Re: [uml-devel] Real fix for rejected patch uaccess-warning

[Jeff Dike <jdike@addtoit.com>]

On Fri, Mar 10, 2006 at 04:22:41PM +0100, Blaisorblade wrote:
> 686:		if (get_user(c, buf))
> where "buf" is a "const char __user *".
> 
> It's complaining because "const" was lost.
> 
> Ultimately, I think we should remove all this copying of pointers and do like
> i386 in this regard - there is only one cast to do, in put_user, as I 
> mentioned in last mail.

OK, my first patch was insane, try this one:

Index: linux-2.6.15/include/asm-um/uaccess.h
===================================================================
--- linux-2.6.15.orig/include/asm-um/uaccess.h	2006-03-23 15:41:15.000000000 -0500
+++ linux-2.6.15/include/asm-um/uaccess.h	2006-03-23 15:48:52.000000000 -0500
@@ -42,10 +42,10 @@
 #define __get_user(x, ptr) \
 ({ \
         const __typeof__(ptr) __private_ptr = ptr; \
-        __typeof__(*(__private_ptr)) __private_val; \
+        __typeof__(x) __private_val; \
         int __private_ret = -EFAULT; \
         (x) = (__typeof__(*(__private_ptr)))0; \
-	if (__copy_from_user(&__private_val, (__private_ptr), \
+	if (__copy_from_user((void *) &__private_val, (__private_ptr),	\
 	    sizeof(*(__private_ptr))) == 0) {\
         	(x) = (__typeof__(*(__private_ptr))) __private_val; \
 		__private_ret = 0; \

The (void *) fixes the warnings all by itself, but I changed the
typeof because that's more correct and fixes some of the warnings by
itself.

What it can't fix is things like (from include/linux/pagemap.h):

	volatile char c;
	ret = __get_user(c, uaddr);

We unavoidably lose the volatile because we can't know it was there,
so the (void *) cast seems necessary in this case.

Looking at this some more, it seems like most of the complexity could
go away.  I think I was avoiding any assignment to the target variable
until I knew that the copy_from_user had succeeded.  I think that was
being too paranoid, and just copy_from_user straight into x should be
fine.

				Jeff


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