Re: stack_used() not accurate?

[Jim Keniston <jkenisto at us dot ibm dot com>]

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 &regs->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