From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47770) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cgvDP-0002sV-Mi for qemu-devel@nongnu.org; Thu, 23 Feb 2017 10:21:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cgvDM-0007hn-E1 for qemu-devel@nongnu.org; Thu, 23 Feb 2017 10:21:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52312) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cgvDM-0007ha-7a for qemu-devel@nongnu.org; Thu, 23 Feb 2017 10:21:52 -0500 References: <1487659615-15820-1-git-send-email-xyjxie@linux.vnet.ibm.com> <5edff645-12e8-d3e0-1849-302b6986c232@ozlabs.ru> <5a0773de-6bc7-474a-82ab-2edd37ce8a93@redhat.com> <92580ca9-47fe-a943-7720-d3cb1fc6d2eb@redhat.com> <3d5e7b5e-4501-86b7-093d-47fb09af585e@redhat.com> <41630a89-e645-7d7e-b7c2-356fd6dcadee@redhat.com> From: Paolo Bonzini Message-ID: <2565ef99-9c16-e836-08c6-0915f5d4b0f8@redhat.com> Date: Thu, 23 Feb 2017 16:21:47 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] memory: make ram device read/write endian sensitive List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Maydell Cc: Alexey Kardashevskiy , Yongji Xie , QEMU Developers , Alex Williamson , zhong@linux.vnet.ibm.com, David Gibson , Paul Mackerras On 23/02/2017 15:35, Peter Maydell wrote: > On 23 February 2017 at 12:53, Paolo Bonzini wrote: >> >> >> On 23/02/2017 13:26, Peter Maydell wrote: >>> On 23 February 2017 at 11:43, Paolo Bonzini wrote: >>>> On 23/02/2017 12:34, Peter Maydell wrote: >>>>> We should probably update the doc comment to note that the >>>>> pointer is to host-endianness memory (and that this is not >>>>> like normal RAM which is target-endian)... >>>> >>>> I wouldn't call it host-endianness memory, and I disagree that normal >>>> RAM is target-endian---in both cases it's just a bunch of bytes. >>>> >>>> However, the access done by the MemoryRegionOps callbacks needs to match >>>> the endianness declared by the MemoryRegionOps themselves. >>> >>> Well, if the guest stores a bunch of integers to the memory, which >>> way round do you see them when you look at the bunch of bytes? >> >> You see them in whatever endianness the guest used. > > I'm confused. I said "normal RAM and this ramdevice memory are > different", and you seem to be saying they're the same. I don't > think they are (in particular I think with a BE guest on an > LE host they'll look different). No, they look entirely the same. The only difference is that they go through MemoryRegionOps instead of memcpy. Paolo