[PATCH v3 4/5] powerpc/lib/sstep: Add prty instruction emulation

[Michael Ellerman]

Segher Boessenkool <segher at kernel.crashing.org> writes:

> On Tue, Jul 25, 2017 at 01:33:19PM +1000, Matt Brown wrote:
>> +static nokprobe_inline void do_prty(struct pt_regs *regs, unsigned long v,
>> +				int size, int ra)
>> +{
>> +	unsigned long long res = v;
>> +
>> +	res = (0x0001000100010001 & res) + (0x0001000100010001 & (res >> 8));
>> +	res = (0x0000000700000007 & res) + (0x0000000700000007 & (res >> 16));
>> +	if (size == 32) {		/* prtyw */
>> +		regs->gpr[ra] = (0x0000000100000001 & res);
>> +		return;
>> +	}
>> +
>> +	res = (0x000000000000000f & res) + (0x000000000000000f & (res >> 32));
>> +	regs->gpr[ra] = res & 1;	/*prtyd */
>> +}
>
> Does 7's and 0xf look strange (since the top bit in the values there
> is always 0).  You always "and" the values with 1 later, you could do
> that immediately (and change + to ^).
>
> A general question about these patches: some things are inside #ifdef
> __powerpc64__, some are not.  It seems it is the wrong macro, and it
> should be used (or not used) consistently?

Why is it the wrong macro? Because we tend to use CONFIG_PPC64 you mean?

I thought the reason some are #ifdef'ed is that some are 64-bit only.
ie. bpermd is 64-bit only ?

cheers