[Bug dynamic-link/14831] [Regression] Segfault in _dl_profile_fixup with IRELATIVE and LD_AUDIT

["amonakov at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14831

Alexander Monakov <amonakov at gmail dot com> changed:

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--- Comment #2 from Alexander Monakov <amonakov at gmail dot com> 2012-11-13 19:10:13 UTC ---
Created attachment 6732
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6732
standalone testcase

Attached a standalone testcase that demonstrates the issue.

This bug is a regression that prevents using LD_AUDIT with any executables that
link against libm.so on some of the recent Linux distributions (and most of
g++-compiled applications link with libm).

I'm not familiar with the rtld guts at all, but here's my understanding of what
happens:

1. elf_machine_lazy_rel calls the ifunc resolver
2. the resolver calls another function in the dso
3. the plt entry(?) has been instrumented for dso profiling, and calls
_dl_profile_fixup.
4. _dl_profile_fixup accesses l->l_reloc_result, which is NULL and will be
allocated later in _dl_relocate_object

It seems to me that instrumenting for profiling is not necessary if the audit
library does not export la_plt* routines. Thus, I think there are two separate
issues here.

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