[libunwind][SystemZ] Unwind out of signal handlers

[uweigand]

Summary

Unwinding out of signal handlers currently does not work since the sigreturn trampoline is not annotated with CFI data.

Fix this by detecting the sigreturn trampoline during unwinding and providing appropriate unwind data manually. This follows closely the approach used by existing code for the AArch64 target.

[danielkiss]

some tests from libcxxabi could be enabled for SystemZ too e.g. libcxxabi/test/forced*

libunwind/src/UnwindCursor.hpp

2673

Please note I recently committed this:
https://reviews.llvm.org/D124522

_info.end_ip need to be set to make forced unwind work.

_info.start_ip = pc;
_info.end_ip = pc;

[uweigand]

Address review comment.

[uweigand]

In D124765#3485544, @danielkiss wrote:

some tests from libcxxabi could be enabled for SystemZ too e.g. libcxxabi/test/forced*

Unfortunately we don't yet support libcxx or libcxxabi at all on SystemZ. (On Linux there's always libstdc++ available as system library.)

libunwind/src/UnwindCursor.hpp

2673

Thanks! I've updated the patch accordingly.

[MaskRay]

libunwind/src/UnwindCursor.hpp

2667

Does s390 use both __kernel_[rt_]sigreturn? It seems that the Linux kernel source references both. For aarch64 there is only the rt_ version.

Just a note for you to double check the comment:)

2684

Best to leave a comment where 160 comes from. It can be a kernel source filename.

2691

2731

Prefer [a,b) ranges

2736

Prefer [a,b) ranges

2737

libunwind/test/signal_unwind.pass.cpp

11

Use an alphabetical order: aarch64, s390x, x86_64

libunwind/test/unwind_leaffunction.pass.cpp

11

Use an alphabetical order: aarch64, s390x, x86_64

[uweigand]

libunwind/src/UnwindCursor.hpp

2667

Yes, we use both - we have two distinct sigreturn vs. rt_sigreturn syscalls (see also the distinction in stepThroughSigreturn below), and there's a VDSO trampoline for each of them.

2684

This is a general property of the s390x ABI (the CFA is always at "incoming SP + 160"). I'll add a comment to that effect.

[uweigand]

Address review comments.