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

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> On 1/21/20 12:13 AM, Alex Bennée wrote:
>> 
>> Richard Henderson <richard.henderson@linaro.org> writes:
>> 
>>> On 1/20/20 1:48 AM, Alex Bennée wrote:
>>>>> +    default:
>>>>> +    sigsegv:
>>>>
>>>> this label looks a little extraneous.
>>>>
>>>> Otherwise:
>>>>
>>>> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
>>>>
>>>
>>> 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.

-- 
Alex Bennée