Re: [PATCH 2/2] aarch64: Allow feature flags to occupy >64 bits

["Richard Earnshaw (lists)" <Richard.Earnshaw@arm.com>]

On 25/09/2023 21:26, Richard Sandiford via Binutils wrote:
> Following on from the previous patch to make the feature macros take
> a word number, this one increases the number of flag words from 1 to 2.
> 
> The patch uses some dummy features to push the number of features
> over 64.  The intention is that these should be reused by real
> features rather than kept as-is.
> ---
>  include/opcode/aarch64.h | 62 +++++++++++++++++++++++++---------------
>  1 file changed, 39 insertions(+), 23 deletions(-)

OK.

R.

> 
> diff --git a/include/opcode/aarch64.h b/include/opcode/aarch64.h
> index 54ac1d85fd4..ab42acac8c2 100644
> --- a/include/opcode/aarch64.h
> +++ b/include/opcode/aarch64.h
> @@ -158,7 +158,11 @@ enum aarch64_feature_bit {
>    /* Common Short Sequence Compression instructions.  */
>    AARCH64_FEATURE_CSSC,
>    /* SME2.  */
> -  AARCH64_FEATURE_SME2
> +  AARCH64_FEATURE_SME2,
> +  DUMMY1,
> +  DUMMY2,
> +  DUMMY3,
> +  AARCH64_NUM_FEATURES
>  };
>  
>  /* These macros take an initial argument X that gives the index into
> @@ -257,50 +261,61 @@ enum aarch64_feature_bit {
>  #define AARCH64_ARCH_NONE(X)	0
>  
>  /* CPU-specific features.  */
> -typedef unsigned long long aarch64_feature_set;
> +typedef struct {
> +  uint64_t flags[(AARCH64_NUM_FEATURES + 63) / 64];
> +} aarch64_feature_set;
>  
>  #define AARCH64_CPU_HAS_FEATURE(CPU,FEAT)	\
> -  ((~(CPU) & AARCH64_FEATBIT (0, FEAT)) == 0)
> +  ((~(CPU).flags[0] & AARCH64_FEATBIT (0, FEAT)) == 0		\
> +   && (~(CPU).flags[1] & AARCH64_FEATBIT (1, FEAT)) == 0)
>  
>  #define AARCH64_CPU_HAS_ALL_FEATURES(CPU,FEAT)	\
> -  ((~(CPU) & (FEAT)) == 0)
> +  ((~(CPU).flags[0] & (FEAT).flags[0]) == 0	\
> +   && (~(CPU).flags[1] & (FEAT).flags[1]) == 0)
>  
>  #define AARCH64_CPU_HAS_ANY_FEATURES(CPU,FEAT)	\
> -  (((CPU) & (FEAT)) != 0)
> +  (((CPU).flags[0] & (FEAT).flags[0]) != 0	\
> +   || ((CPU).flags[1] & (FEAT).flags[1]) != 0)
>  
>  #define AARCH64_SET_FEATURE(DEST, FEAT) \
> -  ((DEST) = FEAT (0))
> +  ((DEST).flags[0] = FEAT (0),		\
> +   (DEST).flags[1] = FEAT (1))
>  
>  #define AARCH64_CLEAR_FEATURE(DEST, SRC, FEAT)		\
> -  ((DEST) = (SRC) & ~AARCH64_FEATBIT (0, FEAT))
> -
> -#define AARCH64_MERGE_FEATURE_SETS(TARG,F1,F2)	\
> -  do						\
> -    {						\
> -      (TARG) = (F1) | (F2);			\
> -    }						\
> +  ((DEST).flags[0] = (SRC).flags[0] & ~AARCH64_FEATBIT (0, FEAT), \
> +   (DEST).flags[1] = (SRC).flags[1] & ~AARCH64_FEATBIT (1, FEAT))
> +
> +#define AARCH64_MERGE_FEATURE_SETS(TARG,F1,F2)		\
> +  do							\
> +    {							\
> +      (TARG).flags[0] = (F1).flags[0] | (F2).flags[0];	\
> +      (TARG).flags[1] = (F1).flags[1] | (F2).flags[1];	\
> +    }							\
>    while (0)
>  
> -#define AARCH64_CLEAR_FEATURES(TARG,F1,F2)	\
> -  do						\
> -    { 						\
> -      (TARG) = (F1) &~ (F2);			\
> -    }						\
> +#define AARCH64_CLEAR_FEATURES(TARG,F1,F2)		\
> +  do							\
> +    {							\
> +      (TARG).flags[0] = (F1).flags[0] &~ (F2).flags[0];	\
> +      (TARG).flags[1] = (F1).flags[1] &~ (F2).flags[1];	\
> +    }							\
>    while (0)
>  
>  /* aarch64_feature_set initializers for no features and all features,
>     respectively.  */
> -#define AARCH64_NO_FEATURES 0
> -#define AARCH64_ALL_FEATURES -1
> +#define AARCH64_NO_FEATURES { { 0, 0 } }
> +#define AARCH64_ALL_FEATURES { { -1, -1 } }
>  
>  /* An aarch64_feature_set initializer for a single feature,
>     AARCH64_FEATURE_<FEAT>.  */
> -#define AARCH64_FEATURE(FEAT) AARCH64_FEATBIT (0, FEAT)
> +#define AARCH64_FEATURE(FEAT) \
> +  { { AARCH64_FEATBIT (0, FEAT), AARCH64_FEATBIT (1, FEAT) } }
>  
>  /* An aarch64_feature_set initializer for a specific architecture version,
>     including all the features that are enabled by default for that architecture
>     version.  */
> -#define AARCH64_ARCH_FEATURES(ARCH) AARCH64_ARCH_##ARCH (0)
> +#define AARCH64_ARCH_FEATURES(ARCH) \
> +  { { AARCH64_ARCH_##ARCH (0), AARCH64_ARCH_##ARCH (1) } }
>  
>  /* Used by AARCH64_CPU_FEATURES.  */
>  #define AARCH64_OR_FEATURES_1(X, ARCH, F1) \
> @@ -325,7 +340,8 @@ typedef unsigned long long aarch64_feature_set;
>  /* An aarch64_feature_set initializer for a CPU that implements architecture
>     version ARCH, and additionally provides the N features listed in "...".  */
>  #define AARCH64_CPU_FEATURES(ARCH, N, ...)			\
> -  AARCH64_OR_FEATURES_##N (0, ARCH, __VA_ARGS__)
> +  { { AARCH64_OR_FEATURES_##N (0, ARCH, __VA_ARGS__),		\
> +      AARCH64_OR_FEATURES_##N (1, ARCH, __VA_ARGS__) } }
>  
>  /* An aarch64_feature_set initializer for the N features listed in "...".  */
>  #define AARCH64_FEATURES(N, ...) \