Re: [Qemu-ppc] [Qemu-devel] [PATCH 04/13] target-ppc: implement lxvll instruction

[Nikunj A Dadhania]

Richard Henderson <address@hidden> writes:

> On 12/05/2016 03:25 AM, Nikunj A Dadhania wrote:
>> +void helper_lxvll(CPUPPCState *env, target_ulong addr,
>> +                  target_ulong xt_num, target_ulong rb)
>> +{
>> +    ppc_vsr_t xt;
>> +
>> +    getVSR(xt_num, &xt, env);
>> +    if (unlikely((rb & 0xFF) == 0)) {
>> +        xt.s128 = int128_make128(0, 0);
>
> Nit: int128_zero.

Sure.

>> +    } else {
>> +        target_ulong end = ((rb & 0xFF) * 8) - 1;
>> +        if (msr_le) {
>> +            xt.u64[LO_IDX] = cpu_ldq_data_ra(env, addr, GETPC());
>> +            addr = addr_add(env, addr, 8);
>> +            xt.u64[HI_IDX] = cpu_ldq_data_ra(env, addr, GETPC());
>> +            xt.s128 = int128_and(xt.s128, mask_u128(127 - end, 127));
>
> The ISA document says that this is a sequence of byte operations.  Which means
> that END < 127 will not access bytes outside of the length.  Which means that
> your code will trigger SIGSEGV near page boundaries when real hardware
> won't.

In that case, I can use I can use cpu_ldub_data_ra()

> I also don't see how this does the right thing for little-endian.

Needs to be in big-endian order - two things
1) LO/HI swapped
2) No byte swapping

AFAIU the example given in ISA, i see the right output in my test.

Regards
Nikunj