Re: [Qemu-devel] [PATCH v2 03/68] target/arm: Convert Data Processing (register)

[Peter Maydell]

On Mon, 19 Aug 2019 at 22:38, Richard Henderson
<address@hidden> wrote:
>
> Convert the register shifted by immediate form of the data
> processing insns.  For A32, we cannot yet remove any code
> because the legacy decoder intertwines the reg-shifted-reg
> and immediate forms.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  target/arm/translate.c | 229 ++++++++++++++++++++++++++++++++++-------
>  target/arm/a32.decode  |  28 +++++
>  target/arm/t32.decode  |  43 ++++++++
>  3 files changed, 264 insertions(+), 36 deletions(-)


> +#define DO_ANY3(NAME, OP, L, K)                                         \
> +    static bool trans_##NAME##_rrri(DisasContext *s, arg_s_rrr_shi *a)  \
> +    { StoreRegKind k = (K); return op_s_rrr_shi(s, a, OP, L, k); }

It's a bit non-obvious that we can return early via the expression K
here (for the "trying to do an old-style exception return in usermode"
case for SUB and MOV), but it does put the check early where we need it.

> +DO_ANY3(SUB, a->s ? gen_sub_CC : tcg_gen_sub_i32, false,
> +        ({
> +            StoreRegKind ret = STREG_NORMAL;
> +            if (a->rd == 15 && a->s) {
> +                /*
> +                 * See ALUExceptionReturn:
> +                 * In User mode, UNPREDICTABLE; we choose UNDEF.
> +                 * In Hyp mode, UNDEFINED.
> +                 */
> +                if (IS_USER(s) || s->current_el == 2) {
> +                    return false;
> +                }
> +                /* There is no writeback of nzcv to PSTATE.  */
> +                a->s = 0;
> +                ret = STREG_EXC_RET;
> +            } else if (a->rd == 13 && a->rn == 13) {
> +                ret = STREG_SP_CHECK;
> +            }
> +            ret;
> +        }))

It turns out that the decode for Thumb means that we don't
need to specifically check that this is Arm mode before allowing
the ALUExceptionReturn handling.

Reviewed-by: Peter Maydell <address@hidden>

thanks
-- PMM