Commit d9ad8bc0 authored Apr 05, 2009 by Bart Van Assche Committed by Ingo Molnar Apr 07, 2009

branch tracer: 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@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <srostedt@redhat.com>
LKML-Reference: <200904051620.02311.bart.vanassche@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 1bbe2a83

include/linux/compiler.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -76,7 +76,8 @@ 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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