From owner-freebsd-xen@freebsd.org Tue Dec 13 06:54:36 2016 Return-Path: Delivered-To: freebsd-xen@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id E4527C75398 for ; Tue, 13 Dec 2016 06:54:36 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id CD1D71FCA for ; Tue, 13 Dec 2016 06:54:36 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from bugs.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id uBD6sa9G026366 for ; Tue, 13 Dec 2016 06:54:36 GMT (envelope-from bugzilla-noreply@freebsd.org) From: bugzilla-noreply@freebsd.org To: freebsd-xen@FreeBSD.org Subject: [Bug 215209] Kernel panic at boot under XEN: integer divide fault while in kernel mode Date: Tue, 13 Dec 2016 06:54:36 +0000 X-Bugzilla-Reason: AssignedTo CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: CURRENT X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: commit-hook@freebsd.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: freebsd-xen@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-xen@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Discussion of the freebsd port to xen - implementation and usage List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 13 Dec 2016 06:54:37 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D215209 --- Comment #7 from commit-hook@freebsd.org --- A commit references this bug: Author: cperciva Date: Tue Dec 13 06:54:14 UTC 2016 New revision: 310013 URL: https://svnweb.freebsd.org/changeset/base/310013 Log: Check that blkfront devices have a non-zero number of sectors and a non-zero sector size. Such a device would be a virtual disk of zero bytes; clearly not useful, and not something we should try to attach. As a fortuitous side effect, checking that these values are non-zero here results in them not *becoming* zero later on the function. This odd behaviour began with r309124 (clang 3.9.0) but is challenging to debug; making any changes to this function whatsoever seems to affect the llvm optimizer behaviour enough to make the unexpected zeroing of the sector_size variable cease. PR: 215209 Security: The potential for variables to unexpectedly become zero has worrying consequences for security in general, but not so much in this particular context. Changes: head/sys/dev/xen/blkfront/blkfront.c --=20 You are receiving this mail because: You are the assignee for the bug. You are on the CC list for the bug.=