Initial WebAssembly/WASI cross-compilation support

[matthewbauer]

Motivation for this change

Need to add LLVM 8 to get this working. Can compile basic C programs. Things like C++ are unfortunately not supported right now.

/cc @ElvishJerricco

Test case:

with import <nixpkgs> {
  crossSystem = (import <nixpkgs/lib>).systems.examples.wasi32;
};
let
  cpp = builtins.toFile "test.c++" ''
    #include <iostream>

    int main() {
      std::cout << "Hello world!" << std::endl;
    }
  '';
in runCommandCC "cross-test" {} ''
      $CXX -o test ${cpp}
      ${stdenv.hostPlatform.emulator buildPackages} test > $out
''

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.

---

[ElvishJerricco]

Just took a cursory glance. Will do a more in depth review tomorrow.

In general though, this looks like several PRs in one. Stuff like the new version of llvm and the V8 changes seem like they should be different PRs to get better review.

[matthewbauer]

Yeah good point, i can split into llvm8 init, wasm init, and the v8 update.

[qknight]

this looks really cool!

[ElvishJerricco]

This should probably switch to https://github.com/CraneStation/wasi-sysroot for libc. WASI is likely to become pretty standard, unlike both the jfbastien and the WebGHC ones.

[matthewbauer]

@ElvishJerricco Yeah i agree on that. Ideally the jfbastien and webghc musl stuff could be upstreamed. But right now that's not really a real ABI. Luckily we can reuse most of the changes here though.

[matthewbauer]

@GrahamcOfBorg eval

[dtzWill]

WOOHOOO! Awesome work! \o/

…

On Tue, 23 Apr 2019 19:44:42 -0700, Matthew Bauer ***@***.***> wrote: Merged #56555 into staging. -- You are receiving this because your review was requested. Reply to this email directly or view it on GitHub: #56555 (comment) part: text/html