g (void)
{
return f();
}
--eh-frame-hdr
--no-eh-frame-hdr
Request (--eh-frame-hdr) or suppress (--no-eh-frame-hdr) the
creation of ".eh_frame_hdr" section and ELF "PT_GNU_EH_FRAME"
segment header.
--no-ld-generated-unwind-info
Request creation of ".eh_frame" unwind info for linker generated
code sections like PLT. This option is on by default if linker
generated unwind info is supported.
--enable-new-dtags
--disable-new-dtags
This linker can create the new dynamic tags in ELF. But the older
ELF systems may not understand them. If you specify
--enable-new-dtags, the new dynamic tags will be created as needed
and older dynamic tags will be omitted. If you specify
--disable-new-dtags, no new dynamic tags will be created. By
default, the new dynamic tags are not created. Note that those
options are only available for ELF systems.
--hash-size=number
Set the default size of the linker's hash tables to a prime number
close to number. Increasing this value can reduce the length of
time it takes the linker to perform its tasks, at the expense of
increasing the linker's memory requirements. Similarly reducing
this value can reduce the memory requirements at the expense of
speed.
--hash-style=style
Set the type of linker's hash table(s). style can be either "sysv"
for classic ELF ".hash" section, "gnu" for new style GNU
".gnu.hash" section or "both" for both the classic ELF ".hash" and
new style GNU ".gnu.hash" hash tables. The default depends upon
how the linker was configured, but for most Linux based systems it
will be "both".
--compress-debug-sections=none
--compress-debug-sections=zlib
--compress-debug-sections=zlib-gnu
--compress-debug-sections=zlib-gabi
On ELF platforms, these options control how DWARF debug sections
are compressed using zlib.
--compress-debug-sections=none doesn't compress DWARF debug
sections. --compress-debug-sections=zlib-gnu compresses DWARF
debug sections and renames them to begin with .zdebug instead of
.debug. --compress-debug-sections=zlib-gabi also compresses DWARF
debug sections, but rather than renaming them it sets the
SHF_COMPRESSED flag in the sections' headers.
The --compress-debug-sections=zlib option is an alias for
--compress-debug-sections=zlib-gabi.
Note that this option overrides any compression in input debug
sections, so if a binary is linked with
--compress-debug-sections=none for example, then any compressed
debug sections in input files will be uncompressed before they are
copied into the output binary.
The default compression behaviour varies depending upon the target
involved and the configure options used to build the toolchain.
The default can be determined by examining the output from the
linker's --help option.
--reduce-memory-overheads
This option reduces memory requirements at ld runtime, at the
expense of linking speed. This was introduced to select the old
O(n^2) algorithm for link map file generation, rather than the new
O(n) algorithm which uses about 40% more memory for symbol storage.
Another effect of the switch is to set the default hash table size
to 1021, which again saves memory at the cost of lengthening the
linker's run time. This is not done however if the --hash-size
switch has been used.
The --reduce-memory-overheads switch may be also be used to enable
other tradeoffs in future versions of the linker.
--build-id
--build-id=style
Request the creation of a ".note.gnu.build-id" ELF note section or
a ".buildid" COFF section. The contents of the note are unique
bits identifying this linked file. style can be "uuid" to use 128
random bits, "sha1" to use a 160-bit SHA1 hash on the normative
parts of the output contents, "md5" to use a 128-bit MD5 hash on
the normative parts of the output contents, or "0xhexstring" to use
a chosen bit string specified as an even number of hexadecimal
digits ("-" and ":" characters between digit pairs are ignored).
If style is omitted, "sha1" is used.
The "md5" and "sha1" styles produces an identifier that is always
the same in an identical output file, but will be unique among all
nonidentical output files. It is not intended to be compared as a
checksum for the file's contents. A linked file may be changed
later by other tools, but the build ID bit string identifying the
original linked file does not change.
Passing "none" for style disables the setting from any "--build-id"
options earlier on the command line.
The i386 PE linker supports the -shared option, which causes the output
to be a dynamically linked library (DLL) instead of a normal
executable. You should name the output "*.dll" when you use this
option. In addition, the linker fully supports the standard "*.def"
files, which may be specified on the linker command line like an object
file (in fact, it should precede archives it exports symbols from, to
ensure that they get linked in, just like a normal object file).
In addition to the options common to all targets, the i386 PE linker
support additional command-line options that are specific to the i386
PE target. Options that take values may be separated from their values
by either a space or an equals sign.
--add-stdcall-alias
If given, symbols with a stdcall suffix (@nn) will be exported as-
is and also with the suffix stripped. [This option is specific to
the i386 PE targeted port of the linker]
--base-file file
Use file as the name of a file in which to save the base addresses
of all the relocations needed for generating DLLs with dlltool.
[This is an i386 PE specific option]
--dll
Create a DLL instead of a regular executable. You may also use
-shared or specify a "LIBRARY" in a given ".def" file. [This
option is specific to the i386 PE targeted port of the linker]
--enable-long-section-names
--disable-long-section-names
The PE variants of the COFF object format add an extension that
permits the use of section names longer than eight characters, the
normal limit for COFF. By default, these names are only allowed in
object files, as fully-linked executable images do not carry the
COFF string table required to support the longer names. As a GNU
extension, it is possible to allow their use in executable images
as well, or to (probably pointlessly!) disallow it in object
files, by using these two options. Executable images generated
with these long section names are slightly non-standard, carrying
as they do a string table, and may generate confusing output when
examined with non-GNU PE-aware tools, such as file viewers and
dumpers. However, GDB relies on the use of PE long section names
to find Dwarf-2 debug information sections in an executable image
at runtime, and so if neither option is specified on the command-
line, ld will enable long section names, overriding the default and
technically correct behaviour, when it finds the presence of debug
information while linking an executable image and not stripping
symbols. [This option is valid for all PE targeted ports of the
linker]
--enable-stdcall-fixup
--disable-stdcall-fixup
If the link finds a symbol that it cannot resolve, it will attempt
to do "fuzzy linking" by looking for another defined symbol that
differs only in the format of the symbol name (cdecl vs stdcall)
and will resolve that symbol by linking to the match. For example,
the undefined symbol "_foo" might be linked to the function
"_foo@12", or the undefined symbol "_bar@16" might be linked to the
function "_bar". When the linker does this, it prints a warning,
since it normally should have failed to link, but sometimes import
libraries generated from third-party dlls may need this feature to
be usable. If you specify --enable-stdcall-fixup, this feature is
fully enabled and warnings are not printed. If you specify
--disable-stdcall-fixup, this feature is disabled and such
mismatches are considered to be errors. [This option is specific
to the i386 PE targeted port of the linker]
--leading-underscore
--no-leading-underscore
For most targets default symbol-prefix is an underscore and is
defined in target's description. By this option it is possible to
disable/enable the default underscore symbol-prefix.
--export-all-symbols
If given, all global symbols in the objects used to build a DLL
will be exported by the DLL. Note that this is the default if
there otherwise wouldn't be any exported symbols. When symbols are
explicitly exported via DEF files or implicitly exported via
function attributes, the default is to not export anything else
unless this option is given. Note that the symbols "DllMain@12",
"DllEntryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will
not be automatically exported. Also, symbols imported from other
DLLs will not be re-exported, nor will symbols specifying the DLL's
internal layout such as those beginning with "_head_" or ending
with "_iname". In addition, no symbols from "libgcc", "libstd++",
"libmingw32", or "crtX.o" will be exported. Symbols whose names
begin with "__rtti_" or "__builtin_" will not be exported, to help
with C++ DLLs. Finally, there is an extensive list of cygwin-
private symbols that are not exported (obviously, this applies on
when building DLLs for cygwin targets). These cygwin-excludes are:
"_cygwin_dll_entry@12", "_cygwin_crt0_common@8",
"_cygwin_noncygwin_dll_entry@12", "_fmode", "_impure_ptr",
"cygwin_attach_dll", "cygwin_premain0", "cygwin_premain1",
"cygwin_premain2", "cygwin_premain3", and "environ". [This option
is specific to the i386 PE targeted port of the linker]
--exclude-symbols symbol,symbol,...
Specifies a list of symbols which should not be automatically
exported. The symbol names may be delimited by commas or colons.
[This option is specific to the i386 PE targeted port of the
linker]
--exclude-all-symbols
Specifies no symbols should be automatically exported. [This
option is specific to the i386 PE targeted port of the linker]
--file-alignment
Specify the file alignment. Sections in the file will always begin
at file offsets which are multiples of this number. This defaults
to 512. [This option is specific to the i386 PE targeted port of
the linker]
--heap reserve
--heap reserve,commit
Specify the number of bytes of memory to reserve (and optionally
commit) to be used as heap for this program. The default is 1MB
reserved, 4K committed. [This option is specific to the i386 PE
targeted port of the linker]
--image-base value
Use value as the base address of your program or dll. This is the
lowest memory location that will be used when your program or dll
is loaded. To reduce the need to relocate and improve performance
of your dlls, each should have a unique base address and not
overlap any other dlls. The default is 0x400000 for executables,
and 0x10000000 for dlls. [This option is specific to the i386 PE
targeted port of the linker]
--kill-at
If given, the stdcall suffixes (@nn) will be stripped from symbols
before they are exported. [This option is specific to the i386 PE
targeted port of the linker]
--large-address-aware
If given, the appropriate bit in the "Characteristics" field of the
COFF header is set to indicate that this executable supports
virtual addresses greater than 2 gigabytes. This should be used in
conjunction with the /3GB or /USERVA=value megabytes switch in the
"[operating systems]" section of the BOOT.INI. Otherwise, this bit
has no effect. [This option is specific to PE targeted ports of
the linker]
--disable-large-address-aware
Reverts the effect of a previous --large-address-aware option.
This is useful if --large-address-aware is always set by the
compiler driver (e.g. Cygwin gcc) and the executable does not
support virtual addresses greater than 2 gigabytes. [This option
is specific to PE targeted ports of the linker]
--major-image-version value
Sets the major number of the "image version". Defaults to 1.
[This option is specific to the i386 PE targeted port of the
linker]
--major-os-version value
Sets the major number of the "os version". Defaults to 4. [This
option is specific to the i386 PE targeted port of the linker]
--major-subsystem-version value
Sets the major number of the "subsystem version". Defaults to 4.
[This option is specific to the i386 PE targeted port of the
linker]
--minor-image-version value
Sets the minor number of the "image version". Defaults to 0.
[This option is specific to the i386 PE targeted port of the
linker]
--minor-os-version value
Sets the minor number of the "os version". Defaults to 0. [This
option is specific to the i386 PE targeted port of the linker]
--minor-subsystem-version value
Sets the minor number of the "subsystem version". Defaults to 0.
[This option is specific to the i386 PE targeted port of the
linker]
--output-def file
The linker will create the file file which will contain a DEF file
corresponding to the DLL the linker is generating. This DEF file
(which should be called "*.def") may be used to create an import
library with "dlltool" or may be used as a reference to
automatically or implicitly exported symbols. [This option is
specific to the i386 PE targeted port of the linker]
--enable-auto-image-base
--enable-auto-image-base=value
Automatically choose the image base for DLLs, optionally starting
with base value, unless one is specified using the "--image-base"
argument. By using a hash generated from the dllname to create
unique image bases for each DLL, in-memory collisions and
relocations which can delay program execution are avoided. [This
option is specific to the i386 PE targeted port of the linker]
--disable-auto-image-base
Do not automatically generate a unique image base. If there is no
user-specified image base ("--image-base") then use the platform
default. [This option is specific to the i386 PE targeted port of
the linker]
--dll-search-prefix string
When linking dynamically to a dll without an import library, search
for "<string><basename>.dll" in preference to "lib<basename>.dll".
This behaviour allows easy distinction between DLLs built for the
various "subplatforms": native, cygwin, uwin, pw, etc. For
instance, cygwin DLLs typically use "--dll-search-prefix=cyg".
[This option is specific to the i386 PE targeted port of the
linker]
--enable-auto-import
Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA
imports from DLLs, thus making it possible to bypass the dllimport
mechanism on the user side and to reference unmangled symbol names.
[This option is specific to the i386 PE targeted port of the
linker]
The following remarks pertain to the original implementation of the
feature and are obsolete nowadays for Cygwin and MinGW targets.
Note: Use of the 'auto-import' extension will cause the text
section of the image file to be made writable. This does not
conform to the PE-COFF format specification published by Microsoft.
Note - use of the 'auto-import' extension will also cause read only
data which would normally be placed into the .rdata section to be
placed into the .data section instead. This is in order to work
around a problem with consts that is described here:
http://www.cygwin.com/ml/cygwin/2004-09/msg01101.html
Using 'auto-import' generally will 'just work' -- but sometimes you
may see this message:
"variable '<var>' can't be auto-imported. Please read the
documentation for ld's "--enable-auto-import" for details."
This message occurs when some (sub)expression accesses an address
ultimately given by the sum of two constants (Win32 import tables
only allow one). Instances where this may occur include accesses
to member fields of struct variables imported from a DLL, as well
as using a constant index into an array variable imported from a
DLL. Any multiword variable (arrays, structs, long long, etc) may
trigger this error condition. However, regardless of the exact
data type of the offending exported variable, ld will always detect
it, issue the warning, and exit.
There are several ways to address this difficulty, regardless of
the data type of the exported variable:
One way is to use --enable-runtime-pseudo-reloc switch. This leaves
the task of adjusting references in your client code for runtime
environment, so this method works only when runtime environment
supports this feature.
A second solution is to force one of the 'constants' to be a
variable -- that is, unknown and un-optimizable at compile time.
For arrays, there are two possibilities: a) make the indexee (the
array's address) a variable, or b) make the 'constant' index a
variable. Thus:
extern type extern_array[];
extern_array[1] -->
{ volatile type *t=extern_array; t[1] }
or
extern type extern_array[];
extern_array[1] -->
{ volatile int t=1; extern_array[t] }
For structs (and most other multiword data types) the only option
is to make the struct itself (or the long long, or the ...)
variable:
extern struct s extern_struct;
extern_struct.field -->
{ volatile struct s *t=&extern_struct; t->field }
or
extern long long extern_ll;
extern_ll -->
{ volatile long long * local_ll=&extern_ll; *local_ll }
A third method of dealing with this difficulty is to abandon
'auto-import' for the offending symbol and mark it with
"__declspec(dllimport)". However, in practice that requires using
compile-time #defines to indicate whether you are building a DLL,
building client code that will link to the DLL, or merely
building/linking to a static library. In making the choice
between the various methods of resolving the 'direct address with
constant offset' problem, you should consider typical real-world
usage:
Original:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d\n",arr[1]);
}
Solution 1:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
/* This workaround is for win32 and cygwin; do not "optimize" */
volatile int *parr = arr;
printf("%d\n",parr[1]);
}
Solution 2:
--foo.h
/* Note: auto-export is assumed (no __declspec(dllexport)) */
#if (defined(_WIN32) || defined(__CYGWIN__)) && \
!(defined(FOO_BUILD_DLL) || defined(FOO_STATIC))
#define FOO_IMPORT __declspec(dllimport)
#else
#define FOO_IMPORT
#endif
extern FOO_IMPORT int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d\n",arr[1]);
}
A fourth way to avoid this problem is to re-code your library to
use a functional interface rather than a data interface for the
offending variables (e.g. set_foo() and get_foo() accessor
functions).
--disable-auto-import
Do not attempt to do sophisticated linking of "_symbol" to
"__imp__symbol" for DATA imports from DLLs. [This option is
specific to the i386 PE targeted port of the linker]
--enable-runtime-pseudo-reloc
If your code contains expressions described in --enable-auto-import
section, that is, DATA imports from DLL with non-zero offset, this
switch will create a vector of 'runtime pseudo relocations' which
can be used by runtime environment to adjust references to such
data in your client code. [This option is specific to the i386 PE
targeted port of the linker]
--disable-runtime-pseudo-reloc
Do not create pseudo relocations for non-zero offset DATA imports
from DLLs. [This option is specific to the i386 PE targeted port
of the linker]
--enable-extra-pe-debug
Show additional debug info related to auto-import symbol thunking.
[This option is specific to the i386 PE targeted port of the
linker]
--section-alignment
Sets the section alignment. Sections in memory will always begin
at addresses which are a multiple of this number. Defaults to
0x1000. [This option is specific to the i386 PE targeted port of
the linker]
--stack reserve
--stack reserve,commit
Specify the number of bytes of memory to reserve (and optionally
commit) to be used as stack for this program. The default is 2MB
reserved, 4K committed. [This option is specific to the i386 PE
targeted port of the linker]
--subsystem which
--subsystem which:major
--subsystem which:major.minor
Specifies the subsystem under which your program will execute. The
legal values for which are "native", "windows", "console", "posix",
and "xbox". You may optionally set the subsystem version also.
Numeric values are also accepted for which. [This option is
specific to the i386 PE targeted port of the linker]
The following options set flags in the "DllCharacteristics" field
of the PE file header: [These options are specific to PE targeted
ports of the linker]
--high-entropy-va
Image is compatible with 64-bit address space layout randomization
(ASLR). This option also implies --dynamicbase and
--enable-reloc-section.
--dynamicbase
The image base address may be relocated using address space layout
randomization (ASLR). This feature was introduced with MS Windows
Vista for i386 PE targets. This option also implies
--enable-reloc-section.
--forceinteg
Code integrity checks are enforced.
--nxcompat
The image is compatible with the Data Execution Prevention. This
feature was introduced with MS Windows XP SP2 for i386 PE targets.
--no-isolation
Although the image understands isolation, do not isolate the image.
--no-seh
The image does not use SEH. No SE handler may be called from this
image.
--no-bind
Do not bind this image.
--wdmdriver
The driver uses the MS Windows Driver Model.
--tsaware
The image is Terminal Server aware.
--insert-timestamp
--no-insert-timestamp
Insert a real timestamp into the image. This is the default
behaviour as it matches legacy code and it means that the image
will work with other, proprietary tools. The problem with this
default is that it will result in slightly different images being
produced each time the same sources are linked. The option
--no-insert-timestamp can be used to insert a zero value for the
timestamp, this ensuring that binaries produced from identical
sources will compare identically.
--enable-reloc-section
Create the base relocation table, which is necessary if the image
is loaded at a different image base than specified in the PE
header.
The C6X uClinux target uses a binary format called DSBT to support
shared libraries. Each shared library in the system needs to have a
unique index; all executables use an index of 0.
--dsbt-size size
This option sets the number of entries in the DSBT of the current
executable or shared library to size. The default is to create a
table with 64 entries.
--dsbt-index index
This option sets the DSBT index of the current executable or shared
library to index. The default is 0, which is appropriate for
generating executables. If a shared library is generated with a
DSBT index of 0, the "R_C6000_DSBT_INDEX" relocs are copied into
the output file.
The --no-merge-exidx-entries switch disables the merging of
adjacent exidx entries in frame unwind info.
--branch-stub
This option enables linker branch relaxation by inserting branch
stub sections when needed to extend the range of branches. This
option is usually not required since C-SKY supports branch and call
instructions that can access the full memory range and branch
relaxation is normally handled by the compiler or assembler.
--stub-group-size=N
This option allows finer control of linker branch stub creation.
It sets the maximum size of a group of input sections that can be
handled by one stub section. A negative value of N locates stub
sections after their branches, while a positive value allows stub
sections to appear either before or after the branches. Values of
1 or -1 indicate that the linker should choose suitable defaults.
The 68HC11 and 68HC12 linkers support specific options to control the
memory bank switching mapping and trampoline code generation.
--no-trampoline
This option disables the generation of trampoline. By default a
trampoline is generated for each far function which is called using
a "jsr" instruction (this happens when a pointer to a far function
is taken).
--bank-window name
This option indicates to the linker the name of the memory region
in the MEMORY specification that describes the memory bank window.
The definition of such region is then used by the linker to compute
paging and addresses within the memory window.
The following options are supported to control handling of GOT
generation when linking for 68K targets.
--got=type
This option tells the linker which GOT generation scheme to use.
type should be one of single, negative, multigot or target. For
more information refer to the Info entry for ld.
The following options are supported to control microMIPS instruction
generation and branch relocation checks for ISA mode transitions when
linking for MIPS targets.
--insn32
--no-insn32
These options control the choice of microMIPS instructions used in
code generated by the linker, such as that in the PLT or lazy
binding stubs, or in relaxation. If --insn32 is used, then the
linker only uses 32-bit instruction encodings. By default or if
--no-insn32 is used, all instruction encodings are used, including
16-bit ones where possible.
--ignore-branch-isa
--no-ignore-branch-isa
These options control branch relocation checks for invalid ISA mode
transitions. If --ignore-branch-isa is used, then the linker
accepts any branch relocations and any ISA mode transition required
is lost in relocation calculation, except for some cases of "BAL"
instructions which meet relaxation conditions and are converted to
equivalent "JALX" instructions as the associated relocation is
calculated. By default or if --no-ignore-branch-isa is used a
check is made causing the loss of an ISA mode transition to produce
an error.
--compact-branches
--no-compact-branches
These options control the generation of compact instructions by the
linker in the PLT entries for MIPS R6.
For the pdp11-aout target, three variants of the output format can be
produced as selected by the following options. The default variant for
pdp11-aout is the --omagic option, whereas for other targets --nmagic
is the default. The --imagic option is defined only for the pdp11-aout
target, while the others are described here as they apply to the
pdp11-aout target.
-N
--omagic
Mark the output as "OMAGIC" (0407) in the a.out header to indicate
that the text segment is not to be write-protected and shared.
Since the text and data sections are both readable and writable,
the data section is allocated immediately contiguous after the text
segment. This is the oldest format for PDP11 executable programs
and is the default for ld on PDP11 Unix systems from the beginning
through 2.11BSD.
-n
--nmagic
Mark the output as "NMAGIC" (0410) in the a.out header to indicate
that when the output file is executed, the text portion will be
read-only and shareable among all processes executing the same
file. This involves moving the data areas up to the first possible
8K byte page boundary following the end of the text. This option
creates a pure executable format.
-z
--imagic
Mark the output as "IMAGIC" (0411) in the a.out header to indicate
that when the output file is executed, the program text and data
areas will be loaded into separate address spaces using the split
instruction and data space feature of the memory management unit in
larger models of the PDP11. This doubles the address space
available to the program. The text segment is again pure, write-
protected, and shareable. The only difference in the output format
between this option and the others, besides the magic number, is
that both the text and data sections start at location 0. The -z
option selected this format in 2.11BSD. This option creates a
separate executable format.
--no-omagic
Equivalent to --nmagic for pdp11-aout.
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) 1991-2020 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-2.35.1 2020-10-09 LD(1)