Re: çåï[PATCH] perf core: Use KSTK_ESP() instead of pt_regs->sp while output user regs

[Jan Beulich]

>>> Andy Lutomirski <luto@xxxxxxxxxxxxxx> 01/02/15 7:03 PM >>>
>On Jan 2, 2015 8:11 AM, "Jan Beulich" <jbeulich@xxxxxxxx> wrote:
>> Trying to guess what you mean by "this": A stack switch gets expressed by
>> CFI annotations just like any other frame pointer adjustments. See for example
>> the CFI_DEF_CFA_REGISTER use in the SAVE_ARGS_IRQ macro.
>>
>> If that wasn't your question, please be more precise.
>
>Sorry, my question was vague.
>
>Is there any way to consume these annotations at runtime in the
>kernel?  The goal would be for perf's NMI handler to consume the CFI
>data to figure out the userspace registers.  I'm guessing that the
>answer might be no, because we seem to be compiling with
>-fno-asynchronous-unwind-tables and we don't seem to be putting any
>.eh_frame stuff into the final kernel image.
>
>I had thought that someone implemented runtime DWARF unwinding, though.

Yes, we do have such code in our kernels, but Linus continues to veto it going
into his tree.

Jan

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