Re: [Qemu-devel] [PATCH] target-arm: crypto: fix BE host support

[Peter Maydell <peter.maydell@linaro.org>]

On 2 January 2015 at 15:17, Laszlo Ersek <lersek@redhat.com> wrote:
> On 01/02/15 15:18, Ard Biesheuvel wrote:
>> (ie if you store 0x112233445566778899aabbccddeeff00 as a 64 bit write
>> to VFP register D0 then regs[0] will be
>> 0x112233445566778899aabbccddeeff00 regardless of host endianness. That
>> is, the least significant 8 bits of D0 will be (regs[0] & 0xff). (This
>> isn't the same number as if you do the union-type-punning thing with
>> union { uint64_t l; uint8_t b[8]; } and look at b[0].)

This example is confusing because I carefully said "64 bit write"
and then used a 128 bit constant. What I meant was:

 ie if you store 0x1122334455667788 as a 64 bit write
 to VFP register D0 then regs[0] will be
 0x1122334455667788 regardless of host endianness.

For 128 bit vectors, if you store
0x112233445566778899aabbccddeeff00 to Q0 then you get
regs[0] == 0x99aabbccddeeff00
regs[1] == 0x1122334455667788

(as is required architecturally in order for a subsequent guest
read from D0 to do the right thing).

-- PMM