[swift-dev] JIT-ting Swift

[Alex Denisov]

> The `main` entry point ought to be a standard C "main" function. The argv argument is an UnsafeMutablePointer<UnsafeMutablePointer<Int8>?>, which ought to be ABI-compatible with a char** in C.


That was my assumption when I started, thank you for confirmation :)

> When JIT'ing Swift, the value of argv doesn't matter because we replace the process' arguments dynamically https://github.com/apple/swift/blob/master/lib/Immediate/Immediate.cpp#L318.

Hm, can you tell a bit more about this? I do not load the runtime, my crash may be caused by something not being initialized.
Here is my simplified use-case: I compile a swift project with tests into bitcode, then I load the bitcode into memory, and then compile and execute a program using ORC JIT.

> Do you have a trace for the crash?

Sure, here it is: https://gist.github.com/AlexDenisov/2a8d9b0d391de73a97bce9e33a650f0f#file-trace-txt-L22-L42


> On 6 Mar 2017, at 20:14, Robert Widmann <devteam.codafi at gmail.com> wrote:
> 
> %Sp is not an argument, it is the space necessary to hold a reference to the CommandLine enumeration's static argv member.  
> 
> When JIT'ing Swift, the value of argv doesn't matter because we replace the process' arguments dynamically https://github.com/apple/swift/blob/master/lib/Immediate/Immediate.cpp#L318.  Do you have a trace for the crash?
> 
> ~Robert Widmann
> 
> 2017/03/06 12:33、Alex Denisov via swift-dev <swift-dev at swift.org> のメッセージ:
> 
>> Hi there,
>> 
>> I could not find a list for swift-corelibs-xctest so I am posting it here.
>> 
>> I am trying to run tests based on XCTest (https://github.com/apple/swift-corelibs-xctest) using LLVM's JIT.
>> Everything is working good so far. However, I am getting a crash.
>> Based on a shallow investigation I can see that this is somehow related to the way Swift treats the command line arguments. Or, to be more precise, to the way I pass the arguments to the swift's 'main' function.
>> 
>> What I did so far is not different from what I do to run C or C++ using JIT:
>> 
>> auto main = ((int (*)(int, const char **))(intptr_t)mainPointer);
>> const int argc = 1;
>> const char *argv[] = { "some-name", NULL };
>> auto result = main(argc, argv);
>> 
>> Based on what I see in the IR[1] the 'argv' has type "%Sp = type <{ i8* }>", which seems to be a struct with a pointer to something.
>> 
>> So the question is: what is being passed as a second argument to the 'main' function of a swift program?
>> 
>> Any other advice on JIT-ting Swift are more than welcome :)
>> 
>> [1] https://gist.github.com/AlexDenisov/3c10540b544e82cfb6e58e1452491904
>> -- 
>> AlexDenisov
>> Software Engineer, https://lowlevelbits.org
>> 
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-- 
AlexDenisov
Software Engineer, https://lowlevelbits.org