Re: [PATCH v2 4/5] target/riscv: FP extension requirements

[Weiwei Li]

在 2022/5/15 上午10:56, Tsukasa OI 写道:
> QEMU allowed inconsistent configurations that made floating point
> arithmetic effectively unusable.
>
> This commit adds certain checks for consistent FP arithmetic:
>
> -   F requires Zicsr
> -   Zfinx requires Zicsr
> -   Zfh/Zfhmin require F
> -   D requires F
> -   V requires D

Why 'V requires D'? I know partial vector instructions require D, 
However,  I think they  just like c.fsd

instruction requires D, not 'C requires D' or 'D requires C'. Is there 
any rvv spec change I don't know?

Regards.

Weiwei Li

> Because F/D/Zicsr are enabled by default (and an error will not occur unless
> we manually disable one or more of prerequisites), this commit just enforces
> the user to give consistent combinations.
>
> Signed-off-by: Tsukasa OI <research_trasio@irq.a4lg.com>
> ---
>   target/riscv/cpu.c | 25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index 0854ca9103..f910a41407 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -610,11 +610,36 @@ static void riscv_cpu_realize(DeviceState *dev, Error 
> **errp)
>               cpu->cfg.ext_ifencei = true;
>           }
>   
> +        if (cpu->cfg.ext_f && !cpu->cfg.ext_icsr) {
> +            error_setg(errp, "F extension requires Zicsr");
> +            return;
> +        }
> +
> +        if ((cpu->cfg.ext_zfh || cpu->cfg.ext_zfhmin) && !cpu->cfg.ext_f) {
> +            error_setg(errp, "Zfh/Zfhmin extensions require F extension");
> +            return;
> +        }
> +
> +        if (cpu->cfg.ext_d && !cpu->cfg.ext_f) {
> +            error_setg(errp, "D extension requires F extension");
> +            return;
> +        }
> +
> +        if (cpu->cfg.ext_v && !cpu->cfg.ext_d) {
> +            error_setg(errp, "V extension requires D extension");
> +            return;
> +        }
> +
>           if (cpu->cfg.ext_zdinx || cpu->cfg.ext_zhinx ||
>               cpu->cfg.ext_zhinxmin) {
>               cpu->cfg.ext_zfinx = true;
>           }
>   
> +        if (cpu->cfg.ext_zfinx && !cpu->cfg.ext_icsr) {
> +            error_setg(errp, "Zfinx extension requires Zicsr");
> +            return;
> +        }
> +
>           if (cpu->cfg.ext_zk) {
>               cpu->cfg.ext_zkn = true;
>               cpu->cfg.ext_zkr = true;