Re: Watchpoint prorogation to child threads

[Phil Muldoon <pmuldoon@redhat.com>]

Mark Wielaard wrote:
> Hi Phil,
>
> On Tue, 2008-02-26 at 16:11 +0000, Phil Muldoon wrote:
>   
>> Mark Wielaard wrote:
>>     
>>> It would be nice if this is similar to the breakpoints. Low-level
>>> breakpoints are the same on a clone (because they are really just
>>> markers in the code segment which is the same), but they are cleared on
>>> exec (because then the memory of the process is reset). 
>>>       
>> I'm not sure I understand, are breakpoints propagated on clone or not? I 
>> think they should, and I think I agree on the similarity.
>>     
>
> Yes, the low-level breakpoints are propagated (by virtue of them being
> actually inside the code segment that are shared between clones). But
> higher-level Code observers still work per Task, so on that level you
> need to register a new Code observer for a new Task to get notified when
> they trigger (they still trigger of course, but if nobody is
> listening...). I assume a Watch is similar to a Code, both being
> TaskObservers (and the comments look funnily similar).
>
>   

Yep, sure will. The comments/code is based entirely of the breakpoint 
code. So far the only operational difference is the length attribute, 
and that watchpoints are inserted/removed/trapped via register bit 
shifting instead of the memory insertions that the code breakpoints do 
at set-up. If the similarity continues throughout implementation I might 
very well refactor them to one common interface. We'll see.

>> To be honest, not thought about the exec issue, but yeah  I guess the 
>> memory is reset.
>>     
>
> The memory is, and for low-level breakpoints we reset the internal data
> structures for that reason on an exec event. Since you are implementing
> low-level watchpoints with hardware support in the cpu register you
> might have to also clear those (if the kernel doesn't do that for you on
> an exec).
>   

Uknown at the moment, but fixing to find out.

Regards

Phil