Richard Henderson <r...@redhat.com> writes:
> 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
Seems to be the same:
#0 0x00400ae2 in foo() ()
#1 0x77d793fc in __mips16_call_stub_df_0 () at ...
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
(this is a gdb built from 7.4 branch FWIW).
Richard
