Need help with gas directive .cfi_sections

[Sharyathi Nagesh <sharyath at in dot ibm dot com>]

Hi
 	We need some help and guidance with some issues we are facing. We are exploring option to 
unwind through linux kernel dumps using dwarf information. Major challenge we are facing is 
with respect to unwinding through the exception framework. Even through exception handler 
code has gas directive to emit debug information (x86 & x86_64) by default it works only 
with .eh_frame. Earlier we had observed that relying on eh_frame to unwind is not reliable 
and hence we are exploring .debug_frame.

	So as I understand in October a patch was provided to implement .cfi_sections directive 
which will help to emit dwarf information in .debug_frame. I tested this with latest 
binutils from cvs.

We need clarification on these issues

1. We wanted to know from which version of GCC can we expect to see .cfi_section directive.
I need this information, so that I can modify code in entry_32.S code in linux kernel to
some thing like this

#if GCC_VERSION > 4.5 (say)
#define CFI_SECTIONS .cfi_sections
#else
#define CFI_SECTIONS NULL
#endif

Any suggestions on when it will be part of GCC and what will be the best way to code without 
braking the compatibility will be greatly helpful

---------------------------------------------------------------------------------------------
2. We tried generating .debug_frame information with the latest binutils tools and We saw
some anomalies. We wanted to confirm if it is due to usage issues,of gas or assembly code,
or there is indeed some issues with the .cfi_sections patch

This is what we did (Under PPC64 arch)
We assembled this code:
--------------------
test.s:

.global test1
test1:
        .cfi_startproc
        .cfi_signal_frame
        .cfi_sections .debug_frame
        .cfi_def_cfa_offset 8
        .cfi_def_cfa r3, 4
        .cfi_endproc
        mr      10,9
        blr
--------------------
assemble using as from the latest binutils
./as test.s
--------------------
This is the dwarf .debug_frame information that we got

00000060 00000014 ffffffff CIE
  Version:               1
  Augmentation:          ""
  Code alignment factor: 4
  Data alignment factor: -8
  Return address column: 65

  DW_CFA_def_cfa: r1 ofs 0
  DW_CFA_def_cfa_offset: 8
  DW_CFA_def_cfa: r3 ofs 4
  DW_CFA_nop
  DW_CFA_nop
  DW_CFA_nop

00000078 00000014 00000060 FDE cie=00000060 pc=00000000..00000000

We were concerned with the address range of the FDE, both low_pc and high_pc both are
00000000. So why is it shown like that? Should not it be range of virtual address where this 
text segment will be loaded in memory ?

We had this query as unwinding without proper range will become difficult

So please do let me know your thoughts, It will help us greatly
Thanks
Sharyathi N