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

Thu Oct 20 14:09:41 PDT 2016

> On 20 Oct 2016, at 20:57, Steven Wu <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.

I will be happy to help with anything that could help to push this forward especially with a guidance from you and Lang. As for us, the time is not really critical as we have a lot of other things to cover, however once there will be something that we could help with here, feel free to distribute any work to me and Alex.

> 
>> 
>> 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?

Unfortunately that’s not how this project is supposed to work. The algorithm that is already working for C++ is roughly the following:

1. We compile original test suite with its system under test, then run the test suite before doing any mutations, record the result.
2. We make 1 mutation in one module, recompile only that module, replace original module with mutated one, run them again using JIT, record the results of running a mutated version.
3. Repeat step 2 many times (in order of thousand times and more), collect the statistics.
4. Observe results.

So given the following procedure it makes the most of sense to use JIT. As I said this is working perfectly for C++ already and now we are very excited about the opportunity to bring the same to iOS.

> 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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