Re: [PATCH 14/16] target/arm: Implement ESB instruction

[Richard Henderson <richard.henderson@linaro.org>]

On 4/11/22 09:18, Peter Maydell wrote:
>> +      ESB        ---- 0011 0010 0000 1111 ---- 0001 0000
>> +    ]
> 
> Why don't we decode bits [11:8] here? I see it's the same
> as YIELD/WFE/WFI, but I'm not sure why we're not decoding
> those bits in those insns either...

See page F4-7074 in H.a, where bits [11:8] of the imm12 field are described with 'xxxx'.

>> +static bool trans_ESB(DisasContext *s, arg_ESB *a)
>> +{
>> +    if (dc_isar_feature(aa32_ras, s) &&
>> +        arm_dc_feature(s, ARM_FEATURE_EL2) &&
>> +        s->current_el <= 1) {
> 
> This is doing the right thing for M-profile but only rather
> indirectly because it happens to get caught by the FEATURE_EL2
> check.

Yes, I had though that a feature, reducing the number of checks, but...


> I think it would be safer to explicitly check for
> not-M-profile (which then gives you a place to put the
> "For M-profile minimal-RAS ESB can be a NOP" comment that got
> removed above).

... fair enough.

> I think a comment noting that without RAS we must NOP would
> be useful here.

Ok.


r~