Re: [Qemu-devel] [PATCH v11 23/29] target/arm: [tcg] Port to translate_insn

[Richard Henderson]

On 07/10/2017 03:47 AM, Lluís Vilanova wrote:
> Richard Henderson writes:
>
> > On 07/07/2017 07:18 AM, Lluís Vilanova wrote:
> > > There was no code being generated after this specific case, but I haven't
> > > checked if DISAS_EXC is set in any other place that is not immediately followed
> > > by a "goto done_generating".
>
> > Typically we haven't actually done a goto, but simply exit the loop and emit
> > nothing within the final cleanup (tb_stop?).
>
> The case handled by DISAS_SKIP ignores tb_stop() (the target code can simply
> return when DISAS_EXC is found instead of DISAS_SKIP) *and* gen_io_end(); this
> last one is never omitted when DISAS_EXC is found now, and theoretically
> DISAS_EXC can be set by any target-specific hook. Thus my question if the
> generic call to gen_io_end() should check for DISAS_EXC too (I have no idea if
> it would be an error to call it with DISAS_EXC set, or whether it makes sense to
> for a target to set it so that gen_io_start() is called but gen_io_end() is then
> skipped by a DISAS_EXC set in ops->translate_insn()).

It is not an error to call gen_io_start when gen_io_end isn't called (or isn't 
reached).  There are many ways that can happen.

The reason that arm does the goto after the gen_exception for single-stepping 
was simply convenience.  Nothing would have gone wrong if it had used

        dc->is_jmp = DISAS_EXC;
        break;

instead.


r~