Linux powerpc new system call instruction and ABI

[Nicholas Piggin]

Excerpts from Dmitry V. Levin's message of May 20, 2021 1:06 pm:
> On Thu, May 20, 2021 at 12:40:36PM +1000, Nicholas Piggin wrote:
> [...]
>> > Looks like struct pt_regs.trap already contains the information that could
>> > be used to tell 'sc' from 'scv': if (pt_regs.trap & ~0xf) == 0x3000, then
>> > it's scv.  Is my reading of arch/powerpc/include/asm/ptrace.h correct?
>> 
>> Hmm, I think it is. Certainly in the kernel regs struct it is, I had in 
>> my mind that we put it to 0xc00 when populating the user struct for
>> compatibility, but it seems not. So I guess this would work.
> 
> OK, can we state that (pt_regs.trap & ~0xf) == 0x3000 is a part of the scv
> ABI, so it's not going to change and could be relied upon by userspace?
> Could this be documented in Documentation/powerpc/syscall64-abi.rst,
> please?

Yeah I think we can do that. The kernel doesn't care what is put in the
userspace pt_regs.trap too much so if this is your preferred approach
then I will document it in the ABI.

Thanks,
Nick