On Sat, Aug 05, 2017 at 12:26:03PM +1000, Bruce Evans wrote: > > +#define minor(x) ((int)(x)) > > Another nice simplification. Strictly, it should be (int)(dev_t)(x) since > the pseudo-prototype says that the arg is converted to dev_t, but yesterday > I couldn't see any differences even for exotic x and exotic arches. > > Today I can see some difference for exotic x and perverse implementations. > E.g., x with extra bits in a large signed integer type to invoke > implementation-defined behaviour, and a perverse implementation that > truncates to 0 for direct conversion to int but does the right thing > for indirect conversion). But we depend on the implementation doing > the right thing for other casts to int. > > Also, if dev_t == uintptr_t, it is valid for the caller to keep dev_t's > in void *'s internally but not to pass void * to minor() or major() > according to the prototype. However, casting in the macros breaks the > warning for this. I think pure macros should not cast their args or > pretend to have prototypes, but require callers to pass args of supported > types. The old dev_t macros were closer to this -- they have expressions > like ((x) << 8) which will fail if x is not an integral type or give > wrong results ix x has extra bits. So you are arguing to keep the & 0xffffffff operation ? I think this is not needed, since your note about cast being equivalent holds for all supported architectures and I do not see anywhere a contract for the operations to work on non-dev_t.
So are you fine with the posted patch to sys/types.h ? _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
