[Bug target/47324] g++.dg/torture/stackalign failures with -O3 -g at -m32 on darwin

["howarth at nitro dot med.uc.edu" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47324

--- Comment #8 from Jack Howarth <howarth at nitro dot med.uc.edu> 2011-02-07 21:07:59 UTC ---
The Apple linker developer has looked at the failing eh-alloc-1.C case and had
the following comments...

> Also, did you ever get a
> chance to look at the stackalign_testcase2.tar.bz2 test case from radar ID 6407474, "stackalign
> failures for -O3 -g at -m32 with Xcode 3.1.2 and 3.2A number of gcc 4", in a debug version of
> the Snow Leopard unwinder? This bug is still very confusing.

I just took a look at the eh-alloc.exe case.  The case built with -g fails when
running on Lion
 (with the darwin unwinder) and the case built without -g works fine.  I
stepped through the 
unwinding.  The function foo() uses dynamic stack alignment and the dwarf
unwind info uses 
expressions to specify where the CFA is.   In the bad case (with -g) the
expression has a push 
of register 5 (ESP) where as the good case has a push of register 4 (EBP) in
the expression.

I recall that some bug cropped up long ago with the register numbering for
i386.  
Two register numbers were swapped.  The end result is the eh_frame register
numbering and 
DWARF debug info registering number are different.

I suspect that using -g is forcing the eh_frame creation to use the DWARF debug
info register 
numbering.  You can see the difference with dwarfdump:

[/tmp]> dwarfdump --eh-frame
stackalign_testcase2/stackalign_with_g/eh-alloca-1.exe | grep -A8 __Z3fooi
    start_addr: 0x00001d20 __Z3fooi
    range_size: 0x000000b8 (end_addr = 0x00001dd8)
  LSDA address: 0x00002094
  Instructions: 0x00001d20: CFA=esp+4     eip=[esp]
                DW_CFA_advance_loc4 (4)
                DW_CFA_def_cfa (ecx, 0)
                0x00001d24: CFA=ecx       eip=[ecx-4]
                DW_CFA_advance_loc4 (7)
                DW_CFA_expression (esp, expr(esp0))         
[/tmp]> dwarfdump --eh-frame
stackalign_testcase2/stackalign_without_g/eh-alloca-1.exe | grep -A8 __Z3fooi
    start_addr: 0x00001d20 __Z3fooi
    range_size: 0x000000b8 (end_addr = 0x00001dd8)
  LSDA address: 0x00002094
  Instructions: 0x00001d20: CFA=esp+4     eip=[esp]
                DW_CFA_advance_loc4 (4)
                DW_CFA_def_cfa (ecx, 0)
                0x00001d24: CFA=ecx       eip=[ecx-4]
                DW_CFA_advance_loc4 (7)
                DW_CFA_expression (ebp, expr(ebp0))
[/tmp]>