On Thu, Jul 5, 2018 at 9:17 AM, Bart Van Assche <[email protected]> wrote: > The macro __is_constexpr() causes sparse to report the following: > > warning: expression using sizeof(void) > > Avoid this by using __builtin_constant_p() instead. > > Fixes: 3c8ba0d61d04 ("kernel.h: Retain constant expression output for > max()/min()") > Signed-off-by: Bart Van Assche <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Martin Uecker <[email protected]> > Cc: Kees Cook <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Miguel Ojeda <[email protected]> > Cc: <[email protected]> > --- > include/linux/kernel.h | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index d23123238534..a9f0d0d48971 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -811,13 +811,19 @@ static inline void ftrace_dump(enum ftrace_dump_mode > oops_dump_mode) { } > #define __typecheck(x, y) \ > (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) > > +#ifndef __CHECKER__ > /* > * This returns a constant expression while determining if an argument is > * a constant expression, most importantly without evaluating the argument. > - * Glory to Martin Uecker <[email protected]> > + * Glory to Martin Uecker <[email protected]>. However, > this > + * macro causes sparse to report the warning "expression using sizeof(void)". > + * Hence use __builtin_constant_p() instead when using sparse. > */ > #define __is_constexpr(x) \ > (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8))) > +#else > +#define __is_constexpr(x) __builtin_constant_p((x)) > +#endif > > #define __no_side_effects(x, y) \ > (__is_constexpr(x) && __is_constexpr(y))
I'm fine with this; it'll only activate for sparse. I'd like to get Linus's eyes on it, though, since this macro caused us SO much pain that I'm nervous to change it without some greater level of review. :) Acked-by: Kees Cook <[email protected]> Thanks! -Kees -- Kees Cook Pixel Security
