[JAVA,libtool] Big libjava is biiiig.

Wed May 6 15:58:00 GMT 2009

[ Boh! I allowed my emailer to autocomplete the address and misdirected this
to the -patches list. Apologies for the reposting to gcc@, but it'll break
the threading if I just send a forward to java@. ]
 Hi,
 As I'm sure everyone concerned is aware, libgcj is currently a bit of a
monolith. Wighing in at 93M for a static archive, 73M for a shared library
(win32), it exports 82720 symbols. Which is unfortunately 17184 more than the
system limit (64k) for a Windows DLL.
 The idea of breaking libjava up into smaller sublibraries has been mooted at
least a couple of times before (e.g. [*], [**]), but it's always raised issues
relating to backward compatibility.
 On windows we have no such back-compat issues to worry about; libjava has
not worked as a DLL in who-knows-how-long-if-ever. I envisage that we could
very easily break it up into a bunch of separate (but presumably quite
inter-dependent) DLLs, and as a convenience we could provide a 'top-level'
libjava import library[***] that merged all the import libraries for the
individual DLLs.
 So I'm currently experimenting with a patch that adds a new option
"--enable-libgcj-sublibs" in libjava/configure.ac. I may need to add a
dummy-link-and-relink stage to get the interdependencies working right, or I
might have to hack something in libtool, but the basic approach of adding a
bunch of extra libtool declarations based on $(filter)ing the full list of
dependencies from the complete libgcj_la_LIBADD definition seemed a reasonable
way to go:
+if BUILD_SUBLIBS
+libgcj_gnu_la_LIBADD = $(filter gnu/%.lo,$(libgcj_la_LIBADD)) -L$(here)/.libs
libgcj.la
+libgcj_java_la_LIBADD = $(filter java/%.lo,$(libgcj_la_LIBADD))
-L$(here)/.libs libgcj.la
+libgcj_javax_la_LIBADD = $(filter javax/%.lo,$(libgcj_la_LIBADD))
-L$(here)/.libs libgcj.la
+libgcj_misc_la_LIBADD = $(filter-out gnu/%.lo java/%.lo
javax/%.lo,$(libgcj_la_LIBADD)) -L$(here)/.libs libgcj.la
+endif
 Questions:
1) Would this be a reasonable approach, specifically i) in adding a configure
option to cause sublibraries to be built, and ii) in using gmake's $(filter)
construct to crudely subdivide the libraries like this?
2) Given that there's a bit of a logjam upstream, and not likely to be
another libtool release betwen now and the end of stage1, would it be
acceptable (in general) to hack on our in-tree libtool first and send patches
upstream second (thus still avoiding any potential future merge lossage)?
 cheers,
 DaveK
-- 
[*] - http://gcc.gnu.org/ml/gcc/2005-04/threads.html#01450
[**] - http://gcc.gnu.org/ml/java-patches/2005-q1/threads.html#00225
[***] - For those not familiar, when windows executables import symbols from
DLLs, they do so by statically linking against a so-named 'import library'
that contains .data section stubs that build the structures that constitute
the final exe's table of imports as understood by the runtime loader.