perf: Move mmap page data_head offset assertion out of header

Having the build time assertion in header is making the perf
build fail on x86 with:

  ../../include/linux/perf_event.h:411:32: error: variably modified \
		‘__assert_mmap_data_head_offset’ at file scope [-Werror]

I'm moving the build time validation out of the header, because
I think it's better than to lessen the perf build warn/error
check.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: acme@redhat.com
Cc: a.p.zijlstra@chello.nl
Cc: paulus@samba.org
Cc: cjashfor@linux.vnet.ibm.com
Cc: fweisbec@gmail.com
Link: http://lkml.kernel.org/r/1332513680-7870-1-git-send-email-jolsa@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index dc3b05272511..3f92a19aa11e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7116,6 +7116,13 @@ void __init perf_event_init(void)
 
         /* do not patch jump label more than once per second */
         jump_label_rate_limit(&perf_sched_events, HZ);
+
+        /*
+         * Build time assertion that we keep the data_head at the intended
+         * location.  IOW, validation we got the __reserved[] size right.
+         */
+        BUILD_BUG_ON((offsetof(struct perf_event_mmap_page, data_head))
+                     != 1024);
 }
 
 static int __init perf_event_sysfs_init(void)