cross-compilation fails when dependencies have build-scripts

[noonien]

To reproduce, one can copy the cross-windows example, and add this as a dependency:

serde = { version = "1.0.125", features = [ "derive" ] }

Remember to cargo update to update the lock file!

This is the output i get:

$ nix build
error: builder for '/nix/store/8n1iakh91cyin8ljvnl7nphrdgys5al2-cross-windows-0.1.0.drv' failed with exit code 101;
       last 10 log lines:
       >   = note: "cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-Wl,--eh-frame-hdr" "-L" "/nix/store/7817a002q6061ly4w913mqd81r8wbg7w-rust-nightly-mixed/lib/rustlib/x86_64-unknown-linux-gnu/lib" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.0.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.1.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.10.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.11.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.12.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.13.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.14.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.15.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.2.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.3.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.4.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.5.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.6.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.7.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.8.rcgu.o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.build_script_build.87w02aon-cgu.9.rcgu.o" "-o" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e" "/build/source/target/release/build/proc-macro2-3a9ea7babb00e00e/build_script_build-3a9ea7babb00e00e.1hszvpc0qdb2i936.rcgu.o" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/build/source/target/release/deps" "-L" "/nix/store/7817a002q6061ly4w913mqd81r8wbg7w-rust-nightly-mixed/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-61556e43b375c2c0.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-787faa8b02fbd963.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libminiz_oxide-dda4c0b69607e93b.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libadler-4b7dae8949ac132c.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject-978e97832b309706.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libaddr2line-073b1b693304b876.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libgimli-c07f996a53ee6558.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-0ae8ed6a282247d0.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-978dd04958b6ebcc.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-14b94bdd9a47d665.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-bff7534e4dfcef6c.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-022f1a0e7cd794ec.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-ff456575f1773ef0.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-3aeb407930ebd519.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-6ab1ee6dbc17ad08.rlib" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-166dae07beec0398.rlib" "-Wl,--end-group" "/nix/store/m3j63f9br5qi3za971bj2jxjpbm6pba6-rust-std-nightly-2021-03-25/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-761b290f47712921.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc"
       >   = note: /nix/store/xdii8qvch5h8chyp0z2is2qzky565w68-binutils-2.35.1/bin/ld: /nix/store/qah4dp8h83cqyc5n19a5rw85hlmmmrwh-pthreads-w32-2.9.1-x86_64-w64-mingw32/lib/libpthread.a: error adding symbols: file format not recognized
       >           collect2: error: ld returned 1 exit status
       >           
       >
       >
       > error: aborting due to previous error
       >
       >
       > [naersk] cargo returned with exit code 101, exiting
       For full logs, run 'nix log /nix/store/8n1iakh91cyin8ljvnl7nphrdgys5al2-cross-windows-0.1.0.drv'

[noonien]

From what I can tell, compilation is done in two stages, first it compiles and runs the build scripts (for procmacros and build.rs), then the cross-compilation phase occurs.

The first phase requires a native compiler, but because

NIX_LDFLAGS= -L/nix/store/rp555fl22y5c89whw9b541c34165a5kc-mcfgthreads-x86_64-w64-mingw32-git/lib -L/nix/store/8mrj7m3r50gfhz964n72rlyhin8qpbm1-mingw-w64-x86_64-w64-mingw32-6.0.0-pthreads-x86_64-w64-mingw32/lib -L/nix/store/72r6kaspk4sf7dzzlyc9n0m5l9lhylr8-pthreads-w32-x86_64-w64-mingw32-2.9.1/lib

the native compiler cannot interpret libpthread.a when compiling the build scripts.

To verify this, running export NIX_LDFLAGS= before manually running a cargo build seems to advance to the cross compilation stage, which then obviously fails, because it cannot find libpthread.a anymore.

[noonien]

export CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUSTFLAGS="-C link-args=$NIX_LDFLAGS" 
export NIX_LDFLAGS=
cargo build --release --target x86_64-pc-windows-gnu --verbose

doing this seems to fix the build for me, however, this will probably fail if the build scripts have dependencies that need to be specified

[noonien]

preBuild = ''
  export CARGO_TARGET_X86_64_PC_WINDOWS_GNU_RUSTFLAGS="-C link-args=''$(echo $NIX_LDFLAGS | tr ' ' '\n' | grep -- '^-L' | tr '\n' ' ')"
  export NIX_LDFLAGS=
'';

adding this seems to fix compilation, however, this is pretty much a hack.

[Patryk27]

FWIW, something like that should work (following the cross-windows + serde example):

strictDeps = true;

depsBuildBuild = with pkgs; [
  pkgsCross.mingwW64.stdenv.cc
  pkgsCross.mingwW64.windows.pthreads
];

I'll try to refresh the example once I find some time 🙂