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LD(1) GNU Development Tools LD(1)
NAME
ld - Using 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 Edi-
tor 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",
or the manual ld: the GNU linker, 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 com-
patible as possible with other linkers. As a result, you have many choices to con-
trol 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 differ-
ent 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 out-
put, 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. Note that specifying a script in this
way merely augments the main linker script; use the -T option to replace the
default linker script entirely.
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 preceeded by two dashes. This is to reduce con-
fusion 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,--startgroup foo.o bar.o -Wl,--endgroup
This is important, because otherwise the compiler driver program may silently drop
the linker options, resulting in a bad link.
Here is a table of the generic command line switches accepted by the GNU linker:
-akeyword
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.
-Aarchitecture
--architecture=architecture
In the current release of ld, this option is useful only for the Intel 960 fam-
ily of architectures. In that ld configuration, the architecture argument
identifies the particular architecture in the 960 family, enabling some safe-
guards and modifying the archive-library search path.
Future releases of ld may support similar functionality for other architecture
families.
-b input-format
--format=input-format
ld may be configured to support more than one kind of object file. If your ld
is configured this way, you can use the -b option to specify the binary format
for input object files that follow this option on the command line. Even when
ld is configured to support alternative object formats, you don’t usually need
to specify this, as ld should be configured to expect as a default input format
the most usual format on each machine. input-format is a text string, the name
of a particular format supported by the BFD libraries. (You can list the
available binary formats with objdump -i.)
You may want to use this option if you are linking files with an unusual binary
format. You can also use -b to switch formats explicitly (when linking object
files of different formats), by including -b input-format before each group of
object files in a particular format.
The default format is taken from the environment variable "GNUTARGET".
You can also define the input format from a script, using the command "TARGET";
-c MRI-commandfile
--mri-script=MRI-commandfile
For compatibility with linkers produced by MRI, ld accepts script files written
in an alternate, restricted command language, described in the MRI Compatible
Script Files section of GNU ld documentation. Introduce MRI script files with
the option -c; use the -T option to run linker scripts written in the general-
purpose ld scripting language. If MRI-cmdfile does not exist, ld looks for it
in the directories specified by any -L options.
-d
-dc
-dp These three options are equivalent; multiple forms are supported for compati-
bility with other linkers. They assign space to common symbols even if a relo-
catable output file is specified (with -r). The script command "FORCE_COM-
MON_ALLOCATION" has the same effect.
-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 automat-
ically exported. The library names may be delimited by commas or colons. Spec-
ifying "--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.
-E
--export-dynamic
When creating a dynamically linked executable, 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 this option, 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 version script to control what symbols should be added to
the dynamic symbol table if the output format supports it. See the description
of --version-script in @ref{VERSION}.
-EB Link big-endian objects. This affects the default output format.
-EL Link little-endian objects. This affects the default output format.
-f
--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 alterna-
tive 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" environ-
ment 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 func-
tion. By default, the linker uses "_fini" as the function to call.
-g Ignored. Provided for compatibility with other tools.
-Gvalue
--gpsize=value
Set the maximum size of objects to be optimized using the GP register to size.
This is only meaningful for object file formats such as MIPS ECOFF which sup-
ports putting large and small objects into different sections. This is ignored
for other object file formats.
-hname
-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.
-larchive
--library=archive
Add archive file archive to the list of files to link. This option may be used
any number of times. ld will search its path-list for occurrences of
"libarchive.a" for every archive specified.
On systems which support shared libraries, ld may also search for libraries
with extensions other than ".a". Specifically, on ELF and SunOS systems, ld
will search a directory for a library with an extension of ".so" before search-
ing for one with an extension of ".a". By convention, a ".so" extension indi-
cates a shared library.
The linker will search an archive only once, at the location where it is speci-
fied 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.
-Lsearchdir
--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.
If searchdir begins with "=", then the "=" will be replaced by the sysroot pre-
fix, a path specified when the linker is configured.
The default set of paths searched (without being specified with -L) depends on
which emulation mode ld is using, and in some cases also on how it was config-
ured.
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.
-memulation
Emulate the emulation linker. You can list the available emulations with the
--verbose or -V options.
If the -m option is not used, the emulation is taken from the "LDEMULATION"
environment variable, if that is defined.
Otherwise, the default emulation depends upon how the linker was configured.
-M
--print-map
Print a link map to the standard output. A link map provides information about
the link, including the following:
* Where object files and symbols are mapped into memory.
* How common symbols are allocated.
* All archive members included in the link, with a mention of the symbol
which caused the archive member to be brought in.
-n
--nmagic
Turn off page alignment of sections, and mark the output as "NMAGIC" if possi-
ble.
-N
--omagic
Set the text and data sections to be readable and writable. Also, do not page-
align the data segment, and disable linking against shared libraries. If the
output format supports Unix style magic numbers, mark the output as "OMAGIC".
Note: Although a writable text section is allowed for PE-COFF targets, it does
not conform to the format specification published by Microsoft.
--no-omagic
This option negates most of the effects of the -N option. It sets the text
section to be read-only, and forces the data segment to be page-aligned. Note
- this option does not enable linking against shared libraries. Use -Bdynamic
for this.
-o output
--output=output
Use output as the name for the program produced by ld; if this option is not
specified, the name a.out is used by default. The script command "OUTPUT" can
also specify the output file name.
-O level
If level is a numeric values greater than zero ld optimizes the output. This
might take significantly longer and therefore probably should only be enabled
for the final binary.
-q
--emit-relocs
Leave relocation sections and contents in fully linked exececutables. Post
link analysis and optimization tools may need this information in order to per-
form correct modifications of executables. This results in larger executables.
This option is currently only supported on ELF platforms.
-r
--relocatable
Generate relocatable output---i.e., generate an output file that can in turn
serve as input to ld. This is often called partial linking. As a side effect,
in environments that support standard Unix magic numbers, this option also sets
the output file’s magic number to "OMAGIC". If this option is not specified,
an absolute file is produced. When linking C++ programs, this option will not
resolve references to constructors; to do that, use -Ur.
When an input file does not have the same format as the output file, partial
linking is only supported if that input file does not contain any relocations.
Different output formats can have further restrictions; for example some
"a.out"-based formats do not support partial linking with input files in other
formats at all.
This option does the same thing as -i.
-R filename
--just-symbols=filename
Read symbol names and their addresses from filename, but do not relocate it or
include it in the output. This allows your output file to refer symbolically
to absolute locations of memory defined in other programs. You may use this
option more than once.
For compatibility with other ELF linkers, if the -R option is followed by a
directory name, rather than a file name, it is treated as the -rpath option.
-s
--strip-all
Omit all symbol information from the output file.
-S
--strip-debug
Omit debugger symbol information (but not all symbols) from the output file.
-t
--trace
Print the names of the input files as ld processes them.
-T scriptfile
--script=scriptfile
Use scriptfile as the linker script. This script replaces ld’s default linker
script (rather than adding to it), so commandfile must specify everything nec-
essary to describe the output file. If scriptfile does not exist in the cur-
rent directory, "ld" looks for it in the directories specified by any preceding
-L options. Multiple -T options accumulate.
-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 addi-
tional undefined symbols. This option is equivalent to the "EXTERN" linker
script command.
-Ur For anything other than C++ programs, this option is equivalent to -r: it gen-
erates 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 con-
structors, unlike -r. It does not work to use -Ur on files that were them-
selves linked with -Ur; once the constructor table has been built, it cannot be
added to. Use -Ur only for the last partial link, and -r for the others.
--unique[=SECTION]
Creates a separate output section for every input section matching SECTION, or
if the optional wildcard SECTION argument is missing, for every orphan input
section. An orphan section is one not specifically mentioned in a linker
script. You may use this option multiple times on the command line; It pre-
vents the normal merging of input sections with the same name, overriding out-
put section assignments in a linker script.
-v
--version
-V Display the version number for ld. The -V option also lists the supported emu-
lations.
-x
--discard-all
Delete all local symbols.
-X
--discard-locals
Delete all temporary local symbols. For most targets, this is all local sym-
bols whose names begin with L.
-y symbol
--trace-symbol=symbol
Print the name of each linked file in which symbol appears. This option may be
given any number of times. On many systems it is necessary to prepend an
underscore.
This option is useful when you have an undefined symbol in your link but don’t
know where the reference is coming from.
-Y path
Add path to the default library search path. This option exists for Solaris
compatibility.
-z keyword
The recognized keywords are:
combreloc
Combines multiple reloc sections and sorts them to make dynamic symbol
lookup caching possible.
defs
Disallows undefined symbols in object files. Undefined symbols in shared
libraries are still allowed.
initfirst
This option is only meaningful when building a shared object. It marks the
object so that its runtime initialization will occur before the runtime
initialization of any other objects brought into the process at the same
time. Similarly the runtime finalization of the object will occur after
the runtime finalization of any other objects.
interpose
Marks the object that its symbol table interposes before all symbols but
the primary executable.
loadfltr
Marks the object that its filters be processed immediately at runtime.
muldefs
Allows multiple definitions.
nocombreloc
Disables multiple reloc sections combining.
nocopyreloc
Disables production of copy relocs.
nodefaultlib
Marks the object that the search for dependencies of this object will
ignore any default library search paths.
nodelete
Marks the object shouldn’t be unloaded at runtime.
nodlopen
Marks the object not available to "dlopen".
nodump
Marks the object can not be dumped by "dldump".
now When generating an executable or shared library, mark it to tell the
dynamic linker to resolve all symbols when the program is started, or when
the shared library is linked to using dlopen, instead of deferring function
call resolution to the point when the function is first called.
origin
Marks the object may contain $ORIGIN.
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 refer-
ences are created. Normally, an archive is searched only once in the order
that it is specified on the command line. If a symbol in that archive is
needed to resolve an undefined symbol referred to by an object in an archive
that appears later on the command line, the linker would not be able to resolve
that reference. By grouping the archives, they all be searched repeatedly
until all possible references are resolved.
Using this option has a significant performance cost. It is best to use it
only when there are unavoidable circular references between two or more
archives.
--accept-unknown-input-arch
--no-accept-unknown-input-arch
Tells the linker to accept input files whose architecture cannot be recognised.
The assumption is that the user knows what they are doing and deliberately
wants to link in these unknown input files. This was the default behaviour of
the linker, before release 2.14. The default behaviour from release 2.14
onwards is to reject such input files, and so the --accept-unknown-input-arch
option has been added to restore the old behaviour.
--as-needed
--no-as-needed
This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the
command line after the --as-needed option. Normally, the linker will add a
DT_NEEDED tag for each dynamic library mentioned on the command line, regard-
less of whether the library is actually needed. --as-needed causes DT_NEEDED
tags to only be emitted for libraries that satisfy some reference from regular
objects. --no-as-needed restores the default behaviour.
--add-needed
--no-add-needed
This option affects the treatment of dynamic libraries from ELF DT_NEEDED tags
in dynamic libraries mentioned on the command line after the --no-add-needed
option. Normally, the linker will add a DT_NEEDED tag for each dynamic library
from DT_NEEDED tags. --no-add-needed causes DT_NEEDED tags will never be emit-
ted for those libraries from DT_NEEDED tags. --add-needed restores the default
behaviour.
-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 depen-
dencies 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.
-Bsymbolic
When creating a shared library, bind references to global symbols to the defi-
nition within the shared library, if any. Normally, it is possible for a pro-
gram 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.
--check-sections
--no-check-sections
Asks the linker not to check section addresses after they have been assigned to
see if there 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.
--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 pro-
cessed by a script if necessary. The symbols are printed out, sorted by name.
For each symbol, a list of file names is given. If the symbol is defined, the
first file listed is the location of the definition. The remaining files con-
tain references to the symbol.
--no-define-common
This option inhibits the assignment of addresses to common symbols. The script
command "INHIBIT_COMMON_ALLOCATION" has the same effect.
The --no-define-common option allows decoupling the decision to assign
addresses to Common symbols from the choice of the output file type; otherwise
a non-Relocatable output type forces assigning addresses to Common symbols.
Using --no-define-common allows Common symbols that are referenced from a
shared library to be assigned addresses only in the main program. This elimi-
nates the unused duplicate space in the shared library, and also prevents any
possible confusion over resolving to the wrong duplicate when there are many
dynamic modules with specialized search paths for runtime symbol resolution.
--defsym symbol=expression
Create a global symbol in the output file, containing the absolute address
given by expression. You may use this option as many times as necessary to
define multiple symbols in the command line. A limited form of arithmetic is
supported for the expression in this context: you may give a hexadecimal con-
stant or the name of an existing symbol, or use "+" and "-" to add or subtract
hexadecimal constants or symbols. If you need more elaborate expressions, con-
sider 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 read-
able 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.
--dynamic-linker file
Set the name of the dynamic linker. This is only meaningful when generating
dynamically linked ELF executables. The default dynamic linker is normally
correct; don’t use this unless you know what you are doing.
--fatal-warnings
Treat all warnings as errors.
--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.
--no-gc-sections
--gc-sections
Enable garbage collection of unused input sections. It is ignored on targets
that do not support this option. This option is not compatible with -r. The
default behaviour (of not performing this garbage collection) can be restored
by specifying --no-gc-sections on the command line.
--help
Print a summary of the command-line options on the standard output and exit.
--target-help
Print a summary of all target specific options on the standard output and exit.
-Map mapfile
Print a link map to the file mapfile. See the description of the -M option,
above.
--no-keep-memory
ld normally optimizes for speed over memory usage by caching the symbol tables
of input files in memory. This option tells ld to instead optimize for memory
usage, by rereading the symbol tables as necessary. This may be required if ld
runs out of memory space while linking a large executable.
--no-undefined
-z defs
Report unresolved symbol references from regular object files. This is done
even if the linker is creating a non-symbolic shared library. The switch
--[no-]allow-shlib-undefined controls the behaviour for reporting unresolved
references found in shared libraries being linked in.
--allow-multiple-definition
-z muldefs
Normally when a symbol is defined multiple times, the linker will report a
fatal error. These options allow multiple definitions and the first definition
will be used.
--allow-shlib-undefined
--no-allow-shlib-undefined
Allows (the default) 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 reason that --allow-shlib-undefined is the default is that the shared
library being specified at link time may not be the same as the one that is
available at load time, so the symbols might actually be resolvable at load
time. Plus there are some systems, (eg BeOS) where undefined symbols in shared
libraries is normal. (The kernel patches them at load time to select which
function is most appropriate for the current architecture. This is used for
example to dynamically select an appropriate memset function). Apparently it
is also normal for HPPA shared libraries to have undefined symbols.
--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 differ-
ent 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-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 what-
soever.
-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 for-
mat 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 for-
mats with objdump -i.) The script command "OUTPUT_FORMAT" can also specify the
output format, but this option overrides it.
-pie
--pic-executable
Create a position independent executable. This is currently only supported on
ELF platforms. Position independent executables are similar to shared
libraries in that they are relocated by the dynamic linker to the virtual
address the OS chooses for them (which can vary between invocations). Like
normal dynamically linked executables they can be executed and symbols defined
in the executable cannot be overridden by shared libraries.
-qmagic
This option is ignored for Linux compatibility.
-Qy This option is ignored for SVR4 compatibility.
--relax
An option with machine dependent effects. This option is only supported on a
few targets.
On some platforms, the --relax option performs global optimizations that become
possible when the linker resolves addressing in the program, such as relaxing
address modes and synthesizing new instructions in the output object file.
On some platforms these link time global optimizations may make symbolic debug-
ging 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.
--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 over-
rides -s and -S.
-rpath dir
Add a directory to the runtime library search path. This is used when linking
an ELF executable with shared objects. All -rpath arguments are concatenated
and passed to the runtime linker, which uses them to locate shared objects at
runtime. The -rpath option is also used when locating shared objects which are
needed by shared objects explicitly included in the link; see the description
of the -rpath-link option. If -rpath is not used when linking an ELF exe-
cutable, the contents of the environment variable "LD_RUN_PATH" will be used if
it is defined.
The -rpath option may also be used on SunOS. By default, on SunOS, the linker
will form a runtime search patch out of all the -L options it is given. If a
-rpath option is used, the runtime search path will be formed exclusively using
the -rpath options, ignoring the -L options. This can be useful when using
gcc, which adds many -L options which may be on NFS mounted filesystems.
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-relo-
catable 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 specify-
ing a list of names separated by colons, or by appearing multiple times.
This option should be used with caution as it overrides the search path that
may have been hard compiled into a shared library. In such a case it is possi-
ble 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. It is for the native linker only.
3. On an ELF system, if the -rpath and "rpath-link" options were not used,
search the contents of the environment variable "LD_RUN_PATH". It is for
the native linker only.
4. On SunOS, if the -rpath option was not used, search any directories speci-
fied using -L options.
5. For a native linker, the contents of the environment variable
"LD_LIBRARY_PATH".
6. For a native ELF linker, the directories in "DT_RUNPATH" or "DT_RPATH" of a
shared library are searched for shared libraries needed by it. The
"DT_RPATH" entries are ignored if "DT_RUNPATH" entries exist.
7. The default directories, normally /lib and /usr/lib.
8. For a native linker on an ELF system, if the file /etc/ld.so.conf exists,
the list of directories found in that file.
If the required shared library is not found, the linker will issue a warning
and continue with the link.
-shared
-Bshareable
Create a shared library. This is currently only supported on ELF, XCOFF and
SunOS platforms. On SunOS, the linker will automatically create a shared
library if the -e option is not used and there are undefined symbols in the
link.
--sort-common
This option tells ld to sort the common symbols by size when it places them in
the appropriate output sections. First come all the one byte symbols, then all
the two byte, then all the four byte, and then everything else. This is to
prevent gaps between symbols due to alignment constraints.
--sort-section name
This option will apply "SORT_BY_NAME" to all wildcard section patterns in the
linker script.
--sort-section alignment
This option will apply "SORT_BY_ALIGNMENT" to all wildcard section patterns in
the linker script.
--split-by-file [size]
Similar to --split-by-reloc but creates a new output section for each input
file when size is reached. size defaults to a size of 1 if not given.
--split-by-reloc [count]
Tries to creates extra sections in the output file so that no single output
section in the file contains more than count relocations. This is useful when
generating huge relocatable files for downloading into certain real time ker-
nels 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 exe-
cution time and memory usage.
--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 ta-
ble. This can reduce the size of an output file with full debugging informa-
tion 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 hex-
adecimal 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.
--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
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.
--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 ver-
sion hierarchy for the library being created. This option is only meaningful
on ELF platforms which support shared libraries.
--warn-common
Warn when a common symbol is combined with another common symbol or with a sym-
bol definition. Unix linkers allow this somewhat sloppy practise, but linkers
on some other operating systems do not. This option allows you to find
potential problems from combining global symbols. Unfortunately, some C
libraries use this practise, so you may get some warnings about symbols in the
libraries as well as in your programs.
There are three kinds of global symbols, illustrated here by C examples:
int i = 1;
A definition, which goes in the initialized data section of the output
file.
extern int i;
An undefined reference, which does not allocate space. There must be
either a definition or a common symbol for the variable somewhere.
int i;
A common symbol. If there are only (one or more) common symbols for a
variable, it goes in the uninitialized data area of the output file. The
linker merges multiple common symbols for the same variable into a single
symbol. If they are of different sizes, it picks the largest size. The
linker turns a common symbol into a declaration, if there is a definition
of the same variable.
The --warn-common option can produce five kinds of warnings. Each warning con-
sists 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 defi-
nition 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. Typ-
ically, the alignment will be set by an input section. The address will only
be changed if it not explicitly specified; that is, if the "SECTIONS" command
does not specify a start address for the section.
--warn-shared-textrel
Warn if the linker adds a DT_TEXTREL to a shared object.
--warn-unresolved-symbols
If the linker is going to report an unresolved symbol (see the option --unre-
solved-symbols) it will normally generate an error. This option makes it gen-
erate 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 func-
tion should be called "__wrap_symbol". If it wishes to call the system func-
tion, 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 with-
out 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".
--enable-new-dtags
--disable-new-dtags
This linker can create the new dynamic tags in ELF. But the older ELF systems
may not understand them. If you specify --enable-new-dtags, the dynamic tags
will be created as needed. If you specify --disable-new-dtags, no new dynamic
tags will be created. By default, the new dynamic tags are not created. Note
that those options are only available for ELF systems.
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.
--reduce-memory-overheads
This option reduces memory requirements at ld runtime, at the expense of link-
ing speed. This was introduced to 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 affect 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 trade-
offs in future versions of the linker.
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 sup-
ports 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 addi-
tional 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 spe-
cific 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-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]
--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 any-
thing else unless this option is given. Note that the symbols "DllMain@12",
"DllEntryPoint@0", "DllMainCRTStartup@12", and "impure_ptr" will not be auto-
matically 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", "cyg-
win_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]
--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 amount 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 mem-
ory 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 ‘‘Charateristics’’ field of the COFF
header is set to indicate that this executable supports virtual addresses
greater than 2 gigabytes. This should be used in conjuction with the /3GB or
/USERVA=value megabytes switch in the ‘‘[operating systems]’’ section of the
BOOT.INI. Otherwise, this bit has no effect. [This option is specific to PE
targeted ports of the linker]
--major-image-version value
Sets the major number of the ‘‘image version’’. Defaults to 1. [This option
is specific to the i386 PE targeted port of the linker]
--major-os-version value
Sets the major number of the ‘‘os version’’. Defaults to 4. [This option is
specific to the i386 PE targeted port of the linker]
--major-subsystem-version value
Sets the major number of the ‘‘subsystem version’’. Defaults to 4. [This
option is specific to the i386 PE targeted port of the linker]
--minor-image-version value
Sets the minor number of the ‘‘image version’’. Defaults to 0. [This option
is specific to the i386 PE targeted port of the linker]
--minor-os-version value
Sets the minor number of the ‘‘os version’’. Defaults to 0. [This option is
specific to the i386 PE targeted port of the linker]
--minor-subsystem-version value
Sets the minor number of the ‘‘subsystem version’’. Defaults to 0. [This
option is specific to the i386 PE targeted port of the linker]
--output-def file
The linker will create the file file which will contain a DEF file correspond-
ing to the DLL the linker is generating. This DEF file (which should be called
"*.def") may be used to create an import library with "dlltool" or may be used
as a reference to automatically or implicitly exported symbols. [This option
is specific to the i386 PE targeted port of the linker]
--out-implib file
The linker will create the file file which will contain an import lib corre-
sponding to the DLL the linker is generating. This import lib (which should be
called "*.dll.a" or "*.a" may be used to link clients against the generated
DLL; this behaviour makes it possible to skip a separate "dlltool" import
library creation step. [This option is specific to the i386 PE targeted port
of the linker]
--enable-auto-image-base
Automatically choose the image base for DLLs, unless one is specified using the
"--image-base" argument. By using a hash generated from the dllname to create
unique image bases for each DLL, in-memory collisions and relocations which can
delay program execution are avoided. [This option is specific to the i386 PE
targeted port of the linker]
--disable-auto-image-base
Do not automatically generate a unique image base. If there is no user-speci-
fied image base ("--image-base") then use the platform default. [This option
is specific to the i386 PE targeted port of the linker]
--dll-search-prefix string
When linking dynamically to a dll without an import library, search for
"<string><basename>.dll" in preference to "lib<basename>.dll". This behaviour
allows easy distinction between DLLs built for the various "subplatforms":
native, cygwin, uwin, pw, etc. For instance, cygwin DLLs typically use
"--dll-search-prefix=cyg". [This option is specific to the i386 PE targeted
port of the linker]
--enable-auto-import
Do sophisticated linking of "_symbol" to "__imp__symbol" for DATA imports from
DLLs, and create the necessary thunking symbols when building the import
libraries with those DATA exports. Note: Use of the ’auto-import’ extension
will cause the text section of the image file to be made writable. This does
not conform to the PE-COFF format specification published by Microsoft.
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 pos-
sibilities: a) make the indexee (the array’s address) a variable, or b) make
the ’constant’ index a variable. Thus:
extern type extern_array[];
extern_array[1] -->
{ volatile type *t=extern_array; t[1] }
or
extern type extern_array[];
extern_array[1] -->
{ volatile int t=1; extern_array[t] }
For structs (and most other multiword data types) the only option is to make
the struct itself (or the long long, or the ...) variable:
extern struct s extern_struct;
extern_struct.field -->
{ volatile struct s *t=&extern_struct; t->field }
or
extern long long extern_ll;
extern_ll -->
{ volatile long long * local_ll=&extern_ll; *local_ll }
A third method of dealing with this difficulty is to abandon ’auto-import’ for
the offending symbol and mark it with "__declspec(dllimport)". However, in
practise that requires using compile-time #defines to indicate whether you are
building a DLL, building client code that will link to the DLL, or merely
building/linking to a static library. In making the choice between the vari-
ous 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 func-
tional interface rather than a data interface for the offending variables (e.g.
set_foo() and get_foo() accessor functions). [This option is specific to the
i386 PE targeted port of the linker]
--disable-auto-import
Do not attempt to do sophisticated linking of "_symbol" to "__imp__symbol" for
DATA imports from DLLs. [This option is specific to the i386 PE targeted port
of the linker]
--enable-runtime-pseudo-reloc
If your code contains expressions described in --enable-auto-import section,
that is, DATA imports from DLL with non-zero offset, this switch will create a
vector of ’runtime pseudo relocations’ which can be used by runtime environment
to adjust references to such data in your client code. [This option is spe-
cific to the i386 PE targeted port of the linker]
--disable-runtime-pseudo-reloc
Do not create pseudo relocations for non-zero offset DATA imports from DLLs.
This is the default. [This option is specific to the i386 PE targeted port of
the linker]
--enable-extra-pe-debug
Show additional debug info related to auto-import symbol thunking. [This
option is specific to the i386 PE targeted port of the linker]
--section-alignment
Sets the section alignment. Sections in memory will always begin at addresses
which are a multiple of this number. Defaults to 0x1000. [This option is spe-
cific to the i386 PE targeted port of the linker]
--stack reserve
--stack reserve,commit
Specify the amount 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 val-
ues 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 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.
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 proce-
dure 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 "COL-
LECT_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, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002, 2003, 2004
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 1.1 or any later version pub-
lished 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-2.15.94.0.2.2 2005-06-29 LD(1)
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