Re: [discuss] Re: [PATCH 2/3] reliable stack trace support(x86-64)

From: Jan Beulich
Date: Thu May 18 2006 - 05:35:41 EST

>>> Andi Kleen <ak@xxxxxxx> 16.05.06 19:05 >>>
>On Tuesday 16 May 2006 18:06, Jan Beulich wrote:
>> >>> Andi Kleen <ak@xxxxxxx> 16.05.06 17:13 >>>
>> On Tuesday 16 May 2006 16:21, Jan Beulich wrote:
>> >> These are the x86_64-specific pieces to enable reliable stack traces. The
>> >> only restriction with this is that it currently cannot unwind across the
>> >> interrupt->normal stack boundary, as that transition is lacking proper
>> >> annotation.
>> >
>> >It would be nice if you could submit a patch to fix that.
>> But I don't know how to fix it. See my other mail
>which mail?

Reply to Ingo (with you on cc) regarding patch 1/3. Just saying that I don't know much about expressions here.

>> - I have no experience with expressions, nor have I ever seen them in
>> use.
>I remember Jim Houston used a hack of just loading the old stack into a register
>and defining that as a base register in CFI. I guess i would be willing
>to trade a few moves for that (should be pretty much free on a OOO CPU anyways)
>You think that trick would work?

I don't think that would, because without CONFIG_DEBUG_INFO none of the preserved registers get saved, hence there's no
register to use for this. Thus the price would not only be a move, but also a save/push and a reload/pop.

>> >> +#define UNW_PC(frame) (frame)->
>> >> +#define UNW_SP(frame) (frame)->regs.rsp
>> >
>> >I think we alreay have instruction_pointer(). Better add a stack_pointer()
>> >in ptrace.h too.
>> I could do that, but the macros will have to remain, as they don't access pt_regs directly, so I guess it'd be
>> pointless to change it.
>UNW_PC() is instruction_pointer(&frame->regs), isn't it?

Yes. But the intention is that the user of UNW_PC doesn't need to know any details of what fields frame has (i.e. the
parameter of UNW_PC must only be frame), so you can't replace it with instruction_pointer().

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