Avoid uninitialized result in sem_open when file does not exist

A static analyzer apparently reported an uninitialized use of the
variable result in sem_open in the case where the file is required to
exist but does not exist.

The report appears to be correct; set result to SEM_FAILED in that
case, and add a test for it.

Note: the test passes for me even without the sem_open fix, I guess
because result happens to get value SEM_FAILED (i.e. 0) when
uninitialized.

Tested for x86_64.

3 files changed, 37 insertions, 0 deletions

diff --git a/sysdeps/pthread/Makefile b/sysdeps/pthread/Makefile
index 4c1dc04..7f52e7d 100644
--- a/sysdeps/pthread/Makefile
+++ b/sysdeps/pthread/Makefile
@@ -256,6 +256,7 @@ tests += \
   tst-sem14 \
   tst-sem15 \
   tst-sem16 \
+  tst-sem17 \
   tst-setuid3 \
   tst-signal1 \
   tst-signal2 \
diff --git a/sysdeps/pthread/sem_open.c b/sysdeps/pthread/sem_open.c
index e412361..dab7341 100644
--- a/sysdeps/pthread/sem_open.c
+++ b/sysdeps/pthread/sem_open.c
@@ -76,6 +76,7 @@ __sem_open (const char *name, int oflag, ...)
 	    goto try_create;
 
 	  /* Return.  errno is already set.  */
+	  result = SEM_FAILED;
 	}
       else
 	/* Check whether we already have this semaphore mapped and
diff --git a/sysdeps/pthread/tst-sem17.c b/sysdeps/pthread/tst-sem17.c
new file mode 100644
index 0000000..c3f05d1
--- /dev/null
+++ b/sysdeps/pthread/tst-sem17.c
@@ -0,0 +1,35 @@
+/* Test sem_open with missing file.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <semaphore.h>
+
+#include <support/check.h>
+
+int
+do_test (void)
+{
+  sem_unlink ("/glibc-tst-sem17");
+  errno = 0;
+  sem_t *s = sem_open ("/glibc-tst-sem17", 0);
+  TEST_VERIFY (s == SEM_FAILED);
+  TEST_COMPARE (errno, ENOENT);
+  return 0;
+}
+
+#include <support/test-driver.c>