On Fri, Jan 17, 2014 at 06:52:57PM +0000, Peter Maydell wrote: > On 17 January 2014 17:53, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > > Specifically, the KVM API says "here's a uint8_t[] byte > > array and a length", and the current QEMU code treats that > > as "this is a byte array written as if the guest CPU > > (a) were in TARGET_WORDS_BIGENDIAN order and (b) wrote its > > I/O access to this buffer rather than to the device". > > > > The KVM API docs don't actually specify the endianness > > semantics of the byte array, but I think that that really > > needs to be nailed down. I can think of a couple of options: > > * always LE > > * always BE > > [these first two are non-starters because they would > > break either x86 or PPC existing code] > > * always the endianness the guest is at the time > > * always some arbitrary endianness based purely on the > > endianness the KVM implementation used historically > > * always the endianness of the host QEMU binary > > * something else? > > > > Any preferences? Current QEMU code basically assumes > > "always the endianness of TARGET_WORDS_BIGENDIAN", > > which is pretty random. > > Having thought a little more about this, my opinion is: > > * we should specify that the byte order of the mmio.data > array is host kernel endianness (ie same endianness > as the QEMU process itself) [this is what it actually > is, I think, for all the cases that work today] I completely agree, given that it's too late to be set on always LE/BE, I think the natural choice is something that allows a user to cast the byte array to an appropriate pointer type and dereference it. And I think we need to amend the KVM API docs to specify this. -- Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
