linux-kernel - Re: [2.6.29] Fix for enabling branch profiling makes sparse unusable

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Message-ID: <20090408175850.GA1158@elte.hu>
Date:	Wed, 8 Apr 2009 19:58:50 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Bart Van Assche <bart.vanassche@...il.com>
Cc:	Steven Rostedt <srostedt@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.29] Fix for enabling branch profiling makes sparse
	unusable


* Bart Van Assche <bart.vanassche@...il.com> wrote:

> On Sun, Apr 5, 2009 at 4:20 PM, Bart Van Assche
> <bart.vanassche@...il.com> wrote:
> > One of the changes between kernels 2.6.28 and 2.6.29 is that a branch profiler
> > has been added for if() statements. Unfortunately this patch makes the sparse
> > output unusable with CONFIG_TRACE_BRANCH_PROFILING=y: when branch profiling is
> > enabled, sparse prints so much false positives that the real issues are no
> > longer visible. This behavior can be reproduced as follows:
> > * enable CONFIG_TRACE_BRANCH_PROFILING, e.g. by running make allyesconfig or
> >  make allmodconfig.
> > * run make C=2
> >
> > Result: a huge number of the following sparse warnings.
> > ...
> > include/linux/cpumask.h:547:2: warning: symbol '______r' shadows an earlier one
> > include/linux/cpumask.h:547:2: originally declared here
> > ...
> >
> > The patch below fixes this by disabling branch profiling while analyzing the
> > kernel code with sparse.
> >
> > See also:
> > * http://lkml.org/lkml/2008/11/21/18
> > * http://bugzilla.kernel.org/show_bug.cgi?id=12925
> >
> > Signed-off-by: Bart Van Assche <bart.vanassche@...il.com>
> >
> > --- orig/linux-2.6.29/include/linux/compiler.h  2009-03-23 19:12:14.000000000 -0400
> > +++ linux-2.6.29/include/linux/compiler.h       2009-03-24 08:46:46.000000000 -0400
> > @@ -75,7 +75,8 @@ struct ftrace_branch_data {
> >  * Note: DISABLE_BRANCH_PROFILING can be used by special lowlevel code
> >  * to disable branch tracing on a per file basis.
> >  */
> > -#if defined(CONFIG_TRACE_BRANCH_PROFILING) && !defined(DISABLE_BRANCH_PROFILING)
> > +#if defined(CONFIG_TRACE_BRANCH_PROFILING) \
> > +    && !defined(DISABLE_BRANCH_PROFILING) && !defined(__CHECKER__)
> >  void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
> >
> >  #define likely_notrace(x)      __builtin_expect(!!(x), 1)
> 
> (ping)
> 
> Hello,
> 
> Is there any chance the above patch will get included in the 2.6.30 kernel ?

it already is part of .30-rc1, see 
d9ad8bc0ca823705413f75b50c442a88cc518b35.

	Ingo
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