Re: [PATCH v4 03/45] target/arm: Trap non-streaming usage when Streaming SVE is active

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

On 7/1/22 16:36, Peter Maydell wrote:
>> +    /*
>> +     * The SME exception we are testing for is raised via
>> +     * AArch64.CheckFPAdvSIMDEnabled(), and for AArch32 this is called
>> +     * when EL1 is using A64 or EL2 using A64 and !TGE.
>> +     * See AArch32.CheckAdvSIMDOrFPEnabled().
>> +     */
>> +    if (el == 0
>> +        && FIELD_EX64(env->svcr, SVCR, SM)
>> +        && (!arm_is_el2_enabled(env)
>> +            || (arm_el_is_aa64(env, 2) && !(env->cp15.hcr_el2 & HCR_TGE)))
>> +        && arm_el_is_aa64(env, 1)
>> +        && !sme_fa64(env, el)) {
> 
> I can't get any of:
>   * the logic in the comment
>   * the logic in the C code
>   * the logic in the the pseudocode AArch32.CheckAdvSIMDOrFPEnabled()
>     which causes it to call AArch64.CheckFPEnabled()
> to line up with each other.
> 
> The comment has:
>   * (EL1 A64) OR (EL2 A64 && !TGE)
> The pseudocode has:
>   * (!TGE && EL1 A64) OR (TGE && EL2 A64 && EL1 A64)
>     [seems odd that it is checking the width of EL1 in the TGE case
>      but I haven't followed the logic through to find out why]
> The C code here has:
>   * (!TGE && EL2 A64 && EL1 A64)
> 
> What am I missing ?

I'm looking at 0487H.a... are you looking at a different version?
Because the pseudocode I see isn't what you list above:

> if PSTATE.EL == EL0 && (!EL2Enabled() || (!ELUsingAArch32(EL2) && HCR_EL2.TGE == '0')) &&

> !ELUsingAArch32(EL1) then
So

   (!EL2 || (EL2 A64 && !TGE)) && EL1 A64

which is, as far as I can see, what the C code has.

I'll adjust the comment, anyway.


r~