linux-kernel - Re: sparse warnings in overflow.h

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Message-ID: <CAGXu5j+XFR7BtYPU6G4CeLFREWevN+GC1FPX1hPAYA1LRBM9Bg@mail.gmail.com>
Date:   Thu, 7 Jun 2018 11:35:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: sparse warnings in overflow.h

On Thu, Jun 7, 2018 at 4:01 AM, Miroslav Benes <mbenes@...e.cz> wrote:
>
> Hi Kees,
>
> sparse (make C=1) gives me this warnings today...
>
> ./include/linux/overflow.h:254:13: error: undefined identifier '__builtin_mul_overflow'
> ./include/linux/overflow.h:254:13: error: incorrect type in conditional
> ./include/linux/overflow.h:254:13:    got void
> ./include/linux/overflow.h:256:13: error: undefined identifier '__builtin_add_overflow'
> ./include/linux/overflow.h:256:13: error: incorrect type in conditional
> ./include/linux/overflow.h:256:13:    got void
>
> This hunk obviously fixes it, but I'm really not sure if it is a proper
> fix.
>
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index f1a7492a5cc8..15e55b89e952 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -344,6 +344,6 @@
>   */
>  #define uninitialized_var(x) x = x
>
> -#if GCC_VERSION >= 50100
> +#if GCC_VERSION >= 50100 && !defined(__CHECKER__)
>  #define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
>  #endif
>
> Any idea?

Hi! Yeah, that's probably the correct approach. If the checker doesn't
have it, the builtins need to be disabled. :)

Can you send this with a Signed-off-by line, etc, and I'll take it for
sending to Linus?

Thanks!

-Kees

-- 
Kees Cook
Pixel Security