perf dso: Guard against errno==0 when dso__get_filename() returns NULL

__open_dso() computes fd = -errno when dso__get_filename() returns NULL.
Some failure paths in dso__get_filename() (e.g. binary type mismatch)
return NULL without making a syscall, leaving errno at 0 from a prior
successful call.  fd = -0 = 0, which is stdin — subsequent code treats
it as a valid file descriptor.

Fall back to ENOENT when errno is 0, ensuring fd is always negative on
failure.

The forced ENOENT stays in errno for the callers that check it after a
negative fd.  It must not misdirect the try_to_open_dso() fallback
loop, though: dso__get_filename()'s chroot fallback used to accept a
stale ENOENT even when stat() succeeded on a non-regular file (e.g. a
directory).  Re-stat() there and only take the chroot path when
stat() actually failed with ENOENT [sashiko-bot review of PATCH 1/5].

Fixes: eba5102d2f0b ("perf tools: Add global list of opened dso objects")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Reviewed-by: Ian Rogers <irogers@google.com>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

0 files changed, 0 insertions, 0 deletions