Re: [Qemu-ppc] [PATCH 2/6] target-ppc: Implement darn instruction

[Nikunj A Dadhania]

Nikunj A Dadhania <address@hidden> writes:

> David Gibson <address@hidden> writes:
>
>> [ Unknown signature status ]
>> On Mon, Aug 08, 2016 at 07:33:37AM +1000, Benjamin Herrenschmidt wrote:
>>> On Sun, 2016-08-07 at 23:06 +0530, Nikunj A Dadhania wrote:
>>> > +target_ulong helper_darn(uint32_t l)
>>> > +{
>>> > +    target_ulong r = UINT64_MAX;
>>> > +
>>> > +    if (l <= 2) {
>>> > +        do {
>>> > +            r = random() * random();
>>> > +            r &= l ? UINT64_MAX : UINT32_MAX;
>>> > +        } while (r == UINT64_MAX);
>>> > +    }
>>> > +
>>> > +    return r;
>>> > +}
>>> >  #endif
>>> 
>>> Isn't this a bit week ? Look at the implementation of H_RANDOM...
>>
>> Indeed, you should be using the rng backend that H_RANDOM, virtio-rng
>> and the Intel random number instruction all use.

Can you point me to the intel instruction, I couldn't get rdrand
implementation.

> I was looking at implementing this, AFAIU, I have to get a new RNG
> object in the initialization routine. We would need an instance of this
> per machine. So for pseries I can add in ppc_spapr_init(). I am not sure
> in case of linux-user where should this be initialized.
>
> One other place was init_proc_POWER9(), but that will be per cpu and
> member of CPUPPCState structure. Advantage is it will work for system
> emulation and linux-user both and we would not need a lock.

More issues here. Random backend is not compiled for linux-user, adding
that wasn't difficult, but then rng_backend_request_entropy() uses
qemu_set_fd_handler() which is a stub for linux-user
(stubs/set-fd-handler.c)

Regards,
Nikunj