powerpc/uaccess: Remove calls to __get_user_bad() and __put_user_bad()

__get_user_bad() and __put_user_bad() are functions that are
declared but not defined, in order to make the link fail in
case they are called.

Nowadays, we have BUILD_BUG() and BUILD_BUG_ON() for that, and
they have the advantage to break the build earlier as it breaks
it at compile time instead of link time.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/d7d839e994f49fae4ff7b70fac72bd951272436b.1615398265.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/uaccess.h

@@ -53,8 +53,6 @@ static inline bool __access_ok(unsigned long addr, unsigned long size)
 #define __put_user(x, ptr) \
 	__put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
 
-extern long __put_user_bad(void);
-
 #define __put_user_size(x, ptr, size, retval)			\
 do {								\
 	__label__ __pu_failed;					\
@@ -136,12 +134,10 @@ do {								\
 	case 2: __put_user_asm_goto(x, __pus_addr, label, "sth"); break;	\
 	case 4: __put_user_asm_goto(x, __pus_addr, label, "stw"); break;	\
 	case 8: __put_user_asm2_goto(x, __pus_addr, label); break;		\
-	default: __put_user_bad();				\
+	default: BUILD_BUG();					\
 	}							\
 } while (0)
 
-extern long __get_user_bad(void);
-
 /*
  * This does an atomic 128 byte aligned load from userspace.
  * Upto caller to do enable_kernel_vmx() before calling!
@@ -196,14 +192,13 @@ extern long __get_user_bad(void);
 #define __get_user_size_allowed(x, ptr, size, retval)		\
 do {								\
 	retval = 0;						\
-	if (size > sizeof(x))					\
-		(x) = __get_user_bad();				\
+	BUILD_BUG_ON(size > sizeof(x));				\
 	switch (size) {						\
 	case 1: __get_user_asm(x, (u8 __user *)ptr, retval, "lbz"); break;	\
 	case 2: __get_user_asm(x, (u16 __user *)ptr, retval, "lhz"); break;	\
 	case 4: __get_user_asm(x, (u32 __user *)ptr, retval, "lwz"); break;	\
 	case 8: __get_user_asm2(x, (u64 __user *)ptr, retval);  break;	\
-	default: (x) = __get_user_bad();			\
+	default: BUILD_BUG();					\
 	}							\
 } while (0)