perf record: Add HEADER_BRANCH_STACK tag

This patch adds a new feature bit, namely,
HEADER_BRANCH_STACK.  When present, it indicates
that sample records may contain branch stack.

This could be useful to a viewer to switch to
branch mode without having to parse all the
samples or without a specific cmdline option.

This will be used in a subsequent patch to
enhance perf report with branch stacks.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: peterz@infradead.org
Cc: acme@redhat.com
Cc: asharma@fb.com
Cc: ravitillo@lbl.gov
Cc: vweaver1@eecs.utk.edu
Cc: khandual@linux.vnet.ibm.com
Cc: dsahern@gmail.com
Link: http://lkml.kernel.org/r/1331246868-19905-3-git-send-email-eranian@google.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 17 insertions, 1 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index a7c53a9ef372..be4e1eee782e 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -473,6 +473,9 @@ static int __cmd_record(struct perf_record *rec, int argc, const char **argv)
         if (!have_tracepoints(&evsel_list->entries))
                 perf_header__clear_feat(&session->header, HEADER_TRACE_INFO);
 
+        if (!rec->opts.branch_stack)
+                perf_header__clear_feat(&session->header, HEADER_BRANCH_STACK);
+
         if (!rec->file_new) {
                 err = perf_session__read_header(session, output);
                 if (err < 0)
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index c851495b9b48..0d9b6da86a39 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1023,6 +1023,12 @@ write_it:
         return do_write_string(fd, buffer);
 }
 
+static int write_branch_stack(int fd __used, struct perf_header *h __used,
+                       struct perf_evlist *evlist __used)
+{
+        return 0;
+}
+
 static void print_hostname(struct perf_header *ph, int fd, FILE *fp)
 {
         char *str = do_read_string(fd, ph);
@@ -1315,6 +1321,12 @@ static void print_cpuid(struct perf_header *ph, int fd, FILE *fp)
         free(str);
 }
 
+static void print_branch_stack(struct perf_header *ph __used, int fd __used,
+                               FILE *fp)
+{
+        fprintf(fp, "# contains samples with branch stack\n");
+}
+
 static int __event_process_build_id(struct build_id_event *bev,
                                     char *filename,
                                     struct perf_session *session)
@@ -1519,6 +1531,7 @@ static const struct feature_ops feat_ops[HEADER_LAST_FEATURE] = {
         FEAT_OPA(HEADER_CMDLINE,        cmdline),
         FEAT_OPF(HEADER_CPU_TOPOLOGY,   cpu_topology),
         FEAT_OPF(HEADER_NUMA_TOPOLOGY,  numa_topology),
+        FEAT_OPA(HEADER_BRANCH_STACK,   branch_stack),
 };
 
 struct header_print_data {
diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
index e68f617d082f..21a6be09c129 100644
--- a/tools/perf/util/header.h
+++ b/tools/perf/util/header.h
@@ -27,7 +27,7 @@ enum {
         HEADER_EVENT_DESC,
         HEADER_CPU_TOPOLOGY,
         HEADER_NUMA_TOPOLOGY,
-
+        HEADER_BRANCH_STACK,
         HEADER_LAST_FEATURE,
         HEADER_FEAT_BITS        = 256,
 };