Re: [PATCH 02/17] meson: do not use set10

[Richard Henderson <richard.henderson@linaro.org>]

On 10/15/23 23:31, Paolo Bonzini wrote:
> Make all items of config-host.h consistent.  To keep the --disable-coroutine-pool
> code visible to the compiler, mutuate the IS_ENABLED() macro from Linux.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   include/qemu/compiler.h     | 15 +++++++++++++++
>   meson.build                 |  2 +-
>   tests/unit/test-coroutine.c |  2 +-
>   util/qemu-coroutine.c       |  4 ++--
>   4 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
> index 1109482a000..c797f0d4572 100644
> --- a/include/qemu/compiler.h
> +++ b/include/qemu/compiler.h
> @@ -212,4 +212,19 @@
>   # define QEMU_USED
>   #endif
>   
> +/*
> + * Ugly CPP trick that is like "defined FOO", but also works in C
> + * code.  Useful to replace #ifdef with "if" statements; assumes
> + * the symbol was defined with Meson's "config.set()", so it is empty
> + * if defined.
> + */
> +#define IS_ENABLED(x)                  IS_EMPTY(x)
> +
> +#define IS_EMPTY_JUNK_                 junk,
> +#define IS_EMPTY(value)                IS_EMPTY_(IS_EMPTY_JUNK_##value)
> +
> +/* Expands to either SECOND_ARG(junk, 1, 0) or SECOND_ARG(IS_EMPTY_JUNK_CONFIG_FOO 1, 0)  */
> +#define SECOND_ARG(first, second, ...) second
> +#define IS_EMPTY_(junk_maybecomma)     SECOND_ARG(junk_maybecomma 1, 0)

Clever that.

However, if I had a preference I would go the other way and model after glibc:

Convert everything away from ifdef and always use set01.
Then enable -Wundef so that you catch typos in the usage of these macros.

But this is an improvement of a sort so,
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~