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[184.162.17.179]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-4a72a4b0cb9sm52789391cf.50.2025.06.16.12.22.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 16 Jun 2025 12:22:45 -0700 (PDT) Date: Mon, 16 Jun 2025 15:22:44 -0400 (EDT) From: Nicolas Pitre To: Andrew Morton , David Laight cc: =?ISO-8859-15?Q?Thomas_Wei=DFschuh?= , Oleg Nesterov , =?ISO-8859-15?Q?Uwe_Kleine-K=F6nig?= , Peter Zijlstra , Biju Das , linux-kernel@vger.kernel.org Subject: [PATCH v2] mul_u64_u64_div_u64: fix the division-by-zero behavior Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The current implementation forces a compile-time 1/0 division, which generates an undefined instruction (ud2 on x86) rather than a proper runtime division-by-zero exception. Change to trigger an actual div-by-0 exception at runtime, consistent with other division operations. Use a non-1 dividend to prevent the compiler from optimizing the division into a comparison. Signed-off-by: Nicolas Pitre --- Change from v1 (http://lore.kernel.org/all/q2o7r916-5601-11pn-30pn-8n5ns6p0= 79o7@onlyvoer.pbz): - use OPTIMIZER_HIDE_VAR() in place of the open coded incantation. diff --git a/lib/math/div64.c b/lib/math/div64.c index 5faa29208bdb..bf77b9843175 100644 --- a/lib/math/div64.c +++ b/lib/math/div64.c @@ -212,12 +212,13 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c) =20 #endif =20 - /* make sure c is not zero, trigger exception otherwise */ -#pragma GCC diagnostic push -#pragma GCC diagnostic ignored "-Wdiv-by-zero" - if (unlikely(c =3D=3D 0)) - return 1/0; -#pragma GCC diagnostic pop + /* make sure c is not zero, trigger runtime exception otherwise */ + if (unlikely(c =3D=3D 0)) { + unsigned long zero =3D 0; + + OPTIMIZER_HIDE_VAR(zero); + return ~0UL/zero; + } =20 int shift =3D __builtin_ctzll(c);