diff options
author | Jiri Olsa <jolsa@redhat.com> | 2014-02-26 18:14:26 +0100 |
---|---|---|
committer | Arnaldo Carvalho de Melo <acme@redhat.com> | 2014-02-28 10:39:40 -0300 |
commit | b39c2a57a00a841f057a75b41df4c26173288b66 (patch) | |
tree | dfc60fc25146d8dad4b9143c1759283727f4923c | |
parent | 280e7c48c3b873e4987a63da276ecab25383f494 (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.h | 4 |
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; |