Re: [PATCH] target/nios2: Use gen_io_start/end around wrctl instruction.

[Peter Maydell]

On Thu, 18 Jun 2020 at 18:31, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Thu, 18 Jun 2020 at 04:50, wentongw <wentong.wu@intel.com> wrote:
> >
> > From: Wentong Wu <wentong.wu@intel.com>
> >
> > wrctl instruction on nios2 target will cause checking cpu interrupt,
> > but tcg_handle_interrupt() will call cpu_abort() if the CPU gets an
> > interrupt while it's not in a 'can do IO' state, so around wrctl
> > instruction add gen_io_start/end.
> >
> > Signed-off-by: Wentong Wu <wentong.wu@intel.com>
> > ---
> >  target/nios2/translate.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/target/nios2/translate.c b/target/nios2/translate.c
> > index e17656e6..deaefcaf 100644
> > --- a/target/nios2/translate.c
> > +++ b/target/nios2/translate.c
> > @@ -32,6 +32,7 @@
> >  #include "exec/cpu_ldst.h"
> >  #include "exec/translator.h"
> >  #include "qemu/qemu-print.h"
> > +#include "exec/gen-icount.h"
> >
> >  /* is_jmp field values */
> >  #define DISAS_JUMP    DISAS_TARGET_0 /* only pc was modified dynamically */
> > @@ -518,7 +519,13 @@ static void wrctl(DisasContext *dc, uint32_t code, 
> > uint32_t flags)
> >      /* If interrupts were enabled using WRCTL, trigger them. */
> >  #if !defined(CONFIG_USER_ONLY)
> >      if ((instr.imm5 + CR_BASE) == CR_STATUS) {
> > +        if (tb_cflags(dc->tb) & CF_USE_ICOUNT) {
> > +            gen_io_start();
> > +        }
> >          gen_helper_check_interrupts(dc->cpu_env);
> > +        if (tb_cflags(dc->tb) & CF_USE_ICOUNT) {
> > +            gen_io_end();
> > +        }
>
> You also need to end the TB, which we should do whether
> we're using icount or not. This is awkward because nios2 has
> not correctly implemented the DISAS_UPDATE that is the right
> way to do that.

After some further discussion with other maintainers abotu
the gen_io_start/gen_io_end semantics, it turns out that
I was wrong about the need for gen_io_end -- if you are
going to end the TB after the I/O instruction (which you are
in this case) then you do not need the gen_io_end() call,
it is handled automatically for you by common code. So
you can drop that bit from the next version of this patch.

Sorry for the confusion.

thanks
-- PMM