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[Bug libc/15407] Partial frame info in sysdeps/x86_64/start.S


http://sourceware.org/bugzilla/show_bug.cgi?id=15407

--- Comment #20 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2013-05-10 17:12:50 UTC ---
All GDBs out there behave as described above.

IIUC you are proposing to revert the glibc x86_64 _start CFI patch and change
GDB x86_64 to consider non-CFI code as using %rbp frame pointer.

I do not find it safe, x86_64 code may use %rbp for arbitrary data - even zero
- which will lead to quiet backtrace stop if CFI cannot be found for such code.
 Currently GDB will do unwind into some garbage address so the user sees there
is something broken (due to CFI failed to be found).

i386 already is not safe for accidental %ebp==0 non-CFI unwind stops but i386
is obsoleted by x86_64 + x32 so it is IMO not much worth trying to improve
anything there anymore.

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