[PATCH] gdb: Don't leak memory with TYPE_ALLOC / TYPE_ZALLOC

[Andrew Burgess <andrew.burgess@embecosm.com>]

I ran into the following issue after runnig valgrind on GDB.

Calling TYPE_ALLOC or TYPE_ZALLOC currently allocates memory from
either the objfile obstack or by using malloc.  The problem with this
is that types are allocated either on the objfile obstack, or on the
gdbarch obstack.

As a result, if we discard a type associated with an objfile then
auxiliary data allocated with TYPE_(Z)ALLOC will be correctly
discarded.  But, if we were ever to discard a gdbarch then any
auxiliary type data would be leaked.

This commit ensures that auxiliary type data is allocated from the
same obstack as the type itself, which should reduce leaked memory.

The one problem case that I found with this change was in eval.c,
where in one place we allocate a local type structure, and then used
TYPE_ZALLOC to allocate some space for the type.  This local type is
neither object file owned, nor gdbarch owned, and so the updated
TYPE_ALLOC code is unable to find an objstack to allocate space on.

My proposed solution for this issue is that the space should be
allocated with a direct call to xzalloc.  We could extend TYPE_ALLOC
to check for type->gdbarch being null, and then fall back to a direct
call to xzalloc, however, I think making the rare case of a local type
requiring special handling is not a bad thing, this serves to
highlight that clearing up the memory will require special handling
too.

Tested on X86-64 GNU/Linux with no regressions.

gdb/ChangeLog:

	* gdbtypes.h (TYPE_ALLOC): Allocate space on either the objfile
	obstack, or the gdbarch obstack.
	(TYPE_ZALLOC): Rewrite using TYPE_ALLOC.
	* eval.c (fake_method::fake_method): Call xzalloc directly for a
	type that is neither object file owned, nor gdbarch owned.
---
 gdb/ChangeLog  |  8 ++++++++
 gdb/eval.c     |  2 +-
 gdb/gdbtypes.h | 36 ++++++++++++++++++++----------------
 3 files changed, 29 insertions(+), 17 deletions(-)

diff --git a/gdb/eval.c b/gdb/eval.c
index 2e08e9355f5..baa98e17545 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -685,7 +685,7 @@ fake_method::fake_method (type_instance_flags flags,
 
   TYPE_NFIELDS (type) = num_types;
   TYPE_FIELDS (type) = (struct field *)
-    TYPE_ZALLOC (type, sizeof (struct field) * num_types);
+    xzalloc (sizeof (struct field) * num_types);
 
   while (num_types-- > 0)
     TYPE_FIELD_TYPE (type, num_types) = param_types[num_types];
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index eb7c365b71d..3778b46839c 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -49,6 +49,7 @@
 #include "common/enum-flags.h"
 #include "common/underlying.h"
 #include "common/print-utils.h"
+#include "gdbarch.h"
 
 /* Forward declarations for prototypes.  */
 struct field;
@@ -1717,26 +1718,29 @@ extern const struct floatformat *floatformats_vax_d[BFD_ENDIAN_UNKNOWN];
 extern const struct floatformat *floatformats_ibm_long_double[BFD_ENDIAN_UNKNOWN];
 
 
-/* * Allocate space for storing data associated with a particular
+/* Allocate space for storing data associated with a particular
    type.  We ensure that the space is allocated using the same
    mechanism that was used to allocate the space for the type
    structure itself.  I.e.  if the type is on an objfile's
    objfile_obstack, then the space for data associated with that type
-   will also be allocated on the objfile_obstack.  If the type is not
-   associated with any particular objfile (such as builtin types),
-   then the data space will be allocated with xmalloc, the same as for
-   the type structure.  */
-
-#define TYPE_ALLOC(t,size)  \
-   (TYPE_OBJFILE_OWNED (t) \
-    ? obstack_alloc (&TYPE_OBJFILE (t) -> objfile_obstack, size) \
-    : xmalloc (size))
-
-#define TYPE_ZALLOC(t,size)  \
-   (TYPE_OBJFILE_OWNED (t) \
-    ? memset (obstack_alloc (&TYPE_OBJFILE (t)->objfile_obstack, size),  \
-	      0, size)  \
-    : xzalloc (size))
+   will also be allocated on the objfile_obstack.  If the type is
+   associated with a gdbarch, then the space for data associated with that
+   type will also be allocated on the gdbarch_obstack.
+
+   If a type is not associated with neither an objfile or a gdbarch then
+   you should not use this macro to allocate space for data, instead you
+   should call xmalloc directly, and ensure the memory is correctly freed
+   when it is no longer needed.  */
+
+#define TYPE_ALLOC(t,size)                                              \
+  (obstack_alloc ((TYPE_OBJFILE_OWNED (t)                               \
+                   ? &TYPE_OBJFILE (t)->objfile_obstack                 \
+                   : gdbarch_obstack (TYPE_OWNER (t).gdbarch)),         \
+                  size))
+
+/* See comment on TYPE_ALLOC.  */
+
+#define TYPE_ZALLOC(t,size) (memset (TYPE_ALLOC (t, size), 0, size))
 
 /* Use alloc_type to allocate a type owned by an objfile.  Use
    alloc_type_arch to allocate a type owned by an architecture.  Use
-- 
2.14.4