On Mon, Aug 08, 2005 at 11:10:08AM +0200, Ralf Wildenhues wrote:
> Hi Gleb,
>
> * Gleb Natapov wrote on Sun, Aug 07, 2005 at 11:31:54AM CEST:
> > > > 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());
>
I wrote it in 5 minutes just for demo :) Original project uses libtool.
> - 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.
I know that linking plugin.so with liba solves the issue, but
the question is why RTLD_GLOBAL doesn't take effect in library init function.
Currently the problem was solved by not calling dlopen in init.
--
Gleb.
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