stack_used() not accurate?

[Wenji Huang]

Mike Snitzer wrote:
> Hi,
> 
> When I use the attached script for all ext3 call-chains stack_used()
> is _always_ 481.  I'm running the latest systemtap.git on an RHEL5
> x86_64 system (though older versions of systemtap showed the same
> 481).
> 
> I've tested switching the module from ext3 to others and 481 doesn't change.
> 
> Looking at tapset/context.stp the implementation for stack_used()
> looks fine.  But given the constant 481 I'm seeing is systemtap
> somehow showing systemtap-tainted stack usage?
> 
> Mike

Hi Mike,

I did a test and found it kept the constant value. And I changed to 
another function which is copied and tailored from check_stack_usage(). 
The function is added since 2.6.23, but has no much dependency on kernel 
version. Seems it works fine on my boxes(x86, x86_64).

function stack_used_new:long() %{ /*pure */
  {
          unsigned long *n = end_of_stack(current);
          unsigned long free;
          while (*n == 0)
                  n++;
          free = (unsigned long)n - (unsigned long)end_of_stack(current);

          THIS->__retvalue = THREAD_SIZE - free;
}
%}

Regards,
Wenji