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Re: [rfc] Fix mst_solib_trampoline symbol sections for PLT stubs
On Wed, Oct 31, 2007 at 03:29:53PM +0100, Ulrich Weigand wrote:
> Daniel Jacobowitz:
>
> > Yes. But if the address of the function is not taken somewhere in the
> > executable, then the address of the undefined symbol will generally be
> > left at zero. That should be true most of the time. So while I don't
> > see anything wrong with your approach here, I'm surprised it fixed the
> > testsuite failures; why do they have non-zero addresses? If we're
> > taking their addresses in all cases, we need some new tests.
>
> I think this is because there are function calls from the main
> executable to those functions, and the main executable is not
> compiled with -fPIC. I understand those references will also
> cause the undefined symbol to carry the address of the main
> PLT call stub ...
Interesting. On most platforms, that's not necessary: LD only needs
to set a canonical address in the executable's symtab if the
executable takes the function's address, so this should only happen if
those non-PIC calls were indistinguishable from taking the address.
That's not implemented for PowerPC. I don't know if it's an ABI
requirement or just a missing optimization. Search for "st_value = 0"
in elf32-ppc.c versus elf32-i386.c.
So, this won't help everywhere or fix the root cause, but it does seem
like it would work for PowerPC.
--
Daniel Jacobowitz
CodeSourcery