[Bug debug/43290] ICE in dwarf2out_frame_debug_expr

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2010-03-08 15:12 -------
I've tried, but haven't succeeded, that's why I said the bug is latent there. 
If we can prove this situation can't ever happen on 4.4 or 4.5 (4.5 on this
testcase doesn't use a drap reg at all, so we'd need some other testcase where
it does), then I'll of course do something on our branch only.  But I believe
this is just a general problem.  BTW, even the 4.4 generated unwind info is
bad:
  DW_CFA_advance_loc: 4 to 00000004
  DW_CFA_def_cfa: r1 (ecx) ofs 0
  DW_CFA_advance_loc: 9 to 0000000d
  DW_CFA_expression: r5 (ebp) (DW_OP_reg5)
  DW_CFA_advance_loc: 11 to 00000018
  DW_CFA_def_cfa_expression (DW_OP_breg5: -16; DW_OP_deref)
  DW_CFA_advance_loc: 20 to 0000002c
  DW_CFA_expression: r7 (edi) (DW_OP_breg5: -4)
  DW_CFA_expression: r6 (esi) (DW_OP_breg5: -8)
  DW_CFA_expression: r3 (ebx) (DW_OP_breg5: -12)

   0:   8d 4c 24 04             lea    0x4(%esp),%ecx
   4:   83 e4 e0                and    $0xffffffe0,%esp
   7:   ff 71 fc                pushl  -0x4(%ecx)
   a:   55                      push   %ebp
   b:   89 e5                   mov    %esp,%ebp
   d:   83 ec 78                sub    $0x78,%esp
  10:   89 5c 24 6c             mov    %ebx,0x6c(%esp)
  14:   89 4c 24 68             mov    %ecx,0x68(%esp)
  18:   89 74 24 70             mov    %esi,0x70(%esp)
  1c:   89 7c 24 74             mov    %edi,0x74(%esp)
  20:   e8 00 00 00 00          call   25
<_ZNSt13basic_filebufIcSt11char_traitsIcEE7seekposESt4fposI9mbstate_tEN12_GLOBAL__N_113_Ios_OpenmodeE+0x25>
  25:   5b                      pop    %ebx
  26:   81 c3 03 00 00 00       add    $0x3,%ebx
                        28: R_386_GOTPC _GLOBAL_OFFSET_TABLE_
  2c:   8b 31                   mov    (%ecx),%esi
  2e:   89 4d c4                mov    %ecx,-0x3c(%ebp)
1) Saying that %r5 (ebp) is saved in DW_OP_reg5 looks quite redundant to me.
2) More importantly, %ebx is said to be saved in DW_OP_breg5 - 12 only after
add $0x3, %ebx, so when e.g. a debugger stops in between pop %ebx and add $3,
%ebx, it will think caller's %ebx still lives in %ebx register, which is wrong.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43290