[PATCH 1/2] Use gdbarch obstack to allocate types in alloc_type_arch

[Patrick Palka <patrick@parcs.ath.cx>]

For the command "gdb gdb" valgrind currently reports 100s of individual
memory leaks, 500 of which originate solely out of the function
alloc_type_arch.  This function allocates a "struct type" associated
with the given gdbarch using malloc but apparently the types allocated
by this function are never freed.

This patch fixes these leaks by making the function alloc_type_arch
allocate these gdbarch-associated types on the gdbarch obstack instead
of on the general heap.  Since, from what I can tell, the types
allocated by this function are all fundamental "wired-in" types, such
types would not benefit from more granular memory management anyway.
They would likely live as long as the gdbarch is alive so allocating
them on the gdbarch obstack makes sense.

With this patch, the number of individual vargrind warnings emitted for
the command "gdb gdb" drops from ~800 to ~300.

Tested on x86_64-unknown-linux-gnu.  Does this fix make sense?  It may
not be ideal (more disciplined memory management may be?), but for the
time being it helps reduce the noise coming from valgrind.  Or maybe
there is a good reason that these types are allocated on the heap...

gdb/ChangeLog:

	* gdbtypes.c (alloc_type_arch): Allocate the type on the given
	gdbarch obstack instead of on the heap.  Update commentary
	accordingly.
---
 gdb/gdbtypes.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index ca86fbd..979ed6c 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -187,7 +187,7 @@ alloc_type (struct objfile *objfile)
 
 /* Allocate a new GDBARCH-associated type structure and fill it
    with some defaults.  Space for the type structure is allocated
-   on the heap.  */
+   on the obstack associated with GDBARCH.  */
 
 struct type *
 alloc_type_arch (struct gdbarch *gdbarch)
@@ -198,8 +198,8 @@ alloc_type_arch (struct gdbarch *gdbarch)
 
   /* Alloc the structure and start off with all fields zeroed.  */
 
-  type = XCNEW (struct type);
-  TYPE_MAIN_TYPE (type) = XCNEW (struct main_type);
+  type = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct type);
+  TYPE_MAIN_TYPE (type) = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct main_type);
 
   TYPE_OBJFILE_OWNED (type) = 0;
   TYPE_OWNER (type).gdbarch = gdbarch;
-- 
2.5.0.rc0.5.g91e10c5.dirty