Make it possible to run tests on Linux

.bcr/presubmit.yml

@@ -1,7 +1,7 @@
 bcr_test_module:
   module_path: "bcr_test"
   matrix:
-    platform: ["centos7", "debian10", "macos", "macos_arm64", "ubuntu2004"]
+    platform: ["debian10", "macos", "macos_arm64", "ubuntu2004"]
     bazel: [6.x, 7.x]
   tasks:
     run_tests:

.github/workflows/release.yaml

@@ -474,20 +474,20 @@ jobs:
         set -euo pipefail
 
 
-        file "$BINARY_LINUX_X86_64" | grep ''statically linked'' || (echo "Binary
-        $BINARY_LINUX_X86_64 is not statically linked: $(file "$BINARY_LINUX_X86_64")"
+        file -L "$BINARY_LINUX_X86_64" | grep ''statically linked'' || (echo "Binary
+        $BINARY_LINUX_X86_64 is not statically linked: $(file -L "$BINARY_LINUX_X86_64")"
         && exit 1)
 
-        file "$BINARY_LINUX_X86_64" | grep ''x86-64'' || (echo "Binary $BINARY_LINUX_X86_64
-        is not x86-64: $(file "$BINARY_LINUX_X86_64")" && exit 1)
+        file -L "$BINARY_LINUX_X86_64" | grep ''x86-64'' || (echo "Binary $BINARY_LINUX_X86_64
+        is not x86-64: $(file -L "$BINARY_LINUX_X86_64")" && exit 1)
 
 
-        file "$BINARY_LINUX_AARCH64" | grep ''statically linked'' || (echo "Binary
-        $BINARY_LINUX_AARCH64 is not statically linked: $(file "$BINARY_LINUX_AARCH64")"
+        file -L "$BINARY_LINUX_AARCH64" | grep ''statically linked'' || (echo "Binary
+        $BINARY_LINUX_AARCH64 is not statically linked: $(file -L "$BINARY_LINUX_AARCH64")"
         && exit 1)
 
-        file "$BINARY_LINUX_AARCH64" | grep ''aarch64'' || (echo "Binary $BINARY_LINUX_AARCH64
-        is not aarch64: $(file "$BINARY_LINUX_AARCH64")" && exit 1)
+        file -L "$BINARY_LINUX_AARCH64" | grep ''aarch64'' || (echo "Binary $BINARY_LINUX_AARCH64
+        is not aarch64: $(file -L "$BINARY_LINUX_AARCH64")" && exit 1)
 
 
         echo "All tests passed"

README.md

@@ -4,6 +4,16 @@
 
 This toolchain allows cross-compiling binaries for Linux from various platforms. It can be used to produce binaries which don't dynamically link `libc`, by statically linking `musl`'s `libc` implementation.
 
+## Setup
+
+Setup instructions are available with [each release](https://github.com/bazel-contrib/musl-toolchain/releases).
+
+## Usage
+
+The toolchain automatically enables the `fully_static_link` feature to produce statically linked binaries that run anywhere.
+`cc_binary` targets with dynamic library dependencies (e.g. `dynamic_deps` or `cc_import`s) as well as `cc_test` targets with `--dynamic_mode` at its default value will be linked dynamically. Such binaries require the `musl` dynamic linker to be present at `/lib/ld-musl-<arch>.so.1` on the target system (i.e. the host when running `bazel test` on Linux).
+Since the path to the dynamic linker is hardcoded into the binary as an absolute path, there is no way to supply it hermetically.
+
 ## Comparison with other `cc_toolchain` implementations
 
 ### [aspect-build/gcc-toolchain](https://github.com/aspect-build/gcc-toolchain)

generate-actions.py

@@ -564,11 +564,11 @@ def load_musl_toolchains(extra_exec_compatible_with=[], extra_target_compatible_
 
 set -euo pipefail
 
-file "$BINARY_LINUX_X86_64" | grep 'statically linked' || (echo "Binary $BINARY_LINUX_X86_64 is not statically linked: $(file "$BINARY_LINUX_X86_64")" && exit 1)
-file "$BINARY_LINUX_X86_64" | grep 'x86-64' || (echo "Binary $BINARY_LINUX_X86_64 is not x86-64: $(file "$BINARY_LINUX_X86_64")" && exit 1)
+file -L "$BINARY_LINUX_X86_64" | grep 'statically linked' || (echo "Binary $BINARY_LINUX_X86_64 is not statically linked: $(file -L "$BINARY_LINUX_X86_64")" && exit 1)
+file -L "$BINARY_LINUX_X86_64" | grep 'x86-64' || (echo "Binary $BINARY_LINUX_X86_64 is not x86-64: $(file -L "$BINARY_LINUX_X86_64")" && exit 1)
 
-file "$BINARY_LINUX_AARCH64" | grep 'statically linked' || (echo "Binary $BINARY_LINUX_AARCH64 is not statically linked: $(file "$BINARY_LINUX_AARCH64")" && exit 1)
-file "$BINARY_LINUX_AARCH64" | grep 'aarch64' || (echo "Binary $BINARY_LINUX_AARCH64 is not aarch64: $(file "$BINARY_LINUX_AARCH64")" && exit 1)
+file -L "$BINARY_LINUX_AARCH64" | grep 'statically linked' || (echo "Binary $BINARY_LINUX_AARCH64 is not statically linked: $(file -L "$BINARY_LINUX_AARCH64")" && exit 1)
+file -L "$BINARY_LINUX_AARCH64" | grep 'aarch64' || (echo "Binary $BINARY_LINUX_AARCH64 is not aarch64: $(file -L "$BINARY_LINUX_AARCH64")" && exit 1)
 
 echo "All tests passed"
 EOF

musl-toolchain.BUILD.bazel.template

@@ -24,6 +24,11 @@ filegroup(
 
 filegroup(name = "empty")
 
+filegroup(
+    name = "dynamic_runtime_lib",
+    srcs = glob(["x86_64-linux-musl/lib/*.so*"]),
+)
+
 musl_cc_toolchain_config(name = "k8_musl_toolchain_config", target_arch = "{{target_arch}}")
 
 cc_toolchain(
@@ -40,4 +45,7 @@ cc_toolchain(
     supports_param_files = True,
     toolchain_config = ":k8_musl_toolchain_config",
     toolchain_identifier = "k8-musl-toolchain",
+    dynamic_runtime_lib = ":dynamic_runtime_lib",
+    # Linked in automatically by the toolchain.
+    static_runtime_lib = ":empty",
 )

musl_cc_toolchain_config.bzl

@@ -246,6 +246,11 @@ def _impl(ctx):
 
     dbg_feature = feature(name = "dbg")
 
+    static_link_cpp_runtimes_feature = feature(
+        name = "static_link_cpp_runtimes",
+        enabled = True,
+    )
+
     fully_static_link_feature = feature(
         name = "fully_static_link",
         enabled = True,
@@ -345,6 +350,33 @@ def _impl(ctx):
         ],
     )
 
+    # The default implementation of this feature uses the Google-internal
+    # $EXEC_ORIGIN, which is not available in the open-source dynamic linker.
+    runtime_library_search_directories_feature = feature(
+        name = "runtime_library_search_directories",
+        flag_sets = [
+            flag_set(
+                actions = all_link_actions,
+                flag_groups = [
+                    flag_group(
+                        iterate_over = "runtime_library_search_directories",
+                        flag_groups = [
+                            flag_group(
+                                flags = [
+                                    "-Xlinker",
+                                    "-rpath",
+                                    "-Xlinker",
+                                    "$ORIGIN/%{runtime_library_search_directories}",
+                                ],
+                            ),
+                        ],
+                        expand_if_available = "runtime_library_search_directories",
+                    ),
+                ],
+            ),
+        ],
+    )
+
     coverage_feature = feature(
         name = "coverage",
         provides = ["profile"],
@@ -408,6 +440,7 @@ def _impl(ctx):
         features = [
             random_seed_feature,
             generate_linkmap_feature,
+            runtime_library_search_directories_feature,
             coverage_feature,
             default_compile_flags_feature,
             default_link_flags_feature,
@@ -416,6 +449,7 @@ def _impl(ctx):
             objcopy_embed_flags_feature,
             opt_feature,
             dbg_feature,
+            static_link_cpp_runtimes_feature,
             fully_static_link_feature,
             user_compile_flags_feature,
             sysroot_feature,