From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Igpry-0001L0-F5 for qemu-devel@nongnu.org; Sat, 13 Oct 2007 18:54:06 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Igprw-0001Ja-R3 for qemu-devel@nongnu.org; Sat, 13 Oct 2007 18:54:06 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Igprw-0001JM-KB for qemu-devel@nongnu.org; Sat, 13 Oct 2007 18:54:04 -0400 Received: from relay01.mx.bawue.net ([193.7.176.67]) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1Igprv-00060P-Vk for qemu-devel@nongnu.org; Sat, 13 Oct 2007 18:54:04 -0400 Date: Sat, 13 Oct 2007 23:53:55 +0100 From: Thiemo Seufer Subject: Re: [Qemu-devel] RFC: reverse-endian softmmu memory accessors Message-ID: <20071013225354.GP3379@networkno.de> References: <1192269372.9976.305.camel@rapid> <1192279414.9976.332.camel@rapid> <1192285067.9976.338.camel@rapid> <1192313247.9976.356.camel@rapid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1192313247.9976.356.camel@rapid> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "J. Mayer" Cc: qemu-devel@nongnu.org J. Mayer wrote: > On Sat, 2007-10-13 at 16:17 +0200, J. Mayer wrote: > > On Sat, 2007-10-13 at 16:07 +0300, Blue Swirl wrote: > > > On 10/13/07, J. Mayer wrote: > > > > On Sat, 2007-10-13 at 13:47 +0300, Blue Swirl wrote: > > > > > On 10/13/07, J. Mayer wrote: > > > > > > The problem: > > > > > > some CPU architectures, namely PowerPC and maybe others, offers > > > > > > facilities to access the memory or I/O in the reverse endianness, ie > > > > > > little-endian instead of big-endian for PowerPC, or provide instruction > > > > > > to make memory accesses in the "reverse-endian". This is implemented as > > > > > > a global flag on some CPU. This case is already handled by the PowerPC > > > > > > emulation but is is far from being optimal. Some other implementations > > > > > > allow the OS to store an "reverse-endian" flag in the TLB or the segment > > > > > > descriptors, thus providing per-page or per-segment endianness control. > > > > > > This is mostly used to ease driver migration from a PC platform to > > > > > > PowerPC without taking any care of the device endianness in the driver > > > > > > code (yes, this is bad...). > > > > > > > > > > Nice, this may be useful for Sparc64. It has a global CPU flag for > > > > > endianness, individual pages can be marked as reverse endian, and > > > > > finally there are instructions that access memory in reverse endian. > > > > > The end result is a XOR of all these reverses. Though I don't know if > > > > > any of these features are used at all. > > > > > > > > I realized that I/O accesses for reverse-endian pages were not correct > > > > in the softmmu_template.h header. This new version fixes this. It also > > > > remove duplicated code in the case of unaligned accesses in a > > > > reverse-endian page. > > > > > > I think 64 bit access case is not handled correctly, but to solve that > > > it would be nice to extend the current IO access system to 64 bits. > > > > I think that if it was previously correct, it should still be, but... I > > don't know how much having 64 bits I/O accesses is interresting, as I > > don't know if there are real hw buses that have 64 bits data path... > > > > Here's another version taking care of your remark about ldl memory > > accessors. > > * I replaced all ldl occurences with ldul > > * when TARGET_LONG_BITS == 64, I also added ldsl accessors. And I > > started using it in the PowerPC memory access micro-ops. > > Then the patch is really more invasive than the previous ones. > > This still does not break PowerPC or i386 target, as it seems. > > Here's a new version. The only change is that, for consistency, I did > add the big-endian and little-endian accessors that were documented in > cpu-all.h as unimplemented. The implementation is quite trivial, having > native and reverse-endian accessors available, and changes functionnally > nothing to the previous version. The previous version works fine here, FWIW. Thiemo