Re: [PATCH v4 03/16] powerpc: Use a datatype for instructions

Jordan Niethe's on March 23, 2020 7:28 pm:

On Mon, Mar 23, 2020 at 5:27 PM Nicholas Piggin [off-list ref] wrote:

quoted

Jordan Niethe's on March 20, 2020 3:17 pm:

quoted

Currently unsigned ints are used to represent instructions on powerpc.
This has worked well as instructions have always been 4 byte words.
However, a future ISA version will introduce some changes to
instructions that mean this scheme will no longer work as well. This
change is Prefixed Instructions. A prefixed instruction is made up of a
word prefix followed by a word suffix to make an 8 byte double word
instruction. No matter the endianess of the system the prefix always
comes first. Prefixed instructions are only planned for powerpc64.

Introduce a ppc_inst type to represent both prefixed and word
instructions on powerpc64 while keeping it possible to exclusively have
word instructions on powerpc32, A latter patch will expand the type to
include prefixed instructions but for now just typedef it to a u32.

Later patches will introduce helper functions and macros for
manipulating the instructions so that powerpc64 and powerpc32 might
maintain separate type definitions.

ppc_inst_t I would slightly prefer for a typedef like this.

Are _t types meant to be reserved?

No, just convention that structs are not normally typedefed unless
they are a pervasive interface that gets passed around a lot but
does not get accessed without accessor functions much. When you do
typedef them, add a _t (or less frequently _s/_u/etc). pte_t,
cpumask_t, atomic_t.

Thanks,
Nick