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Peter Anvin" , "Xin Li (Intel)" , Brian Gerst , Nikolay Borisov , linux-kernel@vger.kernel.org, Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Robin Murphy , iommu@lists.linux.dev, Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, llvm@lists.linux.dev, Jakub Jelinek Subject: Re: [PATCH 0/4] Fix the x86 defconfig build with GCC 17 User-Agent: K-9 Mail for Android In-Reply-To: <327c462a-3360-45fa-8398-4c23c1f2bd84@linux.dev> References: <20261104160722.1637541-1-vineet.gupta@linux.dev> <20261104162747.GAautdA2q2lw2gsth2@fat_crate.local> <327c462a-3360-45fa-8398-4c23c1f2bd84@linux.dev> Message-ID: <9A0C01CD-F821-4156-A975-E7FC67C636E1@alien8.de> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On November 4, 2026 6:05:27 PM UTC, Vineet Gupta wrote: >+CC Jakub > >On 11/4/26 8:27 AM, Borislav Petkov wrote: >> On Wed, Nov 04, 2026 at 08:07:17AM -0800, Vineet Gupta wrote: >>> Fix build warnings and failures (CONFIG_WERROR=3Dy) with a GCC 17 buil= d=2E >>> GCC 17 adds -Wconstant-logical-operand which is strict about operands >>> of && or || that fold to a constant other than 0 or 1=2E >> Just from looking at it, my initial reaction would be to disable that o= ption=2E >>=20 >> Because, frankly, I don't see the point=2E > >Here's my 2 cents: > >I wondered if this brings any codegen improvements, since we are telling = the compiler that something is 0 or 1 vs=2E some other range before=2E And = it doesn't, because of the way it is used=2E So focusing on just 1/4=2E > >- Constant bit: __builtin_constant_p(bit) && MASK_BIT_SET(bit) folds at c= ompile time to the same truth value, with or without the !! bool conversion= =2E >- Variable bit: __builtin_constant_p(bit) is 0, so && short-circuits and = the mask is never evaluated=2E > >Basically, the masked value never reaches generated code, so compiler get= s nothing new to work with=2E > >So I did some digging, and turns out that it can be helpful to catch bugs= in the source code itself=2E In fact GCC implemented the toggle at all, wh= en Jakub spotted an issue with a typo: (data->flags && ff_genericize) vs=2E= (data->flags & ff_genericize)=2E > >In kernel, the predicate like *_BIT_SET() not returning a bool is not cle= an IMO and it used to return 0/1 before anyway so its not like we are going= out of the way here=2E > >I'm mildly in the favor of keeping the warning, but ultimately your call,= I can respin with it disabled=2E > >Thx, >-Vineet You might wanna look at the W=3D switches we have for less popular and mor= e noisy options --=20 Small device=2E Typos and formatting crap