nodejs doesn't cross-compile to non-executable hostPlatform

[dwf]

Describe the bug

Cross-compiling nodejs for a hostPlatform whose binaries can't be executed on the buildPlatform fails.

Steps To Reproduce

Steps to reproduce the behavior:

1. nix-build '<nixpkgs>' -A pkgsCross.raspberryPi.nodejs_latest

Also fails with nodejs-slim, nodejs-12_x, nodejs-14_x, etc.

Expected behavior

The package to be built successfully.

Additional context

The problem seems to be that binaries, notably out/Release/bytecode_builtins_list_generator, need to be built with the build environment toolchain, not the host toolchain. Node's build process allows specification of the location of the necessary build compilers via environment variables (AR_host, CXX_host, CC_host, LINK_host, CXXFLAGS_host and LDFLAGS_host are mentioned in one of the links below).

nodejs/node#32717 seems relevant, as does nodejs/node#24317. The latter mentions buildroot getting this right, here's what they do.

Notify maintainers

@goibhniu @gilligan @cko @marsam

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[root@nixos-builder:~]# nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 5.10.74, NixOS, 21.05.3892.70904d4a992 (Okapi)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.16`
 - channels(root): `"nixos-21.05.3892.70904d4a992, unstable-21.11pre323695.9aeeb7574fb"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:

# a list of nixos modules affected by the problem
module:

[dwf]

Adding additional context to this: I've successfully been able to build by using an i686 build platform and the following overlay:

    nodejs-cross = super.nodejs-14_x.overrideAttrs (old: {
      preConfigure = ''
         export CC_host="${self.stdenv.buildPlatform.config}-gcc"
         export CXX_host="${self.stdenv.buildPlatform.config}-g++"
         export LINK_host="${self.stdenv.buildPlatform.config}-g++ -Wl,-lstdc++ -Wl,-lm -B${self.buildPackages.stdenv.glibc}/lib"
      '';
      depsBuildBuild = with self.buildPackages; [ stdenv.cc stdenv.glibc libuv zlib openssl ];
    });

I suspect this isn't quite the right fix though for a number of reasons.

I also wasn't able to find a way to cross-compile from x86-64 to armv6l. It seems one needs a buildPlatform side toolchain with 32-bit support, which would suggest a multiStdenv for the buildPlatform but not the hostPlatform, and I'm not sure how to accomplish that.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/cross-compile-nodejs-broken-python-interpreter/18131/2

[Hjdskes]

I am also running into this (the linked Discourse thread is mine). It looks like buildroot fixes this problem by compiling the build tools for the build platform first, and then using those binaries when compiling for the target platform (https://github.com/buildroot/buildroot/blob/master/package/nodejs/nodejs.mk#L105)

Do you have time to look at this, @goibhniu @gilligan @cko @marsam? I am willing to give this a shot but I'll need some pointers to get started...

[dwf]

The workaround I found is to replace pkgsCross with pkgsi686Linux.pkgsCross, so that you use x86-32 as the build platform. Not ideal as it requires installing a whole heck of a lot of 32-bit dependencies, but it's a testament to Nix that it works at all.