[PATCH V2 1/2] powerpc tools perf: Initialize error code in auxtrace_record_init function

[PATCH V2 1/2] powerpc tools perf: Initialize error code in auxtrace_record_init function

[Athira Rajeev]

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
also because perf record will fail seeing random value in err.

Set err to -EINVAL before invoking auxtrace_record__init() in
builtin-record.c

With the fix,

 # ./perf trace record sleep 1
 [ perf record: Woken up 2 times to write data ]
 [ perf record: Captured and wrote 0.033 MB perf.data (228 samples) ]

Fixes: 1dbfaf94cf66 ("perf powerpc: Add basic CONFIG_AUXTRACE support for VPA pmu on powerpc")
Signed-off-by: Athira Rajeev <atrajeev@linux.ibm.com>
---
Changelog:
v1 -> v2
Addressed review comment from Adrian:
- Set err to -EINVAL before invoking auxtrace_record__init() in
  builtin-record.c
- Added kernel-doc to auxtrace_record__init() in tools/perf/util/auxtrace.c
Addressed review comment from Namhyung:
- Added fixes tag

 tools/perf/arch/powerpc/util/auxtrace.c | 6 ++++++
 tools/perf/builtin-record.c             | 1 +
 2 files changed, 7 insertions(+)

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

[PATCH V2 2/2] tools/perf: Add kernel-doc comment to auxtrace_record__init() function

[Athira Rajeev]

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 <atrajeev@linux.ibm.com>
---
 tools/perf/util/auxtrace.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
index a224687ffbc1..8c0447c54003 100644
--- a/tools/perf/util/auxtrace.c
+++ b/tools/perf/util/auxtrace.c
@@ -896,8 +896,20 @@ 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 pointer to the struct auxtrace_record on success, or NULL on
+ * failure (@err needs to be set).
+ */
 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

Re: [PATCH V2 2/2] tools/perf: Add kernel-doc comment to auxtrace_record__init() function

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The added kernel-doc comment incorrectly documents a NULL return value as strictly a failure, which contradicts the actual API behavior and the implementation directly below it.
--

commit 32a1e931b50aecc6b395f4170e1b7ccb2ad1db6c
Author: Athira Rajeev <atrajeev@linux.ibm.com>

tools/perf: Add kernel-doc comment to auxtrace_record__init() function

This commit adds a kernel-doc comment for auxtrace_record__init() to
describe its parameters and return value. It also rearranges the
__maybe_unused attribute to fix a kernel-doc warning.

> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> --- a/tools/perf/util/auxtrace.c
> +++ b/tools/perf/util/auxtrace.c

[ ... ]

> +/**
> + * 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 pointer to the struct auxtrace_record on success, or NULL on
> + * failure (@err needs to be set).
> + */
>  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;
>  }

Does this kernel-doc comment accurately describe the return value
expectations?

The weak implementation of auxtrace_record__init() directly below this
comment returns NULL and sets *err = 0. Returning NULL with a zero error
code appears to be the designated success path to indicate that no AUX area
tracing hardware is available, rather than a failure.

Could the documentation be updated to reflect that returning NULL with
*err = 0 is a valid success condition?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260501145436.1327-1-atrajeev@linux.ibm.com?part=2