Re: [Qemu-devel] [PATCH] i386: fix breakpoints handling in icount mode

[Frederic Konrad]

On 23/10/2014 07:57, Pavel Dovgaluk wrote:
> > From: Frederic Konrad [mailto:address@hidden
> > On 22/10/2014 13:38, Pavel Dovgalyuk wrote:
> >
> > Hi Pavel,
> > > This patch fixes instructions counting when execution is stopped on
> > > breakpoint (e.g. set from gdb). Without a patch extra instruction is translated
> > > and icount is incremented by invalid value (which equals to number of
> > > executed instructions + 1).
> > >
> > > Signed-off-by: Pavel Dovgalyuk <address@hidden>
> > > ---
> > >    target-i386/translate.c |    3 ++-
> > >    1 files changed, 2 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/target-i386/translate.c b/target-i386/translate.c
> > > index 1284173..193cf9f 100644
> > > --- a/target-i386/translate.c
> > > +++ b/target-i386/translate.c
> > > @@ -8000,7 +8000,7 @@ static inline void gen_intermediate_code_internal(X86CPU 
> > > *cpu,
> > >                    if (bp->pc == pc_ptr &&
> > >                        !((bp->flags & BP_CPU) && (tb->flags & HF_RF_MASK))) {
> > >                        gen_debug(dc, pc_ptr - dc->cs_base);
> > > -                    break;
> > > +                    goto done_generating;
> > This makes sense to me.
> > But I don't see why you don't just "break" like the other instruction in
> > this loop?
> Single break will just exit the breakpoints iteration loop. I'll need an 
> additional flag
> to break the translation loop. ARM does the same thing, anyway :)

Yes that's what I mentioned.
> > >                    }
> > >                }
> > >            }
> > > @@ -8049,6 +8049,7 @@ static inline void gen_intermediate_code_internal(X86CPU 
> > > *cpu,
> > >                break;
> > >            }
> > >        }
> > > +done_generating:
> > >        if (tb->cflags & CF_LAST_IO)
> > >            gen_io_end();
> > Is there any reason why you don't jump over this two lines in case of a
> > breakpoint?
> Shouldn't we switch off can_do_io flag if it was switched on?

Yes but can we switch on can_do_io if we have a breakpoint?

The code is not shown in this patch but there is:

        if (num_insns + 1 == max_insns && (tb->cflags & CF_LAST_IO))
            gen_io_start();

I think you can't reach this code if you exit the translation loop?

Fred
> > >        gen_tb_end(tb, num_insns);
> > I'll give it a try later and I'll let you know.
> Thanks.
>
> Pavel Dovgalyuk