Re: [Qemu-devel] [PATCH 02/10 v11] linux-user: Support tilegx architecture in linux-user

[Peter Maydell]

On 3 June 2015 at 13:30, Chen Gang <address@hidden> wrote:
> On 06/03/2015 01:40 AM, Peter Maydell wrote:
>> On 30 May 2015 at 22:10, Chen Gang <address@hidden> wrote:
>>>
>>> +#ifdef TARGET_TILEGX
>>> +
>>> +static uint64_t get_regval(CPUTLGState *env, uint8_t reg)
>>> +{
>>> +    if (likely(reg < TILEGX_R_COUNT)) {
>>> +        return env->regs[reg];
>>> +    } else if (reg != TILEGX_R_ZERO) {
>>> +        fprintf(stderr, "invalid register r%d for reading.\n", reg);
>>> +        g_assert_not_reached();
>>
>> You don't appear to be guaranteeing that the register value
>> is < TILEGX_R_COUNT anywhere: get_SrcA_X1() and friends
>> mask with 0x3f, but that only means you're guaranteed the
>> value is between 0 and 63, wherease TILEGX_R_COUNT is 56.
>> What does real hardware do if the encoded register value
>> is 56..63 ?
>>
>
> At present, it will g_assert_not_reached() too.

No, it is not possible for hardware to assert!

> 56..62 are hidden to
> outside. So I did not implement them, either. Need we still implement
> them?

You must do something. You can't allow guest code (even
broken guest code) to make QEMU assert. You need to find
out what the hardware does here, and do that.

thanks
-- PMM