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spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:50936 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1l7uMg-0000x7-CJ for qemu-devel@archiver.kernel.org; Fri, 05 Feb 2021 01:13:10 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:57162) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1l7uM0-0000RK-J2 for qemu-devel@nongnu.org; Fri, 05 Feb 2021 01:12:28 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:23363) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1l7uLx-0005ex-Qq for qemu-devel@nongnu.org; Fri, 05 Feb 2021 01:12:28 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612505543; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=/u6m0T3sGyF2+bRRcynnTBD4JbQuEWY+a0zlwup96/0=; b=hl206UWVkaL82yXjtiTU9MjqoGs7ogZH5xAGYVZqvG41/luYE6yitK2t90p8+K5uWSVyjN TiZ/gf6xSaTlvP9Hg260HIuryChRhoHCYaB/ZZ3WaKsddeqnN7tYyHqzo74deBFdcHifgU WSMjMRn4MgUb1+w1MFzkqrY0EOOyLOY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-320-3TyD3peCMyG-_b8NkTb9rw-1; Fri, 05 Feb 2021 01:12:20 -0500 X-MC-Unique: 3TyD3peCMyG-_b8NkTb9rw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 763F2BBEE2; Fri, 5 Feb 2021 06:12:19 +0000 (UTC) Received: from thuth.remote.csb (ovpn-112-46.ams2.redhat.com [10.36.112.46]) by smtp.corp.redhat.com (Postfix) with ESMTP id BCC01194A4; Fri, 5 Feb 2021 06:12:13 +0000 (UTC) Subject: Re: [PATCH v2] target/s390x/arch_dump: Fixes for the name field in the PT_NOTE section To: Christian Borntraeger , qemu-devel@nongnu.org, Cornelia Huck References: <20210204164117.721110-1-thuth@redhat.com> <8674a570-93f7-24dc-10b8-0c3577c0841f@de.ibm.com> From: Thomas Huth Message-ID: <1d54bafb-b995-0052-e9f9-2572e69dcc11@redhat.com> Date: Fri, 5 Feb 2021 07:12:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <8674a570-93f7-24dc-10b8-0c3577c0841f@de.ibm.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.351, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.182, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-s390x@nongnu.org, Richard Henderson , David Hildenbrand Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 04/02/2021 18.00, Christian Borntraeger wrote: > On 04.02.21 17:41, Thomas Huth wrote: >> According to the "ELF-64 Object File Format" specification: >> >> "The first word in the entry, namesz, identifies the length, in >> bytes, of a name identifying the entry’s owner or originator. The name field >> contains a null-terminated string, with padding as necessary to ensure 8- >> byte alignment for the descriptor field. The length does not include the >> terminating null or the padding." >> >> So we should not include the terminating NUL in the length field here. >> >> Also there is a compiler warning with GCC 9.3 when compiling with >> the -fsanitize=thread compiler flag: >> >> In function 'strncpy', >> inlined from 's390x_write_elf64_notes' at ../target/s390x/arch_dump.c:219:9: >> /usr/include/x86_64-linux-gnu/bits/string_fortified.h:106:10: error: >> '__builtin_strncpy' specified bound 8 equals destination size >> [-Werror=stringop-truncation] >> >> Since the name should always be NUL-terminated, let's use g_strlcpy() to >> silence this warning. And while we're at it, also add an assert() to make >> sure that the provided names always fit the size field (which is fine for >> the current callers, the function is called once with "CORE" and once with >> "LINUX" as a name). >> >> Signed-off-by: Thomas Huth >> --- >> v2: Use g_strlcpy instead of strncpy > > > With this patch I do get > > WARNING: possibly corrupt Elf64_Nhdr: n_namesz: 0 n_descsz: 4 n_type: 88 > > when running crash on the elf file created by dump-guest-memory. Without the > patch everything is fine. Drat! Looking at the crash sources: https://github.com/crash-utility/crash/blob/master/s390x.c#L378 ... it seems like crash is rather rounding up to the next 4 bytes boundary instead of the next 8 bytes boundary. Thus things go wrong now when QEMU writes writes the "CORE" notes section. In the old code we were using 4 + 1 as a lengths, so crash correctly rounded this up to 8. But now with 4 as a length, this does not work right anymore :-( Seems like I either misunderstood the "ELF-64 Object File Format" specification, or this is a bug in the crash utility (it should either add 1 to n_namesz for the trailing NUL or pad to 8 instead of 4)? Anyway, it's maybe better to keep the "+ 1" in QEMU for now to avoid breaking things, I guess? Thomas