Re: [PATCH v1] perf symbol: Fix ENOENT case for filename__read_build_id

[James Clark <james.clark@linaro.org>]

On 07/12/2025 2:23 am, Ian Rogers 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")
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
> Note, a shorter version of this patch appeared in a series
> cleaning/refactoring the build id reading code:
> https://lore.kernel.org/lkml/20251201205509.195451-11-irogers@google.com/
> It is sent without the refactor for the sake of fixing the bug in an
> earlier release.

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

> ---
>   tools/perf/builtin-buildid-cache.c | 6 ++++--
>   tools/perf/util/libbfd.c           | 4 +++-
>   tools/perf/util/symbol-elf.c       | 4 +++-
>   tools/perf/util/symbol-minimal.c   | 4 +++-
>   4 files changed, 13 insertions(+), 5 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) {
> -		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/libbfd.c b/tools/perf/util/libbfd.c
> index 0099b415decc..edf0829e9635 100644
> --- a/tools/perf/util/libbfd.c
> +++ b/tools/perf/util/libbfd.c
> @@ -391,8 +391,10 @@ int libbfd__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;
>   
>   	fd = open(filename, O_RDONLY);
>   	if (fd < 0)
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index 957143fbf8a0..d1dcafa4b3b8 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -902,8 +902,10 @@ 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;
>   
>   	err = kmod_path__parse(&m, filename);
>   	if (err)
> diff --git a/tools/perf/util/symbol-minimal.c b/tools/perf/util/symbol-minimal.c
> index c6b17c14a2e9..8221dc9868f7 100644
> --- a/tools/perf/util/symbol-minimal.c
> +++ b/tools/perf/util/symbol-minimal.c
> @@ -104,8 +104,10 @@ 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;
>   
>   	fd = open(filename, O_RDONLY);
>   	if (fd < 0)