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

[Richard Henderson <rth@twiddle.net>]

On 07/07/2017 01:13 AM, Lluís Vilanova wrote:
>>> +    if (dc->ss_active && !dc->pstate_ss) {
>>> +        /* Singlestep state is Active-pending.
>>> +         * If we're in this state at the start of a TB then either
>>> +         *  a) we just took an exception to an EL which is being debugged
>>> +         *     and this is the first insn in the exception handler
>>> +         *  b) debug exceptions were masked and we just unmasked them
>>> +         *     without changing EL (eg by clearing PSTATE.D)
>>> +         * In either case we're going to take a swstep exception in the
>>> +         * "did not step an insn" case, and so the syndrome ISV and EX
>>> +         * bits should be zero.
>>> +         */
>>> +        assert(dc->base.num_insns == 1);
>>> +        gen_exception(EXCP_UDEF, syn_swstep(dc->ss_same_el, 0, 0),
>>> +                      default_exception_el(dc));
>>> +        dc->base.is_jmp = DISAS_SKIP;
> 
>> This is surely DISAS_EXC -- see gen_step_complete_exception.
>> Why introduce a new name?
> 
> The original code goes straight to done_generating here, and that's the purpose
> of DISAS_SKIP (skip the code executed between the end of the loop and the
> done_generating label).

That is the purpose of DISAS_EXC too.  We've called a noreturn helper to raise 
an exception and all following code is unreached.  If there *was* any code 
being emitted afterward, that is arguably a bug.


r~