Re: [Qemu-devel] out of bounds in set_cc_op()

[Paolo Bonzini]

On 21/12/2017 15:13, Laurent Vivier wrote:
> Le 21/12/2017 à 15:10, Paolo Bonzini a écrit :
>> On 21/12/2017 14:32, Laurent Vivier wrote:
>>> Le 21/12/2017 à 14:07, Laurent Vivier a écrit :
>>>> Le 21/12/2017 à 13:49, Thomas Huth a écrit :
>>>>> On 20.12.2017 22:56, Paolo Bonzini wrote:
>>>>>> On 20/12/2017 20:20, Peter Maydell wrote:
>>>>>>> On the x86/sanitizer build, new runtime errors:
>>>>>>>   GTESTER check-qtest-m68k
>>>>>>> /home/petmay01/linaro/qemu-for-merges/target/m68k/translate.c:230:12:
>>>>>>> runtime error: index -1 out of bounds for type 'const uint8_t [11]'
>>>>>>>
>>>>>>> ...and similar fails on one or two boards on most of the other
>>>>>>> guest architectures.
>>>>>>
>>>>>> These are preexisting bugs, now exposed by the boot-serial-test.
>>>>>> Thomas, can you identify the architectures that have a problem and
>>>>>> notify the maintainers?  In the meanwhile I'll keep the boot-serial-test
>>>>>> enhancements queued locally, and remove them from the pull request.
>>>>>
>>>>>  Laurent, Richard,
>>>>>
>>>>> looks like old_op is -1 when set_cc_op() is called here for the first
>>>>> time. The problem can be reproduced by running the mini-kernel directly.
>>>>> Just get http://people.redhat.com/~thuth/m68k-uart.bin and run QEMU like
>>>>> this:
>>>>>
>>>>>  qemu-system-m68k -nographic -kernel  ~/tmp/m68k-uart.bin -serial none
>>>>>
>>>>> That kernel only contains these few instructions:
>>>>>
>>>>>   0x41, 0xf9, 0xfc, 0x06, 0x00, 0x00,     /* lea 0xfc060000,%a0 */
>>>>>   0x10, 0x3c, 0x00, 0x54,                 /* move.b #'T',%d0 */
>>>>>   0x11, 0x7c, 0x00, 0x04, 0x00, 0x08,     /* move.b #4,8(%a0) */
>>>>>   0x11, 0x40, 0x00, 0x0c,                 /* move.b %d0,12(%a0) */
>>>>>   0x60, 0xfa                              /* bra.s  loop */
>>>>>
>>>>> The problem occurs during the second instruction (i.e. the first move.b).
>>>>>
>>>>> Do you have any ideas where this -1 in s->cc_op could come from?
>>>>
>>>> I think it comes from CCOp: it's the value of CC_OP_DYNAMIC.
>>>>
>>>> We should not use it to access cc_op_live[].
>>>>
>>>> I try to find a fix, but I think Richard knows this better than me.
>>>
>>> This should fix the problem, but I'd like Richard checks it...
>>>
>>> diff --git a/target/m68k/translate.c b/target/m68k/translate.c
>>> index b60909222c..721b5801da 100644
>>> --- a/target/m68k/translate.c
>>> +++ b/target/m68k/translate.c
>>> @@ -225,6 +225,11 @@ static void set_cc_op(DisasContext *s, CCOp op)
>>>      s->cc_op = op;
>>>      s->cc_op_synced = 0;
>>>
>>> +    if (old_op == CC_OP_DYNAMIC) {
>>> +        tcg_gen_discard_i32(QREG_CC_OP);
>>> +        return;
>>> +    }
>>
>> This tcg_gen_discard_i32 is correct, but all flags were potentially live
>> and can be discarded if the new op uses it(*).  So I'd replace "return"
>> with "old_op = CC_OP_FLAGS".
> 
> Yes, I agree, we can also have:
> 
> iff --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,
> @@ -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);
> +    }
>  }
> 
>  /* Update the CPU env CC_OP state.  */
> 
> 

Yes, this is good too.  After my pull request is in, feel free to take
Thomas's m68k boot-serial-test patch in your tree.

Paolo