trace function argument

[Christian Kaiser]

Ananth N Mavinakayanahalli wrote:
> On Tue, Jun 16, 2009 at 11:47:08AM +0200, Christian Kaiser wrote:
>> Ananth N Mavinakayanahalli wrote:
>>> On Tue, Jun 16, 2009 at 11:08:35AM +0200, Christian Kaiser wrote:
> 
>>> With debuginfoless kernels, you can do pretty much what you cite with
>>> DTrace above.
>> I am not sure if I understand you right. If I can do pretty much the same, 
>> how is it working then? Let's take your example from above. How can I print 
>> out 'clone_flags' with debuginfoless kernels?
> 
> With debuginfoless kernels, you can't refer to variables by name, rather
> using arg1, arg2, etc. See tapset/<arch>/registers.stp for more
> information. For eg:
> 
> $ stap -ve 'probe kprobe.function("do_fork") { printf("clone_flags = %x\n", ulong_arg(1)) exit() }'
> Pass 1: parsed user script and 53 library script(s) in 300usr/0sys/306real ms.
> Pass 2: analyzed script: 1 probe(s), 4 function(s), 1 embed(s), 0 global(s) in 0usr/0sys/4real ms.
> Pass 3: translated to C into "/tmp/stapnc3ps4/stap_21b73cfa060f885eb93a27cf4013ed70_2418.c" in 0usr/0sys/0real ms.
> Pass 4: compiled C into "stap_21b73cfa060f885eb93a27cf4013ed70_2418.ko" in 1490usr/230sys/1711real ms.
> Pass 5: starting run.
> clone_flags = 1200011
> Pass 5: run completed in 10usr/30sys/2234real ms.

Ok, so 'arg0' for dtrace is 'ulong_arg(1)' for systemtap. That was 
unclear to me!

Thank you!

   Christian

-- 
Christian Kaiser, Software Engineer, Dolphin Interconnect Solutions
http://www.dolphinics.com