Re: [PATCH v8 30/62] target/riscv: Update fp_status when float rounding mode changes

[LIU Zhiwei]

On 2020/6/3 12:27, Richard Henderson wrote:
> On 5/21/20 2:43 AM, LIU Zhiwei wrote:
> > @@ -174,6 +175,9 @@ static int write_frm(CPURISCVState *env, int csrno, 
> > target_ulong val)
> >       env->mstatus |= MSTATUS_FS;
> >   #endif
> >       env->frm = val & (FSR_RD >> FSR_RD_SHIFT);
> > +    if (!riscv_cpu_set_rounding_mode(env, env->frm)) {
> > +        return -1;
> > +    }
> This will raise an exception immediately in helper_csrrw().
>
> According to Section 8.2, the no exception should occur until the next fp
> operation that uses the invalid frm.
>
> You're doing this just fine in helper_set_rounding_mode(), which is sufficient
> for scalar fp ops.  Without looking forward to later patches, I suppose we'll
> need to do something else for vector fp ops.
Hi Richard,

I think you are right.  Maybe I should transmit frm to ctx->frm, and 
check ctx->frm in vector fp ops.

We can set ctx->frm = env->frm instead of ctx->frm = -1 in 
riscv_tr_init_disas_context.
And  remove the sentence ctx->frm = rm; from gen_set_rm.

Is it right?

Zhiwei
> r~