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

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2014-10-22 13:38, Pavel Dovgalyuk wrote:
> 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;
>                  }
>              }
>          }
> @@ -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();
>      gen_tb_end(tb, num_insns);
> 
> 
> 

Didn't looked into why, just bisected that this patch breaks at least
certain guest-originated break- or watchpoints in TCG mode. Can be
triggered by booting a Linux kernel with kgdb self-tests enabled. The
result is some false reporting of a host-originated debug stop to
gdb_set_stop_cpu while gdbserver_state is NULL -> SEGV.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux