Re: [PATCH 08/16] hw/virtio: Replace HOST_BIG_ENDIAN #ifdef with runtime if() check

[Farhan Ali <alifm@linux.ibm.com>]

On 10/10/2025 6:42 AM, Philippe Mathieu-Daudé wrote:
> Replace compile-time #ifdef with a runtime check to ensure all code
> paths are built and tested. This reduces build-time configuration
> complexity and improves maintainability.
>
> No functional change intended.
>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   include/hw/virtio/virtio-access.h | 6 +-----
>   hw/virtio/vhost.c                 | 7 +++----
>   2 files changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
> index 07aae69042a..80328912ad3 100644
> --- a/include/hw/virtio/virtio-access.h
> +++ b/include/hw/virtio/virtio-access.h
> @@ -149,11 +149,7 @@ static inline uint64_t virtio_ldq_p(VirtIODevice *vdev, const void *ptr)
>   
>   static inline uint16_t virtio_tswap16(VirtIODevice *vdev, uint16_t s)
>   {
> -#if HOST_BIG_ENDIAN
> -    return virtio_access_is_big_endian(vdev) ? s : bswap16(s);
> -#else
> -    return virtio_access_is_big_endian(vdev) ? bswap16(s) : s;
> -#endif
> +    return HOST_BIG_ENDIAN ^ virtio_access_is_big_endian(vdev) ? s : bswap16(s);

This patch breaks virtio devices(at least input/net devices) on s390x. I 
am not sure if ^ is the right check here? Changing the logic back to how 
it was fixes it for me.

Thanks

Farhan

>   }
>   
>   static inline uint16_t virtio_lduw_phys_cached(VirtIODevice *vdev,
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 266a11514a1..6343477b42f 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1168,11 +1168,10 @@ static inline bool vhost_needs_vring_endian(VirtIODevice *vdev)
>       if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
>           return false;
>       }
> -#if HOST_BIG_ENDIAN
> -    return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_LITTLE;
> -#else
> +    if (HOST_BIG_ENDIAN) {
> +        return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_LITTLE;
> +    }
>       return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
> -#endif
>   }
>   
>   static int vhost_virtqueue_set_vring_endian_legacy(struct vhost_dev *dev,