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authorJiri Olsa <jolsa@redhat.com>2014-02-26 18:14:26 +0100
committerArnaldo Carvalho de Melo <acme@redhat.com>2014-02-28 10:39:40 -0300
commitb39c2a57a00a841f057a75b41df4c26173288b66 (patch)
treedfc60fc25146d8dad4b9143c1759283727f4923c
parent280e7c48c3b873e4987a63da276ecab25383f494 (diff)
perf tools: Fix strict alias issue for find_first_bit
When compiling perf tool code with gcc 4.4.7 I'm getting following error: CC util/session.o cc1: warnings being treated as errors util/session.c: In function ‘perf_session_deliver_event’: tools/perf/util/include/linux/bitops.h:109: error: dereferencing pointer ‘p’ does break strict-aliasing rules tools/perf/util/include/linux/bitops.h:101: error: dereferencing pointer ‘p’ does break strict-aliasing rules util/session.c:697: note: initialized from here tools/perf/util/include/linux/bitops.h:101: note: initialized from here make[1]: *** [util/session.o] Error 1 make: *** [util/session.o] Error 2 The aliased types here are u64 and unsigned long pointers, which is safe for the find_first_bit processing. This error shows up for me only for gcc 4.4 on 32bit x86, even for -Wstrict-aliasing=3, while newer gcc are quiet and scream here for -Wstrict-aliasing={2,1}. Looks like newer gcc changed the rules for strict alias warnings. The gcc documentation offers workaround for valid aliasing by using __may_alias__ attribute: http://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Type-Attributes.html Using this workaround for the find_first_bit function. Signed-off-by: Jiri Olsa <jolsa@redhat.com> Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com> Cc: David Ahern <dsahern@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1393434867-20271-1-git-send-email-jolsa@redhat.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
-rw-r--r--tools/perf/util/include/linux/bitops.h4
1 files changed, 3 insertions, 1 deletions
diff --git a/tools/perf/util/include/linux/bitops.h b/tools/perf/util/include/linux/bitops.h
index 45cf10a562bd..dadfa7e54287 100644
--- a/tools/perf/util/include/linux/bitops.h
+++ b/tools/perf/util/include/linux/bitops.h
@@ -87,13 +87,15 @@ static __always_inline unsigned long __ffs(unsigned long word)
return num;
}
+typedef const unsigned long __attribute__((__may_alias__)) long_alias_t;
+
/*
* Find the first set bit in a memory region.
*/
static inline unsigned long
find_first_bit(const unsigned long *addr, unsigned long size)
{
- const unsigned long *p = addr;
+ long_alias_t *p = (long_alias_t *) addr;
unsigned long result = 0;
unsigned long tmp;