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

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Message-ID: <20090804133515.GB23807@Krystal>
Date:	Tue, 4 Aug 2009 09:35:15 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Giuseppe CAVALLARO <peppe.cavallaro@...com>
Cc:	ltt-dev@...ts.casi.polymtl.ca,
	Matt Fleming <matt@...sole-pimps.org>,
	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, rostedt@...dmis.org
Subject: sh: Add ftrace syscall tracing support (was: Re: [ltt-dev] [PATCH]
	sh: added LTT_DUMP_TABLES support)

* 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.

I would also consider other instructions than 2 consecutive "tst" to
extend test with a 2 bytes mask. Something like loading an integer in a
register and testing with the register rather than doing 2 immediate
value tests.

Mathieu


> Regards,
> Peppe
> 
> > 
> > Mathieu
> > 
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-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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