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Options
for Linking
The following options come
into play when the compiler links object files into an executable output
file. They are meaningless if the compiler is not doing a link step.
object-file-name
A filename
that does not end in a special recognized suffix is considered to name
an object file or library. (Object files are distinguished from libraries
by the linker according to the file contents.) If linking is done, these
object files are used as input to the linker.
-c
-S
-E
If any of these
options is used, then the linker is not run, and object filenames should
not be used as arguments. See Options
Controlling the Kind of Output.
-llibrary
Search the library named library
when linking.
It makes a difference where
in the command you write this option; the linker searches processes libraries
and object files in the order they are specified. Thus, foo.o
-lz bar.o searches
library z
after file foo.o
but before bar.o.
If bar.o
refers to functions in z,
those functions may not be loaded.
The linker searches a standard
list of directories for the library, which is actually a file named liblibrary.a.
The linker then uses this file as if it had been specified precisely by
name.
The directories searched
include several standard system directories plus any that you specify with
-L.
Normally the files found
this way are library filesarchive files whose members are object files.
The linker handles an archive file by scanning through it for members which
define symbols that have so far been referenced but not defined. But if
the file that is found is an ordinary object file, it is linked in the
usual fashion.
The only difference between
using an -l
option and specifying a filename is that -l
surrounds library with lib
and .a
and searches several directories.
-lobjc
You need this
special case of the -l
option in order to link an Objective C program.
-nostartfiles
Do not use the
standard system startup files when linking. The standard system libraries
are used normally, unless -nostdlib
or -nodefaultlibs
is used.
-nodefaultlibs
Do not use the
standard system libraries when linking. Only the libraries you specify
will be passed to the linker. The standard startup files are used normally,
unless -nostartfiles
is used.
-nostdlib
Do not use the
standard system startup files or libraries when linking. No startup files
and only the libraries you specify will be passed to the linker.
One of the standard libraries
bypassed by -nostdlib
and
-nodefaultlibs
is libgcc.a,
a library of internal subroutines that GNU CC uses to overcome shortcomings
of particular machines, or special needs for some languages. (See the discussions
in Building and Installing
a Cross-Compiler; also, see libgcc.a
and Cross-Compilers for more discussion
of libgcc.a.)
In most cases, you need
libgcc.a
even when you want to avoid other standard libraries. In other words, when
you specify -nostdlib
or -nodefaultlibs
you should usually specify -lgcc
as well. This ensures that you have no unresolved references to internal
GNU CC library subroutines. (For example, __main,
used to ensure C++ constructors will be called; see collect2.)
-s
Remove all symbol
table and relocation information from the executable.
-static
On systems that
support dynamic linking, this prevents linking with the shared libraries.
On other systems, this option has no effect.
-shared
Produce a shared
object which can then be linked with other objects to form an executable.
Not all systems support this option. You must also specify -fpic
or -fPIC
on some systems when you specify this option.
-symbolic
Bind references
to global symbols when building a shared object. Warn about any unresolved
references (unless overridden by the link editor option -Xlinker
-z -Xlinker defs).
Only a few systems support this option.
-Xlinker
option
Pass option
as an option to the linker. You can use this to supply system-specific
linker options which GNU CC does not know how to recognize. If you want
to pass an option that takes an argument, you must use
-Xlinker
twice, once for the option and once for the argument. For example, to pass
-assert definitions,
you must write -Xlinker
-assert -Xlinker definitions.
It does not work to write
-Xlinker "-assert
definitions"
because this passes the entire string as a single argument, which is not
what the linker expects.
-Wl, option
Pass option
as an option to the linker. If option
contains commas, it is split into multiple options at the commas.
-u symbol
Pretend the symbol
symbol
is undefined, to force linking of library modules to define it. You can
use -u
multiple times with different symbols to force loading of additional library
modules.