Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 2 Nov 2022 12:33:33 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc:     Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>,
        luc.vanoostenryck@gmail.com, nathan@kernel.org,
        ndesaulniers@google.com, trix@redhat.com, dlatypov@google.com,
        vitor@massaru.org, gustavoars@kernel.org,
        linux-hardening@vger.kernel.org, llvm@lists.linux.dev,
        jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com,
        rodrigo.vivi@intel.com, tvrtko.ursulin@linux.intel.com,
        airlied@linux.ie, daniel@ffwll.ch, linux-kernel@vger.kernel.org,
        intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-sparse@vger.kernel.org, arnd@kernel.org, mchehab@kernel.org,
        mauro.chehab@linux.intel.com
Subject: Re: [PATCH v5] overflow: Introduce overflows_type() and
 castable_to_type()
Message-ID: <202211021233.02BF0D38@keescook>
References: <20220926191109.1803094-1-keescook@chromium.org>
 <20221024201125.1416422-1-gwan-gyeong.mun@intel.com>
 <307b90cb-b80d-6ce3-14ae-4a0b2ee5e447@prevas.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <307b90cb-b80d-6ce3-14ae-4a0b2ee5e447@prevas.dk>
Precedence: bulk

On Wed, Nov 02, 2022 at 12:52:32PM +0100, Rasmus Villemoes wrote:
> On 24/10/2022 22.11, Gwan-gyeong Mun wrote:
> > From: Kees Cook <keescook@chromium.org>
> > 
> > Implement a robust overflows_type() macro to test if a variable or
> > constant value would overflow another variable or type. This can be
> > used as a constant expression for static_assert() (which requires a
> > constant expression[1][2]) when used on constant values. This must be
> > constructed manually, since __builtin_add_overflow() does not produce
> > a constant expression[3].
> > 
> > Additionally adds castable_to_type(), similar to __same_type(), but for
> > checking if a constant value would overflow if cast to a given type.
> > 
> 
> > +#define __overflows_type_constexpr(x, T) (			\
> > +	is_unsigned_type(typeof(x)) ?				\
> > +		(x) > type_max(typeof(T)) ? 1 : 0		\
> > +	: is_unsigned_type(typeof(T)) ?				\
> > +		(x) < 0 || (x) > type_max(typeof(T)) ? 1 : 0	\
> > +		: (x) < type_min(typeof(T)) ||			\
> > +		  (x) > type_max(typeof(T)) ? 1 : 0)
> > +
> 
> Can't all these instances of "foo ? 1 : 0" be simplified to "foo"? That
> would improve the readability of this thing somewhat IMO.

Oh, good point. :P I'll fix these.

-- 
Kees Cook