From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: Re: [PATCH] pc: e820 qemu_cfg tables need to be packed Date: Thu, 14 Oct 2010 22:20:25 +0200 Message-ID: <201010142220.26329.arnd@arndb.de> References: <20101014183249.23510.29196.stgit@s20.home> <4CB75EA4.9080004@codemonkey.ws> <1287086288.2987.10.camel@x201> Mime-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: Jes Sorensen , Alex Williamson , kvm@vger.kernel.org To: qemu-devel@nongnu.org Return-path: In-Reply-To: <1287086288.2987.10.camel@x201> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org On Thursday 14 October 2010 21:58:08 Alex Williamson wrote: > If it works anywhere (I assume it works on 32bit), then it's only > because it happened to get the alignment right. This just makes 64bit > hosts get it right too. I don't see any compatibility issues, > non-packed + 64bit = broken. Thanks, I would actually assume that only x86-32 hosts got it right, because all 32 bit hosts I've seen other than x86 also define 8 byte alignment for uint64_t. You might however consider making it __attribute((__packed__, __aligned__(4))) instead of just packed, because otherwise you make the alignment one byte, which is not only different from what it used to be on x86-32 but also will cause inefficient compiler outpout on platforms that don't have unaligned word accesses in hardware. Arnd