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

- NAME
- SYNOPSIS
- DESCRIPTION
  - EXTRALIBS
  - LDLOADLIBS and LD_RUN_PATH
  - BSLOADLIBS
- PORTABILITY
  - VMS implementation
  - Win32 implementation
- SEE ALSO

# NAME

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

# SYNOPSIS

`require ExtUtils::Liblist;`

`ExtUtils::Liblist::ext($self, $potential_libs, $verbose);`

# DESCRIPTION

This utility takes a list of libraries in the form `-llib1 -llib2 -llib3` and prints out lines suitable for inclusion in an extension Makefile. 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 scalar values: EXTRALIBS, BSLOADLIBS, LDLOADLIBS, and LD_RUN_PATH. Some of these don't mean anything on VMS and Win32. See the details about those platform specifics below.

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 by the ld command when the shared object is built/linked. See LDLOADLIBS below.

- For dynamic extensions 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 actually 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 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.

# PORTABILITY

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

## VMS implementation

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 -l and -L prefices 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 accomodate 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 and EXTRALIBS are always identical under VMS, and BSLOADLIBS and LD_RIN_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.

## Win32 implementation

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

- Input library and path specifications are accepted with or without the -l and -L prefices used by Unix linkers. `-lfoo` specifies the library `foo.lib` and `-Ls:ome\dir` specifies a directory to look for the libraries that follow. 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. The `$Config{lib_ext}` suffix will be appended to any entries that are not directories and don't already have the suffix. 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.

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

- If `$potential_libs` is empty, the return value will be empty. Otherwise, the libraries specified by `$Config{libs}` (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` as well as in `$Config{libpth}`. For each library that is found, a space-separated list of fully qualified library pathnames is generated. You may specify an entry that matches `/:nodefault/i` in `$potential_libs` to disable the appending of default libraries found in `$Config{libs}` (this should be only needed very rarely).

- 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.

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

# SEE ALSO

MakeMaker