Always use cross for musl targets on Linux

Ubuntu runners lack musl-g++, which causes C++ compilation to fail for
musl targets even when the host architecture matches. Forcing cross for
all musl targets on Linux fixes this since cross's Docker images have a
complete musl toolchain including C++. Fixes GH #22.

Also adds a C++ file to test-project (compiled via the cc crate) to
catch regressions of this in CI, and removes the now-dead musl-tools
install step from action.yml.

Reported by @RaulTrombin (Raul Victor Trombin). GH #22.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: autarch

.github/workflows/test.yml

@@ -25,13 +25,11 @@ jobs:
 
           - name: Linux-x86_64
             runs-on: ubuntu-24.04
-            # It's important to use a musl target here to make sure that the step to install
-            # musl-tools works.
             target: x86_64-unknown-linux-musl
             cache-cross-binary: true
             expect-file-re: "ELF.+x86-64"
-            expect-cross: ""
-            expect-stripped: "--expect-stripped"
+            expect-cross: "--expect-cross"
+            expect-stripped: ""
             can-execute: true
 
           - name: Linux-x86_64 (beta)
@@ -40,8 +38,8 @@ jobs:
             toolchain: beta
             cache-cross-binary: true
             expect-file-re: "ELF.+x86-64"
-            expect-cross: ""
-            expect-stripped: "--expect-stripped"
+            expect-cross: "--expect-cross"
+            expect-stripped: ""
             can-execute: true
 
           - name: Linux-x86_64 (nightly)
@@ -50,8 +48,8 @@ jobs:
             toolchain: nightly
             cache-cross-binary: true
             expect-file-re: "ELF.+x86-64"
-            expect-cross: ""
-            expect-stripped: "--expect-stripped"
+            expect-cross: "--expect-cross"
+            expect-stripped: ""
             can-execute: true
 
           - name: Linux-x86_64 (force cross)

Changes.md

@@ -3,6 +3,9 @@
 - Fixed a bug in calculating the `cross` binary's hash.
 - Fixed cache key handling to deal with spaces in cache key elements, for example in the OS version.
   Reported by @gdubicki (Greg Dubicki). GH #50. Fixes #51.
+- This action now always uses `cross` for `musl` targets on Linux, even when the host architecture
+  matches the target. This fixes C++ compilation failures caused by the lack of `musl-g++` on Ubuntu
+  runners. Reported by @RaulTrombin (Raul Victor Trombin). GH #22.
 
 ## 1.0.6 - 2026-03-15
 

action.yml

@@ -157,18 +157,6 @@ runs:
       env:
         GITHUB_TOKEN: ${{ inputs.GITHUB_TOKEN }}
 
-    - name: Install musl-tools on Linux if target includes "musl"
-      shell: bash
-      run: |
-        if dpkg -l musl-tools | grep -q "^ii\s*musl-tools"; then
-            exit 0
-        fi
-        sudo apt-get update --yes && \
-            sudo apt-get install --yes musl-tools
-      if:
-        steps.determine-cross-compile.outputs.needs-cross != 'true' && contains(inputs.target,
-        'musl')
-
     - name: Set build command
       id: set-build-command
       shell: bash

set-cross-compile.py

@@ -53,9 +53,10 @@ def check_needs_cross(target: str) -> bool:
 
     target = target.lower()
 
-    # Check for x86_64 Linux targets on x86_64 Linux host
+    # Check for x86_64 Linux targets on x86_64 Linux host. We always use cross for musl targets
+    # because the Ubuntu runner lacks a C++ compiler for musl (musl-g++).
     if (
-        re.search(r"x86_64.+linux-(?:gnu|musl)", target)
+        re.search(r"x86_64.+linux-gnu", target)
         and "x86_64" in system_info
         and "linux" in system_info
     ):
@@ -66,9 +67,10 @@ def check_needs_cross(target: str) -> bool:
     # because then we need 32-bit C headers, 32-bit C libs to link to, etc.
 
     # Check if both host and target are ARM Linux. I'm assuming here that for things like
-    # "arm-linux-androideabi" or "armv7-unknown-linux-ohos" we'd still need cross.
+    # "arm-linux-androideabi" or "armv7-unknown-linux-ohos" we'd still need cross. We always use
+    # cross for musl targets because the Ubuntu runner lacks a C++ compiler for musl (musl-g++).
     if (
-        re.search(r"(?:aarch64|arm).+linux-(?:gnu|musl)", target)
+        re.search(r"(?:aarch64|arm).+linux-gnu", target)
         and ("arm" in system_info or "aarch64" in system_info)
         and "linux" in system_info
     ):

test-project/Cargo.lock

@@ -15,6 +15,9 @@ path = "src/bin1.rs"
 name = "bin2"
 path = "src/bin2.rs"
 
+[build-dependencies]
+cc = "1"
+
 # workaround for https://github.com/cross-rs/cross/issues/1345
 [package.metadata.cross.target.x86_64-unknown-netbsd]
 pre-build = [

test-project/Cargo.toml

@@ -0,0 +1,6 @@
+fn main() {
+    cc::Build::new()
+        .cpp(true)
+        .file("src/hello.cpp")
+        .compile("hello");
+}

test-project/build.rs

@@ -1,4 +1,9 @@
+extern "C" {
+    fn hello_cpp() -> i32;
+}
+
 fn main() {
+    let _ = unsafe { hello_cpp() };
     println!("Hello, world!");
 }
 

test-project/src/bin1.rs

@@ -0,0 +1,4 @@
+extern "C" int hello_cpp() {
+    int a = 3, b = 1;
+    return a < b ? a : b;
+}