m68k: Fix xchg/cmpxchg to fail to link if given an inappropriate pointer

Fix the m68k versions of xchg() and cmpxchg() to fail to link if given an
inappropriately sized pointer rather than BUG()'ing at runtime.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Greg Ungerer <gerg@uclinux.org>
cc: linux-m68k@lists.linux-m68k.org

arch/m68k/include/asm/system.h

@@ -68,6 +68,8 @@ asmlinkage void resume(void);
 struct __xchg_dummy { unsigned long a[100]; };
 #define __xg(x) ((volatile struct __xchg_dummy *)(x))
 
+extern unsigned long __invalid_xchg_size(unsigned long, volatile void *, int);
+
 #ifndef CONFIG_RMW_INSNS
 static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int size)
 {
@@ -92,7 +94,8 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz
 		x = tmp;
 		break;
 	default:
-		BUG();
+		tmp = __invalid_xchg_size(x, ptr, size);
+		break;
 	}
 
 	local_irq_restore(flags);
@@ -126,6 +129,9 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz
 			 "jne 1b"
 			 : "=&d" (x) : "d" (x), "m" (*__xg(ptr)) : "memory");
 		break;
+	default:
+		x = __invalid_xchg_size(x, ptr, size);
+		break;
 	}
 	return x;
 }
@@ -135,6 +141,9 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz
 
 #define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
 
+extern unsigned long __invalid_cmpxchg_size(volatile void *,
+					    unsigned long, unsigned long, int);
+
 /*
  * Atomic compare and exchange.  Compare OLD with MEM, if identical,
  * store NEW in MEM.  Return the initial value in MEM.  Success is
@@ -162,6 +171,9 @@ static inline unsigned long __cmpxchg(volatile void *p, unsigned long old,
 				      : "=d" (old), "=m" (*(int *)p)
 				      : "d" (new), "0" (old), "m" (*(int *)p));
 		break;
+	default:
+		old = __invalid_cmpxchg_size(p, old, new, size);
+		break;
 	}
 	return old;
 }