Build s390x binaries using musl libc

Building using musl until NixOS/nixpkgs#306473 is resolved.

Refers to cri-o/cri-o#7911

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

conmon-rs/client/src/main.rs

@@ -34,3 +34,13 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         })
         .await
 }
+
+/// Workaround for rustc bug: https://github.com/rust-lang/rust/issues/47493
+///
+/// It shouldn't even be possible to reach this function, thanks to panic=abort,
+/// but libcore is compiled with unwinding enabled and that ends up making unreachable
+/// references to this.
+#[no_mangle]
+extern "C" fn _Unwind_Resume() -> ! {
+    unreachable!("Unwinding not supported");
+}

conmon-rs/server/src/main.rs

@@ -7,3 +7,13 @@ fn main() -> Result<()> {
         .start()
         .context("start server")
 }
+
+/// Workaround for rustc bug: https://github.com/rust-lang/rust/issues/47493
+///
+/// It shouldn't even be possible to reach this function, thanks to panic=abort,
+/// but libcore is compiled with unwinding enabled and that ends up making unreachable
+/// references to this.
+#[no_mangle]
+extern "C" fn _Unwind_Resume() -> ! {
+    unreachable!("Unwinding not supported");
+}

nix/default-s390x.nix

@@ -1,6 +1,9 @@
 (import ./nixpkgs.nix {
   crossSystem = {
-    config = "s390x-unknown-linux-gnu";
+    # TODO: Switch back to glibc when
+    # https://github.com/NixOS/nixpkgs/issues/306473
+    # is resolved.
+    config = "s390x-unknown-linux-musl";
   };
   overlays = [ (import ./overlay.nix) ];
 }).callPackage ./derivation.nix

nix/derivation.nix

@@ -7,13 +7,25 @@ with pkgs; rustPlatform.buildRustPackage {
     capnproto
     protobuf
   ];
-  buildInputs = [
-    glibc
-    glibc.static
-  ];
+  buildInputs =
+    if stdenv.hostPlatform.isMusl then [
+      libunwind
+    ] else [
+      glibc
+      glibc.static
+    ];
   RUSTFLAGS = [
     "-Ctarget-feature=+crt-static"
+  ] ++ lib.optionals stdenv.hostPlatform.isMusl [
+    "-Cpanic=abort"
+    "-Clink-args=-nostartfiles"
+    "-Clink-args=-L${libunwind}/lib"
   ];
+  # Patch nix v0.27.1 for musl
+  preBuild = lib.optionalString stdenv.hostPlatform.isMusl ''
+    sed -i 's;target_arch = "s390x";target_arch = "s390x" , not(target_env = "musl");g' \
+      /build/cargo-vendor-dir/nix-0.27.1/src/sys/statfs.rs
+  '';
   stripAllList = [ "bin" ];
   cargoLock = {
     lockFile = lib.cleanSource ./.. + "/Cargo.lock";

nix/overlay.nix

@@ -2,4 +2,6 @@ let
   static = import ./static.nix;
 in
 self: super:
-{ }
+{
+  libunwind = (static super.libunwind);
+}