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

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Message-Id: <200904051620.02311.bart.vanassche@gmail.com>
Date:	Sun, 5 Apr 2009 16:20:02 +0200
From:	Bart Van Assche <bart.vanassche@...il.com>
To:	Steven Rostedt <srostedt@...hat.com>, Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [2.6.29] Fix for enabling branch profiling makes sparse unusable

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)
--
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