Re: [PATCH v4 1/6] xen: implement byteswap

["Roger Pau Monné" <roger.pau@citrix.com>]

On Mon, May 23, 2022 at 05:52:17AM -0400, Lin Liu wrote:
> diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
> index 933aec09a9..ae029afa14 100644
> --- a/xen/include/xen/compiler.h
> +++ b/xen/include/xen/compiler.h
> @@ -185,4 +185,28 @@
>  # define CLANG_DISABLE_WARN_GCC_COMPAT_END
>  #endif
>  
> +#ifndef __has_builtin
> +/*
> + * Backwards compatibility for GCC < 10.
> + * All supported versions of Clang support __has_builtin
> + * */
> +#define __has_builtin(x) GCC_has ## x
> +
> +#define GCC_has__builtin_bswap16 (CONFIG_GCC_VERSION >= 40800)
> +#define GCC_has__builtin_bswap32 (CONFIG_GCC_VERSION >= 40400)
> +#define GCC_has__builtin_bswap64 (CONFIG_GCC_VERSION >= 40400)
> +#endif
> +
> +#ifndef __ORDER_LITTLE_ENDIAN__
> +# define __ORDER_LITTLE_ENDIAN__ 1234
> +#endif
> +
> +#ifndef __ORDER_BIG_ENDIAN__
> +# define __ORDER_BIG_ENDIAN__ 4321
> +#endif
> +
> +/* Indirect macros required for expanded argument pasting. */
> +#define PASTE_(a, b) a ## b
> +#define PASTE(a, b) PASTE_(a, b)

I think it would be better if byteswap.h included lib.h, rather than
moving the PASTE define into compiler.h.

Likewise the __ORDER_{BIG,LITTLE}_ENDIAN__ defines would be better
placed in byteswap.h itself if possible IMO, since it's not strictly
related to the compiler.

Thanks, Roger.