Re: Pointer chain paranoia

[Mike Mason <mmlnx@us.ibm.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