libc/x86: fix stack unwinding and backtrace information

When compiled without framepointer, the DWARF-2 CFI data is required
for proper stack unwinding.

This patch adds the CFI information to:
 * syscalls (so we get proper backtrace even for release builds)
   the ebx hack was removed as it would complicate the CFI generation
 * new thread stub function (so the backtrace is clean for user
   created threads)

Also pads the signal return trampolines separate from other functions.
If CFI info was found for signal return code (which seems to happen if
it's located right next a valid function), it will not be recognized
as signal trampoline (gcc unwinder and gdb check first CFI info, and
only if it does not exists it compares the exact opcode sequence to
see if we are at signal return code block). This fixes a real crash
if thread is cancelled and the cancellation handler fails to detect the
signal return frame.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>

0 files changed, 0 insertions, 0 deletions