Re: [PATCH 10/27] Replace config-time define HOST_WORDS_BIGENDIAN

Thomas Huth
2022-03-16T10:29:07Z

On 16/03/2022 10.53, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> Replace a config-time define with a compile time condition
> define (compatible with clang and gcc) that must be declared prior to
> its usage. This avoids having a global configure time define, but also
> prevents from bad usage, if the config header wasn't included before.
>
> This can help to make some code independent from qemu too.
>
> gcc supports __BYTE_ORDER__ from about 4.6 and clang from 3.2.
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
[...]
> @@ -188,7 +188,7 @@ CPU_CONVERT(le, 64, uint64_t)
> * a compile-time constant if you pass in a constant. So this can be
> * used to initialize static variables.
> */
> -#if defined(HOST_WORDS_BIGENDIAN)
> +#if HOST_BIG_ENDIAN
> # define const_le32(_x) \
> ((((_x) & 0x000000ffU) << 24) | \
> (((_x) & 0x0000ff00U) << 8) | \
> @@ -211,7 +211,7 @@ typedef union {
>
> typedef union {
> float64 d;
> -#if defined(HOST_WORDS_BIGENDIAN)
> +#if HOST_BIG_ENDIAN
> struct {
> uint32_t upper;
> uint32_t lower;
> @@ -235,7 +235,7 @@ typedef union {
>
> typedef union {
> float128 q;
> -#if defined(HOST_WORDS_BIGENDIAN)
> +#if HOST_BIG_ENDIAN
> struct {
> uint32_t upmost;
> uint32_t upper;
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index 0a5e67fb970e..7fdd88adb368 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -7,6 +7,8 @@
> #ifndef COMPILER_H
> #define COMPILER_H
>
> +#define HOST_BIG_ENDIAN (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)

Why don't you do it this way instead:

#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define HOST_WORDS_BIGENDIAN 1
#endif

... that way you could avoid the churn in all the other files?

Thomas