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MAN page from Fedora 6 perl-ExtUtils-MakeMaker-6.46-1.fc6.rf.noarch.rpm

ExtUtils::Liblist

Section: User Contributed Perl Documentation (3)
Updated: 2008-09-27
Index 

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 extensionMakefile. Extra library paths may be included with the form"-L/another/path" this will affect the searches for all subsequentlibraries.

It returns an array of four or five scalar values: EXTRALIBS,BSLOADLIBS, LDLOADLIBS, LD_RUN_PATH, and, optionally, a reference tothe array of the filenames of actual libraries. Some of these don'tmean anything unless on Unix. See the details about those platformspecifics 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 extensionlibrary. See EXTRALIBS below.
* For dynamic extensions at build/link time
by the ld command when the shared object is built/linked. SeeLDLOADLIBS below.
* For dynamic extensions at load time
by the DynaLoader when the shared object is loaded. See BSLOADLIBSbelow.
 

EXTRALIBS

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

LDLOADLIBS and LD_RUN_PATH

List of those libraries which can or must be linked into the sharedlibrary when created using ld. These may be static or dynamiclibraries. LD_RUN_PATH is a colon separated list of the directoriesin LDLOADLIBS. It is passed as an environment variable to the processthat links the shared library. 

BSLOADLIBS

List of those libraries that are needed but can be linked indynamically at run time on this platform. SunOS/Solaris does not needthis because ld records the information (from LDLOADLIBS) into theobject file. This list is used to create a .bs (bootstrap) file. 

PORTABILITY

This module deals with a lot of system dependencies and has quite afew architecture specific "if"s in the code. 

VMS implementation

The version of ext() which is executed under VMS differs from theUnix-OS/2 version in several respects:
*
Input library and path specifications are accepted with or without the"-l" and "-L" prefixes used by Unix linkers. If neither prefix ispresent, a token is considered a directory to search if it is in facta directory, and a library to search for otherwise. Authors who wishtheir extensions to be portable to Unix or OS/2 should use the Unixprefixes, 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 VMSnaming conventions, ext() looks for files named libshr and librtl;it also looks for liblib and liblib to accommodate Unix conventionsused in some ported software.
*
For each library that is found, an appropriate directive for a linker optionsfile is generated. The return values are space-separated strings ofthese directives, rather than elements used on the linker command line.
*
LDLOADLIBS contains both the libraries found based on $potential_libs andthe CRTLs, if any, specified in Config.pm. EXTRALIBS contains just thoselibraries found based on $potential_libs. BSLOADLIBS and LD_RUN_PATHare always empty.

In addition, an attempt is made to recognize several common Unix librarynames, and filter them out or convert them to their VMS equivalents, asappropriate.

In general, the VMS version of ext() should properly handle input fromextensions originally designed for a Unix or VMS environment. If youencounter 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 theUnix-OS/2 version in several respects:
*
If $potential_libs is empty, the return value will be empty.Otherwise, the libraries specified by $Config{perllibs} (see Config.pm)will be appended to the list of $potential_libs. The librarieswill 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 qualifiedlibrary pathnames is generated.
*
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 lookfor the libraries that follow.

An entry of the form "-lfoo" specifies the library "foo", which may bespelled differently depending on what kind of compiler you are using. Ifyou are using GCC, it gets translated to "libfoo.a", but for other win32compilers, it becomes "foo.lib". If no files are found by those translatednames, one more attempt is made to find them using either "foo.a" or"libfoo.lib", depending on whether GCC or some other win32 compiler isbeing used, respectively.

If neither the "-L" or "-l" prefix is present in an entry, the entry isconsidered a directory to search if it is in fact a directory, and alibrary to search for otherwise. The $Config{lib_ext} suffix willbe appended to any entries that are not directories and don't already havethe suffix.

Note that the "-L" and "-l" prefixes are not required, but authorswho wish their extensions to be portable to Unix or OS/2 should use theprefixes, since the Unix-OS/2 version of ext() requires them.

*
Entries cannot be plain object files, as many Win32 compilers willnot handle object files in the place of libraries.
*
Entries in $potential_libs beginning with a colon and followed byalphanumeric characters are treated as flags. Unknown flags will be ignored.

An entry that matches "/:nodefault/i" disables the appending of defaultlibraries found in $Config{perllibs} (this should be only needed very rarely).

An entry that matches "/:nosearch/i" disables all searching forthe 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 bevalid files or directories.

An entry that matches "/:search/i" reenables searching forthe libraries specified after it. You can put it at the end toenable searching for default libraries specified by $Config{perllibs}.

*
The libraries specified may be a mixture of static libraries andimport libraries (to link with DLLs). Since both kinds are usedpretty transparently on the Win32 platform, we do not attempt todistinguish between them.
*
LDLOADLIBS and EXTRALIBS are always identical under Win32, and BSLOADLIBSand LD_RUN_PATH are always empty (this may change in future).
*
You must make sure that any paths and path components are properlysurrounded 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 orderto protect the spaces.

*
Since this module is most often used only indirectly from extension"Makefile.PL" files, here is an example "Makefile.PL" entry to adda library to the build process for an extension:

        LIBS => ['-lgl']

When using GCC, that entry specifies that MakeMaker should first lookfor "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 searchfails to find the library, it looks at the next item in the list. The":nosearch" flag will prevent searching for the libraries that follow,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 ofmoving the "-Ld:\mesalibs" to the correct place in the linkercommand line.

 

SEE ALSO

ExtUtils::MakeMaker


 

Index

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

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