Re: [PATCH v2 10/10] perf symbol: Fix ENOENT case for filename__read_build_id

[Ian Rogers]

On Mon, Dec 1, 2025 at 12:55 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> Some callers of filename__read_build_id assume the error value must be
> -1, fix by making them handle all < 0 values.
>
> If is_regular_file fails in filename__read_build_id then it could be
> the file is missing (ENOENT) and it would be wrong to return
> -EWOULDBLOCK in that case. Fix the logic so -EWOULDBLOCK is only
> reported if other errors with stat haven't occurred.
>
> Fixes: 834ebb5678d7 ("perf tools: Don't read build-ids from non-regular files")

We might want to prioritize this fix.

> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/builtin-buildid-cache.c | 6 ++++--
>  tools/perf/util/symbol.c           | 3 ++-
>  2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/builtin-buildid-cache.c b/tools/perf/builtin-buildid-cache.c
> index c98104481c8a..539e779e3268 100644
> --- a/tools/perf/builtin-buildid-cache.c
> +++ b/tools/perf/builtin-buildid-cache.c
> @@ -276,12 +276,14 @@ static bool dso__missing_buildid_cache(struct dso *dso, int parm __maybe_unused)
>  {
>         char filename[PATH_MAX];
>         struct build_id bid = { .size = 0, };
> +       int err;
>
>         if (!dso__build_id_filename(dso, filename, sizeof(filename), false))
>                 return true;
>
> -       if (filename__read_build_id(filename, &bid) == -1) {

This check here is clearly wrong when -EWOULDBLOCK is returned from
James' change.

> -               if (errno == ENOENT)
> +       err = filename__read_build_id(filename, &bid);
> +       if (err < 0) {
> +               if (err == -ENOENT)
>                         return false;
>
>                 pr_warning("Problems with %s file, consider removing it from the cache\n",
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 76dc5b70350a..f43e30019e21 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -2008,8 +2008,9 @@ int filename__read_build_id(const char *filename, struct build_id *bid)
>         if (!filename)
>                 return -EFAULT;
>
> +       errno = 0;
>         if (!is_regular_file(filename))
> -               return -EWOULDBLOCK;
> +               return errno == 0 ? -EWOULDBLOCK : -errno;

I've made the fix after the other changes as it is simpler to fix in
one filename__read_build_id rather than all the libbfd, .. variants.
If we don't want the series in the short-term perhaps we still want to
carry some parts of this fix.

Thanks,
Ian

>
>         err = kmod_path__parse(&m, filename);
>         if (err)
> --
> 2.52.0.158.g65b55ccf14-goog
>