[PATCH v4 00/16] Initial Prefixed Instruction support

[Nicholas Piggin]

Jordan Niethe's on March 23, 2020 7:25 pm:
> On Mon, Mar 23, 2020 at 5:22 PM Nicholas Piggin <npiggin at gmail.com> wrote:
>>
>> Jordan Niethe's on March 20, 2020 3:17 pm:
>> > A future revision of the ISA will introduce prefixed instructions. A
>> > prefixed instruction is composed of a 4-byte prefix followed by a
>> > 4-byte suffix.
>> >
>> > All prefixes have the major opcode 1. A prefix will never be a valid
>> > word instruction. A suffix may be an existing word instruction or a
>> > new instruction.
>> >
>> > This series enables prefixed instructions and extends the instruction
>> > emulation to support them. Then the places where prefixed instructions
>> > might need to be emulated are updated.
>> >
>> > The series is based on top of:
>> > https://patchwork.ozlabs.org/patch/1232619/ as this will effect
>> > kprobes.
>> >
>> > v4 is based on feedback from Nick Piggins, Christophe Leroy and Daniel Axtens.
>> > The major changes:
>> >     - Move xmon breakpoints from data section to text section
>> >     - Introduce a data type for instructions on powerpc
>>
>> Thanks for doing this, looks like a lot of work, I hope it works out :)
>>
> Yes it did end up touching a lot of places. I started thinking that
> that maybe it would be simpler to just use a u64 instead of the struct
> for  instructions.
> If we always keep the word instruction / prefix in the lower bytes,
> all of the current masking should still work and we can use operators
> again instead of ppc_inst_equal(), etc.

Yeah.. I think now that you've done it, I prefer it this way.

> It also makes printing easier. We could just #define INST_FMT %llx or
> #define INST_FMT %x on powerpc32 and use that for printing out
> instructions.

Well, not sure about that. Would it make endian concerns more
complicated? Print format for prefix might be '%016llx', but we
don't want that for all instructions only prefixed ones, and I
don't know if that is the way to go either.

We'll want to adopt some convention for displaying prefixed
instruction bytes, but I don't know what what works best. I wonder
if binutils or any userspace tools have a convention.

Which reminds me, you might have missed show_instructions()?
Although maybe you don't need that until we start using them in
the kernel.

Thanks,
Nick