Re: [PATCH v2 3/5] linux-user/i386: Emulate x86_64 vsyscalls

[Paolo Bonzini]

On 21/01/20 17:15, Alex Bennée wrote:
> 
> Richard Henderson <address@hidden> writes:
> 
>> On 1/21/20 12:13 AM, Alex Bennée wrote:
>>>
>>> Richard Henderson <address@hidden> writes:
>>>
>>>> On 1/20/20 1:48 AM, Alex Bennée wrote:
>>>>>> +    default:
>>>>>> +    sigsegv:
>>>>>
>>>>> this label looks a little extraneous.
>>>>>
>>>>> Otherwise:
>>>>>
>>>>> Reviewed-by: Alex Bennée <address@hidden>
>>>>>
>>>>
>>>> Look a little further down:
>>>>
>>>>> +    default:
>>>>> +    sigsegv:
>>>>> +        /* Like force_sig(SIGSEGV).  */
>>>>> +        gen_signal(env, TARGET_SIGSEGV, TARGET_SI_KERNEL, 0);
>>>>> +        return;
>>>>> +    }
>>>>> +
>>>>> +    /*
>>>>> +     * Validate the return address.
>>>>> +     * Note that the kernel treats this the same as an invalid entry 
>>>>> point.
>>>>> +     */
>>>>> +    if (get_user_u64(caller, env->regs[R_ESP])) {
>>>>> +        goto sigsegv;
>>>>> +    }
>>>
>>> Wouldn't this read better:
>>>
>>>     /*
>>>      * Validate the entry point.  We have already validated the page
>>>      * during translation, now verify the offset.
>>>      */
>>>     switch (env->eip & ~TARGET_PAGE_MASK) {
>>>     case 0x000:
>>>         syscall = TARGET_NR_gettimeofday;
>>>         break;
>>>     case 0x400:
>>>         syscall = TARGET_NR_time;
>>>         break;
>>>     case 0x800:
>>>         syscall = TARGET_NR_getcpu;
>>>         break;
>>>     default:
>>>         syscall = -1;
>>>         break;
>>>     }
>>>
>>>     /*
>>>      * If we have an invalid entry point or an invalid return address we
>>>      * generate a SIGSEG.
>>>      */
>>>     if (syscall < 0 || get_user_u64(caller, env->regs[R_ESP])) {
>>>         gen_signal(env, TARGET_SIGSEGV, TARGET_SI_KERNEL, 0);
>>>         return;
>>>     }
>>>
>>
>> Only if you have a violent goto allergy.
> 
> gotos have their place but jumping backwards is confusing to eye. If the
> compiler want to mess with layout after then it is free to do so.

I agree, if anything I'd place the sigsegv label at the end of the
function but Alex's version is just fine too.

Paolo