On 05/06/2015 17:08, Peter Maydell wrote: >> > Can someone add a checkpatch rule that forbids shifting left U or UL >> > constants (i.e. only ULL)? That would alleviate my concerns with these >> > ubsan warnings. > > ...but things like "(1U << 31)" are entirely valid.
They're only valid until someone does a ~ on them. I think it's reasonable to forbid them in our coding standards, if we want to fix ubsan's warning of (1 << 31). I don't think it's reasonable for compiler writers to exploit the undefinedness of (1 << 31) anyway, and if it were possible to shut up ubsan about this particular kind of undefined behavior, I would prefer it. Paolo
