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Re: [Qemu-devel] [PATCH] target-arm: crypto: fix BE host support
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] target-arm: crypto: fix BE host support |
Date: |
Fri, 2 Jan 2015 17:36:05 +0000 |
On 2 January 2015 at 15:17, Laszlo Ersek <address@hidden> 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