On Mon, Jan 12, 2015 at 11:37 AM, Borislav Petkov <b...@alien8.de> wrote:
> Andy, please trim your replies.
>
> On Mon, Jan 12, 2015 at 11:25:39AM -0800, Andy Lutomirski wrote:
>> I think that some users don't want the CFI_REL_OFFSET.
>
> Why? I thought those two annotations are independent? As you said:
>
> "IOW, one is to keep the stack frame tracking consistent and the other
> is to tell the unwinder about the register we just saved."
>
> Sounds to me like we want both...
>
Dumb example:
pushq_cfi $__KERNEL_DS /* ss */
This doesn't save anything that the unwinder would care about.
Better example:
pushq_cfi \child_rip /* rip */
CFI_REL_OFFSET rip,0
Doing this with a macro would need a fancier macro.
Then there's crap like:
pushq_cfi %rdi
SCHEDULE_USER
popq_cfi %rdi
I would need to look a lot more carefully to figure out whether this
would need CFI_REL_OFFSET.
If we actually had a DWARF unwinder in the kernel, maybe we could have
real test cases :-/
--Andy
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