Re: accessing kernel global variables?

[Om Narasimhan <om dot turyx at gmail dot com>]

Ananth N Mavinakayanahalli wrote:
> On Sun, Sep 07, 2008 at 07:49:34PM -0700, Om Narasimhan wrote:
> > For example, kernel/pid.c:38 in my tree defines pid_max as,
> >
> > int pid_max = PID_MAX_DEFAULT;
> >
> > When I try printing this value using the below scriptlet I get errors.
> >
> > $ sudo stap -g -u -vv  -e 'probe begin { printf("pid_max = %d\n", $pid_max) 
> > ; exit() }'
<snip>
> stap -ve 'probe kernel.function("find_get_pid") {printf("pid_max = %d\n", $pid_max); exit()}'
>
> Pass 1: parsed user script and 43 library script(s) in 330usr/0sys/453real ms.
> Pass 2: analyzed script: 1 probe(s), 2 function(s), 0 embed(s), 0 global(s) in 390usr/650sys/9779real ms.
> Pass 3: translated to C into "/tmp/stapAS2qBy/stap_d737858677ec9922f479339c1fe4be44_851.c" in 170usr/270sys/482real ms.
> Pass 4: compiled C into "stap_d737858677ec9922f479339c1fe4be44_851.ko" in 3180usr/430sys/5443real ms.
> Pass 5: starting run.
> pid_max = 32768
>
> Any function in kernel/pid.c may also be used.
Thanks.
So, the systemtap script _cannot_ access kernel global variables 
independent of the context it runs in. From any function context within 
kernel/pid.c, this variable is within scope, so are any (static/global) 
variables defined in that file.

Is my understanding correct?
Thanks,
Om.