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


From: Richard Henderson
Subject: Re: [PATCH v8 30/62] target/riscv: Update fp_status when float rounding mode changes
Date: Tue, 2 Jun 2020 21:27:51 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0

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.


r~



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