[PATCH] perf build-id: Fix off-by-one bug when printing kernel/module build-id

[PATCH] perf build-id: Fix off-by-one bug when printing kernel/module build-id

[Michael Petlan]

When changing sprintf functions to snprintf, one byte got lost. Since
snprintf ones do not handle the '\0' terminating character, the number
of printed characters is 40, while sizeof(sbuild_id) is 41, including
the terminating '\0' character. This makes the later check fail so that
nothing is printed.

Fix that.

Before:
    [Michael@Carbon ~]$ perf buildid-list -k
    [Michael@Carbon ~]$

After:
    [Michael@Carbon ~]$ perf buildid-list -k
    a527806324d543c4bc3ff2f9c9519d494fed5f68
    [Michael@Carbon ~]$

Fixes: fccaaf6fbbc5 ("perf build-id: Change sprintf functions to snprintf")

Signed-off-by: Michael Petlan <mpetlan@redhat.com>
---
 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 a91bbb34ac94..e0881b0ac38f 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 + 1 != sizeof(sbuild_id))
 		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 + 1 != sizeof(sbuild_id))
 		return ret < 0 ? ret : -EINVAL;
 
 	return fprintf(fp, "%s\n", sbuild_id);
-- 
2.47.3

Re: [PATCH] perf build-id: Fix off-by-one bug when printing kernel/module build-id

[Ian Rogers]

On Tue, May 19, 2026 at 3:39 PM Michael Petlan <mpetlan@redhat.com> wrote:
>
> When changing sprintf functions to snprintf, one byte got lost. Since
> snprintf ones do not handle the '\0' terminating character, the number
> of printed characters is 40, while sizeof(sbuild_id) is 41, including
> the terminating '\0' character. This makes the later check fail so that
> nothing is printed.
>
> Fix that.
>
> Before:
>     [Michael@Carbon ~]$ perf buildid-list -k
>     [Michael@Carbon ~]$
>
> After:
>     [Michael@Carbon ~]$ perf buildid-list -k
>     a527806324d543c4bc3ff2f9c9519d494fed5f68
>     [Michael@Carbon ~]$
>
> Fixes: fccaaf6fbbc5 ("perf build-id: Change sprintf functions to snprintf")
>
> Signed-off-by: Michael Petlan <mpetlan@redhat.com>

Tested-by: Ian Rogers <irogers@google.com>
also Sashiko is green for this patch:
https://sashiko.dev/#/patchset/20260519223855.191637-1-mpetlan%40redhat.com

Thanks!
Ian

> ---
>  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 a91bbb34ac94..e0881b0ac38f 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 + 1 != sizeof(sbuild_id))
>                 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 + 1 != sizeof(sbuild_id))
>                 return ret < 0 ? ret : -EINVAL;
>
>         return fprintf(fp, "%s\n", sbuild_id);
> --
> 2.47.3
>

Re: [PATCH] perf build-id: Fix off-by-one bug when printing kernel/module build-id

[Arnaldo Carvalho de Melo]

On Wed, May 20, 2026 at 08:55:51AM -0700, Ian Rogers wrote:
> On Tue, May 19, 2026 at 3:39 PM Michael Petlan <mpetlan@redhat.com> wrote:
> >
> > When changing sprintf functions to snprintf, one byte got lost. Since
> > snprintf ones do not handle the '\0' terminating character, the number
> > of printed characters is 40, while sizeof(sbuild_id) is 41, including
> > the terminating '\0' character. This makes the later check fail so that
> > nothing is printed.
> >
> > Fix that.
> >
> > Before:
> >     [Michael@Carbon ~]$ perf buildid-list -k
> >     [Michael@Carbon ~]$
> >
> > After:
> >     [Michael@Carbon ~]$ perf buildid-list -k
> >     a527806324d543c4bc3ff2f9c9519d494fed5f68
> >     [Michael@Carbon ~]$
> >
> > Fixes: fccaaf6fbbc5 ("perf build-id: Change sprintf functions to snprintf")
> >
> > Signed-off-by: Michael Petlan <mpetlan@redhat.com>
> 
> Tested-by: Ian Rogers <irogers@google.com>
> also Sashiko is green for this patch:
> https://sashiko.dev/#/patchset/20260519223855.191637-1-mpetlan%40redhat.com

Thanks, applied to perf-tools-next, for v7.2.

- Arnaldo

Re: [PATCH] perf build-id: Fix off-by-one bug when printing kernel/module build-id

[Namhyung Kim]

On Wed, May 20, 2026 at 03:51:12PM -0300, Arnaldo Carvalho de Melo wrote:
> On Wed, May 20, 2026 at 08:55:51AM -0700, Ian Rogers wrote:
> > On Tue, May 19, 2026 at 3:39 PM Michael Petlan <mpetlan@redhat.com> wrote:
> > >
> > > When changing sprintf functions to snprintf, one byte got lost. Since
> > > snprintf ones do not handle the '\0' terminating character, the number
> > > of printed characters is 40, while sizeof(sbuild_id) is 41, including
> > > the terminating '\0' character. This makes the later check fail so that
> > > nothing is printed.
> > >
> > > Fix that.
> > >
> > > Before:
> > >     [Michael@Carbon ~]$ perf buildid-list -k
> > >     [Michael@Carbon ~]$
> > >
> > > After:
> > >     [Michael@Carbon ~]$ perf buildid-list -k
> > >     a527806324d543c4bc3ff2f9c9519d494fed5f68
> > >     [Michael@Carbon ~]$
> > >
> > > Fixes: fccaaf6fbbc5 ("perf build-id: Change sprintf functions to snprintf")
> > >
> > > Signed-off-by: Michael Petlan <mpetlan@redhat.com>
> > 
> > Tested-by: Ian Rogers <irogers@google.com>
> > also Sashiko is green for this patch:
> > https://sashiko.dev/#/patchset/20260519223855.191637-1-mpetlan%40redhat.com
> 
> Thanks, applied to perf-tools-next, for v7.2.

I sent out this a month ago, but forgot to ping for inclusion.

https://lore.kernel.org/linux-perf-users/20260420180858.129075-1-namhyung@kernel.org/

Anyway, I'm ok with fixing it either way.

Thanks,
Namhyung