Re: [RFC PATCH] target/s390x: move tcg_gen_insn_start to s390x_tr_insn_start

[Richard Henderson <richard.henderson@linaro.org>]

On 10/11/21 8:57 AM, Alex Bennée wrote:
> We use INDEX_op_insn_start to make the start of instruction
> boundaries. If we don't do it in the .insn_start hook things get
> confused especially now plugins want to use that marking to identify
> the start of instructions and will bomb out if it sees instrumented
> ops before the first instruction boundary.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   target/s390x/tcg/translate.c | 25 ++++++++++++++++++++++---
>   1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/target/s390x/tcg/translate.c b/target/s390x/tcg/translate.c
> index f284870cd2..fe145ff2eb 100644
> --- a/target/s390x/tcg/translate.c
> +++ b/target/s390x/tcg/translate.c
> @@ -6380,9 +6380,6 @@ static DisasJumpType translate_one(CPUS390XState *env, DisasContext *s)
>       /* Search for the insn in the table.  */
>       insn = extract_insn(env, s);
>   
> -    /* Emit insn_start now that we know the ILEN.  */
> -    tcg_gen_insn_start(s->base.pc_next, s->cc_op, s->ilen);
> -
>       /* Not found means unimplemented/illegal opcode.  */
>       if (insn == NULL) {
>           qemu_log_mask(LOG_UNIMP, "unimplemented opcode 0x%02x%02x\n",
> @@ -6550,8 +6547,30 @@ static void s390x_tr_tb_start(DisasContextBase *db, CPUState *cs)
>   {
>   }
>   
> +/*
> + * We just enough partial instruction decoding here to calculate the
> + * length of the instruction so we can drop the INDEX_op_insn_start
> + * before anything else is emitted in the TCGOp stream.
> + *
> + * See extract_insn for the full decode.
> + */
>   static void s390x_tr_insn_start(DisasContextBase *dcbase, CPUState *cs)
>   {
> +    CPUS390XState *env = cs->env_ptr;
> +    DisasContext *s = container_of(dcbase, DisasContext, base);
> +    uint64_t insn, pc = s->base.pc_next;
> +    int op, ilen;
> +
> +    if (unlikely(s->ex_value)) {
> +        ilen = s->ex_value & 0xf;
> +    } else {
> +        insn = ld_code2(env, s, pc);  /* FIXME: don't reload same pc twice */

I think we might as well delay the set of ilen until after the normal load, rather than 
introduce a fixme.

r~

> +        op = (insn >> 8) & 0xff;
> +        ilen = get_ilen(op);
> +    }
> +
> +    /* Emit insn_start now that we know the ILEN.  */
> +    tcg_gen_insn_start(s->base.pc_next, s->cc_op, ilen);
>   }
>   
>   static void s390x_tr_translate_insn(DisasContextBase *dcbase, CPUState *cs)
>