Hi Gleb, * Gleb Natapov wrote on Sun, Aug 07, 2005 at 11:31:54AM CEST: > On Tue, Aug 02, 2005 at 03:44:05PM +0200, Ralf Wildenhues wrote: > > * Gleb Natapov wrote on Mon, Aug 01, 2005 at 04:58:03PM CEST: *snip* > > > After investigation of the problem I found that liba.so tries to load > > > plugin.so from library constructor. Even if liba.so is dlopen with > > > RTLD_GLOBAL flag set, plugin.so can't resolve symbols from liba.so > > > > Just so we don't misunderstand each other: what exactly do you mean by > > library constructor? Are you overwriting DT_INIT? (If so, you are a far > > way from portable shared libraries.) > I am talking about function marked __attribute__((constructor)).
Yes, that is what I meant. > Portability is not an issue for me. OK. You should look into it more. > > > Program 'prog' calls dlopen(liba.so, RTLD_GLOBAL), in constructor liba.so > > > calls dlopen(plugin.so) and this call fails with unresolved symbols > > > from liba.so. > > > > > > If we add function init_a() to liba.so and move dlopen(plugin.so) from > > > constructor to the function and we call this function from 'prog' after > > > dlopen (liba.so, RTLD_GLOBAL) then everything works as expected. > > > > Best would be if you showed short reproducible code. Not that I know > > whether I could help you then. > > > Attached. To compile run following: > $ gcc liba.c -shared -o liba.so > $ gcc plugin.c -shared -o plugin.so > $ gcc prog.c -ldl -o prog Some notes: - In general, you _must_ use -fPIC to compile the code that ends up in shared objects. Above will fail blatantly on x86_64, for example. - You should make use of dlerror, for example like this, in the failure case: fprintf (stderr, "Load of plugin.so failed: %s\n", dlerror()); - Quoting 'info gcc Link\ Options': | | (1) On some systems, `gcc -shared' needs to build supplementary stub | code for constructors to work. On multi-libbed systems, `gcc -shared' | must select the correct support libraries to link against. Failing to | supply the correct flags may lead to subtle defects. Supplying them in | cases where they are not necessary is innocuous. So, for example, using gcc plugin.c -shared -o plugin.so -L. -la and then using LD_LIRBARY_PAH=. ./prog will succeed. > Notice that second dlopen of plugin.so succeeds. HTH, Ralf _______________________________________________ http://lists.gnu.org/mailman/listinfo/libtool
