ExtUtils::Liblist - determine libraries to use and how to use them

  require ExtUtils::Liblist;

  $MM->ext($potential_libs, $verbose, $need_names);

  # Usually you can get away with:
  ExtUtils::Liblist->ext($potential_libs, $verbose, $need_names)

This utility takes a list of libraries in the form CW-llib1 -llib2 -llib3 and returns lines suitable for inclusion in an extension Makefile. Extra library paths may be included with the form CW-L/another/path this will affect the searches for all subsequent libraries.

It returns an array of four or five scalar values: EXTRALIBS, BSLOADLIBS, 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 CW$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 LDLOADLIBS below.

* For dynamic extensions at load time

by the DynaLoader when the shared object is loaded. See BSLOADLIBS below.

List of libraries that need to be linked with when linking a perl binary which includes this extension. Only those libraries that actually exist are included. These are written to a file and used when linking perl.

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.

List of those libraries that are needed but can be linked in dynamically 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.

This module deals with a lot of system dependencies and has quite a few architecture specific CWifs in the code.

The version of ext() which is executed under VMS differs from the Unix-OS/2 version in several respects:

•

Input library and path specifications are accepted with or without the CW-l and CW-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.

•

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 conventions used in some ported software.

•

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.

•

LDLOADLIBS contains both the libraries found based on CW$potential_libs and the CRTLs, if any, specified in Config.pm. EXTRALIBS contains just those libraries found based on CW$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 equivalents, 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.

The version of ext() which is executed under Win32 differs from the Unix-OS/2 version in several respects:

•

If CW$potential_libs is empty, the return value will be empty. Otherwise, the libraries specified by CW$Config{perllibs} (see Config.pm) will be appended to the list of CW$potential_libs. The libraries will be searched for in the directories specified in CW$potential_libs, CW$Config{libpth}, and in CW$Config{installarchlib}/CORE. For each library that is found, a space-separated list of fully qualified library pathnames is generated.

•

Input library and path specifications are accepted with or without the CW-l and CW-L prefixes used by Unix linkers. An entry of the form CW-La:\foo specifies the CWa:\foo directory to look for the libraries that follow. An entry of the form CW-lfoo specifies the library CWfoo, which may be spelled differently depending on what kind of compiler you are using. If you are using GCC, it gets translated to CWlibfoo.a, but for other win32 compilers, it becomes CWfoo.lib. If no files are found by those translated names, one more attempt is made to find them using either CWfoo.a or CWlibfoo.lib, depending on whether GCC or some other win32 compiler is being used, respectively. If neither the CW-L or CW-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 CW$Config{lib_ext} suffix will be appended to any entries that are not directories and don't already have the suffix. Note that the CW-L and CW-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.

•

Entries cannot be plain object files, as many Win32 compilers will not handle object files in the place of libraries.

•

Entries in CW$potential_libs beginning with a colon and followed by alphanumeric characters are treated as flags. Unknown flags will be ignored. An entry that matches CW/:nodefault/i disables the appending of default libraries found in CW$Config{perllibs} (this should be only needed very rarely). An entry that matches CW/:nosearch/i disables all searching for the libraries specified after it. Translation of CW-Lfoo and CW-lfoo still happens as appropriate (depending on compiler being used, as reflected by CW$Config{cc}), but the entries are not verified to be valid files or directories. An entry that matches CW/:search/i reenables searching for the libraries specified after it. You can put it at the end to enable searching for default libraries specified by CW$Config{perllibs}.

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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 distinguish between them.

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LDLOADLIBS and EXTRALIBS are always identical under Win32, and BSLOADLIBS and LD_RUN_PATH are always empty (this may change in future).

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You must make sure that any paths and path components are properly surrounded with double-quotes if they contain spaces. For example, CW$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.

•

Since this module is most often used only indirectly from extension CWMakefile.PL files, here is an example CWMakefile.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 CWlibgl.a (followed by CWgl.a) in all the locations specified by CW$Config{libpth}. When using a compiler other than GCC, the above entry will search for CWgl.lib (followed by CWlibgl.lib). If the library happens to be in a location not in CW$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 CWgl as before. If that search fails to find the library, it looks at the next item in the list. The CW:nosearch flag will prevent searching for the libraries that follow, so it simply returns the value as CW-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 CW-libpath:d:\mesalibs mesa.lib user32.lib. When using the Borland compiler, the second item is returned as CW-Ld:\mesalibs mesa.lib user32.lib, and MakeMaker takes care of moving the CW-Ld:\mesalibs to the correct place in the linker command line.

ExtUtils::MakeMaker