Re: [Qemu-devel] [PATCH v2 35/68] target/arm: Convert CPS (privileged)

[Peter Maydell]

On Sun, 25 Aug 2019 at 18:28, Richard Henderson
<address@hidden> wrote:
>
> On 8/25/19 9:20 AM, Peter Maydell wrote:
> > On Mon, 19 Aug 2019 at 22:38, Richard Henderson
> > <address@hidden> wrote:
> >>
> >> Signed-off-by: Richard Henderson <address@hidden>
> >> ---
> >>  target/arm/translate.c       | 87 +++++++++++++++---------------------
> >>  target/arm/a32-uncond.decode |  3 ++
> >>  target/arm/t32.decode        |  3 ++
> >>  3 files changed, 42 insertions(+), 51 deletions(-)
> >> diff --git a/target/arm/t32.decode b/target/arm/t32.decode
> >> index 18c268e712..354ad77fe6 100644
> >> --- a/target/arm/t32.decode
> >> +++ b/target/arm/t32.decode
> >> @@ -44,6 +44,7 @@
> >>  &bfi             !extern rd rn lsb msb
> >>  &sat             !extern rd rn satimm imm sh
> >>  &pkh             !extern rd rn rm imm tb
> >> +&cps             !extern mode imod M A I F
> >>
> >>  # Data-processing (register)
> >>
> >> @@ -340,6 +341,8 @@ CLZ              1111 1010 1011 ---- 1111 .... 1000 
> >> ....      @rdm
> >>      SMC          1111 0111 1111 imm:4 1000 0000 0000 0000     &i
> >>      HVC          1111 0111 1110 ....  1000 .... .... ....     \
> >>                   &i imm=%imm16_16_0
> >> +    CPS          1111 0011 1010 1111 1000 0 imod:2 M:1 A:1 I:1 F:1 mode:5 
> >> \
> >> +                 &cps
> >
> > In T32 the CPS insn overlaps with the hint space (hint insns have
> > bits [10:8] all-zeroes, whereas all the valid CPS insns have either
> > M set or one of the imod bits set) -- why doesn't it need to be
> > in the same insn group as the hints? If we're going to put it
> > separated in the .decode file from the insns it overlaps with
> > I guess a comment to that effect would help so it doesn't get
> > inadvertently reordered with them.
>
> It is grouped.  It's not immediately visible in the patch because there are a
> *lot* of insns that overlap with the hints and 3 lines of context are
> insufficient to see that.
>
> But the grouping is semi-visible in the indentation here.

I'm still confused, I think. The hint space is
+  NOP            1111 0011 1010 1111 1000 0000 ---- ----
(plus the more specific hint insns before that pattern with
fixed values in the [7:0] bits).
CPS falls into that space; but you've placed it with
SMC and HVC which don't fall into the hint space, because
they have 0111 in bits [27:24], not 0011.

thanks
-- PMM