[PATCH] Add CTF support to GDB [2/4] Fix a bug of function dwarf_expr_frame_base

[Hui Zhu <hui_zhu@mentor.com>]

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After I add prev patch to GDB, the GDB got crash when a trace frame didn't include all the variables that it should include.
I think this issue should be handle because the trace frame didn't include all the variables will be always happen (What I use is GDB and gdbserver).
So I post this patch to handle it.

Thanks,
Hui

2012-11-20  Hui Zhu  <hui_zhu@mentor.com>

	* dwarf2loc.c (dwarf_expr_frame_base): Add check for the return
	value of get_frame_block.

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--- a/dwarf2loc.c
+++ b/dwarf2loc.c
@@ -332,11 +332,15 @@ dwarf_expr_frame_base (void *baton, cons
      this_base method.  */
   struct symbol *framefunc;
   struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
+  struct block *bl = get_frame_block (debaton->frame, NULL);
+
+  if (bl == NULL)
+    error (_("No symbol table info available.\n"));
 
   /* Use block_linkage_function, which returns a real (not inlined)
      function, instead of get_frame_function, which may return an
      inlined function.  */
-  framefunc = block_linkage_function (get_frame_block (debaton->frame, NULL));
+  framefunc = block_linkage_function (bl);
 
   /* If we found a frame-relative symbol then it was certainly within
      some function associated with a frame. If we can't find the frame,