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[Bug backtrace/14646] [x32] backtrace doesn't work before main


http://sourceware.org/bugzilla/show_bug.cgi?id=14646

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2012-09-30 21:16:04 UTC ---
amd64_x32_init_abi has

  tdep->sp_regnum_from_eax = AMD64_RSP_REGNUM;
  tdep->pc_regnum_from_eax = AMD64_RIP_REGNUM;

But unwind frame info is based on the real RSP/RIP
registers.  Pseudo sp/pc registers don't work with
frame related codes:

[hjl@gnu-tools-1 gdb]$ egrep "pc_regnum|sp_regnum" *fram*.c 
dwarf2-frame.c:  if (regnum == gdbarch_pc_regnum (gdbarch))
dwarf2-frame.c:  else if (regnum == gdbarch_sp_regnum (gdbarch))
dwarf2-frame.c:          == gdbarch_sp_regnum (gdbarch)))
dwarf2-frame-tailcall.c:  if (regnum == gdbarch_pc_regnum (this_gdbarch))
dwarf2-frame-tailcall.c:  else if (cache->prev_sp_p && regnum ==
gdbarch_sp_regnum (this_gdbarch))
dwarf2-frame-tailcall.c:      int sp_regnum;
dwarf2-frame-tailcall.c:      sp_regnum = gdbarch_sp_regnum (prev_gdbarch);
dwarf2-frame-tailcall.c:      if (sp_regnum == -1)
dwarf2-frame-tailcall.c:      prev_sp = frame_unwind_register_unsigned
(this_frame, sp_regnum);
frame.c:      && gdbarch_pc_regnum (gdbarch) >= 0
frame.c:                      gdbarch_pc_regnum (gdbarch),
frame.c:                      gdbarch_pc_regnum (gdbarch),
frame.c:     the gdbarch_sp_regnum register is meaningful.  */
frame.c:  if (gdbarch_sp_regnum (gdbarch) >= 0)
frame.c:                    gdbarch_sp_regnum (gdbarch));
[hjl@gnu-tools-1 gdb]$ 

It is to print

(gdb) p $sp
$1 = (void *) 0xffffd028

instead of

(gdb) p $sp
$1 = 4294955048

But it breaks frame unwind.

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