GCC Bugzilla Bug 17994

avr-gcc-v:
Reading specs from c:/programs/WinAVR/bin/../lib/gcc/avr/3.4.1/specs
Configured with: ../gcc-3.4.1/configure --prefix=e:/avrdev/install
--build=mingw32 --host=mingw32 --target=avr --enable-languages=c,c++
Thread model: single
gcc version 3.4.1

command line:
avr-gcc -gdwarf-2 anycode.c  -o anyobject.elf

No matter how I tweak the command line parameters to avr-gcc I am unable to make
it output dwarf2 callstack information (.debug_frame). I have confirmed that
this is a missing feature for the AVR port.

Hi, 
 
I have been reviewing PR19885 and come to the following conclusions: 
 
1.) As expected, Torleif is right: I can confirm that the problem exists,  
2.) it should, however, probably be called rather a request for enhancement 
than a bug: Beside call stack information the debugging info should be ok in 
principle. 
3.) There seems to be only one little part missing in order to add the call 
stack information as well: The back-end needs to provide the information at 
which memory address the debugger could localize the return address. This would 
require to implement the target hook INCOMING_RETURN_ADDR_RTX and use the 
RTX_FRAME_RELATED_P predicate for all of the prologue/epilogue insn. 
 
I think the best way to address this issue would be to resolve this issue 
simultaneously when switching from asm-prologue/epilogue to 
RTL-prologue/epilogue. Since Andy Hutchinson is just working on this issue, we 
might soon have a solution. Hopefully :-). Would be very helpfull to have call 
stack info in avrstudio. 
 
Yours, 
 
Bjoern 
 
P.S.:  
I hope you will not be flaming me for adding you on the CC list. :-) Just 
thought that you might be interrested since I know you are working on the 
prologue/epilogue issue. 

Hi Torleif,

Please check more recent versions such as 4.3.2, 4.3.3, or 4.4.0. There are
.debug_frame sections in there, but I don't know if it contains the information
that you're looking for.

Thanks,
Eric Weddington

I tried gcc 4.3.2 from the WinAVR distribution and also avr-gcc 4.4.1.

The short story is: There is call frame information there, but not enough.
Specifically, the Call Frame instructions to reconstruct the pc to unwind rule
table are still missing, but the CIE and FDE are present. 

I compared gcc and avr-gcc output on linux with the following results:

gcc:
-----------------------------------------------------------------------
The section .debug_frame contains:

00000000 00000010 ffffffff CIE
  Version:               1
  Augmentation:          ""
  Code alignment factor: 1
  Data alignment factor: -4
  Return address column: 8

  DW_CFA_def_cfa: r4 (esp) ofs 4
  DW_CFA_offset: r8 (eip) at cfa-4
  DW_CFA_nop
  DW_CFA_nop

00000014 00000024 00000000 FDE cie=00000000 pc=08048394..0804840a
  DW_CFA_advance_loc: 4 to 08048398
  DW_CFA_def_cfa: r1 (ecx) ofs 0
  DW_CFA_register: r4 (esp) in r1 (ecx)
  DW_CFA_advance_loc: 6 to 0804839e
  DW_CFA_def_cfa: r4 (esp) ofs 4
  DW_CFA_advance_loc: 1 to 0804839f
  DW_CFA_def_cfa_offset: 8
  DW_CFA_offset: r5 (ebp) at cfa-8
  DW_CFA_advance_loc: 2 to 080483a1
  DW_CFA_def_cfa_register: r5 (ebp)
  DW_CFA_advance_loc: 1 to 080483a2
  DW_CFA_offset: r4 (esp) at cfa-12
  DW_CFA_nop
  DW_CFA_nop

0000003c 00000014 00000000 FDE cie=00000000 pc=0804840a..0804841c
  DW_CFA_advance_loc: 1 to 0804840b
  DW_CFA_def_cfa_offset: 8
  DW_CFA_offset: r5 (ebp) at cfa-8
  DW_CFA_advance_loc: 2 to 0804840d
  DW_CFA_def_cfa_register: r5 (ebp)

-----------------------------------------------------------------------

avr-gcc 

-----------------------------------------------------------------------
00000000 0000000c ffffffff CIE
  Version:               1
  Augmentation:          ""
  Code alignment factor: 1
  Data alignment factor: -1
  Return address column: 36

  DW_CFA_def_cfa: r32 ofs 0

00000010 0000000c 00000000 FDE cie=00000000 pc=000000ce..00000160

00000020 0000000c 00000000 FDE cie=00000000 pc=00000160..0000018c

-----------------------------------------------------------------------