[PATCH 1/2] aarch64: use macro trickery to automate feature array size replication

[Jan Beulich]

On 06.06.2025 14:27, Richard Earnshaw wrote:
> --- a/include/opcode/aarch64.h
> +++ b/include/opcode/aarch64.h
> @@ -290,13 +290,44 @@ enum aarch64_feature_bit {
>    AARCH64_NUM_FEATURES
>  };
>  
> +typedef uint64_t aarch64_feature_word;
> +#define AARCH64_BITS_PER_FEATURE_WORD 64
> +
> +/* Maximum number of features that we can currently support.  If you
> +   need to increase this value you will need to increase the number of
> +   replication statements in AA64_REPLICATE below.  */
> +#define AARCH64_MAX_FEATURES (AARCH64_BITS_PER_FEATURE_WORD * 2)

Maybe you can get away without this (and hence without any need to keep
two things in sync)?

> +static_assert (AARCH64_MAX_FEATURES > AARCH64_NUM_FEATURES,

(As an aside - isn't >= sufficient here?)

> +	       "Insufficent capacity in AARCH64_MAX_FEATURES");
> +
> +#define AA64_REPLICATE(SEP, BODY, ...)	\
> +  BODY (0, __VA_ARGS__) SEP		\
> +  BODY (1, __VA_ARGS__)

Move the static_assert() further down and use

#define XYZ_BODY(x, ...) [x] = (x)

static_assert (AARCH64_BITS_PER_FEATURE_WORD
	       * sizeof ((char[]){ AA64_REPLICATE (REP_COMMA, XYZ_BODY) })
	       >= AARCH64_NUM_FEATURES,
	       "Insufficient repetitions in AA64_REPLICATE()");

Jan