From nobody Sun May 10 06:04:21 2026 Received: from mail.loongson.cn (mail.loongson.cn [114.242.206.163]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 015A117F4F2 for ; Tue, 31 Dec 2024 07:28:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=114.242.206.163 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1735630104; cv=none; b=rxxB6lFpd7HmcMpd8EOU+Jbt2pYdvw0UAJfDrKDHBIgTkc49hCU1sz9sNTKPbJx865T5NQ1r6UCp0EAcDH0tSBtP934DrBs07i5xKRaDQEuW7FwIJl/tOO78UppZSaMREPbA5zY8tXz36Xupv6FE0wVeycd2x6pqBdsY8lZqPRo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1735630104; c=relaxed/simple; bh=tjKmDjYuugvkR57s3EQZ8Pj6Woao6xb8cvGVYcaC18c=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=OBcsUOlgWPffNZYUKHh9FoeCSGuz8M0lXs5QC1cR+FoZhSqPsK+/d8vN3D5qm5KM7kXVIZxhqWay2o5cXXD0/dR8RUmxPOnftPniYxRm9lDjbp3QqmA8/vup0D+XbEiWEo7dskcccKPjlqYerJQJS/OOp8lS/UbKuw6AQWWayOw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn; spf=pass smtp.mailfrom=loongson.cn; arc=none smtp.client-ip=114.242.206.163 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=loongson.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=loongson.cn Received: from loongson.cn (unknown [113.200.148.30]) by gateway (Coremail) with SMTP id _____8DxGeAMnXNnpU5cAA--.49860S3; Tue, 31 Dec 2024 15:28:12 +0800 (CST) Received: from linux.localdomain (unknown [113.200.148.30]) by front1 (Coremail) with SMTP id qMiowMBxTMUHnXNnqxoPAA--.8697S2; Tue, 31 Dec 2024 15:28:08 +0800 (CST) From: Tiezhu Yang To: Alex Deucher , =?UTF-8?q?Christian=20K=C3=B6nig?= , Xinhui Pan , Harry Wentland , Leo Li , Rodrigo Siqueira Cc: Nathan Chancellor , Josh Poimboeuf , Peter Zijlstra , loongarch@lists.linux.dev, amd-gfx@lists.freedesktop.org, llvm@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [PATCH] drm/amd/display: Harden callers of division functions Date: Tue, 31 Dec 2024 15:28:06 +0800 Message-ID: <20241231072806.4936-1-yangtiezhu@loongson.cn> X-Mailer: git-send-email 2.42.0 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 X-CM-TRANSID: qMiowMBxTMUHnXNnqxoPAA--.8697S2 X-CM-SenderInfo: p1dqw3xlh2x3gn0dqz5rrqw2lrqou0/ X-Coremail-Antispam: 1Uk129KBj93XoWxWry8uF1ktw1UJFWUCFWUJrc_yoW5Gr4Dpa 13GFyUZryDZFZ7tFZ7CF17WFW3Aa93GF4v9a15Cws5u347Zan8ur43J3Z5Gr429ryIyF4a vF4DKrWjqF1vyrcCm3ZEXasCq-sJn29KB7ZKAUJUUUUx529EdanIXcx71UUUUU7KY7ZEXa sCq-sGcSsGvfJ3Ic02F40EFcxC0VAKzVAqx4xG6I80ebIjqfuFe4nvWSU5nxnvy29KBjDU 0xBIdaVrnRJUUUBIb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I20VC2zVCF04k26cxKx2 IYs7xG6rWj6s0DM7CIcVAFz4kK6r106r15M28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48v e4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_JFI_Gr1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI 0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVW8Jr0_Cr1UM28EF7xvwVC2z280aVCY1x0267AK xVW8Jr0_Cr1UM2kKe7AKxVWUAVWUtwAS0I0E0xvYzxvE52x082IY62kv0487Mc804VCY07 AIYIkI8VC2zVCFFI0UMc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7IYx2IY67AKxVWU AVWUtwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4UM4x0Y48IcxkI7V AKI48JMxkF7I0En4kS14v26r1q6r43MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY 6r1j6r4UMxCIbckI1I0E14v26r126r1DMI8I3I0E5I8CrVAFwI0_Jr0_Jr4lx2IqxVCjr7 xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUtVW8ZwCIc40Y0x0EwIxGrwCI42IY6xII jxv20xvE14v26r1I6r4UMIIF0xvE2Ix0cI8IcVCY1x0267AKxVW8JVWxJwCI42IY6xAIw2 0EY4v20xvaj40_Jr0_JF4lIxAIcVC2z280aVAFwI0_Jr0_Gr1lIxAIcVC2z280aVCY1x02 67AKxVW8JVW8JrUvcSsGvfC2KfnxnUUI43ZEXa7IU84E_tUUUUU== Content-Type: text/plain; charset="utf-8" There are objtool warnings compiled with the latest mainline LLVM: dc_fixpt_recip() falls through to next function dc_fixpt_sinc() spl_fixpt_recip() falls through to next function spl_fixpt_sinc() Here are the call paths: dc_fixpt_recip() dc_fixpt_from_fraction() complete_integer_division_u64() div64_u64_rem() spl_fixpt_recip() spl_fixpt_from_fraction() spl_complete_integer_division_u64() spl_div64_u64_rem() This was introduced by a change in Clang from a few months: [SimplifyCFG] Deduce paths unreachable if they cause div/rem UB) https://github.com/llvm/llvm-project/commit/37932643abab Since the ASSERT does not do anything to prevent the divide by zero (just flags it with WARN_ON) and the rest of the code doesn't either, the callers of division functions should harden them against dividing by zero to avoid undefined behavior. Keep the current ASSERT for the aim of debugging, just add BUG() to stop control flow if the divisior is zero. Suggested-by: Nathan Chancellor Suggested-by: Xi Ruoyao Suggested-by: Rui Wang Signed-off-by: Tiezhu Yang Link: https://lore.kernel.org/lkml/20241220223403.GA2605890@ax162/ --- drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c | 1 + drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c | 1 + 2 files changed, 2 insertions(+) diff --git a/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c b/drivers/g= pu/drm/amd/display/dc/basics/fixpt31_32.c index 88d3f9d7dd55..e15391e36b40 100644 --- a/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c +++ b/drivers/gpu/drm/amd/display/dc/basics/fixpt31_32.c @@ -52,6 +52,7 @@ static inline unsigned long long complete_integer_divisio= n_u64( unsigned long long result; =20 ASSERT(divisor); + BUG_ON(!divisor); =20 result =3D div64_u64_rem(dividend, divisor, remainder); =20 diff --git a/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c b/drivers/= gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c index 131f1e3949d3..ce2036950808 100644 --- a/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c +++ b/drivers/gpu/drm/amd/display/dc/spl/spl_fixpt31_32.c @@ -30,6 +30,7 @@ static inline unsigned long long spl_complete_integer_div= ision_u64( unsigned long long result; =20 SPL_ASSERT(divisor); + BUG_ON(!divisor); =20 result =3D spl_div64_u64_rem(dividend, divisor, remainder); =20 --=20 2.42.0