[PATCH, libitm]: GTM_longjmp: Jump indirect from memory address

[Uros Bizjak]

On Tue, Feb 14, 2012 at 1:15 AM, Richard Henderson <rth@redhat.com> wrote:

>>>> -     movq    56(%rsi), %rdx
>>>>       movl    %edi, %eax
>>>>       cfi_def_cfa(%rcx, 0)
>>>> -     cfi_register(%rip, %rdx)
>>>>       movq    %rcx, %rsp
>>>> -     jmp     *%rdx
>>>> +     jmp     *56(%rsi)
>>>
>>> If you're going to do that, the correct fix for the unwind info is
>>>
>>> - cfi_register(%rip, %rdx)
>>> + cfi_offset(%rip, 56)
>>
>> Hm, we just defined new CFA as rcx+0, so we should define location of
>> rip relative to new CFA. Since CFA points to stack slot just before
>> return address was pushed, new rip lies at CFA-8 for 64bit resp. CFA-4
>> for x86_32. Did I get these .cfi directives correctly?
>
> No.  The value at %rcx-8 is total garbage.  There no guarantee that
> the call stack leading to this abort has anything in common with the
> call stack that created the jmpbuf, except *above* %rcx, the new CFA.
>
> The new rip is at rsi+56.  You can see that in that you jump to it.

Thanks for the explanation, I will commit the patch with your suggested change.

Uros.