From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 54386 invoked by alias); 19 Oct 2017 09:51:15 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 54195 invoked by uid 89); 19 Oct 2017 09:51:15 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-0.9 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,RP_MATCHES_RCVD autolearn=no version=3.3.2 spammy=H*UA:56.0 X-HELO: foss.arm.com Received: from usa-sjc-mx-foss1.foss.arm.com (HELO foss.arm.com) (217.140.101.70) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 19 Oct 2017 09:51:14 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8A425F; Thu, 19 Oct 2017 02:51:12 -0700 (PDT) Received: from [10.2.206.255] (armadillo.cambridge.arm.com [10.2.206.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 131E33F483; Thu, 19 Oct 2017 02:51:11 -0700 (PDT) Subject: Re: [PATCH] [AArch64 Linux] Get rid of top byte from tagged address To: Yao Qi , gdb-patches@sourceware.org References: <1508400527-20718-1-git-send-email-yao.qi@linaro.org> From: Ramana Radhakrishnan Message-ID: Date: Thu, 19 Oct 2017 09:51:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:56.0) Gecko/20100101 Thunderbird/56.0 MIME-Version: 1.0 In-Reply-To: <1508400527-20718-1-git-send-email-yao.qi@linaro.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-IsSubscribed: yes X-SW-Source: 2017-10/txt/msg00595.txt.bz2 On 10/19/17 9:08 AM, Yao Qi wrote: > ARMv8 supports tagged address, that is, the top one byte in address > is ignored. It is always enabled on aarch64-linux. The patch clear > the top byte of the virtual address, at the point before GDB/GDBserver > pass the address to /proc or ptrace syscall. The top byte of address is > still retained in the rest of GDB, because these bits can be used by > different applications in different ways. That is reason I didn't > implement gdbarch method addr_bits_remove to get rid of them. I think you also want to point people at ... https://www.kernel.org/doc/Documentation/arm64/tagged-pointers.txt regards Ramana