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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 9A827CA9EC9 for ; Fri, 1 Nov 2019 05:50:40 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 27C372086D for ; Fri, 1 Nov 2019 05:50:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RwkCmO95" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 27C372086D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 642126B0005; Fri, 1 Nov 2019 01:50:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5F2D06B0006; Fri, 1 Nov 2019 01:50:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 508A06B0007; Fri, 1 Nov 2019 01:50:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0043.hostedemail.com [216.40.44.43]) by kanga.kvack.org (Postfix) with ESMTP id 2E5F06B0005 for ; Fri, 1 Nov 2019 01:50:39 -0400 (EDT) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with SMTP id 558D78249980 for ; Fri, 1 Nov 2019 05:50:38 +0000 (UTC) X-FDA: 76106634156.14.trail46_3fba026c7af24 X-HE-Tag: trail46_3fba026c7af24 X-Filterd-Recvd-Size: 4414 Received: from mail-pg1-f194.google.com (mail-pg1-f194.google.com [209.85.215.194]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Fri, 1 Nov 2019 05:50:37 +0000 (UTC) Received: by mail-pg1-f194.google.com with SMTP id f19so5759553pgn.13 for ; Thu, 31 Oct 2019 22:50:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=R7x8NUIAlgbXdU8mi/JI7VU+oQptSs1SZGjlLDYkhdQ=; b=RwkCmO95W/bQ8Q1hr1l7zILksvtnwVlib+fK1nL1sPE0OmakqQeTAxpybiH12RqQNp SaTze74tFOBqxZsAHXLdb2UM1mrhBdigN467W+8a2RT/dCUC1M1pK9ycuasiDEvnW9Tb QK5d3DgwF9E3+hdyy2Cx/QQhjtUNFiFFidW9brm1ED+cCGqhDCcMJOmZiGENHsqM1LLQ a/uupDIBS8aOzuhWqeGphJ/Su9qbjgvjtaino8DZ7oHJf3r5gzkqHDOzma8hcr5sqbdH ObRjFova43NKP3c4Qh4o0Wyf12FNL5uKo7Lt1S3lRNlSr1/KZhDtwbbFkfkzK2t+gMqO VQ2w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=R7x8NUIAlgbXdU8mi/JI7VU+oQptSs1SZGjlLDYkhdQ=; b=f94I1LKQ4fGHhIm/CXXGmb0r5Paj1pzzZfMUJzsSXpjp+9k08gDG8B8klI9fUrLT+N ixv0IZqmjlPnB77fSin5FPwhrqQjYWxh4vUFQ+h19CekXsVjl7wGhZv0WOahCBgaJJw/ TdRXwmCSam8nnByJAOCcqvx8X2njRFP0XqY88W9TCMBZJ3zzWCcc8i5k3Fnf0PWEiWyv DTd5eH+waHxYnWQrYa0A1nvh3hYTTFBTHiNNcz6iFd29cF78NuLe1XD1Pd0QyM0s/G/m DZIdCwOp6O6DuEu80oF63ZKYTPJKqIGbGA9YDb/q1nPxuPPj1a/wPPsJYSzqHLJqfSrO +CYg== X-Gm-Message-State: APjAAAVyythHNFSQWnN3pG8qn74R2pwZpwdB9IcX48o2Hhcj8rRWFjDr 4OV+O1LPVeoOYHFi6w6EaYg= X-Google-Smtp-Source: APXvYqwwtXiR/hrEHdoF+FUig/BeCLWGdpxq56UkKsv4XHwjrnlY0MPVWyIKyuWXEWFjyqtF8GTvIg== X-Received: by 2002:a17:90a:a406:: with SMTP id y6mr13122649pjp.106.1572587436750; Thu, 31 Oct 2019 22:50:36 -0700 (PDT) Received: from localhost ([2401:fa00:8f:203:250d:e71d:5a0a:9afe]) by smtp.gmail.com with ESMTPSA id e198sm5446534pfh.83.2019.10.31.22.50.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 31 Oct 2019 22:50:35 -0700 (PDT) Date: Fri, 1 Nov 2019 14:50:33 +0900 From: Sergey Senozhatsky To: glider@google.com Cc: Vegard Nossum , Dmitry Vyukov , linux-mm@kvack.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, aryabinin@virtuozzo.com, luto@kernel.org, ard.biesheuvel@linaro.org, arnd@arndb.de, hch@lst.de, dmitry.torokhov@gmail.com, edumazet@google.com, ericvh@gmail.com, gregkh@linuxfoundation.org, harry.wentland@amd.com, herbert@gondor.apana.org.au, mingo@elte.hu, axboe@kernel.dk, martin.petersen@oracle.com, schwidefsky@de.ibm.com, mst@redhat.com, monstr@monstr.eu, pmladek@suse.com, sergey.senozhatsky@gmail.com, rostedt@goodmis.org, tiwai@suse.com, tytso@mit.edu, tglx@linutronix.de, wsa@the-dreams.de, gor@linux.ibm.com, iii@linux.ibm.com, mark.rutland@arm.com, willy@infradead.org, rdunlap@infradead.org, andreyknvl@google.com, elver@google.com Subject: Re: [PATCH RFC v2 02/25] stackdepot: prevent Clang from optimizing away stackdepot_memcmp() Message-ID: <20191101055033.GA226263@google.com> References: <20191030142237.249532-1-glider@google.com> <20191030142237.249532-3-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030142237.249532-3-glider@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On (19/10/30 15:22), glider@google.com wrote: > Clang may replace stackdepot_memcmp() with a call to instrumented bcmp(), > which is exactly what we wanted to avoid creating stackdepot_memcmp(). > Add a compiler barrier() to prevent optimizations. [..] > @@ -163,6 +163,11 @@ int stackdepot_memcmp(const unsigned long *u1, const unsigned long *u2, > unsigned int n) > { > for ( ; n-- ; u1++, u2++) { > + /* > + * Prevent Clang from replacing this function with a bcmp() > + * call. > + */ > + barrier(); > if (*u1 != *u2) > return 1; > } Would 'volatile' do the trick? -ss