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Peter Anvin" , "Li,Rongqing" , Steven Rostedt , linux-kernel@vger.kernel.org, x86@kernel.org Subject: Re: [PATCH] x86/math64: handle #DE in mul_u64_u64_div_u64() Message-ID: <20250722132147.GB2845@redhat.com> References: <20250721130422.GA31640@redhat.com> <20250721192053.58843751@pumpkin> <20250722105034.GA2845@redhat.com> <20250722130947.0c97c96a@pumpkin> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250722130947.0c97c96a@pumpkin> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On 07/22, David Laight wrote: > > On Tue, 22 Jul 2025 12:50:35 +0200 > Oleg Nesterov wrote: > > > static inline u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div) > > { > > char ok = 0; > > u64 q; > > > > asm ("mulq %3; 1: divq %4; movb $1,%1; 2:\n" > > _ASM_EXTABLE(1b, 2b) > > : "=a" (q), "+r" (ok) > > That needs to be "+q" (ok) Thanks... I will never understand the asm constraints. > > if (ok) > > return q; > > BUG_ON(!div); > > WARN_ON_ONCE(1); > > I know there are are a lot of WARN_ON_ONCE(1) out there, > but maybe WARN_ON_ONCE("muldiv overflow") would be better? > (The linker will merge the strings). OK. If you are fine with this version I'll send V2. /* * Returns ULONG_MAX when the result doesn't fit u64. */ static inline u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div) { char ok = 0; u64 q; asm ("mulq %3; 1: divq %4; movb $1,%1; 2:\n" _ASM_EXTABLE(1b, 2b) : "=a" (q), "+q" (ok) : "a" (a), "rm" (mul), "rm" (div) : "rdx"); if (ok) return q; BUG_ON(!div); WARN_ONCE(1, "muldiv overflow.\n"); return ~(u64)0; } Oleg.