linux-kernel - Re: [PATCH][RFC] kprobes: Add user entry-handler in kretprobes

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Message-ID: <473ACCBE.9010308@in.ibm.com>
Date:	Wed, 14 Nov 2007 15:53:58 +0530
From:	Srinivasa Ds <srinivasa@...ibm.com>
To:	Abhishek Sagar <sagar.abhishek@...il.com>
CC:	linux-kernel@...r.kernel.org, prasanna@...ibm.com,
	davem@...emloft.net, anil.s.keshavamurthy@...el.com,
	Jim Keniston <jkenisto@...ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [PATCH][RFC] kprobes: Add user entry-handler in kretprobes

Abhishek Sagar wrote:

> the entry handler is called with the appropriate return instance. I
> haven't put any explicit "match" test here for ri. The reason is that
> the correct ri would be passed to both the entry and return handlers
> as trampoline_handler() explicitly matches them to the correct task.
> Note that all pending return instances of a function are chained in
> LIFO order. S the entry-handler which gets called last, should have
> its return handler called first (in case of multiple pending return
> instances).
> 

No, eventhough return instances are chained in an order, order of execution of 
return handler entirely depends on which process returns first(some process may 
return from 2 line of the function and some process may return from last line
of the function). So entry_handler() which gets executed last doesn't guarantee 
that its return handler will be executed first(because it took a lot time
to return).

So only thing to match the entry_handler() with its return_handler() is 
return probe instance(ri)'s address, which user has to take care explicitly 
(Hence I feel sol a) would be nice). 

Thanks
 Srinivasa DS

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