linux-kernel - Re: sh: Add ftrace syscall tracing support (was: Re: [ltt-dev] [PATCH] sh: added LTT_DUMP

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Message-ID: <20090804214815.GC4084@console-pimps.org>
Date:	Tue, 4 Aug 2009 22:48:15 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	Giuseppe CAVALLARO <peppe.cavallaro@...com>,
	ltt-dev@...ts.casi.polymtl.ca, Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	rostedt@...dmis.org
Subject: Re: sh: Add ftrace syscall tracing support (was: Re: [ltt-dev]
	[PATCH] sh: added LTT_DUMP_TABLES support)

On Tue, Aug 04, 2009 at 09:35:15AM -0400, Mathieu Desnoyers wrote:
> * Giuseppe CAVALLARO (peppe.cavallaro@...com) wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > Hi Mathieu,
> > 
> > Mathieu Desnoyers wrote:
> > > So now we only need to fix entry-common.S to get everything working.
> > 
> > I've just noticed that this has been already done:
> > http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Flethal%2Fsh-2.6.git;a=commitdiff_plain;h=c652d780c9cf7f860141de232b37160fe013feca;hp=c1340c053be7a43d837a3acb352d5008be865a55
> > I think it will be necessary to to re-add the _TIF_KERNEL_TRACE against
> > this modifications, only.
> > 
> 
> Hrm, I don't like the approach taken there. It extends the bitmasks for
> _TIF_WORK_SYSCALL_MASK and _TIF_ALLWORK_MASK beyond 8 bits, and adds a &
> 0xff in the assembly whenever needed. This begs for a bug to be
> introduced.
> 
> If we need something like that on SH, we should probably declare a 8-bit
> only bitmask for those assembly sites which does not need the
> FTRACE_SYSCALL thread flag, and another mask for sites which need to
> test the 2 bytes.
> 

If I remember correctly, I originally split TIF_WORK_SYSCALL_MASK into a
high 8-bit and low 8-bit chunks. However, I think I remember Paul saying
that wasn't the best way to do it.

I've no issue with doing it either way.
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