[PATCH] infcmd.c: Don't attempt to record a NULL value after a finish command

[Kevin Buettner <kevinb@redhat.com>]

Architectures which use RETURN_VALUE_STRUCT_CONVENTION will have a
NULL return value after executing a finish command.  See get_return_value()
in infcmd.c.

This patch avoids an eventual SIGSEV (caused by attempting to
derefrence a NULL pointer) by adding a suitable test to
finish_command_fsm_should_stop().

I encountered this problem while testing msp430:

(gdb) PASS: gdb.base/structs.exp: zed L<n> for finish; return 1 structs-tc
finish
Run till exit from #0  fun1 () at /ironwood1/sourceware-git/msp430-elf/../binutils-gdb/gdb/testsuite/gdb.base/structs.c:125
ERROR: Process no longer exists

gdb/ChangeLog:
    	* infcmd.c (finish_command_fsm_should_stop): Don't attempt to
    	record a NULL value.
---
 gdb/infcmd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index c4d7d8b..6be95e4 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1788,7 +1788,7 @@ finish_command_fsm_should_stop (struct thread_fsm *self)
 	internal_error (__FILE__, __LINE__,
 			_("finish_command: function has no target type"));
 
-      if (TYPE_CODE (rv->type) != TYPE_CODE_VOID)
+      if (rv->value != NULL && TYPE_CODE (rv->type) != TYPE_CODE_VOID)
 	{
 	  struct value *func;