From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 54536 invoked by alias); 19 Oct 2017 13:22:54 -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 54527 invoked by uid 89); 19 Oct 2017 13:22:53 -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,SPF_HELO_PASS autolearn=no version=3.3.2 spammy=H*M:8d29 X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Thu, 19 Oct 2017 13:22:52 +0000 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9803AB64B; Thu, 19 Oct 2017 13:22:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 9803AB64B Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx09.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=palves@redhat.com Received: from [127.0.0.1] (ovpn04.gateway.prod.ext.ams2.redhat.com [10.39.146.4]) by smtp.corp.redhat.com (Postfix) with ESMTP id E8205D5640; Thu, 19 Oct 2017 13:22:50 +0000 (UTC) Subject: Re: [PATCH] [AArch64 Linux] Get rid of top byte from tagged address To: Yao Qi References: <1508400527-20718-1-git-send-email-yao.qi@linaro.org> <561ea277-4b4c-ae82-01e1-1cde96cb54f2@redhat.com> <86po9jv29n.fsf@gmail.com> <98b855a4-77df-1bd6-d20d-5b2611cc8f83@redhat.com> <86h8uvuvj8.fsf@gmail.com> Cc: gdb-patches@sourceware.org From: Pedro Alves Message-ID: <0e7b4aad-698f-dfe6-8d29-2270bf31f1b6@redhat.com> Date: Thu, 19 Oct 2017 13:22:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <86h8uvuvj8.fsf@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-SW-Source: 2017-10/txt/msg00607.txt.bz2 On 10/19/2017 02:17 PM, Yao Qi wrote: > Pedro Alves writes: > >> This means with something like: >> >> #define tagptr(PTR) \ >> ((typeof (PTR)) ((uintptr_t) (PTR) | 0xf000000000000000ULL)) >> >> strcat (buf, "hello\n"); >> >> char *ptr = tagptr(buf); // assume this is hidden from view. >> >> write (1, ptr, 6); // kernel rejects this. >> > > Right, it returns -1, and errno is EFAULT. > >> and then the user might be puzzled because stepping through >> that code: >> >> (gdb) print ptr >> (gdb) print ptr[0] >> >> etc. works without error. > > That is right/expected to me, because in the c code, we can still access > ptr[0] without any error, like "char c = ptr[0]", so it is reasonable > that we can access them in GDB. Kernel rejects that address, doesn't > mean we can't access that address. OK, that's reasonable. Thanks, Pedro Alves