Re: [PATCH] Semihost SYS_READC implementation (v4)

[Peter Maydell]

On Thu, 14 Nov 2019 at 20:52, Richard Henderson
<address@hidden> wrote:
> Yet another reason why I prefer any semi-hosting call to use an encoding that
> is otherwise reserved illegal.
>
> For this, you have to make up your mind: is it important to execute the
> instructions as specified by the ISA, or as specified by the semi-hosting 
> spec?
>
> In this case, semi-hosting defines an "entry nop" that begins the sequence, 
> and
> I think that we are well within our rights to ignore the validity of "insn1
> insn2 || other-insn".

Perhaps. I think you get the same issue with
  insn1 || insn2
vs
  insn1 || some-other-insn

though. (And the spec has wording that explicitly wants the
latter to be handled with the normal "I'm a hint instruction"
behaviour of insn1.)

-- PMM