[PATCH] Unwinding CFI for x86_64 signal frame (__restore_rt)

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

Frysk debugger in development would like to properly unwind signal frames
without any hacks as has been done in the gdb case. Provided patch sets proper
CFI unwind information for `__restore_rt'.

`__restore_rt' CFI is fixed only for x86_64 (tested on Fedora Core
kernel-xen-2.6.18-1.2849.fc6.x86_64) as on i386 (kernel-2.6.18-1.2747.el5.i686)
is in use VDSOed `__kernel_sigreturn' instead (with proper CFI already).
Still i386 should get fixed a similiar way but I do not have an easy testcase.

Currently gdb identifies signal frames using strcmp ("__restore_rt", ...)
(`amd64_linux_sigtramp_p') and gdb has also hardcoded arch-dependent unwind
info (register locations) for the signal frames.

I was told gcc is using `MD_FALLBACK_FRAME_STATE_FOR' (for exceptions
unwinding) but it is not suitable for ptrace(2)ing remote debuggers.

Testcase in glibc is not provided as the whole DWARF/CFI unwinding requires
framework IMO out of the glibc testcases' scope.


Regards,
Jan


Original Bug:
	https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=217087

Testcase provided in libunwind testsuite forked in the Frysk repository:
	CVSROOT=:pserver:anoncvs@sources.redhat.com:/cvs/frysk
	CVS Repository=frysk-imports/libunwind
	testcase: tests/run-ptrace-stepper
	Requires patch: http://sourceware.org/bugzilla/show_bug.cgi?id=3590

Attachment: glibc-signal-unwind-cfi.patch
Description: Text document