[Dwarf-Discuss] doubt parsing CIE in eh_frame

Francesco Zappa Nardelli francesco.zappa.nardelli at gmail.com
Mon May 23 14:10:34 PDT 2016


Dear DWARF-discuss

I am writing a parser of eh-frame informations and I have a doubt about a
behaviour of readelf.

On a (statically linked) binary readelf reports the following eh-frame CIE
entry:

00006f38 0000000000000014 00000000 CIE
 Version:               1
 Augmentation:          "zRS"
 Code alignment factor: 1
 Data alignment factor: -8
 Return address column: 16
 Augmentation data:     1b

 DW_CFA_nop
 DW_CFA_nop
 DW_CFA_nop
 DW_CFA_nop
 DW_CFA_nop
 DW_CFA_nop

and readelf interprets this bytecode as:

00006f38 0000000000000014 00000000 CIE "zRS" cf=1 df=-8 ra=16
  LOC           CFA
0000000000000000 rax+0

My doubt is: where does the rax+0 come from?  Is rax some kind of a default
for CFA computation?  The bytecode does not provide any real instruction
here and my parser/interpreter fails with “undefined cfa”.

Thank in advance.

-francesco
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