[LLVMdev] Using LLVM to compile Objective-C on an Xbox 360

Sherief Farouk sherief at mganin.com
Thu May 27 11:12:30 PDT 2010 

Why? I think the discussion belongs here, and the topic doesn't seem to include proprietary information - a lot of 360 info has been made public through MS material. Other info can be discussed without much disclosure (we can refer to TCRs by three-letter category and number, etc).

- Sherief

On May 27, 2010, at 1:15 PM, Alex Rosenberg wrote:

> Please create a thread on DevNet to discuss this further.
> 
> Alex
> 
> On May 27, 2010, at 9:26 AM, Kevin Wooten wrote:
> 
>> By linux derivative I meant that it borrows the linux GCC ABI... and  
>> it does.  You can compile with an off the shelf GCC cross compiler  
>> and link the resultant object files ones compiled with the PS3  
>> provided version.   We have done it.
>> 
>> Also, as both an XBox 360 and PS3 developer, there seems to me to be  
>> nothing in the TCRs/TRCs that preclude us from using a different  
>> compiler.  There are rules about symbol inclusion and other  
>> resultant binary requirements... but as of yet I have not found  
>> specific ones stopping us from using a compiler that works.  In  
>> either case the LLVM rewriter solves any other these issues as we  
>> would be just be compiling C.
>> 
>> On May 27, 2010, at 8:09 AM, Alex Rosenberg wrote:
>> 
>>> PS3 is not "a Linux derivative." The compilers supplied by SCE for  
>>> PS3 game development are highly customized and support a customized  
>>> ABI that will take some time to adjust LLVM and Clang to support.
>>> 
>>> You'd likely also run afoul of a TRC or two, similar to the  
>>> problems you'll face with Microsoft TCRs mentioned earlier.
>>> 
>>> Alex
>>> 
>>> On May 27, 2010, at 12:15 AM, Kevin Wooten wrote:
>>> 
>>>> Implementing the backend (or editing the current PPC backend as  
>>>> needed) is a definite option.  This seems to be the real  
>>>> question... which is easier... maintaining the PPC backend or  
>>>> maintaining the rewriter.  Currently (in admittedly trivial tests)  
>>>> I have gotten the rewriter to work and output C code.  There are  
>>>> some outstanding issues to do with linking and accessing the  
>>>> reflection information objective-c provides (and the rewriter  
>>>> properly outputs) but I am sure the person/people who wrote the  
>>>> rewriter can answer those fairly simply (or else the rewriter  
>>>> would be fairly useless).
>>>> 
>>>> As far as the runtime goes there is an implementation for windows,  
>>>> linux and most likely the PS3 (since it is already a linux  
>>>> derivative using GCC as mentioned).  If we have to create a  
>>>> runtime for PS3 and XBox that seems trivial as the functions are  
>>>> very basic in nature.
>>>> 
>>>> My comments on OpenStep were more meant to point to the fact that  
>>>> we would write our own library; really just throwing all notion of  
>>>> OpenStep away.  Instead of NSObject we would create our own base  
>>>> DObject or something along with a DString, DAarry, DSet, DMap,  
>>>> etc.  Truthfully this would be our plan anyway because we want to  
>>>> follow the lead of OSX and provide these objects "toll free  
>>>> bridged"... meaning we would implement them using a std c++  
>>>> library object (e.g. std::basic_string or std::vector) as the  
>>>> first member of the object which will allow us to cast a DString  
>>>> to std::string or DArray to std::vector without any manual or  
>>>> automatic marshaling. As mentioned this is how OSX implements its  
>>>> NS classes, by using the equivalent CF version which again allows  
>>>> casting between the objects.
>>>> 
>>>> On May 26, 2010, at 6:19 PM, Dale Johannesen wrote:
>>>> 
>>>>> llvm can output C code, but that target has bitrotted severely  
>>>>> over the last few months and nobody seems to be interested in  
>>>>> fixing it.  You may need to do some work there.  Alternatively  
>>>>> you could implement the PPC ABI that you need.  There are several  
>>>>> examples of supporting multiple ABIs on the same hardware, x86  
>>>>> being the most obvious.  A lot of simple stuff will probably Just  
>>>>> Work with the existing PPC ABI, more complicated stuff may not.   
>>>>> (Only 32-bit PPC is really maintained, though, there are probably  
>>>>> lots of problems with 64-bit.)
>>>>> 
>>>>> Objective C in llvm, AFAIK, is only used on the MacOSX targets  
>>>>> and only tested there.   There are sufficient secret handshakes  
>>>>> between the compiler and the ObjC runtime that it is unlikely to  
>>>>> Just Work in an untested environment.  OpenStep has a familial  
>>>>> relationship to MacOSX ObjC runtime, but they aren't the same and  
>>>>> are unlikely to still be binary compatible at this point.  You  
>>>>> may need to do some work there also.
>>>>> 
>>>>> Summary, you can probably get this approach to work, but it's not  
>>>>> as easy as you're hoping.
>>>>> 
>>>>> On May 26, 2010, at 5:20 PMPDT, kdubb wrote:
>>>>> 
>>>>>> We are looking at using Objective-C/C++ in a new game engine.   
>>>>>> Objective C's duality of being both very dynamic and very "C"  
>>>>>> gives us exactly what we need to make the SDK and engineering of  
>>>>>> games simpler.
>>>>>> 
>>>>>> This means that we will need a way to compile it on all  
>>>>>> platforms our games will target.  Currently the major platforms  
>>>>>> we are concerned with include... PC, Mac, XBox 360, PS3,  
>>>>>> iPhone.  Now the PC, Mac, iPhone and PS3 are fairly simple.  If  
>>>>>> we build our own OpenStep libraries we can simply use LLVM to  
>>>>>> compile directly to these platforms; the PS3 although  
>>>>>> proprietary uses GCC as a C/C++ compiler so I am assuming  
>>>>>> Objective-C can be used fairly simply.  This leaves us with the  
>>>>>> XBox 360.
>>>>>> 
>>>>>> The 360 is a special chip (PowerPC based) with, as far as I have  
>>>>>> researched, a special ABI (Windows derivative).  I haven't the  
>>>>>> faintest clue of whether code from the LLVM PPC backend would  
>>>>>> even work on the 360, much less interoperate with the system  
>>>>>> libraries. So my formulated solution has become this: use an  
>>>>>> LLVM backend to output C code and then compile that code with  
>>>>>> using MS's XBox 360 compiler. I believe I have read that LLVM  
>>>>>> has a C backend already but I don't know how to select it.
>>>>>> 
>>>>>> If I can get a proof of concept showing Objective-C code running  
>>>>>> on the 360 we are off to the races.  Any help is appreciated  
>>>>>> just not sure if all the pieces/parts exist and/or what I am  
>>>>>> missing.  So... is this feasible?  If so... how do I get LLVM to  
>>>>>> output C code?
>>>>>> 
>>>>>> Thanks,
>>>>>> Kevin
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>>>>> 
>>>> 
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>> 
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