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

[Frederic Konrad]

On 23/10/2014 09:52, Pavel Dovgaluk wrote:
> > From: Frederic Konrad [mailto:address@hidden
> > 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?
> This is not the only gen_io_start call. It is called from some of the 
> instructions'
> translation functions, that could precede the breakpoint.
>
> Pavel Dovgalyuk
True, there are 8 others place where gen_io_start is called in this 
file, but they
seems to be each time followed by a gen_io_end?

eg:

static inline void gen_ins(DisasContext *s, TCGMemOp ot)
{
    if (use_icount)
        gen_io_start();
    gen_string_movl_A0_EDI(s);
    /* Note: we must do this dummy write first to be restartable in
       case of page fault. */
    tcg_gen_movi_tl(cpu_T[0], 0);
    gen_op_st_v(s, ot, cpu_T[0], cpu_A0);
    tcg_gen_trunc_tl_i32(cpu_tmp2_i32, cpu_regs[R_EDX]);
    tcg_gen_andi_i32(cpu_tmp2_i32, cpu_tmp2_i32, 0xffff);
    gen_helper_in_func(ot, cpu_T[0], cpu_tmp2_i32);
    gen_op_st_v(s, ot, cpu_T[0], cpu_A0);
    gen_op_movl_T0_Dshift(ot);
    gen_op_add_reg_T0(s->aflag, R_EDI);
    if (use_icount)
        gen_io_end();
}