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.)
The command-line options to ld may be specified in any order, and
may be repeated at will. Repeating most 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 objects files 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 can not 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 should only be used to augment the main
linker script; if you want to use some command that logically can only
appear once, such as the SECTIONS or MEMORY command, you
must replace the default linker script using the `-T' option.
See section 3. Command Language.
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, `--oformat' and
`--oformat' are equivalent. 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, `--oformat srec' and
`--oformat=srec' are equivalent. Unique abbreviations of the names
of multiple-letter options are accepted.
-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 family of architectures. In that ld configuration, the
architecture argument identifies the particular architecture in
the 960 family, enabling some safeguards and modifying the
archive-library search path. See section ld and the Intel 960 family, for details.
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'.)
See section 5. BFD.
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.
See section 2.2 Environment Variables.
You can also define the input
format from a script, using the command TARGET; see 3.8 Option Commands.
-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
MRI Compatible Script Files. 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. See section 3.8 Option Commands.
-e entry
--entry=entry
Use entry as the explicit symbol for beginning execution of your
program, rather than the default entry point. See section 3.6 The Entry Point, for a
discussion of defaults and other ways of specifying the
entry point.
-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.
-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 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.
--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.
-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 supports 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').
-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 searching for one with an extension of
.a. By convention, a .so extension indicates a shared
library.
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.
-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.
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. See section 2.2 Environment Variables.
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
Set the text segment to be read only, and mark the output as
NMAGIC if possible.
-N
--omagic
Set the text and data sections to be readable and writable. Also, do
not page-align the data segment. If the output format supports Unix
style magic numbers, mark the output as OMAGIC.
-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.
-r
--relocateable
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'.
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 commandfile
--script=commandfile
Read link commands from the file commandfile. These commands
replace ld's default link script (rather than adding to it), so
commandfile must specify everything necessary to describe the
target format. You must use this option if you want to use a command
which can only appear once in a linker script, such as the
SECTIONS or MEMORY command. See section 3. Command Language. If
commandfile does not exist, 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 additional undefined symbols.
-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. For most targets, this is all local
symbols 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
This option is ignored for Solaris compatibility.
-( archives -)
--start-group archives --end-group
The archives should be a list of archive files. They may be
either explicit file names, or `-l' options.
The specified archives are searched repeatedly until no new undefined
references are created. Normally, an archive is searched only once in
the order that it is specified on the command line. If a symbol in that
archive is needed to resolve an undefined symbol referred to by an
object in an archive that appears later on the command line, the linker
would not be able to resolve that reference. By grouping the archives,
they all be searched repeatedly until all possible references are
resolved.
Using this option has a significant performance cost. It is best to use
it only when there are unavoidable circular references between two or
more archives.
-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.
-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.
-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.
--cref
Output a cross reference table. If a linker map file is being
generated, the cross reference table is printed to the map file.
Otherwise, it is printed on the standard output.
The format of the table is intentionally simple, so that it may be
easily processed by a script if necessary. The symbols are printed out,
sorted by name. For each symbol, a list of file names is given. If the
symbol is defined, the first file listed is the location of the
definition. The remaining files contain references to the symbol.
--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 (see section Assignment: Symbol Definitions). Note: there should be no
white space between symbol, the equals sign ("="), and
expression.
--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.
-EB
Link big-endian objects. This affects the default output format.
-EL
Link little-endian objects. This affects the default output format.
--embedded-relocs
This option is only meaningful when linking MIPS embedded PIC code,
generated by the -membedded-pic option to the GNU compiler and
assembler. It causes the linker to create a table which may be used at
runtime to relocate any data which was statically initialized to pointer
values. See the code in testsuite/ld-empic for details.
--help
Print a summary of the command-line 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-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-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.
--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. See section 5. BFD.
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 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 overrides `-s' and `-S'.
-rpath dir
Add a directory to the runtime library search path. This is used when
linking an ELF executable with shared objects. All -rpath
arguments are concatenated and passed to the runtime linker, which uses
them to locate shared objects at runtime. The -rpath option is
also used when locating shared objects which are needed by shared
objects explicitly included in the link; see the description of the
-rpath-link option. If -rpath is not used when linking an
ELF executable, the contents of the environment variable
LD_RUN_PATH will be used if it is defined.
The -rpath option may also be used on SunOS. By default, on
SunOS, the linker will form a runtime search patch out of all the
-L options it is given. If a -rpath option is used, the
runtime search path will be formed exclusively using the -rpath
options, ignoring the -L options. This can be useful when using
gcc, which adds many -L options which may be on NFS mounted
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-relocateable 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 linker uses the following search paths to locate required shared
libraries.
Any directories specified by -rpath-link options.
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.
On an ELF system, if the -rpath and rpath-link options
were not used, search the contents of the environment variable
LD_RUN_PATH.
On SunOS, if the -rpath option was not used, search any
directories specified using -L options.
For a native linker, the contents of the environment variable
LD_LIBRARY_PATH.
The default directories, normally `/lib' and `/usr/lib'.
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 bytes, then all the four bytes, and then
everything else. This is to prevent gaps between symbols due to
alignment constraints.
--split-by-file
Similar to --split-by-reloc but creates a new output section for
each input file.
--split-by-reloc count
Trys 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 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.
--stats
Compute and display statistics about the operation of the linker, such
as execution 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 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.
-Tbss org
-Tdata org
-Ttext org
Use org as the starting address for--respectively--the
bss, data, or the text segment of the output file.
org must be a single hexadecimal integer;
for compatibility with other linkers, you may omit the leading
`0x' usually associated with hexadecimal values.
-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.
--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 if using a default builtin script.
--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 heirarchy for the library being created. This option
is only meaningful on ELF platforms which support shared libraries.
See section 3.7 Version Script.
--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.
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
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
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
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
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 (see section 3.4 Specifying Output Sections).
--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.
--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 (int c)
{
printf ("malloc called with %ld\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.