cmd/go: Cross compiling Go c archives for iOS does not generate bitcode

[swisspol]

Go 1.5.1 on OS X 10.10.5 with Xcode 7

Even if setting CC and CXX to include -fembed-bitcode while building against the iPhoneOS SDK, the resulting static library does not contain bitcode.

I made a sample test project here: https://github.com/swisspol/Go-Bridge

[minux]

The Go toolchain doesn't generate LLVM bitcode.
so unfortunately there is nothing to do here.

LLVM bitcode format is unstable, so pretty much you've
to use LLVM to generate bitcode. But the gc toolchain
will definitely use LLVM.

[swisspol]

I figured as much with the new Go toolchain. That might turn into a major problem going forward though, assuming Go wants to support mobile development on iOS (which is I assume the intent of https://github.com/golang/mobile/).

Bitcode is part of the new app thining, and submission to the App Store for WatchOS apps must already be in bitcode. It's currently optional for iOS apps, but maybe it will be required for iOS 10 next year. I would bet that it is at most 2 years away. Apple has a long history of architecture transitions and they are typically quite aggressive as well.

PS: What do you mean by the "gc toolchain"?

[minux]

LLVM still lacks essential features to support the Go runtime (i.e. stack map, write barriers?). Perhaps the write barrier thing isn't too big as we can emulate it, but we cannot emulate stack map without also implement our own stack -- then much of the benefit of LLVM is gone.) If bitcode is required, then iOS development might need to use an alternative toolchain (e.g. llgo), until we figure out a way to support a LLVM backend (probably won't happen because gc has always been using its own backend and it allows much faster evolution as we don't need to wait before required features are implemented in 3rdparty software) The gc toolchain refers to the toolchain in this GitHub repository.

[swisspol]

Got it, thanks.