unwinding info for stg_catch_frame is wrong

Minimized stg_catch_frame (Small.cmm):

#define CATCH_FRAME 34

#define SIZEOF_StgCatchFrame (SIZEOF_StgHeader+16)

INFO_TABLE_RET(stg_catch_frame, CATCH_FRAME,
               bits64 info_ptr, bits64 exceptions_blocked, gcptr handler)
    return (gcptr ret)
{
    unwind Sp = Sp + SIZEOF_StgCatchFrame;
    return (ret);
}

Compile "inplace/bin/ghc-stage2" -O2 -g -c Small.cmm using GHC HEAD.

objdump -D for stg_catch_frame_info:

0000000000000010 <stg_catch_frame_info>:
  10:   48 83 c5 18             add    $0x18,%rbp
  14:   ff 65 00                jmpq   *0x0(%rbp)

readelf --debug-dump=frames-interp Small.o:

Contents of the .debug_frame section:

00000000 0000000000000014 ffffffff CIE "" cf=1 df=-8 ra=16
   LOC           CFA      rbp   rsp   ra
0000000000000000 rbp+0    v+0   s     c+0

00000018 000000000000002c 00000000 FDE cie=00000000 pc=000000000000000f..0000000000000017
   LOC           CFA      rbp   rsp   ra
000000000000000f rbp+0    v+0   s     c+0
000000000000000f rbp+24   v+0   s     c+0
0000000000000010 rbp+0    v+0   s     c+0

• *How do I know this is wrong?**

http://www.dwarfstd.org/doc/dwarf-2.0.0.pdf has a nice example in Appendix 5 (page 101 of the pdf). The question that I had was if the CFA value at LOC is after or before the instruction at LOC executes. Appendix 5 clearly shows that it's **before**.

Hence for LOC = 0x10 here CFA shouldn't have changed. It can and should change at LOC = 0x14.

For comparison this is what 8.0.2 produced (and it worked more often):

0000000000000010 <stg_catch_frame_info>:
  10:   48 83 c5 18             add    $0x18,%rbp
  14:   ff 65 00                jmpq   *0x0(%rbp)

Contents of the .debug_frame section:

00000000 0000000000000014 ffffffff CIE "" cf=1 df=-8 ra=16
   LOC           CFA      rbp   rsp   ra
0000000000000000 rbp+0    v+0   s     c+0

00000018 0000000000000024 00000000 FDE cie=00000000 pc=000000000000000f..0000000000000017
   LOC           CFA      rbp   rsp   ra
000000000000000f rbp+0    v+0   s     c+0
000000000000000f rbp+24   v+0   s     c+0

Debugging follows in the comments.

Trac metadata

Trac field	Value
Version
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	bgamari, simonmar
Operating system
Architecture