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

From: Jeremy Fitzhardinge
Date: Mon Jun 15 2009 - 16:15:14 EST

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

# skip eip/esp to get at eflags
addl $16,%esp

# 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...

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