On Mon, May 14, 2018 at 11:08:59AM +0100, Mark Rutland wrote: > On Mon, May 14, 2018 at 11:00:53AM +0100, Dave Martin wrote: > > On Mon, May 14, 2018 at 10:46:24AM +0100, Mark Rutland wrote: > > > -/* Check all the bits are accounted for */ > > > -#define SCTLR_EL2_BUILD_BUG_ON_MISSING_BITS BUILD_BUG_ON((SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != ~0) > > > - > > > +#if (SCTLR_EL2_SET ^ SCTLR_EL2_CLEAR) != 0xffffffff > > > +#error "Inconsistent SCTLR_EL2 set/clear bits" > > > +#endif > > > > Can we have a comment on the != 0xffffffff versus != ~0 here? > > > > The subtle differences in evaluation semantics between #if and > > other contexts here may well trip people up during maintenance... > > Do you have any suggestion as to the wording? > > I'm happy to add a comment, but I don't really know what to say. How about the following? /* Watch out for #if evaluation rules: ~0 is not ~(int)0! */ Cheers ---Dave
