[swift-dev] JIT-ting Swift

[Joe Groff]

> 
> On Mar 6, 2017, at 9:33 AM, Alex Denisov via swift-dev <swift-dev at swift.org> wrote:
> 
> 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 :)

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.

-Joe

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