[swift-dev] Proof-of-concept port of Swift for Android

[Geordie Jay]

Hi @zhuowei. I have been (somewhat verbosely) documenting my progress getting your SwiftAndroid build working on the reddit thread here https://www.reddit.com/r/swift/comments/3w0xrd/im_patching_the_opensource_swift_compiler_to/ <https://www.reddit.com/r/swift/comments/3w0xrd/im_patching_the_opensource_swift_compiler_to/> (as ephemer9). Given that I’ve now worked through a lot of issues, I think together we can make this build repeatable for everyone (that is if you need my help at all - you seem to be doing a mighty fine job yourself so far). What I’d like to do is work on the JNI integration part of this. Before I can though, I have to get through a few problems here still:

After dealing with the dependency issues (see reddit), the SwiftAndroid build finally completed. It had plenty of warnings along the way, but in the end I was left with binaries that seemed to do something. I was then able to use swiftc to compile for linux x86_64 as usual. I couldn't figure out how to cross-compile to armv7 though. This is what I tried:

    swiftc -target armv7-none-linux-androideabi -target-cpu armv7 test.swift

This unfortunately produces a segfault on my machine: "<unknown>:0: error: the clang compiler does not support '-mcpu=armv7'"

Removing -target-cpu from the `swiftc` call leads to an error about missing `swift.ld` for architecture x86_64. It is looking under android/x86_64 - I symlinked the linker file from android/armv7 into that path and got this instead:

    me at linuxbox:~# swiftc -target armv7-none-linux-androideabi test.swift -vSwift version 2.2-dev (LLVM 7bae82deaa, Clang 53d04af5ce, Swift 65921fc110)
    Target: armv7-none-linux-android
    /me/swift/build/Ninja-Release/swift-linux-x86_64/bin/swift -frontend -c -primary-file test.swift -target armv7-none-linux-android -disable-objc-interop -color-diagnostics -module-name test -o /tmp/test-706f67.o
    /me/swift/build/Ninja-Release/swift-linux-x86_64/bin/swift-autolink-extract /tmp/test-706f67.o -o /tmp/test-58bef6.autolink
    /usr/bin/clang++ /tmp/test-706f67.o -L /me/swift/build/Ninja-Release/swift-linux-x86_64/lib/swift/android -Xlinker -rpath -Xlinker /me/swift/build/Ninja-Release/swift-linux-x86_64/lib/swift/android -lswiftCore @/tmp/test-58bef6.autolink -Xlinker -T /me/swift/build/Ninja-Release/swift-linux-x86_64/lib/swift/android/x86_64/swift.ld -o test
    /usr/bin/ld: /tmp/test-706f67.o: Relocations in generic ELF (EM: 40)
    /usr/bin/ld: /tmp/test-706f67.o: Relocations in generic ELF (EM: 40)
    /tmp/test-706f67.o: error adding symbols: File in wrong format
    clang: error: linker command failed with exit code 1 (use -v to see invocation)
    <unknown>:0: error: link command failed with exit code 1 (use -v to see invocation)

I’m assuming this is because it’s trying to link the armv7 binary with the x86_64 standard library or something illogical like that. In any case I’m a little stuck now as to how to proceed. Given that clang is telling me it doesn’t support armv7, I imagine I’m just entering the wrong arguments for swiftc. Or do I have to make LLVM-IR first and link using the android toolchain for now? Can you or anyone else give me an idea as to how to cross-compile using swiftc?

Many thanks,
Geordie
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