[LLVMdev] Running Objective-C in the JIT

[Jean-Daniel Dupas]

The runtime sources contains all the code to load a Mach-O binary.

I think the main function is 
PRIVATE_EXTERN void _read_images(header_info **hList, uint32_t hCount)
in 

http://opensource.apple.com/source/objc4/objc4-493.11/runtime/objc-runtime-new.mm


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