[PATCH v2 2/5] Don't return stale data from fbsd_pid_to_exec_file for kernel processes.

[John Baldwin <jhb@FreeBSD.org>]

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.
---
 gdb/ChangeLog  | 5 +++++
 gdb/fbsd-nat.c | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 29cfbb287b..804dd4f402 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-01-03  John Baldwin  <jhb@FreeBSD.org>
+
+	* fbsd-nat.c (fbsd_pid_to_exec_file) [KERN_PROC_PATHNAME]: Return
+	NULL for an empty pathname.
+
 2018-01-03  John Baldwin  <jhb@FreeBSD.org>
 
 	* fbsd-tdep.c (KVE_STRUCTSIZE, KVE_START, KVE_END, KVE_OFFSET)
diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
index ec4eed9abe..7b1d1bf148 100644
--- a/gdb/fbsd-nat.c
+++ b/gdb/fbsd-nat.c
@@ -63,7 +63,7 @@ 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;
+    return buflen == 0 ? NULL : buf;
 #endif
 
   xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
-- 
2.15.1