Re: [PATCH 02/10] compiler.h: drop fallback overflow checkers

[Nathan Chancellor]

On 9/14/2021 8:33 AM, Nick Desaulniers wrote:
> On Fri, Sep 10, 2021 at 5:04 PM Nathan Chancellor <nathan@xxxxxxxxxx> wrote:
> > On Fri, Sep 10, 2021 at 04:40:39PM -0700, Nick Desaulniers wrote:
> > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> > > index 0f12345c21fb..4669632bd72b 100644
> > > --- a/include/linux/overflow.h
> > > +++ b/include/linux/overflow.h
> > > @@ -6,12 +6,9 @@
> > >   #include <linux/limits.h>
> > >
> > >   /*
> > > - * In the fallback code below, we need to compute the minimum and
> > > - * maximum values representable in a given type. These macros may also
> > > - * be useful elsewhere, so we provide them outside the
> > > - * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
> > > - *
> > > - * It would seem more obvious to do something like
> > > + * We need to compute the minimum and maximum values representable in a given
> > > + * type. These macros may also be useful elsewhere. It would seem more obvious
> > > + * to do something like:
> > >    *
> > >    * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
> > >    * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
> >
> > The signed and type macros right below this comment can be removed as
> > they were only used in the !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW case.
>
> Did you check for users outside of this header?
>
> I see:
> type_min ->
> lib/test_scanf.c:189
> include/rdma/uverbs_ioctl.h:951
> include/rdma/uverbs_ioctl.h:973
>
> type_max ->
> lib/test_scanf.c:189
> lib/test_scanf.c:190
> include/rdma/uverbs_ioctl.h:952
> include/rdma/uverbs_ioctl.h:962
> include/rdma/uverbs_ioctl.h:974
> include/rdma/uverbs_ioctl.h:985
>
> is_signed_type has many many users throughout the kernel.
>
> Or were you referring to other defines?

Ah, I did not even think to look outside this file, I figured they were 
intended to only be used here :/ good catch.

> > Also applies to the tools/ version.
>
> The version in tools/ should probably be "refreshed" ie. copy+pasted
> over.  Why there is a separate copy under tools/...

Yes, they probably should, as I noted in commit d0ee23f9d78b ("tools: 
compiler-gcc.h: Guard error attribute use with __has_attribute"). At the 
same time, I don't really want to do it :)

Cheers,
Nathan