x86 runtime deps in ARM glibc (and most other binaries)

[illegalprime]

Issue description

building some cross-compiled packages and inspecting their run-time closures:

nix build -f . pkgsCross.aarch64-multiplatform.glibc
nix-store -q --tree result

will show that result depends on /nix/store/b9iyqcsd1gmlfagpi4xqqlswcpx079r1-aarch64-unknown-linux-gnu-stage-final-gcc-debug-7.4.0 (on master d46bf20).

this is because the package isn't spliced correctly:

$ tree -L 2 /nix/store/b9iyqcsd1gmlfagpi4xqqlswcpx079r1-aarch64-unknown-linux-gnu-stage-final-gcc-debug-7.4.0
/nix/store/b9iyqcsd1gmlfagpi4xqqlswcpx079r1-aarch64-unknown-linux-gnu-stage-final-gcc-debug-7.4.0
├── aarch64-unknown-linux-gnu
│   ├── include
│   ├── lib
│   ├── lib64
│   └── sys-include
├── bin
│   ├── aarch64-unknown-linux-gnu-c++
│   ├── aarch64-unknown-linux-gnu-cpp
│   ├── aarch64-unknown-linux-gnu-g++
│   ├── aarch64-unknown-linux-gnu-gcc
│   ├── aarch64-unknown-linux-gnu-gcc-7.4.0
│   ├── aarch64-unknown-linux-gnu-gcc-ar
│   ├── aarch64-unknown-linux-gnu-gcc-nm
│   ├── aarch64-unknown-linux-gnu-gcc-ranlib
│   ├── aarch64-unknown-linux-gnu-gcov
│   ├── aarch64-unknown-linux-gnu-gcov-dump
│   └── aarch64-unknown-linux-gnu-gcov-tool
├── include
├── lib
│   ├── gcc
│   └── libcc1.a
├── lib64 -> lib
├── libexec
│   └── gcc
├── nix-support
│   └── propagated-build-inputs
└── share
    └── locale

The cross compiled packages depend on the aarch64-unknown-linux-gnu/lib folder, but this path also contains x86 binaries in it! (like aarch64-unknown-linux-gnu-gcc).

This causes a bunch of other run-time x86 dependencies to be packaged with the cross-compiled binaries.

@matthewbauer pointed me here: https://github.com/matthewbauer/nixpkgs/blob/static-nix/pkgs/development/compilers/gcc/builder.sh#L203-L287, which is possibly broken.

Trying to move the ARM libs into the lib output caused a cyclic dependency between the lib output and the normal output :( so I'm stuck & posting this issue.

Steps to reproduce

build a cross-compiled binary with a cross gcc, notice that it has x86 binaries in it's run-time closure (assuming the build system is x86):

nix build -f . pkgsCross.aarch64-multiplatform.glibc
nix path-info -r $(readlink -f result) | while read f; do find $f -type f -exec file {} + | grep $(uname -m | tr _ -); done

Technical details

• system: "x86_64-linux"
• host os: Linux 4.20.6-arch1-1-ARCH, Antergos Linux, noversion
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.2.1
• channels(root): "nixpkgs-19.09pre171945.b36dc66bfea"
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixpkgs