On Tue, Jan 13, 2015 at 11:35:35AM +0200, Michael S. Tsirkin wrote: > 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: Oh, I see you have written a better patch already. Please ignore mine. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
