[PATCH] perf build-id: Fix wrong return value checking

[PATCH] perf build-id: Fix wrong return value checking

[Namhyung Kim]

The {sysfs,filename}__snprintf_build_id() both return the actual length
of build-ID.  But in their fprintf counterparts check with sbuild_id
length which contain a terminating NUL bytes.  So they cannot match.

This resulted in perf buildid-list -k prints nothing.  With this fix,
it can show the following result.

  $ perf buildid-list -k
  9524074000cb36cf2559a5b52f0555dab47da553

Fixes: fccaaf6fbbc59910e ("perf build-id: Change sprintf functions to snprintf")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/builtin-buildid-list.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/builtin-buildid-list.c b/tools/perf/builtin-buildid-list.c
index a91bbb34ac946360..8ad39ff9a4b8a4b4 100644
--- a/tools/perf/builtin-buildid-list.c
+++ b/tools/perf/builtin-buildid-list.c
@@ -61,7 +61,7 @@ static int sysfs__fprintf_build_id(FILE *fp)
 	int ret;
 
 	ret = sysfs__snprintf_build_id("/", sbuild_id, sizeof(sbuild_id));
-	if (ret != sizeof(sbuild_id))
+	if (ret != sizeof(sbuild_id) - 1)
 		return ret < 0 ? ret : -EINVAL;
 
 	return fprintf(fp, "%s\n", sbuild_id);
@@ -73,7 +73,7 @@ static int filename__fprintf_build_id(const char *name, FILE *fp)
 	int ret;
 
 	ret = filename__snprintf_build_id(name, sbuild_id, sizeof(sbuild_id));
-	if (ret != sizeof(sbuild_id))
+	if (ret != sizeof(sbuild_id) - 1)
 		return ret < 0 ? ret : -EINVAL;
 
 	return fprintf(fp, "%s\n", sbuild_id);
-- 
2.54.0.rc1.555.g9c883467ad-goog

Re: [PATCH] perf build-id: Fix wrong return value checking

[James Clark]

On 20/04/2026 19:08, Namhyung Kim wrote:
> The {sysfs,filename}__snprintf_build_id() both return the actual length
> of build-ID.  But in their fprintf counterparts check with sbuild_id
> length which contain a terminating NUL bytes.  So they cannot match.
> 
> This resulted in perf buildid-list -k prints nothing.  With this fix,
> it can show the following result.
> 
>    $ perf buildid-list -k
>    9524074000cb36cf2559a5b52f0555dab47da553
> 
> Fixes: fccaaf6fbbc59910e ("perf build-id: Change sprintf functions to snprintf")
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Reviewed-by: James Clark <james.clark@linaro.org>

> ---
>   tools/perf/builtin-buildid-list.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/builtin-buildid-list.c b/tools/perf/builtin-buildid-list.c
> index a91bbb34ac946360..8ad39ff9a4b8a4b4 100644
> --- a/tools/perf/builtin-buildid-list.c
> +++ b/tools/perf/builtin-buildid-list.c
> @@ -61,7 +61,7 @@ static int sysfs__fprintf_build_id(FILE *fp)
>   	int ret;
>   
>   	ret = sysfs__snprintf_build_id("/", sbuild_id, sizeof(sbuild_id));
> -	if (ret != sizeof(sbuild_id))
> +	if (ret != sizeof(sbuild_id) - 1)
>   		return ret < 0 ? ret : -EINVAL;
>   
>   	return fprintf(fp, "%s\n", sbuild_id);
> @@ -73,7 +73,7 @@ static int filename__fprintf_build_id(const char *name, FILE *fp)
>   	int ret;
>   
>   	ret = filename__snprintf_build_id(name, sbuild_id, sizeof(sbuild_id));
> -	if (ret != sizeof(sbuild_id))
> +	if (ret != sizeof(sbuild_id) - 1)
>   		return ret < 0 ? ret : -EINVAL;
>   
>   	return fprintf(fp, "%s\n", sbuild_id);