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Options for Linking
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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
-
-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 lib
ffb
rary 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 standar
ffb
d 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.
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