Re: [Qemu-devel] [PATCH v3 10/22] target/arm: Allow EL change hooks to do IO

[Peter Maydell <peter.maydell@linaro.org>]

On 12 April 2018 at 18:08, Aaron Lindsay <alindsay@codeaurora.org> wrote:
> On Apr 12 17:53, Peter Maydell wrote:
>> On 16 March 2018 at 20:31, Aaron Lindsay <alindsay@codeaurora.org> wrote:
>> > During code generation, surround CPSR writes and exception returns which
>> > call the EL change hooks with gen_io_start/end. The immediate need is
>> > for the PMU to access the clock and icount during EL change to support
>> > mode filtering.
>> >
>> > Signed-off-by: Aaron Lindsay <alindsay@codeaurora.org>
>> > ---
>> >  target/arm/translate-a64.c | 2 ++
>> >  target/arm/translate.c     | 4 ++++
>> >  2 files changed, 6 insertions(+)
>> >
>> > diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
>> > index 31ff047..e1ae676 100644
>> > --- a/target/arm/translate-a64.c
>> > +++ b/target/arm/translate-a64.c
>> > @@ -1919,7 +1919,9 @@ static void disas_uncond_b_reg(DisasContext *s, uint32_t insn)
>> >              unallocated_encoding(s);
>> >              return;
>> >          }
>> > +        gen_io_start();
>> >          gen_helper_exception_return(cpu_env);
>> > +        gen_io_end();
>>
>> You don't want to call gen_io_start() or gen_io_end() unless
>> tb_cflags(s->base.tb) & CF_USE_ICOUNT) is true.
>>
>> (Ditto in the other cases below.)
>
> I assume there's nothing tricky about this and updating this as follows
> is sufficient?

Yes, that's sufficient. (The other thing that needs to happen
for a gen_io_start/end is that the insn has to end the TB --
but in all these cases that's already true as they set
s->base.is_jmp = DISAS_EXIT.)

thanks
-- PMM