Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

Jeremy Fitzhardinge
2009-06-15T20:15:10Z

On 06/15/09 12:04, Linus Torvalds wrote:
> That's an odd way of writing it.
>
> Don't we have a per-cpu segment here? I'd much rather just see it do
> something like this (_before_ restoring the regular registers)
>
> movq EIP(%esp),%rax
> movq ESP(%esp),%rdx
> movq %rax,gs:saved_esp
> movq %rdx,gs:saved_eip
>
> # restore regular regs
> RESTORE_ALL
>
> # skip eip/esp to get at eflags
> addl $16,%esp
> popfq
>
> # restore rsp/rip
> movq gs:saved_esp,%rsp
> jmpq *(gs:saved_eip)
>
> but I haven't thought deeply about it. Maybe there's something wrong with
> the above.
>

We have to restore the usermode %gs somewhere...

J