dtrace discuss - Jun 2011 - issue dtracing function return value in pid provider

Hello,

I need to use the pid provider to trace the inputs and return value of 
the following function

calc_guest_util(rs_guest_util_t *gutil, int ncpu, int fcpu)
   {
<snip>
    return ((100.0 * (double)used_cycles) / (double)(total_cycles));
   }

I can trace the input arguments with the following dscript (if there''s
a
quicker and cleaver dscript to do that please correct me):

#!/usr/sbin/dtrace -qs

typedef struct rs_guest_util {
         uint64_t        lifespan;
         uint64_t        wallclock_delta;
         uint64_t        active_delta;
         uint64_t        stopped_cycles;
         uint64_t        yielded_cycles;
  } rs_guest_util_t;

pid$1::calc_guest_util:entry
{
self->guest=((rs_guest_util_t *)(copyin(arg0,sizeof(rs_guest_util_t))));
printf("arg0 %x\n",arg0);
printf("ncpu %d\n",arg1);
printf("fcup %d\n",arg2);
printf("active delta %d\n",self->guest->active_delta);
printf("stopped cycles %d\n",self->guest->stopped_cycles);
printf("yielded cycles %d\n",self->guest->yielded_cycles);
}

Then I added the following to trace the return value of the function

pid$1::calc_guest_util:return
{
printf("return %x\n",arg1);
}

But I get the following output:

arg0 ffbffb80
ncpu 8
fcup 0
active delta 583970560
stopped cycles 0
yielded cycles 4652066048
total cycles 4671764480
return ffbffb80

As you can see the return value is an address, actually the same address 
as arg0 in entry.
I suspect I''m doing something wrong in dtrace but I can''t
realize
what....Could you please advice?

Regards
Andrea


/
/
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://mail.opensolaris.org/pipermail/dtrace-discuss/attachments/20110612/ad7a3f20/attachment.html>

Hey Andrea,
> As you can see the return value is an address, actually the same address as
> arg0 in entry.
> I suspect I''m doing something wrong in dtrace but I can''t
realize
> what....Could you please advice?
The return type of calc_guest_util() was cut off, but I infer that
it''s a double. DTrace doesn''t have much by way of support for
floating-point values -- adding access to the floating-point registers
and support for manipulating floating-point datatypes have long been
RFEs for DTrace. I''d offer to add them to illumos, but I doubt that
would be of much help to users of Oracle Solaris.

Adam

On Sun, Jun 12, 2011 at 4:04 AM, Andrea Cucciarre''
<andrea.cucciarre at oracle.com> wrote:
> Hello,
>
> I need to use the pid provider to trace the inputs and return value of the
> following function
>
> calc_guest_util(rs_guest_util_t *gutil, int ncpu, int fcpu)
> ? {
> ?? <snip>
> ?? return ((100.0 * (double)used_cycles) / (double)(total_cycles));
> ? }
>
> I can trace the input arguments with the following dscript (if
there''s a
> quicker and cleaver dscript to do that please correct me):
>
> #!/usr/sbin/dtrace -qs
>
> typedef struct rs_guest_util {
> ??????? uint64_t??????? lifespan;
> ??????? uint64_t??????? wallclock_delta;
> ??????? uint64_t??????? active_delta;
> ??????? uint64_t??????? stopped_cycles;
> ??????? uint64_t??????? yielded_cycles;
> ?} rs_guest_util_t;
>
> pid$1::calc_guest_util:entry
> {
> self->guest=((rs_guest_util_t *)(copyin(arg0,sizeof(rs_guest_util_t))));
> printf("arg0 %x\n",arg0);
> printf("ncpu %d\n",arg1);
> printf("fcup %d\n",arg2);
> printf("active delta %d\n",self->guest->active_delta);
> printf("stopped cycles %d\n",self->guest->stopped_cycles);
> printf("yielded cycles %d\n",self->guest->yielded_cycles);
> }
>
> Then I added the following to trace the return value of the function
>
> pid$1::calc_guest_util:return
> {
> printf("return %x\n",arg1);
> }
>
> But I get the following output:
>
> arg0 ffbffb80
> ncpu 8
> fcup 0
> active delta 583970560
> stopped cycles 0
> yielded cycles 4652066048
> total cycles 4671764480
> return ffbffb80
>
> As you can see the return value is an address, actually the same address as
> arg0 in entry.
> I suspect I''m doing something wrong in dtrace but I can''t
realize
> what....Could you please advice?
>
> Regards
> Andrea
>
>
>
>
> _______________________________________________
> dtrace-discuss mailing list
> dtrace-discuss at opensolaris.org
>


-- 
Adam Leventhal, Delphix
http://dtrace.org/blogs/ahl

275 Middlefield Road, Suite 50
Menlo Park, CA 94025
http://www.delphix.com