FYI: fix possible memory leak in dwarf expression evaluation

[Tom Tromey <tromey at redhat dot com>]

I'm checking this in.

If evaluation of a dwarf expression causes a call to error(), the dwarf
expression context will be leaked.  I found this by reading the code.

The fix is to install a cleanup that destroys the context.

Built and regtested on x86-64 (compile farm).

Tom

2009-08-11  Tom Tromey  <tromey@redhat.com>

	* dwarf2loc.c (dwarf2_evaluate_loc_desc): Make a cleanup.
	(dwarf2_loc_desc_needs_frame): Likewise.
	* dwarf2expr.h (make_cleanup_free_dwarf_expr_context): Declare.
	* dwarf2expr.c (free_dwarf_expr_context_cleanup): New function.
	(make_cleanup_free_dwarf_expr_context): Likewise.
	* dwarf2-frame.c (execute_stack_op): Make a cleanup.

Index: dwarf2-frame.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2-frame.c,v
retrieving revision 1.95
diff -u -r1.95 dwarf2-frame.c
--- dwarf2-frame.c	6 Aug 2009 23:25:49 -0000	1.95
+++ dwarf2-frame.c	11 Aug 2009 20:35:54 -0000
@@ -352,8 +352,11 @@
 {
   struct dwarf_expr_context *ctx;
   CORE_ADDR result;
+  struct cleanup *old_chain;
 
   ctx = new_dwarf_expr_context ();
+  old_chain = make_cleanup_free_dwarf_expr_context (ctx);
+
   ctx->gdbarch = get_frame_arch (this_frame);
   ctx->addr_size = addr_size;
   ctx->baton = this_frame;
@@ -369,7 +372,7 @@
   if (ctx->in_reg)
     result = read_reg (this_frame, result);
 
-  free_dwarf_expr_context (ctx);
+  do_cleanups (old_chain);
 
   return result;
 }
Index: dwarf2expr.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2expr.c,v
retrieving revision 1.33
diff -u -r1.33 dwarf2expr.c
--- dwarf2expr.c	10 Jul 2009 15:27:02 -0000	1.33
+++ dwarf2expr.c	11 Aug 2009 20:35:54 -0000
@@ -61,6 +61,22 @@
   xfree (ctx);
 }
 
+/* Helper for make_cleanup_free_dwarf_expr_context.  */
+
+static void
+free_dwarf_expr_context_cleanup (void *arg)
+{
+  free_dwarf_expr_context (arg);
+}
+
+/* Return a cleanup that calls free_dwarf_expr_context.  */
+
+struct cleanup *
+make_cleanup_free_dwarf_expr_context (struct dwarf_expr_context *ctx)
+{
+  return make_cleanup (free_dwarf_expr_context_cleanup, ctx);
+}
+
 /* Expand the memory allocated to CTX's stack to contain at least
    NEED more elements than are currently used.  */
 
Index: dwarf2expr.h
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2expr.h,v
retrieving revision 1.15
diff -u -r1.15 dwarf2expr.h
--- dwarf2expr.h	3 Jan 2009 05:57:51 -0000	1.15
+++ dwarf2expr.h	11 Aug 2009 20:35:54 -0000
@@ -131,6 +131,8 @@
 
 struct dwarf_expr_context *new_dwarf_expr_context (void);
 void free_dwarf_expr_context (struct dwarf_expr_context *ctx);
+struct cleanup *
+    make_cleanup_free_dwarf_expr_context (struct dwarf_expr_context *ctx);
 
 void dwarf_expr_push (struct dwarf_expr_context *ctx, CORE_ADDR value);
 void dwarf_expr_pop (struct dwarf_expr_context *ctx);
Index: dwarf2loc.c
===================================================================
RCS file: /cvs/src/src/gdb/dwarf2loc.c,v
retrieving revision 1.62
diff -u -r1.62 dwarf2loc.c
--- dwarf2loc.c	20 Jul 2009 15:06:13 -0000	1.62
+++ dwarf2loc.c	11 Aug 2009 20:35:54 -0000
@@ -215,6 +215,7 @@
   struct value *retval;
   struct dwarf_expr_baton baton;
   struct dwarf_expr_context *ctx;
+  struct cleanup *old_chain;
 
   if (size == 0)
     {
@@ -228,6 +229,8 @@
   baton.objfile = dwarf2_per_cu_objfile (per_cu);
 
   ctx = new_dwarf_expr_context ();
+  old_chain = make_cleanup_free_dwarf_expr_context (ctx);
+
   ctx->gdbarch = get_objfile_arch (baton.objfile);
   ctx->addr_size = dwarf2_per_cu_addr_size (per_cu);
   ctx->baton = &baton;
@@ -282,7 +285,7 @@
 
   set_value_initialized (retval, ctx->initialized);
 
-  free_dwarf_expr_context (ctx);
+  do_cleanups (old_chain);
 
   return retval;
 }
@@ -346,10 +349,13 @@
   struct needs_frame_baton baton;
   struct dwarf_expr_context *ctx;
   int in_reg;
+  struct cleanup *old_chain;
 
   baton.needs_frame = 0;
 
   ctx = new_dwarf_expr_context ();
+  old_chain = make_cleanup_free_dwarf_expr_context (ctx);
+
   ctx->gdbarch = get_objfile_arch (dwarf2_per_cu_objfile (per_cu));
   ctx->addr_size = dwarf2_per_cu_addr_size (per_cu);
   ctx->baton = &baton;
@@ -373,7 +379,7 @@
           in_reg = 1;
     }
 
-  free_dwarf_expr_context (ctx);
+  do_cleanups (old_chain);
 
   return baton.needs_frame || in_reg;
 }