Re: [PATCH v2] target/riscv: Fix shift count overflow

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 25/2/24 04:27, demin.han wrote:
> The result of (8 - 3 - vlmul) is negtive when vlmul >= 6,

Typo "negative".

> and results in wrong vill.
> 
> Signed-off-by: demin.han <demin.han@starfivetech.com>
> ---
>   target/riscv/vector_helper.c | 5 ++---
>   1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/target/riscv/vector_helper.c b/target/riscv/vector_helper.c
> index 84cec73eb2..fe56c007d5 100644
> --- a/target/riscv/vector_helper.c
> +++ b/target/riscv/vector_helper.c
> @@ -44,6 +44,7 @@ target_ulong HELPER(vsetvl)(CPURISCVState *env, target_ulong s1,
>       target_ulong reserved = s2 &
>                               MAKE_64BIT_MASK(R_VTYPE_RESERVED_SHIFT,
>                                               xlen - 1 - R_VTYPE_RESERVED_SHIFT);
> +    uint16_t vlen = cpu->cfg.vlenb << 3;
>       int8_t lmul;
>   
>       if (vlmul & 4) {
> @@ -53,10 +54,8 @@ target_ulong HELPER(vsetvl)(CPURISCVState *env, target_ulong s1,
>            * VLEN * LMUL >= SEW
>            * VLEN >> (8 - lmul) >= sew
>            * (vlenb << 3) >> (8 - lmul) >= sew
> -         * vlenb >> (8 - 3 - lmul) >= sew
>            */
> -        if (vlmul == 4 ||
> -            cpu->cfg.vlenb >> (8 - 3 - vlmul) < sew) {
> +        if (vlmul == 4 || (vlen >> (8 - vlmul)) < sew) {
>               vill = true;
>           }
>       }