[LLVMdev] Running Objective-C in the JIT

[Julian Storer]

Excellent, thanks very much for your help, I'll keep digging away. I
think I'm starting to understand how it all fits together...

On 8 May 2012 14:34, Jean-Daniel Dupas <devlists at shadowlab.org> wrote:
> And also, the hook to load/unload image is installed in objc-os.m using dyld_register_image_state_change_handler() function.
>
> Le 8 mai 2012 à 15:07, Julian Storer a écrit :
>
>> Thanks for the info!
>>
>> Yes, the problem is certainly that the JITed code isn't registering
>> its classes, but even after digging through all the runtime code I
>> can't find anything that seems suitable for doing this.. The nearest
>> function I could find was _objc_init_image, but that seems to be for
>> win32!
>>
>> I assume that the way it works must be that clang creates some static
>> data structures defining all the class's methods and ivars, and then
>> these data structures are picked up automatically (somehow) by the
>> runtime, which parses them and dynamically registers the classes
>> appropriately..?
>>
>> So the worst-case here seems to be that I might need to write my own
>> utility to do this parsing/registering.. But it'd be nice to at least
>> be able to see some code from the runtime that does this job, so I can
>> understand what's going on, but I can't find anything like that!
>>
>>
>> On 7 May 2012 22:17, Jean-Daniel Dupas <devlists at shadowlab.org> wrote:
>>>
>>>
>>> Le 7 mai 2012 à 17:07, Jules a écrit :
>>>
>>>> Hello, I've been trying to get some OSX code to execute within the JIT,
>>>> and it's been causing me some major headaches!
>>>>
>>>> I'm attempting to JIT-compile some code which uses external OSX obj-C
>>>> classes (Cocoa, etc), and also contains its own embedded obj-C classes.
>>>>
>>>> My first hurdle in doing this was that when the code tried to call Cocoa
>>>> classes, the obj-C selectors weren't being recognised by the host
>>>> process's objc_msgSend function.. After quite a bit of hair-pulling, I
>>>> copied a trick from the lldb::IRForTarget class, which scans the compiled
>>>> module and replaces any selector constants with explicit function calls
>>>> to sel_registerName().. By applying a similar transformation to my own
>>>> modules, I've now managed to successfully invoke selectors on Cocoa classes.
>>>>
>>>> But now I've hit a brick wall trying to use internal obj-C classes (i.e.
>>>> classes that are defined within the JIT-ed code itself). With these, even
>>>> trying to alloc them causes a crash. Does anyone have enough of a grasp of
>>>> what's going on in the JIT and obj-C ABI to be able to give me some
>>>> pointers here!?
>>>>
>>>> Thanks!
>>>
>>>
>>> Obj-C classes are registered by the runtime at module load time.
>>> When a module is loaded, the Obj-C runtime create classes and register them by parsing the module Obj-C data segments.
>>>
>>> My guess is that as you are using JIT, the runtime hook used to detect loading of new module is never called, and your classes are not registered.
>>> You can try to load them manually by using the runtime functions (see https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ObjCRuntimeRef/Reference/reference.html ) and if it's not enough, you may have to download the runtime source code (http://opensource.apple.com/source/objc4/objc4-493.11/) to see what it does when a new module is loaded.
>>>
>>>
>>> -- Jean-Daniel
>>>
>>>
>>>
>>>
>
> -- Jean-Daniel
>
>
>
>