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

[PATCH V3 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 V3 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>
---
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

Re: [PATCH V3 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] Documentation mismatch: `auxtrace_record__init()` can return positive error codes.
--

commit a2b68fba99416692edd38910a4c62adfdf1b490d
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 describing the parameters and return code
for auxtrace_record__init(). It also moves the __maybe_unused attribute to fix
warnings generated by scripts/kernel-doc.

> 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.
> + */

Is this description for case 'c' completely accurate?

Looking at the architecture-specific implementations, such as the one in
tools/perf/arch/x86/util/auxtrace.c, it appears the function can return
positive error codes. For instance, the x86 implementation calls get_cpuid(),
which returns ENOBUFS (a positive integer) on failure. This positive value
is then assigned to *err before returning NULL.

Could this comment be updated to reflect that *err can be any non-zero
value on failure, rather than strictly less than zero?

>  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;
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260502073924.99965-1-atrajeev@linux.ibm.com?part=2

Re: [PATCH V3 2/2] tools/perf: Add kernel-doc comment to auxtrace_record__init() function

[Athira Rajeev]

> On 2 May 2026, at 1:40 PM, sashiko-bot@kernel.org wrote:
> 
> Is this description for case 'c' completely accurate?
> 
> Looking at the architecture-specific implementations, such as the one in
> tools/perf/arch/x86/util/auxtrace.c, it appears the function can return
> positive error codes. For instance, the x86 implementation calls get_cpuid(),
> which returns ENOBUFS (a positive integer) on failure. This positive value
> is then assigned to *err before returning NULL.
> 
> Could this comment be updated to reflect that *err can be any non-zero
> value on failure, rather than strictly less than zero?

Sure

I will update this in next version

Thanks
Athira