perf: Differentiate exec() and non-exec() comm events

perf tools like 'perf report' can aggregate samples by comm strings,
which generally works.  However, there are other potential use-cases.
For example, to pair up 'calls' with 'returns' accurately (from branch
events like Intel BTS) it is necessary to identify whether the process
has exec'd.  Although a comm event is generated when an 'exec' happens
it is also generated whenever the comm string is changed on a whim
(e.g. by prctl PR_SET_NAME).  This patch adds a flag to the comm event
to differentiate one case from the other.

In order to determine whether the kernel supports the new flag, a
selection bit named 'exec' is added to struct perf_event_attr.  The
bit does nothing but will cause perf_event_open() to fail if the bit
is set on kernels that do not have it defined.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/537D9EBE.7030806@intel.com
Cc: Paul Mackerras <paulus@samba.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index d9cd853818ad..5312fae47218 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -302,8 +302,8 @@ struct perf_event_attr {
                                 exclude_callchain_kernel : 1, /* exclude kernel callchains */
                                 exclude_callchain_user   : 1, /* exclude user callchains */
                                 mmap2          :  1, /* include mmap with inode data     */
-
-                                __reserved_1   : 40;
+                                comm_exec      :  1, /* flag comm events that are due to an exec */
+                                __reserved_1   : 39;
 
         union {
                 __u32           wakeup_events;    /* wakeup every n events */
@@ -502,7 +502,12 @@ struct perf_event_mmap_page {
 #define PERF_RECORD_MISC_GUEST_KERNEL           (4 << 0)
 #define PERF_RECORD_MISC_GUEST_USER             (5 << 0)
 
+/*
+ * PERF_RECORD_MISC_MMAP_DATA and PERF_RECORD_MISC_COMM_EXEC are used on
+ * different events so can reuse the same bit position.
+ */
 #define PERF_RECORD_MISC_MMAP_DATA              (1 << 13)
+#define PERF_RECORD_MISC_COMM_EXEC              (1 << 13)
 /*
  * Indicates that the content of PERF_SAMPLE_IP points to
  * the actual instruction that triggered the event. See also