"strict" weak aliases

[David Young <dyoung%pobox.com@localhost>]

Sometimes it is important that the type of an object matches the
type of its weak alias.  See the attached patch that both adds a
type-safe __weak_alias() called __strict_weak_alias(), and fixes a buggy
__weak_alias() that __strict_weak_alias() would have caught during
compilation.

Thanks to Taylor R. Campbell for the incantation that was key
to making this work,

__unused static typeof(alias) *__weak_alias_##alias = &sym;

Does this look ok to commit?

Dave

-- 
David Young             OJC Technologies
dyoung%ojctech.com@localhost      Urbana, IL * (217) 344-0444 x24

Index: sys/sys/cdefs.h
===================================================================
RCS file: /cvsroot/src/sys/sys/cdefs.h,v
retrieving revision 1.86
diff -u -p -r1.86 cdefs.h
--- sys/sys/cdefs.h     23 Jun 2011 12:16:03 -0000      1.86
+++ sys/sys/cdefs.h     21 Jul 2011 19:04:12 -0000
@@ -63,6 +63,14 @@
 #include <sys/cdefs_aout.h>
 #endif
 
+#ifdef __GNUC__
+#define        __strict_weak_alias(alias,sym)                                  
\
+       __unused static typeof(alias) *__weak_alias_##alias = &sym;     \
+       __weak_alias(alias,sym)
+#else
+#define        __strict_weak_alias(alias,sym) __weak_alias(alias,sym)
+#endif
+
 /*
  * Optional marker for size-optimised MD calling convention.
  */
Index: sys/kern/kern_stub.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_stub.c,v
retrieving revision 1.34
diff -u -p -r1.34 kern_stub.c
--- sys/kern/kern_stub.c        6 Jul 2011 18:24:26 -0000       1.34
+++ sys/kern/kern_stub.c        21 Jul 2011 19:04:13 -0000
@@ -82,7 +82,8 @@ __KERNEL_RCSID(0, "$NetBSD: kern_stub.c,
 #include <sys/userconf.h>
 
 bool default_bus_space_is_equal(bus_space_tag_t, bus_space_tag_t);
-bool default_bus_space_handle_is_equal(bus_space_handle_t, bus_space_handle_t);
+bool default_bus_space_handle_is_equal(bus_space_tag_t, bus_space_handle_t,
+    bus_space_handle_t);
 
 /*
  * Nonexistent system call-- signal process (may want to handle it).  Flag
@@ -137,8 +138,9 @@ __weak_alias(bus_space_reservation_map, 
 __weak_alias(bus_space_reservation_unmap, voidop);
 __weak_alias(bus_space_tag_create, eopnotsupp);
 __weak_alias(bus_space_tag_destroy, voidop);
-__weak_alias(bus_space_is_equal, default_bus_space_is_equal);
-__weak_alias(bus_space_handle_is_equal, default_bus_space_handle_is_equal);
+__strict_weak_alias(bus_space_is_equal, default_bus_space_is_equal);
+__strict_weak_alias(bus_space_handle_is_equal,
+    default_bus_space_handle_is_equal);
 __weak_alias(userconf_bootinfo, voidop);
 __weak_alias(userconf_init, voidop);
 __weak_alias(userconf_prompt, voidop);
@@ -277,7 +279,8 @@ nullop(void *v)
 }
 
 bool
-default_bus_space_handle_is_equal(bus_space_handle_t h1, bus_space_handle_t h2)
+default_bus_space_handle_is_equal(bus_space_tag_t t,
+    bus_space_handle_t h1, bus_space_handle_t h2)
 {
 
        return memcmp(&h1, &h2, sizeof(h1)) == 0;