From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-20.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AE5EAC433DB for ; Thu, 25 Feb 2021 17:22:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7180F64F18 for ; Thu, 25 Feb 2021 17:22:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232923AbhBYRWA (ORCPT ); Thu, 25 Feb 2021 12:22:00 -0500 Received: from foss.arm.com ([217.140.110.172]:42116 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232033AbhBYRV4 (ORCPT ); Thu, 25 Feb 2021 12:21:56 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 810F8101E; Thu, 25 Feb 2021 09:21:08 -0800 (PST) Received: from [10.57.49.35] (unknown [10.57.49.35]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9339C3F73D; Thu, 25 Feb 2021 09:21:04 -0800 (PST) Subject: Re: [PATCH] coresight: etm4x: work around clang-12+ build failure To: Arnd Bergmann , Mathieu Poirier , Alexander Shishkin , Nathan Chancellor , Nick Desaulniers Cc: Arnd Bergmann , Mike Leach , Leo Yan , Greg Kroah-Hartman , Sai Prakash Ranjan , coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com References: <20210225094324.3542511-1-arnd@kernel.org> From: Suzuki K Poulose Message-ID: <19c9eba2-c5cd-301f-4dfa-a31c971728f9@arm.com> Date: Thu, 25 Feb 2021 17:20:57 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210225094324.3542511-1-arnd@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/25/21 9:42 AM, Arnd Bergmann wrote: > From: Arnd Bergmann > > clang-12 fails to build the etm4x driver with -fsanitize=array-bounds: > > :1:7: error: expected constant expression in '.inst' directive > .inst (0xd5200000|((((2) << 19) | ((1) << 16) | (((((((((((0x160 + (i * 4))))) >> 2))) >> 7) & 0x7)) << 12) | ((((((((((0x160 + (i * 4))))) >> 2))) & 0xf)) << 8) | (((((((((((0x160 + (i * 4))))) >> 2))) >> 4) & 0x7)) << 5)))|(.L__reg_num_x8)) > ^ > drivers/hwtracing/coresight/coresight-etm4x-core.c:702:4: note: while in macro instantiation > etm4x_relaxed_read32(csa, TRCCNTVRn(i)); > ^ > drivers/hwtracing/coresight/coresight-etm4x.h:403:4: note: expanded from macro 'etm4x_relaxed_read32' > read_etm4x_sysreg_offset((offset), false))) > ^ > drivers/hwtracing/coresight/coresight-etm4x.h:383:12: note: expanded from macro 'read_etm4x_sysreg_offset' > __val = read_etm4x_sysreg_const_offset((offset)); \ > ^ > drivers/hwtracing/coresight/coresight-etm4x.h:149:2: note: expanded from macro 'read_etm4x_sysreg_const_offset' > READ_ETM4x_REG(ETM4x_OFFSET_TO_REG(offset)) > ^ > drivers/hwtracing/coresight/coresight-etm4x.h:144:2: note: expanded from macro 'READ_ETM4x_REG' > read_sysreg_s(ETM4x_REG_NUM_TO_SYSREG((reg))) > ^ > arch/arm64/include/asm/sysreg.h:1108:15: note: expanded from macro 'read_sysreg_s' > asm volatile(__mrs_s("%0", r) : "=r" (__val)); \ > ^ > arch/arm64/include/asm/sysreg.h:1074:2: note: expanded from macro '__mrs_s' > " mrs_s " v ", " __stringify(r) "\n" \ > ^ > > It appears that the __builin_constant_p() check in > read_etm4x_sysreg_offset() falsely returns 'true' here because clang > decides finds that an out-of-bounds access to config->cntr_val[] cannot s/decides finds/decides/ ? > happen, and then it unrolls the loop with constant register numbers. Then > when actually emitting the output, it fails to figure out the value again. > > While this is incorrect behavior in clang, it is easy to work around > by avoiding the out-of-bounds array access. Do this by limiting the > loop counter to the actual dimension of the array. > > Link: https://github.com/ClangBuiltLinux/linux/issues/1310 > Signed-off-by: Arnd Bergmann > --- > drivers/hwtracing/coresight/coresight-etm4x-core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c > index 15016f757828..4cccf874a602 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c > @@ -691,13 +691,13 @@ static void etm4_disable_hw(void *info) > "timeout while waiting for PM stable Trace Status\n"); > > /* read the status of the single shot comparators */ > - for (i = 0; i < drvdata->nr_ss_cmp; i++) { > + for (i = 0; i < min_t(u32, drvdata->nr_ss_cmp, ETM_MAX_SS_CMP); i++) { > config->ss_status[i] = > etm4x_relaxed_read32(csa, TRCSSCSRn(i)); > } > There are more places where we do this. So I believe you need the similar change elsewhere too in the driver. So, that becomes cumbersome for circumventing the compiler issue. Suzuki