Re: [Qemu-devel] [PATCH] target/m68k: fix set_cc_op()

[Richard Henderson]

On 12/21/2017 06:29 AM, Laurent Vivier wrote:
> The first call of set_cc_op() in a new translation sequence
> is done with old_op set to CC_OP_DYNAMIC (-1).
> 
> This will do an out of bound access to the array cc_op_live[].
> 
> We fix that by adding an entry in cc_op_live[] for CC_OP_DYNAMIC,
> and in this case we can also discard QREG_CC_OP.
> 
> Reported-by: Thomas Huth <address@hidden>
> Signed-off-by: Laurent Vivier <address@hidden>
> ---
>  target/m68k/cpu.h       | 2 +-
>  target/m68k/translate.c | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/target/m68k/cpu.h b/target/m68k/cpu.h
> index afae5f68ac..5d03764eab 100644
> --- a/target/m68k/cpu.h
> +++ b/target/m68k/cpu.h
> @@ -182,7 +182,7 @@ void cpu_m68k_set_fpcr(CPUM68KState *env, uint32_t val);
>   */
>  typedef enum {
>      /* Translator only -- use env->cc_op.  */
> -    CC_OP_DYNAMIC = -1,
> +    CC_OP_DYNAMIC,
>  
>      /* Each flag bit computed into cc_[xcnvz].  */
>      CC_OP_FLAGS,
> diff --git a/target/m68k/translate.c b/target/m68k/translate.c
> index b60909222c..61ac1a8e83 100644
> --- a/target/m68k/translate.c
> +++ b/target/m68k/translate.c
> @@ -207,6 +207,7 @@ typedef void (*disas_proc)(CPUM68KState *env, 
> DisasContext *s, uint16_t insn);
>  #endif
>  
>  static const uint8_t cc_op_live[CC_OP_NB] = {
> +    [CC_OP_DYNAMIC] = CCF_C | CCF_V | CCF_Z | CCF_N | CCF_X,
>      [CC_OP_FLAGS] = CCF_C | CCF_V | CCF_Z | CCF_N | CCF_X,
>      [CC_OP_ADDB ... CC_OP_ADDL] = CCF_X | CCF_N | CCF_V,
>      [CC_OP_SUBB ... CC_OP_SUBL] = CCF_X | CCF_N | CCF_V,

These bits are fine.

> @@ -237,6 +238,11 @@ static void set_cc_op(DisasContext *s, CCOp op)
>      if (dead & CCF_V) {
>          tcg_gen_discard_i32(QREG_CC_V);
>      }
> +
> +    /* Discard any computed CC_OP value */
> +    if (old_op == CC_OP_DYNAMIC) {
> +        tcg_gen_discard_i32(QREG_CC_OP);
> +    }

This doesn't help, since the previous setting of CC_OP is certain to be in a
different TB and therefore there is no code within the current TB to discard.


r~