Using latest source-built clang

[kamrann]

The SDK readme mentions that a regular clang build can be used for building WASI targets, and specifies to extract the libclang_rt.* libraries into the installation. I've done so and successfully built a WASI module, but I'm wondering, is there any potential for binary compatibility problems here if my LLVM version differs from whatever was used to generate these libraries that are available for download?

If so, is it possible for me to build everything that's needed from source through some particular LLVM configuration settings?

[alexcrichton]

I believe it should be valid to use an external clang to compile a wasm sysroot (compiler-rt, libc, etc). If you'd like to use a snapshot where everything is all synchronized together from the same version of LLVM you can use the precompiled binaries for wasi-sdk which have artifacts all built from the same commit.

[kamrann]

My project uses C++ modules and other very recent features, so I'm generally tracking close to LLVM head. As such using the full snapshot isn't an option. Currently I'm combining my source-built clang with the sysroot and compiler-rt builtins library from the snapshot, which generally seems to be working but feels potentially unsafe.

Would the recommend approach in this case be to build the this SDK from source, pointing the submodule at the LLVM commit that I want? Can I generally do that, or is the submodule tracking some specific branch/features in LLVM? Ideally I'd reuse my existing clang source build (maybe I could symlink it in place of the submodules?), but if I need to duplicate the build tree then I can do so. I really just want to do things whatever the "proper way" is, to minimize hard to diagnose problems.

[alexcrichton]

In theory it should work to point the submodule to a new commit yeah. There's always the possibility of build system breakage or bugs but those can't really be predicted. FWIW the last few upgrades have gone pretty smoothly. I'd agree that adding an option to the cmake build to use a custom non-repo-based-directory would be reasonable!