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

["Pavel Dovgaluk" <Pavel.Dovgaluk@ispras.ru>]

> From: Frederic Konrad [mailto:fred.konrad@greensocs.com]
> On 23/10/2014 07:57, Pavel Dovgaluk wrote:
> >> From: Frederic Konrad [mailto:fred.konrad@greensocs.com]
> >> 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 <pavel.dovgaluk@ispras.ru>
> >>> ---
> >>>    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