[PATCH v3 2/4] perf: Use a union to clear branch entry bitfields

[Puranjay Mohan]

perf_clear_branch_entry_bitfields() zeroes individual bitfields of struct
perf_branch_entry but has repeatedly fallen out of sync when new fields
were added (new_type and priv were missed).

Wrap the bitfields in an anonymous struct inside a union with a u64
bitfields member, and clear them all with a single assignment. This
avoids having to update the clearing function every time a new bitfield
is added.

Fixes: bfe4daf850f4 ("perf/core: Add perf_clear_branch_entry_bitfields() helper")
Signed-off-by: Puranjay Mohan <puranjay at kernel.org>
---
 include/linux/perf_event.h      |  9 +--------
 include/uapi/linux/perf_event.h | 25 +++++++++++++++----------
 2 files changed, 16 insertions(+), 18 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 48d851fbd8ea..f7360c43f902 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1474,14 +1474,7 @@ static inline u32 perf_sample_data_size(struct perf_sample_data *data,
  */
 static inline void perf_clear_branch_entry_bitfields(struct perf_branch_entry *br)
 {
-	br->mispred	= 0;
-	br->predicted	= 0;
-	br->in_tx	= 0;
-	br->abort	= 0;
-	br->cycles	= 0;
-	br->type	= 0;
-	br->spec	= PERF_BR_SPEC_NA;
-	br->reserved	= 0;
+	br->bitfields = 0;
 }
 
 extern void perf_output_sample(struct perf_output_handle *handle,
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index fd10aa8d697f..c2e7b1b1c4fa 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -1491,16 +1491,21 @@ union perf_mem_data_src {
 struct perf_branch_entry {
 	__u64	from;
 	__u64	to;
-	__u64	mispred   :  1, /* target mispredicted */
-		predicted :  1, /* target predicted */
-		in_tx     :  1, /* in transaction */
-		abort     :  1, /* transaction abort */
-		cycles    : 16, /* cycle count to last branch */
-		type      :  4, /* branch type */
-		spec      :  2, /* branch speculation info */
-		new_type  :  4, /* additional branch type */
-		priv      :  3, /* privilege level */
-		reserved  : 31;
+	union {
+		struct {
+			__u64	mispred   :  1, /* target mispredicted */
+				predicted :  1, /* target predicted */
+				in_tx     :  1, /* in transaction */
+				abort     :  1, /* transaction abort */
+				cycles    : 16, /* cycle count to last branch */
+				type      :  4, /* branch type */
+				spec      :  2, /* branch speculation info */
+				new_type  :  4, /* additional branch type */
+				priv      :  3, /* privilege level */
+				reserved  : 31;
+		};
+		__u64	bitfields;
+	};
 };
 
 /* Size of used info bits in struct perf_branch_entry */
-- 
2.52.0