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=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 52898C433E0 for ; Mon, 1 Jun 2020 12:07:34 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F1A8F20772 for ; Mon, 1 Jun 2020 12:07:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F1A8F20772 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4DE2180007; Mon, 1 Jun 2020 08:07:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 48E5F8E0006; Mon, 1 Jun 2020 08:07:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3A2CF80007; Mon, 1 Jun 2020 08:07:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0201.hostedemail.com [216.40.44.201]) by kanga.kvack.org (Postfix) with ESMTP id 21B888E0006 for ; Mon, 1 Jun 2020 08:07:33 -0400 (EDT) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id C50E68248047 for ; Mon, 1 Jun 2020 12:07:32 +0000 (UTC) X-FDA: 76880518344.07.rate42_246026ffa1a4e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin07.hostedemail.com (Postfix) with ESMTP id 70DC51803F9D1 for ; Mon, 1 Jun 2020 12:07:30 +0000 (UTC) X-HE-Tag: rate42_246026ffa1a4e X-Filterd-Recvd-Size: 3342 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Mon, 1 Jun 2020 12:07:29 +0000 (UTC) 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 EEDE755D; Mon, 1 Jun 2020 05:07:28 -0700 (PDT) Received: from gaia (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3609F3F52E; Mon, 1 Jun 2020 05:07:27 -0700 (PDT) Date: Mon, 1 Jun 2020 13:07:25 +0100 From: Catalin Marinas To: Luis Machado Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Vincenzo Frascino , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Alan Hayward , Omair Javaid Subject: Re: [PATCH v4 18/26] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Message-ID: <20200601120724.GB23419@gaia> References: <20200515171612.1020-1-catalin.marinas@arm.com> <20200515171612.1020-19-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Queue-Id: 70DC51803F9D1 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 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 Fri, May 29, 2020 at 06:25:14PM -0300, Luis Machado wrote: > I have a question about siginfo MTE information. I suppose SEGV_MTESERR will > be the most useful setting for debugging, right? Does si_addr contain the > tagged pointer with the logical tag, a zero-tagged memory address or a > tagged pointer with the allocation tag? The si_addr is zero-tagged currently. We were planning to expose the tag in FAR_EL1 as a separate siginfo field. See these discussions: https://lore.kernel.org/linux-arm-kernel/20200513180914.50892-1-pcc@google.com/ https://lore.kernel.org/linux-arm-kernel/20200521022943.195898-1-pcc@google.com/ In theory, we could add the tag to si_addr for SEGV_MTESERR, it shouldn't break the existing ABI (well, it depends on how you look at it). > From the debugger user's perspective, one would want to see both the logical > tag and the allocation tag. And it would be handy to have both available in > siginfo. Does that make sense? The debugger can access the allocation tag via PTRACE_PEEKMTETAGS. I don't think the kernel should provide this in siginfo. Also, the signal handler can do an LDG and read the allocation tag directly, no need for it to be in siginfo. > Also, when would we see SEGV_MTEAERR, for example? That would provide no > additional information about a particular memory address, which is not that > useful for the debugger. Yeah, we can't really do much here since the hardware doesn't provide us such information. The async mode is only useful as a general test to see if your program has MTE faults but for actual debugging you'd have to switch to synchronous. For glibc at least, I think the mode can be driven by an environment variable. -- Catalin