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Re: stack_used() not accurate?
On Mon, 2008-06-02 at 18:27 -0400, Mike Snitzer wrote:
> On Mon, Jun 2, 2008 at 5:44 PM, Jim Keniston <jkenisto@us.ibm.com> wrote:
...
> >
> > Sorry, I haven't been following this thread for a while, so maybe this
> > has already been mentioned. But keep in mind that on i386, when your
> > breakpoint trap happens in kernel code, esp and ss aren't saved on the
> > stack. So regs->esp and regs->ss contain the top of the pre-trap stack,
> > and the pre-trap stack pointer is ®s->esp, not regs->esp.
>
> OK, so something like this for x86?
>
> function stack_used_new:long() %{
> long free = THREAD_SIZE;
> if (CONTEXT->regs) {
> long curbase = (long)task_stack_page(current);
> long *sp = (long *) &(REG_SP(CONTEXT->regs));
> free = (long)sp - (curbase + sizeof(struct thread_info));
> }
> THIS->__retvalue = THREAD_SIZE - free;
> %}
>
> The results look much more like I'd expect...
Your calculation of free looks correct (although I'd make sp a long
rather than a long* to simplify things a bit).
But your return value seems to include the size of the struct
thread_info, which seems wrong. I'd think you'd want
THIS->__retvalue = (curbase + THREAD_SIZE) - sp;
or
THIS->__retvalue = THREAD_SIZE - (sp & (THREAD_SIZE-1));
That seems more in keeping with the original implementation.
Jim