Re: [PATCH] Pass HWCAP to ifunc resolver

Ulrich Weigand
2016-09-06T15:42:58Z

Andreas Arnez wrote:

> On various GNU Elf architectures, including AArch64, ARM, s390/s390x,
> ppc32/64, and sparc32/64, the dynamic loader passes HWCAP as a parameter
> to each ifunc resolver. Currently there is an open glibc Bugzilla that
> requests this to be generalized to all architectures:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=19766
>
> And various ifunc resolvers already rely on receiving HWCAP. Currently
> GDB always calls an ifunc resolver without any arguments; thus the
> resolver may receive garbage, and based on that, the resolver may decide
> to return a function that is not suited for the given platform.
>
> This patch always passes HWCAP to ifunc resolvers, even on systems where
> the dynamic loader currently behaves otherwise. The rationale is
> that (1) the dynamic loader may get adjusted on those systems as well in
> the future; (2) passing an unused argument should not cause a problem
> with existing resolvers; and (3) the logic is much simpler without such
> a distinction.

This makes sense to me. If necessary, we can always still add platform-
specific call sequences later.

> gdb/ChangeLog:
>
> * elfread.c (auxv.h): New include.
> (elf_gnu_ifunc_resolve_addr): Pass HWCAP to ifunc resolver.
>
> gdb/testsuite/ChangeLog:
>
> * gdb.base/gnu-ifunc-lib.c (resolver_hwcap): New external
> variable declaration.
> (gnu_ifunc): Add parameter hwcap. Store it in resolver_hwcap.
> * gdb.base/gnu-ifunc.c (resolver_hwcap): New global variable.
> * gdb.base/gnu-ifunc.exp: Add test to verify that the resolver
> received HWCAP as its argument.

This is OK.

Thanks,
Ulrich

--
Dr. Ulrich Weigand
GNU/Linux compilers and toolchain
Ulrich.Weigand@de.ibm.com