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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C163BC4332F for ; Fri, 15 Dec 2023 17:02:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=9L5zJDqN4ifF+7lEIjmB6oaUb1/gu0EgmE25fXa6HsU=; b=RYO62N/2UOhbgY sJN5c1mDKbayaeMVCVyls8XYW8/osjpeiqwc5pLXCg5LTqetUuF7jrY8hKy+nlXgYFg/A/HXYfQLP 5xoRoY1x0pkl1ppaqCj/u5oWG+XDR88h+XtDgjaldWAjmRrXLlZfBsHCDKy7hTCMK837xKsT4bogS YIfeLDFc7XyamHG2jNg8YEUBL50pdWPiCNibUqshHGVjRyiFUMFx61Gte2a/nNIMLDKPTj/TmiFEG CWLhnoSMqvDaP9hZSYdVKirwQ+0r0BuTnT1xT89iVucZOI2IG1Bcj79w8Ow5UyoW7yHz+qHBiHVfA 15f52sUdfHlHTsreif7Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rEBZF-003xU6-0E; Fri, 15 Dec 2023 17:01:41 +0000 Received: from mail-yb1-xb2a.google.com ([2607:f8b0:4864:20::b2a]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rEBZC-003xTd-1j for linux-arm-kernel@lists.infradead.org; Fri, 15 Dec 2023 17:01:39 +0000 Received: by mail-yb1-xb2a.google.com with SMTP id 3f1490d57ef6-dbd01358170so405530276.1 for ; Fri, 15 Dec 2023 09:01:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1702659697; x=1703264497; darn=lists.infradead.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=6Nfn9bvVvuLHxdnWDcg+9EWXTr0TX8gO/J71FKN83mM=; b=XyfVKzX7fu6UJB//WyjJ4Vg2P8cB3ns3IYniEZ5SrsJ3x6CK70cgoRN8WO6xhF4OBm J4p2doHpE5t/+qTozkwOKNJqYc0HZkwPu6YJITGG40wWzLTlm3WPEsvJwADGm/ZGLa/g GYMp6OnOWl6UTIGk0B4Acje3r8iyPPG+C61N0CWJIA4IpYnorWOA6vqkX0csKsEKagZJ EpLSIFG8CJCRuV1PMhYSH0YvSxy3VtgfsFRN9VOsqhMBWpFV4S6xERBFhu/vHP52Cd2g fTLRwj0g5/xzk07YfL3fwe6j9m5ALFQfy+fbEnYQunn9YwjrC7m1r02T1TTOGPPHUbSi Mtww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1702659697; x=1703264497; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=6Nfn9bvVvuLHxdnWDcg+9EWXTr0TX8gO/J71FKN83mM=; b=JsPn3n+utPscXxNTQKKRTHZexhyw+SsVQe0FsXpICXil8BPW19rerrx6B1p5JQjgGn oJ9gzRMrSfaoCUuJpZLUTLRXRbqQrulDwhFCREJEa/yfH5YCc0M+Efh0yhbzODjYzrpP 05UVNrutMsClYIAUNXP3KqeWWB2GRbygMLzjjCwcWzVqS8cJrH4d22kSVkhAKgXE+llU TTnzn778BDqpdpaI7KnZtfu8IohxThPI93PM/28Sy94QalhwN3kCFDbXjSrpHHXdwN+Y yfqXpet2bOGd9fYvNIYnqQgcdnwrOpsGsLrebfWhITfEoFW3fJV3MOMHz//sS+E/Jiyc mFJg== X-Gm-Message-State: AOJu0Yyh5tSE1MfIEhOKdVuEStkBP5nWgut/Jgd2iNv4x1kZ1ErfPyXq mMhD2uqAlzRyFCMubVntr7I= X-Google-Smtp-Source: AGHT+IFK38IskUKhPTS6SBpMM4pgyoPjKBgP/iNpKZiqeBw+ns39FwPwr7lqj7g5IHTTuZ+aALnSGg== X-Received: by 2002:a25:d68f:0:b0:db4:5cdd:f6b4 with SMTP id n137-20020a25d68f000000b00db45cddf6b4mr8546969ybg.14.1702659697087; Fri, 15 Dec 2023 09:01:37 -0800 (PST) Received: from localhost ([2601:344:8301:57f0:e177:373d:4717:ff6c]) by smtp.gmail.com with ESMTPSA id c81-20020a25c054000000b00dbd043e4fb8sm150464ybf.31.2023.12.15.09.01.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Dec 2023 09:01:36 -0800 (PST) Date: Fri, 15 Dec 2023 09:01:34 -0800 From: Yury Norov To: Alexander Potapenko Cc: catalin.marinas@arm.com, will@kernel.org, pcc@google.com, andreyknvl@gmail.com, andriy.shevchenko@linux.intel.com, aleksander.lobakin@intel.com, linux@rasmusvillemoes.dk, alexandru.elisei@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, eugenis@google.com, syednwaris@gmail.com, william.gray@linaro.org Subject: Re: [PATCH v10-mte 4/7] arm64: mte: implement CONFIG_ARM64_MTE_COMP Message-ID: References: <20231214110639.2294687-1-glider@google.com> <20231214110639.2294687-5-glider@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231215_090138_574082_9AD24C65 X-CRM114-Status: GOOD ( 18.10 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Dec 15, 2023 at 08:35:43AM -0800, Yury Norov wrote: > On Fri, Dec 15, 2023 at 04:19:27PM +0100, Alexander Potapenko wrote: > > > > > > That looks weird... You're casting address of a 'data' to a bitmap > > > instead of 'data'. At the 1st glance it makes little sense because > > > 'data' is passed as parameter. Moreover, in mte_is_compressed() > > > you pass 'data', not '&data'. Can you please comment on your > > > intention? > > > > Although `data` is a void*, it actually contains 64 bits of compressed > > data, so we pass &data to mte_bitmap_read() to read its contents. > > Perhaps I'd better make `data` an unsigned long to avoid confusion. > > Still don't understand. Let's consider this example: > > yury:linux$ cat tst.c > #include > > unsigned long data[1] = {0xabc}; > > void foo(unsigned long *data) > { > printf("foo: *data\t%lx\n", (unsigned long)*data); > printf("foo: data\t%lx\n", (unsigned long)data); > printf("foo: &data\t%lx\n", (unsigned long)&data); > } > > void bar(unsigned long *data) > { > volatile unsigned long x[100]; > > printf("bar: *data\t%lx\n", (unsigned long)*data); > printf("bar: data\t%lx\n", (unsigned long)data); > printf("bar: &data\t%lx\n", (unsigned long)&data); > } > > int main(int argc, char *argv[]) > { > > foo(data); > bar(data); > > printf("main: *data\t%lx\n", (unsigned long)*data); > printf("main: data\t%lx\n", (unsigned long)data); > printf("main: &data\t%lx\n", (unsigned long)&data); > > return 0; > } > yury:linux$ gcc tst.c -O0 > yury:linux$ ./a.out > foo: *data abc > foo: data 555b2cef9010 > foo: &data 7fff39d6e5f8 > bar: *data abc > bar: data 555b2cef9010 > bar: &data 7fff39d6e2c8 > main: *data abc > main: data 555b2cef9010 > main: &data 555b2cef9010 > > Data and *data have their meaning across scope boundary: a pointer and > a content. The &data is pretty much a random number - a pointer to > somewhere on a function's stack. Isn't? OK, I read now. Your 'void *data' is not a pointer, but an actual data. Very confusing indeed... Maybe add a comment for that cast? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel