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Date: Sun, 15 Mar 2009 05:44:05 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Lai Jiangshan <laijs@cn.fujitsu.com>,
       Steven Rostedt <rostedt@goodmis.org>,
       Peter Zijlstra <peterz@infradead.org>,
       Jiaying Zhang <jiayingz@google.com>, Martin Bligh <mbligh@google.com>
Subject: Re: [RFC][PATCH 2/2] tracing/x86: basic implementation of syscall
	tracing for x86-64
Message-ID: <20090315044405.GB11150@elte.hu>
References: <1236401580-5758-1-git-send-email-fweisbec@gmail.com> <1236401580-5758-3-git-send-email-fweisbec@gmail.com> <20090313163207.GA3354@Krystal> <20090313163702.GA9082@elte.hu> <20090313165020.GD3354@Krystal>
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* Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:

> * Ingo Molnar (mingo@elte.hu) wrote:
> > 
> > * Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> wrote:
> > 
> > > * Frederic Weisbecker (fweisbec@gmail.com) wrote:
> > >
> > > > Provide the ptrace hooks and arch specific syscall numbers 
> > > > to ftrace arch indepedant syscall numbers. For now it only 
> > > > supports 4 syscalls to provide an example.
> > > > 
> > > 
> > > Hi Frederic,
> > > 
> > > I already have the equivalent TIF_KERNEL_TRACE flag in my 
> > > LTTng tree added to every Linux architecture. You might want 
> > > to re-use this work rather than re-doing this. I don't mind 
> > > changing the flag name.
> > 
> > Yeah. Note that the TIF bits are just one part - there are other 
> > bits needed for HAVE_FTRACE_SYSCALLS arch support.
> > 
> > Also, i'd eventually expect the TIF bits to be converted to a 
> > tracehook callback, not spread it to other architectures.
> > 
> 
> The nice part about the TIF bit is that it permits adding this 
> syscall tracing feature without increasing the size of the 
> thread_info struct nor adding any extra tests in entry.S. Does 
> the tracehook callback have these features ?

yes. Tracehook just factors out common interfacing points - with 
one specific implementation for now: ptrace. For syscall tracing 
that means it wraps TIF_SYSCALL_TRACE in essence.

	Ingo