ExtUtils::Liblist
ExtUtils::Liblist(3) User Contributed Perl Documentation ExtUtils::Liblist(3)
NAME
ExtUtils::Liblist - determine libraries to use and how to use them
SYNOPSIS
require ExtUtils::Liblist;
$MM->ext($potential_libs, $verbose, $need_names);
# Usually you can get away with:
ExtUtils::Liblist->ext($potential_libs, $verbose, $need_names)
DESCRIPTION
This utility takes a list of libraries in the form "-llib1 -llib2
-llib3" and returns lines suitable for inclusion in an extension Make-
file. Extra library paths may be included with the form
"-L/another/path" this will affect the searches for all subsequent
libraries.
It returns an array of four or five scalar values: EXTRALIBS, BSLOAD-
LIBS, LDLOADLIBS, LD_RUN_PATH, and, optionally, a reference to the
array of the filenames of actual libraries. Some of these don't mean
anything unless on Unix. See the details about those platform
specifics below. The list of the filenames is returned only if
$need_names argument is true.
Dependent libraries can be linked in one of three ways:
* For static extensions
by the ld command when the perl binary is linked with the extension
library. See EXTRALIBS below.
* For dynamic extensions at build/link time
by the ld command when the shared object is built/linked. See LDLOAD-
LIBS below.
* For dynamic extensions at load time
by the DynaLoader when the shared object is loaded. See BSLOADLIBS
below.
EXTRALIBS
List of libraries that need to be linked with when linking a perl
binary which includes this extension. Only those libraries that actu-
ally exist are included. These are written to a file and used when
linking perl.
LDLOADLIBS and LD_RUN_PATH
List of those libraries which can or must be linked into the shared
library when created using ld. These may be static or dynamic
libraries. LD_RUN_PATH is a colon separated list of the directories in
LDLOADLIBS. It is passed as an environment variable to the process that
links the shared library.
BSLOADLIBS
List of those libraries that are needed but can be linked in dynami-
cally at run time on this platform. SunOS/Solaris does not need this
because ld records the information (from LDLOADLIBS) into the object
file. This list is used to create a .bs (bootstrap) file.
PORTABILITY
This module deals with a lot of system dependencies and has quite a few
architecture specific "if"s in the code.
VMS implementation
The version of ext() which is executed under VMS differs from the
Unix-OS/2 version in several respects:
o Input library and path specifications are accepted with or without
the "-l" and "-L" prefixes used by Unix linkers. If neither prefix
is present, a token is considered a directory to search if it is in
fact a directory, and a library to search for otherwise. Authors who
wish their extensions to be portable to Unix or OS/2 should use the
Unix prefixes, since the Unix-OS/2 version of ext() requires them.
o Wherever possible, shareable images are preferred to object
libraries, and object libraries to plain object files. In accordance
with VMS naming conventions, ext() looks for files named libshr and
librtl; it also looks for liblib and liblib to accommodate Unix con-
ventions used in some ported software.
o For each library that is found, an appropriate directive for a linker
options file is generated. The return values are space-separated
strings of these directives, rather than elements used on the linker
command line.
o LDLOADLIBS contains both the libraries found based on $potential_libs
and the CRTLs, if any, specified in Config.pm. EXTRALIBS contains
just those libraries found based on $potential_libs. BSLOADLIBS and
LD_RUN_PATH are always empty.
In addition, an attempt is made to recognize several common Unix
library names, and filter them out or convert them to their VMS equiva-
lents, as appropriate.
In general, the VMS version of ext() should properly handle input from
extensions originally designed for a Unix or VMS environment. If you
encounter problems, or discover cases where the search could be
improved, please let us know.
Win32 implementation
The version of ext() which is executed under Win32 differs from the
Unix-OS/2 version in several respects:
o If $potential_libs is empty, the return value will be empty. Other-
wise, the libraries specified by $Config{perllibs} (see Config.pm)
will be appended to the list of $potential_libs. The libraries will
be searched for in the directories specified in $potential_libs,
$Config{libpth}, and in "$Config{installarchlib}/CORE". For each
library that is found, a space-separated list of fully qualified
library pathnames is generated.
o Input library and path specifications are accepted with or without
the "-l" and "-L" prefixes used by Unix linkers.
An entry of the form "-La:\foo" specifies the "a:\foo" directory to
look for the libraries that follow.
An entry of the form "-lfoo" specifies the library "foo", which may
be spelled differently depending on what kind of compiler you are
using. If you are using GCC, it gets translated to "libfoo.a", but
for other win32 compilers, it becomes "foo.lib". If no files are
found by those translated names, one more attempt is made to find
them using either "foo.a" or "libfoo.lib", depending on whether GCC
or some other win32 compiler is being used, respectively.
If neither the "-L" or "-l" prefix is present in an entry, the entry
is considered a directory to search if it is in fact a directory, and
a library to search for otherwise. The $Config{lib_ext} suffix will
be appended to any entries that are not directories and don't already
have the suffix.
Note that the "-L" and "-l" prefixes are not required, but authors
who wish their extensions to be portable to Unix or OS/2 should use
the prefixes, since the Unix-OS/2 version of ext() requires them.
o Entries cannot be plain object files, as many Win32 compilers will
not handle object files in the place of libraries.
o Entries in $potential_libs beginning with a colon and followed by
alphanumeric characters are treated as flags. Unknown flags will be
ignored.
An entry that matches "/:nodefault/i" disables the appending of
default libraries found in $Config{perllibs} (this should be only
needed very rarely).
An entry that matches "/:nosearch/i" disables all searching for the
libraries specified after it. Translation of "-Lfoo" and "-lfoo"
still happens as appropriate (depending on compiler being used, as
reflected by $Config{cc}), but the entries are not verified to be
valid files or directories.
An entry that matches "/:search/i" reenables searching for the
libraries specified after it. You can put it at the end to enable
searching for default libraries specified by $Config{perllibs}.
o The libraries specified may be a mixture of static libraries and
import libraries (to link with DLLs). Since both kinds are used
pretty transparently on the Win32 platform, we do not attempt to dis-
tinguish between them.
o LDLOADLIBS and EXTRALIBS are always identical under Win32, and
BSLOADLIBS and LD_RUN_PATH are always empty (this may change in
future).
o You must make sure that any paths and path components are properly
surrounded with double-quotes if they contain spaces. For example,
$potential_libs could be (literally):
"-Lc:\Program Files\vc\lib" msvcrt.lib "la test\foo bar.lib"
Note how the first and last entries are protected by quotes in order
to protect the spaces.
o Since this module is most often used only indirectly from extension
"Makefile.PL" files, here is an example "Makefile.PL" entry to add a
library to the build process for an extension:
LIBS => ['-lgl']
When using GCC, that entry specifies that MakeMaker should first look
for "libgl.a" (followed by "gl.a") in all the locations specified by
$Config{libpth}.
When using a compiler other than GCC, the above entry will search for
"gl.lib" (followed by "libgl.lib").
If the library happens to be in a location not in $Config{libpth},
you need:
LIBS => ['-Lc:\gllibs -lgl']
Here is a less often used example:
LIBS => ['-lgl', ':nosearch -Ld:\mesalibs -lmesa -luser32']
This specifies a search for library "gl" as before. If that search
fails to find the library, it looks at the next item in the list. The
":nosearch" flag will prevent searching for the libraries that fol-
low, so it simply returns the value as "-Ld:\mesalibs -lmesa
-luser32", since GCC can use that value as is with its linker.
When using the Visual C compiler, the second item is returned as
"-libpath:d:\mesalibs mesa.lib user32.lib".
When using the Borland compiler, the second item is returned as
"-Ld:\mesalibs mesa.lib user32.lib", and MakeMaker takes care of mov-
ing the "-Ld:\mesalibs" to the correct place in the linker command
line.
SEE ALSO
ExtUtils::MakeMaker
perl v5.8.6 2007-02-21 ExtUtils::Liblist(3)
