* LP32 should use sa_restorer too. gdb expects this, and future (>= 3.15) x86
kernels will apparently stop supporting the case where SA_RESTORER isn't
set.
* gdb and libunwind care about the exact instruction sequences, so we need to
modify the code slightly in a few cases to match what they're looking for.
* gdb also cares about the exact function names (for some architectures),
so we need to use __restore and __restore_rt rather than __sigreturn and
__rt_sigreturn.
* It's possible that we don't have a VDSO; dl_iterate_phdr shouldn't assume
that getauxval(AT_SYSINFO_EHDR) will return a non-null pointer.
This fixes unwinding through a signal handler in gdb for all architectures.
It doesn't fix libunwind for arm and arm64. I'll keep investigating that...
(cherry picked from commit 36f451a6d93b6807944d99fa23396e039c47e845)
Bug: 17436734
Change-Id: Ic1ea1184db6655c5d96180dc07bcc09628e647cb
7dc2b7b30d