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 <[e-mail]>
Acked-by: Greg Ungerer <[e-mail]>
cc: [e-mail]

arch/m68k/include/asm/system.h

···
 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)
 {
···
 		x = tmp;
 		break;
 	default:
-		BUG();
+		tmp = __invalid_xchg_size(x, ptr, size);
+		break;
 	}
 
 	local_irq_restore(flags);
···
 static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int size)
 {
 	switch (size) {
-	    case 1:
+	case 1:
 		__asm__ __volatile__
 			("moveb %2,%0\n\t"
 			 "1:\n\t"
···
 			 "jne 1b"
 			 : "=&d" (x) : "d" (x), "m" (*__xg(ptr)) : "memory");
 		break;
-	    case 2:
+	case 2:
 		__asm__ __volatile__
 			("movew %2,%0\n\t"
 			 "1:\n\t"
···
 			 "jne 1b"
 			 : "=&d" (x) : "d" (x), "m" (*__xg(ptr)) : "memory");
 		break;
-	    case 4:
+	case 4:
 		__asm__ __volatile__
 			("movel %2,%0\n\t"
 			 "1:\n\t"
 			 "casl %0,%1,%2\n\t"
 			 "jne 1b"
 			 : "=&d" (x) : "d" (x), "m" (*__xg(ptr)) : "memory");
+		break;
+	default:
+		x = __invalid_xchg_size(x, ptr, size);
 		break;
 	}
 	return x;
···
 #include <asm-generic/cmpxchg-local.h>
 
 #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,
···
 		__asm__ __volatile__ ("casl %0,%2,%1"
 				      : "=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;