On 02/16/2012 10:58 AM, Richard Sandiford wrote:
>> As a workaround for 4.7, you can try this hack:
>>
>> .cfi_startproc simple
>> .cfi_def_cfa 29, -1 # fake cfa one byte below sp
>> .cfi_register 29, 29 # "save" sp in itself so we don't use
>> the fake cfa
>> move $18,$31
>> .cfi_register 31, 18
>> ...
>
> Ooh, nice (if that's the word). It certainly fixes the testcase,
> although I had to use -4 rather than -1 in order to defeat
> DWARF2_CIE_DATA_ALIGNMENT. That should still be OK, since the
> stack is 8-byte aligned.
>
> GDB doesn't seem to be able to backtrace through this, but that
> has to come second to correctness. I'll aim to get a tested fix
> in this weekend.
Hmm. I wonder if GDB would be happier with a val_expression,
rather than the "odd" .cfi_register:
// DW_CFA_val_expression r29, { DW_OP_reg29 }
.cfi_escape 0x16,29,1,0x6d
r~
