Re: [PATCH] hw/mips/malta: Fix the malta machine on big endian hosts

[Peter Maydell]

On Thu, 30 Mar 2023 at 16:27, Thomas Huth <thuth@redhat.com> wrote:
>
> Booting a Linux kernel with the malta machine is currently broken
> on big endian hosts. The cpu_to_gt32 macro wants to byteswap a value
> for little endian targets only, but uses the wrong way to do this:
> cpu_to_[lb]e32 works the other way round on big endian hosts! Fix
> it by using the same ways on both, big and little endian hosts.
>
> Fixes: 0c8427baf0 ("hw/mips/malta: Use bootloader helper to set BAR 
> registers")
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  I've checked that both, the kernel from
>  https://landley.net/toybox/downloads/binaries/mkroot/0.8.9/mipsel.tgz
>  and the kernel from
>  https://landley.net/toybox/downloads/binaries/mkroot/0.8.9/mips.tgz
>  now boot fine on both, a little endian (x86) and a big endian (s390x) host.
>
>  hw/mips/malta.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/mips/malta.c b/hw/mips/malta.c
> index af9021316d..b26ed1fc9a 100644
> --- a/hw/mips/malta.c
> +++ b/hw/mips/malta.c
> @@ -629,9 +629,9 @@ static void bl_setup_gt64120_jump_kernel(void **p, 
> uint64_t run_addr,
>
>      /* Bus endianess is always reversed */
>  #if TARGET_BIG_ENDIAN
> -#define cpu_to_gt32 cpu_to_le32
> +#define cpu_to_gt32(x) (x)
>  #else
> -#define cpu_to_gt32 cpu_to_be32
> +#define cpu_to_gt32(x) bswap32(x)
>  #endif

So if we:
 * do nothing to the value on a BE host
 * swap the value on an LE host

isn't that the same as cpu_to_be32() in both cases?

thanks
-- PMM