linux-kernel - Re: [PATCH 08/12] add trace events for each syscall entry/exit

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Date:	Wed, 26 Aug 2009 08:21:09 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, laijs@...fujitsu.com, rostedt@...dmis.org,
	jiayingz@...gle.com, mbligh@...gle.com, lizf@...fujitsu.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 08/12] add trace events for each syscall entry/exit

On Tue, 2009-08-25 at 14:31 -0400, Mathieu Desnoyers wrote:

> (Well, I do not have time currently to look into the gory details
> (sorry), but let's try to take a step back from the problem.)
> 
> The design proposal for this kthread behavior wrt syscalls is based on a
> very specific and current kernel behavior, that may happen to change and
> that I have actually seen proven incorrect. For instance, some
> proprietary Linux driver does very odd things with system calls within
> kernel threads, like invoking them with int 0x80.
> 
> Yes, this is odd, but do we really want to tie the tracer that much to
> the actual OS implementation specificities ?
> 
> That sounds like a recipe for endless breakages and missing bits of
> instrumentation.
> 
> So my advice would be: if we want to trace the syscall entry/exit paths,
> let's trace them for the _whole_ system, and find ways to make it work
> for corner-cases rather than finding clever ways to diminish
> instrumentation coverage.
> 
> Given the ret from fork example happens to be the first event fired
> after the thread is created, we should be able to deal with this problem
> by initializing the thread structure used by syscall exit tracing to an
> initial "ret from fork" value.

So you're saying we should let proprietary crap influence the design of
the kernel in any way?
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