PING [PATCH RFC] PR gdb/17445 fix

Pierre Muller pierre.muller@ics-cnrs.unistra.fr
Thu Nov 6 09:13:00 GMT 2014


  Nobody reacted yet to my first email.

  This email is about a fix to:
  https://sourceware.org/bugzilla/show_bug.cgi?id=17445
The bug report is about a problem that arises if you
use xmm15 a register variable in windows 64-bit code.

  The current GDB code overlaps xmm15 and pc saved addresses,
which leads a wrong backtrace.

  
  The problem relates to an older thread
https://sourceware.org/ml/binutils/2011-01/msg00323.html
and
https://sourceware.org/ml/binutils/2013-12/msg00232.html

  which mainly involved Kai.

Kai, did you see my previous email?
Could you comment on my analysis of the problem.

Pierre Muller

> -----Message d'origine-----
> De : binutils-owner@sourceware.org [mailto:binutils-
> owner@sourceware.org] De la part de Pierre Muller
> Envoyé : mercredi 1 octobre 2014 09:46
> À : binutils@sourceware.org; gdb-patches@sourceware.org
> Objet : [RFC] PR gdb/17445 fix
> 
>   Bug report gdb/17445
> shows that use of explicit xmm15 register in windows x86_64
> code leads to wrong unwinding of stacktrace by GDB.
>   This problem comes from the fact that
> the return address column is set to 32 for x86_64 pe objects,
> while it is 16 for other targets.
>   Dwarf x86_64 register 16 is RIP,
> while register 32 is XMM15.
>   The reason for this was apparently that the value of
> the return address column is also interpreted as the highest
> index of the register that needs to be saved according to the ABI
> which is indeed different for Microsoft.
>   Nevertheless, I found nothing inside DWARF4 documentation
> that makes any relation between the resisters that should be saved
> and the return address column.
>   I came to the conclusion that this is a mis-interpretation
> of the dwarf standard that is specific to GNU bfd-gas-gdb.
>   The patch proposed below tries to fix the current PR
> by removing the above assumptions and restoring RIP
> as return address register for pe(i)-x86-64 targets.
> 
>  Comments most welcome,
> 
> Pierre Muller
> Pascal language maintainer for GDB.
> 
> PS: One problem is that I was not able to correctly run
> the testsuite before and after my patch, as
> there are still cygwin/mingw specific issues with testsuite runs.
> 
> 
> ChangeLog (needs to be split into binutils/gas/gdb directories)
> 
> 2014-10-01  Pierre Muller  <muller@sourceware.org>
> 
>         PR gdb/17445
>         * binutils/dwarf.c (display_debug_frames): Handle return
> address
> column
>         specifically, do not limit num_regs to the value of return
> address
>         column.
>         Modified handling of DW_CFA_restore{_extended} to check that
>         a valid storage is present at restore point.
> 
>         * gas/config/tc-i386.c (x86_dwarf2_return_column): Remove
> special
>         value for x86_64 pe coff return address column.
>         This restores RIP register for return address column.
> 
>         * gdb/dwarf2-frame.c (dwarf2_frame_cache): Avoid double
> handling of
>         return address column.



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