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

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Date:   Tue, 14 Sep 2021 08:33:54 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/10] compiler.h: drop fallback overflow checkers

On Fri, Sep 10, 2021 at 5:04 PM Nathan Chancellor <nathan@...nel.org> 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?

>
> 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/...
-- 
Thanks,
~Nick Desaulniers