Re: Pointer chain paranoia

[Mike Mason <mmlnx at us dot ibm dot com>]

Are pointer chain references in the regular stap language (not embedded C) always safe?  In other words, if I use something of the form $ptr1->ptr2->ptr3->var, does stap automatically convert that to the needed deref() macros? I looked at the resulting module code and I think it does, but want to be sure.

Mike

Stone, Joshua I wrote:
> On Tuesday, November 14, 2006 9:15 AM, Mike Mason wrote:
> > I'm looking for opinions from the systemtap community... How paranoid
> > should we be when following pointer chains in tapsets and scripts?  I
> > think we should use deref() unless we're absolutely sure there's no
> > chance of referencing a null or bad pointer, but, of course, that'll
> > add a lot of code. I'm not sure how you can ever be absolutely sure,
> > particularly for longer chains.  What guidance should we give tapset
> > and script writers?      
> >
> > Mike
>
> I agree with you.  Safety is always more important than efficiency,
> especially in tapsets which may be used by non-guru users.  Any
> questionable pointers should be carefully dereferenced, e.g., parameters
> passed to functions should be assumed bogus.
>
> When a pointer is known to originate from a kernel source, like from
> 'current' or as a return value from a kernel function, then we might
> relax a bit.
>
>
> Josh