[llvm-dev] Is it possible to execute Objective-C code via LLVM JIT?

Fri Nov 11 13:38:46 PST 2016

Just a comment here.  The code in tools/llvm-objdump/MachODump.cpp has requirements beyond being able to parse the Objective-C for the machine it is running on.  It must work cross byte sex, with differing alignment, dealing with both Objc1 & Objc2, pointers of the non-native size and not the native addresses and be robust enough to not crash with bad meta data.  So while it parses the Objective-C meta data it likely is not a good model for execution.

Kev

> On Nov 11, 2016, at 1:26 PM, Steven Wu via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hi Stanislav
> 
> Thanks for checking on this. If you want a quick hack, you can try to read the code in tools/llvm-objdump/MachODump.cpp. There are some c code in there to parse metadata.
> 
> My code is something I put up for my own purpose for debugging/parsing objc metadata. The interface is a bit rough to use but the biggest problem is testing. I have my own binary living out of tree to test the parser but it doesn't make sense to have another parser in tree to do the same thing. I really hope I can replace the code in MachODump, but unfortunately the current error handling model in libObject prevents me from replicate all the functions in MachODump. We are working towards that direction but we are not there yet. In the meantime, I won't mind posting some patches when I have time.
> 
> Steven
> 
> 
>> On Nov 10, 2016, at 2:03 PM, Stanislav Pankevich <s.pankevich at gmail.com <mailto:s.pankevich at gmail.com>> wrote:
>> 
>> Hi Lang, Steven,
>> 
>> Any updates on this? Steven, is there a progress with metadata parser for Objective-C?
>> 
>> Let us know if we can help somehow.
>> 
>> Thanks.
>> 
>> Stanislav
>> 
>>> On 22 Oct 2016, at 03:21, Lang Hames <lhames at gmail.com <mailto:lhames at gmail.com>> wrote:
>>> 
>>> > So no JIT for i386?
>>> 
>>> I didn't realise i386 still used ObjC 1 - all my experiments were on arm64.
>>> 
>>> i386 support for ObjC would be nice to have, but it's not a blocker for adding ObjC 2 support.
>>> 
>>> - Lang.
>>> 
>>> 
>>> On Thu, Oct 20, 2016 at 11:57 AM, Steven Wu <stevenwu at apple.com <mailto:stevenwu at apple.com>> wrote:
>>> 
>>>  
>>>> On Oct 19, 2016, at 11:28 AM, Stanislav Pankevich <s.pankevich at gmail.com <mailto:s.pankevich at gmail.com>> wrote:
>>>> 
>>>> Hi Lang, Steven,
>>>> 
>>>> At this point it seems that the best next step is for Steven to share his code, right? Or is there some other work that can be done in parallel?
>>> 
>>> It will take some time to create patch from my existing implementation. After that, we still need to correctly register the implementation to objc runtime. I dont expect this to be a quick task.
>>> 
>>>> 
>>>> Lang? Steven?
>>>> 
>>>> Here’s small note about my interest here: Alex Denisov and I are working on a tool for mutation testing https://github.com/AlexDenisov/mutang <https://github.com/AlexDenisov/mutang>. Alex has made fascinating progress towards mutation testing of C++ code and we would also like to bring mutation testing to iOS where we are by profession. Currently inability to run Objective-C code via JIT is a critical dependency for our progress on iOS part so I'll be happy to help with this in any way even though my experience with LLVM is very limited.
>>> 
>>> This sounds like an interesting project. Maybe you can generate the object file and statically linked the mutated code for now? 
>>> 
>>> Steven
>>> 
>>>> 
>>>> Thanks.
>>>> 
>>>> Stanislav
>>>> 
>>>>> On 19 Oct 2016, at 01:49, Lang Hames <lhames at gmail.com <mailto:lhames at gmail.com>> wrote:
>>>>> 
>>>>> Hi Steven,
>>>>> 
>>>>> That sounds great. The object file parser would definitely be of interest to JIT clients. Having ObjC 1 support would be nice, but I don't see it as a blocker to committing what you've got: all code produced by the JIT is going to be ObjC-2.
>>> 
>>> So no JIT for i386? 
>>> 
>>> Steven
>>> 
>>>>> 
>>>>> Cheers,
>>>>> Lang.
>>>>> 
>>>>> On Tue, Oct 18, 2016 at 2:22 PM, Steven Wu <stevenwu at apple.com <mailto:stevenwu at apple.com>> wrote:
>>>>> Hi Stanislav, Lang
>>>>> 
>>>>> I have a version of objc metadata parser based on LLVM which can handle objc2 metadata from MachO object and bitcode (bitcode version is even swift compatible). I don't know if there is enough interest for me to upstream it. It probably requires some work to clean up the interface and complete it by adding objc1 support and other object format support.
>>>>> 
>>>>> Steven
>>>>> 
>>>>>> On Oct 18, 2016, at 2:10 PM, Lang Hames via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>>>>> 
>>>>>> Hi Stanislav,
>>>>>> 
>>>>>> I actually looked into this recently. It is possible, but takes some non-trivial effort right now: You have to hook into the JIT memory allocator, parse the objective C metadata sections in the object file, then call the objective C runtime to register any newly added classes, protocols and selectors.
>>>>>> 
>>>>>> I can't release my code as-is: I built it against a hacked up copy of the runtime. The right way to do this would be to write parsers for the objective C metadata, and an Objective-C registration call that uses the parsers and calls the runtime. These should be made available conditionally if the objective C runtime headers are available. This is something that I'd like to get to eventually, but I have a long to-do list. If you or anyone you know is interested in working on it I'd be happy to provide pointers and code review.
>>>>>> 
>>>>>> Cheers,
>>>>>> Lang.
>>>>>> 
>>>>>> On Tue, Oct 18, 2016 at 1:33 PM, Stanislav Pankevich via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>>>>> Hello,
>>>>>> 
>>>>>> Is it possible to execute Objective-C code using LLVM JIT?
>>>>>> 
>>>>>> The original point for my research is this topic on StackOverflow: 
>>>>>> 
>>>>>> All selectors unrecognised when invoking Objective-C methods using the LLVM ExecutionEngine http://stackoverflow.com/questions/10375324/all-selectors-unrecognised-when-invoking-objective-c-methods-using-the-llvm-exec <http://stackoverflow.com/questions/10375324/all-selectors-unrecognised-when-invoking-objective-c-methods-using-the-llvm-exec>
>>>>>> 
>>>>>> Running that example with lli produces the following output:
>>>>>> 
>>>>>> 2016-10-18 21:25:58.332 lli[12970:169282] *** NSForwarding: warning: selector (0x10356a38f) for message 'alloc' does not match selector known to Objective C runtime (0x7fff8e93afb5)-- abort
>>>>>> 2016-10-18 21:25:58.334 lli[12970:169282] +[NSAutoreleasePool alloc]: unrecognized selector sent to class 0x7fff7a562130
>>>>>> 2016-10-18 21:25:58.338 lli[12970:169282] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+[NSAutoreleasePool alloc]: unrecognized selector sent to class 0x7fff7a562130'
>>>>>> 
>>>>>> See also additional discussion here: https://twitter.com/sbpankevich/status/783363161537798144 <https://twitter.com/sbpankevich/status/783363161537798144>.
>>>>>> 
>>>>>> Thanks.
>>>>>> 
>>>>>> Stanislav Pankevich
>>>>>> 
>>>>>> 
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>>>>>> 
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>>>>> 
>>>>> 
>>>> 
>>> 
>>> 
>> 
> 
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