Re: [Qemu-devel] Effective way to test PowerPC lwbrx instruction

[G 3 <programmingkidx@gmail.com>]

On Aug 25, 2016, at 10:30 PM, Thomas Huth wrote:

> On 25.08.2016 18:55, G 3 wrote:
>>
>> On Aug 25, 2016, at 6:03 PM, Thomas Huth wrote:
>>
>>> On 25.08.2016 14:54, G 3 wrote:
>>>> I'm chasing down a bug with QEMU that causes audio to fail on a  
>>>> Mac OS
>>>> guest. In this file:
>>>> https://github.com/nixxcode/AppleUSBAudio-273.4.1/blob/master/ 
>>>> AppleUSBAudioClip.cpp
>>>>
>>>> is where a lot of assembly language code is located. I think one  
>>>> or more
>>>> of the PowerPC instructions might be incorrectly implemented so  
>>>> I am
>>>> checking each one that the file uses. Starting with lwbrx I made  
>>>> this
>>>> program that gives this instruction sample inputs and checks  
>>>> them with
>>>> real outputs. According to the program QEMU implements this  
>>>> instruction
>>>> correctly. Does this program effectively check the lwbrx  
>>>> instruction or
>>>> is it missing something?
>>> ...
>>>>     // Go thru each rA value
>>>>     for(rA = 0; rA <=12; rA=rA+4)
>>>>     {
>>>>         // set the correct answer array for each rA value
>>>>         if(rA == 0)
>>>>             answer_array = answer_array0;
>>>>         else if(rA == 4)
>>>>             answer_array = answer_array4;
>>>>         else if(rA == 8)
>>>>             answer_array = answer_array8;
>>>>         else
>>>>             answer_array = answer_array12;
>>>>
>>>>         // Go thru each rB value
>>>>         for(index = 0; index < rB_size; index++)
>>>>         {
>>>>             asm volatile("lwbrx %0, %1, %2" : "=r" (result) : "b 
>>>> %" (rA),
>>>> "r" (&(rB[index])));
>>>
>>> I think you're not testing the case where rA is r0 here (only  
>>> where the
>>> content of rA is 0) ... and rA == r0 is a special case for this
>>> instruction, see the PowerISA for details. So you'd need a  
>>> separate asm
>>> volatile statement to test this.
>>> (Also a question: What is the "%" here good for? I did not quite
>>> understand why you're using that here)
>>>
>>>  Thomas
>>
>> Thank you very much for commenting. For the case where rA is r0,  
>> are you
>> saying something like this:
>>
>> asm volatile("lwbrx %0, 0, %1" : "=r" (result) :  "r" (&(rB 
>> [index])));
>
> Yes, this is what I had in mind.
>
>> Didn't find the text 'r0' here, but it did mention this:
>> "If GPR RA is 0, then the EA is the contents of GPR RB". Is that the
>> same thing?
>
> Yes, I am normally using "r0" instead of "0" so that it can not be
> confused that easily with an immediate value.
>
> By the way, if you don't know it yet, you can get the official  
> Power ISA
> here:
>
> https://www.power.org/wp-content/uploads/2013/05/ 
> PowerISA_V2.07_PUBLIC.pdf
>
>> The percent is for me to quickly see if any of the test failed.  
>> QEMU is
>> at 100% for this test.
>
> I didn't mean the printf statement, but the % character in the "b%"  
> part
> of the asm volatile statement.

That is something that I copied from Apple's source code I am working  
on.