access variables within functions

[Srikar Dronamraju]

* Rus-Rebreanu Alin-Florin <netblock@gmail.com> [2008-04-14 13:30:48]:

> Hi,
> I have a problem with accessing a variable using systemtap.
> Let's take for example vfs_read in fs/read_write.c:
> ssize_t vfs_read(file,buf,count,pos){
> ssize_t ret;
> ........more code.....
> return ret;
> 
> }
> 
> using stap i want to access "ret". Accessing the parameters of the
> function works just fine with "$var".
> I'm using:
> stap -vvv -e 'probe kernel.function("vfs_read@fs/read_write.c:270")
> {printf("%d",$ret)}'
> It doesn't work. Am I missing something?
> 

I guess you get an output of all zeros.  (If not please let us know the
output you are seeing. )
When using kernel.function() the probe will be place at the start of the
function definition. If you want to place a probe at a particular
statement in code, please use kernel.statement instead.

-Srikar