Re: [Qemu-devel] [PATCH 2/2] s390x: Add laa and laag instructions

[Richard Henderson <rth@twiddle.net>]

On 05/07/2015 06:12 PM, Alexander Graf wrote:
> +static ExitStatus op_laa(DisasContext *s, DisasOps *o)
> +{
> +    TCGv_i64 m2 = tcg_temp_new_i64();
> +
> +    /* XXX should be atomic */
> +    tcg_gen_qemu_ld32s(m2, o->in2, get_mem_index(s));
> +
> +    /* Set r1 to the unmodified contents of m2 */
> +    tcg_gen_mov_i64(o->out, m2);
> +
> +    /* m2 = r3 + m2 */
> +    tcg_gen_add_i64(m2, o->in1, m2);
> +    tcg_gen_qemu_st32(m2, o->in2, get_mem_index(s));
> +
> +    /* Set in2 to the input operand for cc calculation */
> +    tcg_gen_mov_i64(o->in2, o->out);
> +
> +    tcg_temp_free_i64(m2);
> +    return NO_EXIT;
> +}

I don't believe that this computes the right cc.
You need to place m2 into in2, not out.

That said, maybe

  tcg_temp_free_i64(o->in2);
  o->in2 = m2;

is the right way to perform that copy.  Since we
know that in2 was in2_a2, allocating a temp for an
address, we also know we can both (1) free it and
(2) put another temp in there that will be freed.

Don't worry about the atomic-ness of the operation
until some of the many patch sets going round on
that very subject are resolved.  This will be good
enough for system mode for now.

I think maybe the whole target ought to be cleaned
up for the new TCGMemOps.  For this, you could share
the code for LAA and LAAG with the TCGMemOp in insn->data.


r~