On Mon, Jan 12, 2015 at 04:56:54PM -0500, Chris Metcalf wrote:
> Nack for this patch as-is.
>
> On 1/6/2015 10:44 AM, Michael S. Tsirkin wrote:
> >virtio wants to write bitwise types to userspace using put_user.
> >At the moment this triggers sparse errors, since the value is passed
> >through an integer.
> >
> >For example:
> >
> > __le32 __user *p;
> > __le32 x;
> > put_user(x, p);
> >
> >is safe, but currently triggers a sparse warning on tile.
> >
> >The reason has to do with this code:
> > __typeof((x)-(x))
> >which seems to be a way to force check for an integer type.
>
> No, it's purely a way to avoid
>
> warning: cast from pointer to integer of different size
>
> at every place we invoke put_user() with a pointer - which is
> in fact pretty frequent throughout the kernel.
>
> The idiom of
> casting to the difference of the type converts it to a type
> of the same size as the input (whether integral or pointer),
> but guaranteed to be an integral type. Then from there it's safe
> to cast it on to a u64 without generating a warning.
Thanks for the comments. OK, I see, though I wonder why didn't
kbuild notify me about new warnings. Doesn't it build tile?
So if you want to merge your patch, please let me know.
But I think the fix can be much simpler: unsigned long has the same property
without any of the complexity, or problems with sparse. So how about this:
--->
tile: fix put_user sparse errors
virtio wants to write bitwise types to userspace using put_user.
At the moment this triggers sparse errors, since the value is passed
through an integer.
For example:
__le32 __user *p;
__le32 x;
put_user(x, p);
is safe, but currently triggers a sparse warning on tile.
The reason has to do with this code:
__typeof((x)-(x))
which is a way to avoid cast from pointer to integer of different size
warnings.
Fix that up using __force unsigned long cast instead:
this is similar to what many other architectures do.
Note: this does not suppress any useful sparse checks since
the original merely casted x to typeof(x-x).
Tile currently does not trigger sparse warnings when get_user
causes an illegal assignment across bitwise types.
This patch does not attempt to fix this.
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---->
diff --git a/arch/tile/include/asm/uaccess.h b/arch/tile/include/asm/uaccess.h
index b6cde32..9fcbe6f 100644
--- a/arch/tile/include/asm/uaccess.h
+++ b/arch/tile/include/asm/uaccess.h
@@ -246,7 +246,7 @@ extern int __get_user_bad(void)
#define __put_user_4(x, ptr, ret) __put_user_asm(sw, x, ptr, ret)
#define __put_user_8(x, ptr, ret) \
({ \
- u64 __x = (__typeof((x)-(x)))(x); \
+ u64 __x = (u64)(__force unsigned long)(x); \
int __lo = (int) __x, __hi = (int) (__x >> 32); \
asm volatile("1: { sw %1, %2; addi %0, %1, 4 }\n" \
"2: { sw %0, %3; movei %0, 0 }\n" \
--
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