libtool/TODO

GNU Libtool
***********

1. In the near future
=====================

1.1. libtool
------------

* Rather than looking up the linker's hardcode characteristics in a
  table of shell code, use objdump or equivalent to probe a test program
  at configure time.

* Eliminate the warnings from autoconf -Wobsolete.

* Hook the various language dependencies into the autoconf _AC_LANG
  framework.

* We could have an option to hardcode paths into libraries, as well as
  binaries: `... -Wl,-soname -Wl,/tmp/libtest.so.0 ...'.  This is not
  possible on all platforms, and is in part obviated by the ability of
  linking libtool libraries specified with -lname, but it might still
  be desirable.

* Lists of exported symbols should be stored in the pseudo library
  so that the size of lt_preloaded_symbols can be reduced.

* Have some option to tell libtool not to include -L flags that point
  into a certain tree in the dependence list of an installed library.
  For example: -L-$top_builddir would let one link with libtool
  libraries in sibling subdirectories within a project, using the -L
  notation, without getting builddir pathnames ever mentioned in .la
  files that get installed.

* Eric Lemings <elemings@cyberia.lemings.com> writes:
  Because of a growing number of config scripts for packages in GNOME 1.2
  (e.g. glib-config, xml-config, orbit-config. etc), development of GNOME
  2.0 spawned a separate tool called pkg-config that allows all packages
  to use one tool rather than several different scripts to query compile
  flags, link flags, and other configuration data.

  The functionality of pkg-config seems to me to have a lot of overlap
  with the goals of libtool.  I was wondering if anyone had considered
  adding an eighth mode to libtool that just queries the installed
  library for the same information that pkg-config provides.  Since
  most packages that use pkg-config also use libtool, I think this
  would be a good way to reduce maintainer and developer dependencies.

1.2. libtldl
------------

* Fix the following bugs in libltdl:
 - error reporting of tryall_dlopen():
   if the file actually doesn't exist (stat() fails or it wasn't dlpreopened)
   -> report `file not found'
   if it cannot be loaded (e.g. due to missing dependencies)
   -> report dlerror
    open question: which error should be reported if all dlloaders fail
    or if a specific module type can only be loaded by one of them, how report its dlerror?
   Also report dlerror() for dlclose and dlsym if available
 - Make sure that the dependency_libs of a dlpreopened module won't be loaded.


2. In the future
================

2.1. Documentation
------------------

* Need to finalize the documentation, and give a specification of
  `.la' files so that people can depend on their format.  This would be
  a good thing to put before the maintainance notes.

2.2. test suite
---------------

* Rewrite the whole thing in Autotest.  This will enable us to remove
  all the tests/*demo noise, and duplication; and thus speed up bootstrap
  and make writing new tests a whole lot more pleasant.

* We should include tests with convenience libraries and reloadable
  objects in the testsuite.

* Write a test case for linkage with gnu ld scripts (per 2004-08-25 patch
  from Paolo Bonzini).

2.3. libtool
------------

* If not cross-compiling, have the static flag test run the resulting
  binary to make sure everything works.

* Another form of convenience library is to have undocumented utility
  libraries, where only the shared version is installed.

* We could use libtool object convenience libraries that resolve
  symbols to be included in a libtool archive.  This would require some
  sort of -whole-archive option, as well.

* Currently, convenience libraries (.al) are built from .lo objects,
  except when --disable-shared.  When we can build both shared and
  static libraries, we should probably create a .al out of .lo objects
  and also a .a out of .o objects.  The .al would only be used to create
  shared libraries, whereas the .a would be used for creating static
  libraries and programs.  We could also explicitly support `empty'
  convenience libraries, that behave as macros that expand to a set of
  -Rs, -Ls and -ls switches.

* Filenames containing shell meta-characters are not properly handled
  by libtool.  Compiling a file named "a;b.c", for example, fails.

* We could introduce a mechanism to allow for soname rewriting, to
  ease multi-libc support.  Installers could specify a prefix, suffix or
  sed command to modify the soname, and libtool would create the
  corresponding link.  This would allow for rebuilding a library with
  the same version number, but depending on different versions of libc,
  for example.  In the future, we might even have an option to encode
  the sonames of all dependencies of a library into its soname.

2.4. libtool autoconf macros
----------------------------

* The definitions for AC_LTDL_SHLIBEXT, AC_LTDL_SHLIBPATH and
  AC_LTDL_SYSSEARCHPATH  should not rely on the _LT_AC_LTCONFIG_HACK
  macro.  This involves moving the code which sets the variables
  library_names_spec, shlibpath_var and sys_lib_dlsearch_path_spec from
  into a separate macro, and AC_REQUIRING the newly extracted macro in the
  respective ltdl.m4 macros.

2.5. libltdl
------------

* Try to find a work-around for -[all-]static and libltdl on platforms
  that will fail to find dlopening functions in this case.  Maybe
  creating an alternate libltdl that provides only for dlpreopening, or
  creating an additional static library to provide dummy implementations
  of the functions that can't be linked statically.  This could hardly
  be made completely transparent, though.

* Godmar Back writes:
  libltdl uses such stdio functions as fopen, fgets, feof, fclose, and others.
  These functions are not async-signal-safe. While this does not make
  libltdl unusable, it restricts its usefulness and puts an
  unnecessary burden on the user.

  As a remedy, I'd recommend to replace those functions with functions
  that POSIX says are async-signal-safe, such as open, read, close.
  This will require you to handle interrupted system calls and implement
  fgets, but the former isn't hard and there's plenty of implementations
  out from which you can steal the latter.

  I believe relying on async-signal-safe functions to the greatest extent
  possible would greatly improve libltdl's ability to be embedded in and
  used by other systems.

2.6. win32 support
------------------

* Arrange that EXEEXT suffixes are stripped from wrapper script names
  only when needed, and that a timestamp file or a wrapper program is
  created with the EXEEXT suffix, so that `make' doesn't build it every
  time.

* Figure out how to use data items in dlls with win32.
  The difficult part is compiling each object which will be linked with an
  import lib differently than if it will be linked with a static lib.  This
  will almost definitely require that automake pass some hints about linkage
  in to each object compilation line.

* jeffdb@goodnet.com writes:
  all you need to do for mutually dependent .dll's is to create an implib from
  a .def file so it appears that we might need to detect and handle mutual
  dependencies specially on win32 =(O|


3. Wish List
============

* Maybe implement full support for other orthogonal library types
  (libhello_g, libhello_p, 64 vs 32-bit ABI's, etc).  Make these types
  configurable.

* Perhaps the iuse of libltdl could be made cleaner by allowing
  registration of hook functions to call at various points.  This would
  hopefully free the user from having to maintain a parallel module
  list with user data.  This would likely involve being able to carry
  additional per user module data in the lt_dlmodule structure -- perhaps
  in the form of an associative array keyed by user name?


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