Bug#561413: Policy possibly should not recommend *.la files
Russ Allbery <rra@debian.org> writes:
> Policy currently says:
> An ever increasing number of packages are using libtool to do their
> linking. The latest GNU libtools (>= 1.3a) can take advantage of the
> metadata in the installed libtool archive files (*.la files). The main
> advantage of libtool's .la files is that it allows libtool to store and
> subsequently access metadata with respect to the libraries it builds.
> libtool will search for those files, which contain a lot of useful
> information about a library (such as library dependency information for
> static linking). Also, they're *essential* for programs using
> libltdl.
> Given the various problems that we've run into with *.la files,
> particularly around adding unnecessary shared library dependencies, I
> wonder if this paragraph should be revised to be a bit less encouraging
> about retaining *.la files.
Here's a proposed patch that I think says what we now want to say about
*.la files. Objections or seconds?
diff --git a/policy.sgml b/policy.sgml
index 9fe7158..2635fa8 100644
--- a/policy.sgml
+++ b/policy.sgml
@@ -7361,40 +7361,58 @@ strip --strip-unneeded <var>your-lib</var>
</p>
<p>
- An ever increasing number of packages are using
- <prgn>libtool</prgn> to do their linking. The latest GNU
- libtools (>= 1.3a) can take advantage of the metadata in the
- installed <prgn>libtool</prgn> archive files (<file>*.la</file>
- files). The main advantage of <prgn>libtool</prgn>'s
- <file>.la</file> files is that it allows <prgn>libtool</prgn> to
- store and subsequently access metadata with respect to the
- libraries it builds. <prgn>libtool</prgn> will search for
- those files, which contain a lot of useful information about
- a library (such as library dependency information for static
- linking). Also, they're <em>essential</em> for programs
- using <tt>libltdl</tt>.<footnote>
- Although <prgn>libtool</prgn> is fully capable of
- linking against shared libraries which don't have
- <tt>.la</tt> files, as it is a mere shell script it can
- add considerably to the build time of a
- <prgn>libtool</prgn>-using package if that shell script
- has to derive all this information from first principles
- for each library every time it is linked. With the
- advent of <prgn>libtool</prgn> version 1.4 (and to a
- lesser extent <prgn>libtool</prgn> version 1.3), the
- <file>.la</file> files also store information about
- inter-library dependencies which cannot necessarily be
- derived after the <file>.la</file> file is deleted.
+ Packages that use <prgn>libtool</prgn> to create and install
+ their shared libraries install a file containing additional
+ metadata (ending in <file>.la</file>) alongside the library.
+ For public libraries intended for use by other packages, these
+ files normally should not be included in the Debian package,
+ since the information they include is not necessary to link with
+ the shared library on Debian and can add unnecessary additional
+ dependencies to other programs or libraries.<footnote>
+ These files store, among other things, all libraries on which
+ that shared library depends. Unfortunately, if
+ the <file>.la</file> file is present and contains that
+ dependency information, using <prgn>libtool</prgn> when
+ linking against that library will cause the resulting program
+ or library to be linked against those dependencies as well,
+ even if this is unnecessary. This can create unneeded
+ dependencies on shared library packages that would otherwise
+ be hidden behind the library ABI, and can make library
+ transitions to new SONAMEs unnecessarily complicated and
+ difficult to manage.
</footnote>
+ If the <file>.la</file> file is required for that library (if,
+ for instance, it's loaded via <tt>libltdl</tt> in a way that
+ requires that meta-information), the <tt>dependency_libs</tt>
+ setting in the <file>.la</file> file should normally be set to
+ the empty string. If the shared library development package has
+ historically included the <file>.la</file>, it must be retained
+ in the development package (with <tt>dependency_libs</tt>
+ emptied) until all libraries that depend on it have removed or
+ emptied <tt>dependency_libs</tt> in their <file>.la</file>
+ files to prevent linking with those other libraries
+ using <prgn>libtool</prgn> from failing.
+ </p>
+
+ <p>
+ If the <file>.la</file> must be included, it should be included
+ in the development (<tt>-dev</tt>) package, unless the library
+ will be loaded by <prgn>libtool</prgn>'s <tt>libltdl</tt>
+ library. If it is intended for use with <tt>libltdl</tt>,
+ the <file>.la</file> files must go in the run-time library
+ package.
</p>
<p>
- Packages that use <prgn>libtool</prgn> to create shared
- libraries should include the <file>.la</file> files in the
- <tt>-dev</tt> package, unless the package relies on
- <tt>libtool</tt>'s <tt>libltdl</tt> library, in which case
- the <tt>.la</tt> files must go in the run-time library
- package.
+ These requirements for handling of <file>.la</file> files do not
+ apply to loadable modules or libraries not installed in
+ directories searched by default by the dynamic linker. Packages
+ installing loadable modules will frequently need to install
+ the <file>.la</file> files alongside the modules so that they
+ can be loaded by <tt>libltdl</tt>. <tt>dependency_libs</tt>
+ does not need to be modified for libraries or modules that are
+ not installed in directories searched by the dynamic linker by
+ default and not intended for use by other packages.
</p>
<p>
--
Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>
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