Re: [Qemu-devel] [PATCH v1] s390x/cpumodel: wire up cpu type + id for TCG

[David Hildenbrand]

On 02.06.2017 16:04, Aurelien Jarno wrote:
> On 2017-06-02 12:52, David Hildenbrand wrote:
>>
>>>> +
>>>> +#ifndef CONFIG_USER_ONLY
>>>> +void HELPER(stidp)(CPUS390XState *env, uint64_t addr)
>>>> +{
>>>> +    S390CPU *cpu = s390_env_get_cpu(env);
>>>> +    uint64_t cpuid = s390_cpuid_from_cpu_model(cpu->model);
>>>> +
>>>> +    if (addr & 0x7) {
>>>> +        program_interrupt(env, PGM_SPECIFICATION, ILEN_LATER_INC);
>>>> +        return;
>>>> +    }
>>>> +
>>>> +    /* basic mode, write the cpu address into the first 4 bit of the ID */
>>>> +    cpuid |= ((uint64_t)env->cpu_num & 0xf) << 54;
>>>> +    cpu_stq_data(env, addr, cpuid);
>>>> +}
>>>> +#endif
>>>
>>> I don't really see the point of using an helper instead of just updating
>>> the existing code. From what I understand the cpuid does not change at
>>> runtime, so the s390_cpuid_from_cpu_model function can also be called 
>>> from translate.c.
>>>
>>> Aurelien
>>>
>>
>> From what I can see, conditional exceptions are more complicated to
>> implement without helpers (involves generating compares, jumps and so
> 
> In that case you don't need to do any compare an jump. It's a standard
> load/store alignement check, you can just specify the MO_ALIGN flag to
> the tcg_gen_qemu_st_i64 function.
> 

Thanks for the hint, will look into that. And also add low-address
protection checks.

-- 

Thanks,

David