[PATCH V3 1/2] powerpc tools perf: Initialize error code in auxtrace_record_init function

perf trace record fails some cases in powerpc

 # ./perf test "perf trace record and replay"
 128: perf trace record and replay                                    : FAILED!

 # ./perf trace record sleep 1
 # echo $?
   32

This is happening because of non-zero err value from
auxtrace_record__init() function.

 static int record__auxtrace_init(struct record *rec)
 {
        int err;

        if ((rec->opts.auxtrace_snapshot_opts || rec->opts.auxtrace_sample_opts)
            && record__threads_enabled(rec)) {
                pr_err("AUX area tracing options are not available in parallel streaming mode.\n");
                return -EINVAL;
        }

        if (!rec->itr) {
                rec->itr = auxtrace_record__init(rec->evlist, &err);
                if (err)
                        return err;
        }

Here "int err" is not initialised. The code expects "err" to be set
from auxtrace_record__init() function.

Update auxtrace_record__init() in arch/powerpc/util/auxtrace.c to clear
err value in the beginning.

- Clear err value in beginning of function. Any fail later will
set appropriate return code to err.
- Even if we haven't found any event for auxtrace, perf record
should continue for other events. NULL return
will indicate that there is no auxtrace record initialized.
- Not having "err" set here will affect monitoring of other events

27 more lines

diff --git a/tools/perf/arch/powerpc/util/auxtrace.c b/tools/perf/arch/powerpc/util/auxtrace.c
index e39deff6c857..4600a1661b4f 100644
--- a/tools/perf/arch/powerpc/util/auxtrace.c
+++ b/tools/perf/arch/powerpc/util/auxtrace.c

@@ -71,6 +71,12 @@ struct auxtrace_record *auxtrace_record__init(struct evlist *evlist,
 	struct evsel *pos;
 	int found = 0;
 
+	/*
+	 * Set err value to zero here. Any fail later
+	 * will set appropriate return code to err.
+	 */
+	*err = 0;
+
 	evlist__for_each_entry(evlist, pos) {
 		if (strstarts(pos->name, "vpa_dtl")) {
 			found = 1;

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 4a5eba498c02..708825747af5 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c

@@ -865,6 +865,7 @@ static int record__auxtrace_init(struct record *rec)
 	}
 
 	if (!rec->itr) {
+		err = -EINVAL;
 		rec->itr = auxtrace_record__init(rec->evlist, &err);
 		if (err)
 			return err;

-- 
2.47.3

Add documentation comment describing the parameters
and return code for auxtrace_record__init() in util/auxtrace.c

Using "struct evlist *evlist __maybe_unused", gives below
warning with "scripts/kernel-doc".

 # ./scripts/kernel-doc -none tools/perf/util/auxtrace.c
 Warning: tools/perf/util/auxtrace.c:912 function parameter '__maybe_unused' not described in 'auxtrace_record__init'
 Warning: tools/perf/util/auxtrace.c:912 function parameter '__maybe_unused' not described in 'auxtrace_record__init'

Updated  parameter as "struct evlist __maybe_unused *evlist"
With the change, there is no erros/warnings with kernel-doc

Signed-off-by: Athira Rajeev <redacted>
---
Changelog:
v2 -> v3:
Addressed review comment from Sashiko:
Update return value expectation for success and fail
correctly.

 tools/perf/util/auxtrace.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
index a224687ffbc1..6aeccedc7f2d 100644
--- a/tools/perf/util/auxtrace.c
+++ b/tools/perf/util/auxtrace.c

@@ -896,8 +896,23 @@ int auxtrace_parse_aux_action(struct evlist *evlist)
 	return 0;
 }
 
+/**
+ * auxtrace_record__init - Initialize an AUX area tracing record.
+ * @evlist: The list of events to check for AUX area tracing event.
+ * @err: Pointer to an integer to store return code.
+ *
+ * This function looks through the @evlist to determine which AUX area
+ * tracing hardware is being used and initializes the auxtrace_record
+ * structure.
+ *
+ * Return:
+ * a) A pointer to the struct auxtrace_record on success.
+ * b) NULL with @err = 0 if no AUX area tracing event is found/supported
+ *    (not considered an error).
+ * c) NULL with @err < 0 on actual auxtrace_record__init failure.
+ */
 struct auxtrace_record *__weak
-auxtrace_record__init(struct evlist *evlist __maybe_unused, int *err)
+auxtrace_record__init(struct evlist __maybe_unused *evlist, int *err)
 {
 	*err = 0;
 	return NULL;

-- 
2.47.3