Re: [PULL 53/61] target/riscv: Split out the vill from vtype

[Peter Maydell]

On Fri, 21 Jan 2022 at 09:42, Alistair Francis
<alistair.francis@opensource.wdc.com> wrote:
>
> From: LIU Zhiwei <zhiwei_liu@c-sky.com>
>
> We need not specially process vtype when XLEN changes.
>
> Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
> Message-id: 20220120122050.41546-16-zhiwei_liu@c-sky.com
> Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Odd thing I noticed looking at this code: as far as I can see we
may set env->vill to 1 in the vsetvl helper, but there is nowhere
that we set it to 0, so once it transitions to 1 it's stuck there
until the system is reset. Is this really right?

> diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
> index 89621e1996..6c740b92c1 100644
> --- a/target/riscv/cpu.h
> +++ b/target/riscv/cpu.h
> @@ -125,6 +125,7 @@ struct CPURISCVState {
>      target_ulong vl;
>      target_ulong vstart;
>      target_ulong vtype;
> +    bool vill;
>
>      target_ulong pc;
>      target_ulong load_res;
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 502aee84ab..327a2c4f1d 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -60,8 +60,7 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, target_ulong 
> *pc,
>          uint32_t maxsz = vlmax << sew;
>          bool vl_eq_vlmax = (env->vstart == 0) && (vlmax == env->vl) &&
>                             (maxsz >= 8);
> -        flags = FIELD_DP32(flags, TB_FLAGS, VILL,
> -                    FIELD_EX64(env->vtype, VTYPE, VILL));
> +        flags = FIELD_DP32(flags, TB_FLAGS, VILL, env->vill);
>          flags = FIELD_DP32(flags, TB_FLAGS, SEW, sew);
>          flags = FIELD_DP32(flags, TB_FLAGS, LMUL,
>                      FIELD_EX64(env->vtype, VTYPE, VLMUL));
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index 292f7e1624..b11d92b51b 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -283,7 +283,18 @@ static RISCVException write_fcsr(CPURISCVState *env, int 
> csrno,
>  static RISCVException read_vtype(CPURISCVState *env, int csrno,
>                                   target_ulong *val)
>  {
> -    *val = env->vtype;
> +    uint64_t vill;
> +    switch (env->xl) {
> +    case MXL_RV32:
> +        vill = (uint32_t)env->vill << 31;
> +        break;
> +    case MXL_RV64:
> +        vill = (uint64_t)env->vill << 63;
> +        break;
> +    default:
> +        g_assert_not_reached();
> +    }
> +    *val = (target_ulong)vill | env->vtype;
>      return RISCV_EXCP_NONE;
>  }
>
> diff --git a/target/riscv/machine.c b/target/riscv/machine.c
> index a4b7859c2a..740e11fcff 100644
> --- a/target/riscv/machine.c
> +++ b/target/riscv/machine.c
> @@ -124,8 +124,8 @@ static bool vector_needed(void *opaque)
>
>  static const VMStateDescription vmstate_vector = {
>      .name = "cpu/vector",
> -    .version_id = 1,
> -    .minimum_version_id = 1,
> +    .version_id = 2,
> +    .minimum_version_id = 2,
>      .needed = vector_needed,
>      .fields = (VMStateField[]) {
>              VMSTATE_UINT64_ARRAY(env.vreg, RISCVCPU, 32 * RV_VLEN_MAX / 64),
> @@ -134,6 +134,7 @@ static const VMStateDescription vmstate_vector = {
>              VMSTATE_UINTTL(env.vl, RISCVCPU),
>              VMSTATE_UINTTL(env.vstart, RISCVCPU),
>              VMSTATE_UINTTL(env.vtype, RISCVCPU),
> +            VMSTATE_BOOL(env.vill, RISCVCPU),
>              VMSTATE_END_OF_LIST()
>          }
>  };
> diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> index ad505ec9b2..a9484c22ea 100644
> --- a/target/riscv/vector_helper.c
> +++ b/target/riscv/vector_helper.c
> @@ -52,7 +52,8 @@ target_ulong HELPER(vsetvl)(CPURISCVState *env, 
> target_ulong s1,
>          || (ediv != 0)
>          || (reserved != 0)) {
>          /* only set vill bit. */
> -        env->vtype = FIELD_DP64(0, VTYPE, VILL, 1);
> +        env->vill = 1;
> +        env->vtype = 0;
>          env->vl = 0;
>          env->vstart = 0;
>          return 0;
> --
> 2.31.1

thanks
-- PMM