[PATCH] i386: Add a temporary to make put_user more type safe

In some code I am developing I had occasion to change the type of a
variable.  This made the value put_user was putting to user space wrong.
But the code continued to build cleanly without errors.

Introducing a temporary fixes this problem and at least with gcc-3.3.5 does
not cause gcc any problems with optimizing out the temporary.  gcc-4.x
using SSA internally ought to be even better at optimizing out temporaries,
so I don't expect a temporary to become a problem.  Especially because in
all correct cases the types on both sides of the assignment to the
temporary are the same.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/asm-i386/uaccess.h

@@ -197,13 +197,15 @@ extern void __put_user_8(void);
 
 #define put_user(x,ptr)						\
 ({	int __ret_pu;						\
+	__typeof__(*(ptr)) __pu_val;				\
 	__chk_user_ptr(ptr);					\
+	__pu_val = x;						\
 	switch(sizeof(*(ptr))) {				\
-	case 1: __put_user_1(x, ptr); break;			\
-	case 2: __put_user_2(x, ptr); break;			\
-	case 4: __put_user_4(x, ptr); break;			\
-	case 8: __put_user_8(x, ptr); break;			\
-	default:__put_user_X(x, ptr); break;			\
+	case 1: __put_user_1(__pu_val, ptr); break;		\
+	case 2: __put_user_2(__pu_val, ptr); break;		\
+	case 4: __put_user_4(__pu_val, ptr); break;		\
+	case 8: __put_user_8(__pu_val, ptr); break;		\
+	default:__put_user_X(__pu_val, ptr); break;		\
 	}							\
 	__ret_pu;						\
 })