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Re: stack_used() not accurate?

Hi -

On Mon, Jun 02, 2008 at 03:02:07PM -0400, Mike Snitzer wrote:
> [...]
> >>       __asm__ __volatile__("andl %%esp,%0" :
> >>                            "=r" (sp) : "0" (THREAD_SIZE - 1));
> 
> whereas the following c-code does _not_ work:

> if (CONTEXT->regs) {
>     long sp = REG_SP(CONTEXT->regs) & (THREAD_SIZE - 1);
> [...]
> 
> So, given that the calculated "free" is incorrect, this says to me
> that the incorrect value is getting stored in CONTEXT->regs->esp on
> x86 (or the value is stale)?

Why do you think the latter is incorrect?  The asm "esp"-related one
should give you the stack pointer at the moment of the probe handler
execution.  The CONTEXT->regs->esp value should give the stack pointer
at the moment of the probe hit - displaced in time (earlier) and
potentially in space (different stack).  This is the dimension of
imagination.  It is an area which we call the twilight zone.


- FChE
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