Re: [Qemu-devel] [RISU v2 10/11] risu_reginfo_i386: replace xfeature constants with symbolic names

[Alex Bennée]

Jan Bobek <address@hidden> writes:

> The original code used "magic numbers", which made it unclear in
> some places. Include a reference to the Intel manual where the
> constants' meaning is discussed.
>
> Signed-off-by: Jan Bobek <address@hidden>

Reviewed-by: Alex Bennée <address@hidden>

> ---
>  risu_reginfo_i386.c | 48 +++++++++++++++++++++++++++++++--------------
>  1 file changed, 33 insertions(+), 15 deletions(-)
>
> diff --git a/risu_reginfo_i386.c b/risu_reginfo_i386.c
> index 35ff7c8..aba5ae3 100644
> --- a/risu_reginfo_i386.c
> +++ b/risu_reginfo_i386.c
> @@ -22,7 +22,25 @@
>
>  #include <asm/sigcontext.h>
>
> -static uint64_t xfeatures = 3;  /* SSE */
> +/*
> + * Refer to "Intel(R) 64 and IA-32 Architectures Software Developer's
> + * Manual", Volume 1, Section 13.1 "XSAVE-Supported Features and
> + * State-Component Bitmaps" for detailed discussion of these constants
> + * and their meaning.
> + */
> +enum {
> +    XFEAT_X87              = 1 << 0,
> +    XFEAT_SSE              = 1 << 1,
> +    XFEAT_AVX              = 1 << 2,
> +    XFEAT_AVX512_OPMASK    = 1 << 5,
> +    XFEAT_AVX512_ZMM_HI256 = 1 << 6,
> +    XFEAT_AVX512_HI16_ZMM  = 1 << 7,
> +    XFEAT_AVX512           = XFEAT_AVX512_OPMASK
> +                           | XFEAT_AVX512_ZMM_HI256
> +                           | XFEAT_AVX512_HI16_ZMM
> +};
> +
> +static uint64_t xfeatures = XFEAT_X87 | XFEAT_SSE;
>
>  static const struct option extra_ops[] = {
>      {"xfeatures", required_argument, NULL, FIRST_ARCH_OPT },
> @@ -160,34 +178,34 @@ void reginfo_init(struct reginfo *ri, ucontext_t *uc)
>       * Now we know that _fpstate contains XSAVE data.
>       */
>
> -    if (features & (1 << 2)) {
> +    if (features & XFEAT_AVX) {
>          /* YMM_Hi128 state */
> -        void *buf = xsave_feature_buf(xs, 2);
> +        void *buf = xsave_feature_buf(xs, XFEAT_AVX);
>          for (i = 0; i < nvecregs; ++i) {
>              memcpy(&ri->vregs[i].q[2], buf + 16 * i, 16);
>          }
>      }
>
> -    if (features & (1 << 5)) {
> +    if (features & XFEAT_AVX512_OPMASK) {
>          /* Opmask state */
> -        uint64_t *buf = xsave_feature_buf(xs, 5);
> +        uint64_t *buf = xsave_feature_buf(xs, XFEAT_AVX512_OPMASK);
>          for (i = 0; i < 8; ++i) {
>              ri->kregs[i] = buf[i];
>          }
>      }
>
> -    if (features & (1 << 6)) {
> +    if (features & XFEAT_AVX512_ZMM_HI256) {
>          /* ZMM_Hi256 state */
> -        void *buf = xsave_feature_buf(xs, 6);
> +        void *buf = xsave_feature_buf(xs, XFEAT_AVX512_ZMM_HI256);
>          for (i = 0; i < nvecregs; ++i) {
>              memcpy(&ri->vregs[i].q[4], buf + 32 * i, 32);
>          }
>      }
>
>  #ifdef __x86_64__
> -    if (features & (1 << 7)) {
> +    if (features & XFEAT_AVX512_HI16_ZMM) {
>          /* Hi16_ZMM state */
> -        void *buf = xsave_feature_buf(xs, 7);
> +        void *buf = xsave_feature_buf(xs, XFEAT_AVX512_HI16_ZMM);
>          for (i = 0; i < 16; ++i) {
>              memcpy(&ri->vregs[i + 16], buf + 64 * i, 64);
>          }
> @@ -243,7 +261,7 @@ static const char *const regname[NGREG] = {
>  static int get_nvecregs(uint64_t features)
>  {
>  #ifdef __x86_64__
> -    return features & (1 << 7) ? 32 : 16;
> +    return features & XFEAT_AVX512_HI16_ZMM ? 32 : 16;
>  #else
>      return 8;
>  #endif
> @@ -251,9 +269,9 @@ static int get_nvecregs(uint64_t features)
>
>  static int get_nvecquads(uint64_t features)
>  {
> -    if (features & (1 << 6)) {
> +    if (features & XFEAT_AVX512_ZMM_HI256) {
>          return 8;
> -    } else if (features & (1 << 2)) {
> +    } else if (features & XFEAT_AVX) {
>          return 4;
>      } else {
>          return 2;
> @@ -262,9 +280,9 @@ static int get_nvecquads(uint64_t features)
>
>  static char get_vecletter(uint64_t features)
>  {
> -    if (features & (1 << 6 | 1 << 7)) {
> +    if (features & (XFEAT_AVX512_ZMM_HI256 | XFEAT_AVX512_HI16_ZMM)) {
>          return 'z';
> -    } else if (features & (1 << 2)) {
> +    } else if (features & XFEAT_AVX) {
>          return 'y';
>      } else {
>          return 'x';
> @@ -301,7 +319,7 @@ int reginfo_dump(struct reginfo *ri, FILE *f)
>          }
>      }
>
> -    if (features & (1 << 5)) {
> +    if (features & XFEAT_AVX512_OPMASK) {
>          for (i = 0; i < 8; i++) {
>              fprintf(f, "  k%-5d: %016" PRIx64 "\n", i, ri->kregs[i]);
>          }


--
Alex Bennée