Re: [Qemu-devel] [PATCH 2/5] decodetree: Move documentation to docs/decodetree.rst

[Bastian Koppelmann]

On 2/24/19 12:29 AM, Richard Henderson wrote:
> +
> +Argument Sets
> +=============
> +
> +Syntax::
> +
> +  args_def    := '&' identifier ( args_elt )+ ( !extern )?
> +  args_elt    := identifier
> +
> +Each *args_elt* defines an argument within the argument set.
> +Each argument set will be rendered as a C structure "arg_$name"
> +with each of the fields being one of the member arguments.
> +
> +If ``!extern`` is specified, the backing structure is assumed
> +to have been already declared, typically via a second decoder.
> +
> +Argument set examples::
> +
> +  &reg3       ra rb rc
> +  &loadstore  reg base offset
> +


Can we explain why argument sets are useful? This was puzzling for me at 
first. Something like:

This is used to have shared translate functions for instructions with 
differently named arguments. For instance if two variants of the same 
instructions have different sizes in some immediate, we can use a 
argument set to group these immediates together and use the same 
translate functions for both.


Cheers,

Bastian