On 13/12/2022 08.30, Philippe Mathieu-Daudé wrote:
On 13/12/22 01:14, Richard Henderson wrote:
On 12/12/22 17:05, Philippe Mathieu-Daudé wrote:
The device endianness doesn't change during runtime.
What are you talking about? Of course it does.
The host CPU certainly does, but the virtio device doesn't... Does it?
This check only consider the device, not the CPU:
bool virtio_access_is_big_endian(VirtIODevice *vdev)
{
#if defined(LEGACY_VIRTIO_IS_BIENDIAN)
return virtio_is_big_endian(vdev);
#elif TARGET_BIG_ENDIAN
if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
/*Devices conforming to VIRTIO 1.0 or later are always LE.*/
return false;
}
return true;
Well, this part here means that the endianness can indeed change on the
device side during runtime. Depending on whether VIRTIO_F_VERSION_1 is
negotiated or not, the device is little or big endian. Happens on s390x for
example - for legacy virtio, big endian is used, and for modern virtio,
little endian is used instead.
Thomas
