Don't return stale data from fbsd_pid_to_exec_file for kernel processes.

For processes without an associated executable (such as kernel processes),
the kern.proc.pathname.<pid> system control node returns a length of zero
without modifying the user's buffer.  Detect this case and return NULL
rather than the previous contents of the static buffer 'buf'.

gdb/ChangeLog:

	* fbsd-nat.c (fbsd_pid_to_exec_file) [KERN_PROC_PATHNAME]: Return
	NULL for an empty pathname.

1 files changed, 4 insertions, 1 deletions

diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index ec4eed9..d0aaf89 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -63,7 +63,10 @@ fbsd_pid_to_exec_file (struct target_ops *self, int pid)
   mib[3] = pid;
   buflen = sizeof buf;
   if (sysctl (mib, 4, buf, &buflen, NULL, 0) == 0)
-    return buf;
+    /* The kern.proc.pathname.<pid> sysctl returns a length of zero
+       for processes without an associated executable such as kernel
+       processes.  */
+    return buflen == 0 ? NULL : buf;
 #endif
 
   xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);