[PATCH 1/5] perf dso: Guard against errno==0 when dso__get_filename() returns NULL

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

__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.

Fixes: eba5102d2f0b ("perf tools: Add global list of opened dso objects")
Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/dso.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 2309196d8df3111c..fcd4b462992be6f2 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -640,10 +640,13 @@ static int __open_dso(struct dso *dso, struct machine *machine)
 	mutex_lock(dso__lock(dso));
 
 	name = dso__get_filename(dso, machine ? machine->root_dir : "", &decomp);
-	if (name)
+	if (name) {
 		fd = do_open(name);
-	else
+	} else {
+		if (errno == 0)
+			errno = ENOENT;
 		fd = -errno;
+	}
 
 	if (decomp)
 		unlink(name);
-- 
2.55.0