RFC on Makefile.am fixes for (non-portable) linking against libtool modules in KDE

[Stephan Kulow]

Am Thursday 06 March 2003 04:25 schrieb Benjamin Reed:
> I had brought this up previously pre-kde-3.1 while working on the MacOSX 
> port of KDE, but as Sam Magnuson and I are working to get our patches 
> all figured out, I figured I'd better bring it up again.
> 
> The short version is, libtool libraries built as -module's are not meant 
> to be linked against, but through the magic of the ELF library format 
> and libtool not enforcing this policy, it works 95% of the time anyways. 
>   The big problem with this on MacOSX/Darwin is that Darwin's dynamic 
> loader does *not* allow loading libtool modules (or "bundles", in Darwin 
> terms).
> 
> If it was just a few libraries, it would be easy to work around, but 
> KDE's kdeinit library/binary magic does this, and it's all over the 
> place in the KDE code.
> 
> The current "fix" looks something like this:
> 
> ---(Before:)---
> 
> lib_LTLIBRARIES = foo.la
> bin_PROGRAMS    = foo
> 
> foo_la_SOURCES = foo.cpp
> foo_la_LDFLAGS = $(all_libraries) -module
> 
> foo_SOURCES = dummy.cpp
> foo_LDADD   = foo.la
> 
> ---(After:)---
> 
> lib_LTLIBRARIES = libfoo_main.la foo.la
> bin_PROGRAMS    = foo
> 
> libfoo_main_la_SOURCES = foo.cpp
> libfoo_main_la_LDFLAGS = $(all_libraries)
> 
> foo_la_SOURCES = stub_la.cpp
> foo_la_LIBADD  = libfoo_main.la
> 
> foo_SOURCES = stub.cpp
> foo_LDADD   = libfoo_main.la
> 
> stub_la.cpp: stub.cpp
> 	cat stub.cpp > stub_la.cpp
> 
> ---(stub.cpp:)---
> 
> extern "C" int kdemain(int, char* []);
> 
> int main( int argc, char* argv[] )
> {
>          return kdemain(argc, argv);
> }
> 
> ---(fin)---
> 
> ...and then the "int main" gets turned into "int kdemain" inside 
> whatever defines main.  (foo.cpp in this case)
> 
> As you can see, this way of munging it is perfectly doable, but rather 
> brittle -- people who aren't on platforms like darwin (or, apparently, 
> a.out netbsd) will forget and end up breaking things without knowing.
> 
> What I propose is some kind of automake/am_edit trickery to allow this:
> 
> ---(new Makefile.am)---
> 
> # or kdebin_PROGRAMS maybe?
> kdeinit_PROGRAMS = foo
> 
> # foo.cpp contains an int kdemain()
> foo_SOURCES = foo.cpp
> foo_LDADD = <anything but libfoo_main.la>
> 
> ---(fin)---
> 
> ... it would automatically generate the module and shared library 
> versions of the foo code behind the scenes, with an auto-generated stub.cpp.
> 
> Does this seem feasible?  I don't understand automake or am_edit enough 
> to  do this as is, but if someone's willing to dink with it on IRC for a 
> bit to make this auto-generatable, or point me at the right resources to 
> make my own automake macros (which appears to be quite a black art, I've 
> tried), I'm willing to do all the grunt work of fixing the things that 
> need rearranging in the Makefile.am's in the KDE tree.

The general idea sounds nice, but you'll have to learn perl to get it in.

Greetings, Stephan