On Mon, 2014-12-15 at 12:22 +0200, Michael S. Tsirkin wrote: > On Mon, Dec 15, 2014 at 11:40:52AM +1100, Michael Ellerman wrote: > > On Sun, 2014-12-14 at 18:51 +0200, Michael S. Tsirkin wrote: > > > At the moment, if p and x are both tagged as bitwise types, > > > get_user(x, p) produces a sparse warning on many architectures. > > > This is because *p on these architectures is loaded into long > > > (typically using asm), then cast back to typeof(*p). > > > > > > When typeof(*p) is a bitwise type (which is uncommon), such a cast needs > > > __force, otherwise sparse produces a warning. > > > > What does __force actually mean? Force the cast even though it's a bitfield? Or > > does it mean more than that? > > It's not a bitfield = it's a bitwise integer. OK. I didn't know what that meant, but Documentation/sparse.txt taught me. So it's a sparse only thing. > Once you tag a typedef as bitwise, casts to and from > an untypedefed integer cause sparse warnings. > > > ie. are we loosing the ability to detect any actual errors by adding force? > > > > cheers > > I think we aren't: > get_user(x, p) should be equivalent to x = *p except it > validates the pointer is to userspace memory, > and can handle pagefaults. > > Sparse warnings are triggered because these macros use > an untyped integer internally. > > Note that we are casting to typeof(*p) not typeof(x). > Even with the cast, if x and *p are of different types we should get the > warning, so I think we are not loosing the ability to detect any actual > errors. OK. Sounds good then. cheers -- 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
