Add a test for darwin to linux cross-compilation

.github/workflows/tests.yml

@@ -17,8 +17,6 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: test
-      env:
-        BAZELISK_GITHUB_TOKEN: ${{ secrets.BAZELISK_GITHUB_TOKEN }}
       run: tests/scripts/${{ matrix.script }}
   container_test:
     runs-on: ubuntu-latest
@@ -32,6 +30,10 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: test
-      env:
-        BAZELISK_GITHUB_TOKEN: ${{ secrets.BAZELISK_GITHUB_TOKEN }}
       run: tests/scripts/${{ matrix.script }}_test.sh
+  xcompile_test:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: test
+      run: tests/scripts/run_xcompile_tests.sh

platforms/BUILD.bazel

@@ -0,0 +1,37 @@
+# Copyright 2021 The Bazel Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+platform(
+    name = "linux-x86_64",
+    constraint_values = [
+        "@platforms//os:linux",
+        "@platforms//cpu:x86_64",
+    ],
+)
+
+platform(
+    name = "linux-aarch64",
+    constraint_values = [
+        "@platforms//os:osx",
+        "@platforms//cpu:aarch64",
+    ],
+)
+
+platform(
+    name = "darwin-x86_64",
+    constraint_values = [
+        "@platforms//os:osx",
+        "@platforms//cpu:x86_64",
+    ],
+)

tests/BUILD.bazel

@@ -20,9 +20,12 @@ cc_library(
     hdrs = ["stdlib.h"],
 )
 
+# We want to emulate the behavior of cc_binary but be able to run the target as
+# a test, so we use a cc_test target with linkstatic.
 cc_test(
     name = "stdlib_test",
     srcs = ["stdlib_test.cc"],
+    linkstatic = True,
     deps = [":stdlib"],
 )
 

tests/scripts/run_xcompile_tests.sh

@@ -0,0 +1,53 @@
+#!/bin/bash
+# Copyright 2021 The Bazel Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -euo pipefail
+
+source "$(dirname "${BASH_SOURCE[0]}")/bazel.sh"
+"${bazel}" version
+
+binpath="$("${bazel}" info bazel-bin)/tests/stdlib_test"
+
+check_with_image() {
+  if "${CI:-false}"; then
+    # macOS GitHub Action Runners do not have docker installed on them.
+    return
+  fi
+  local image="$1"
+  docker run --rm --mount "type=bind,source=${binpath},target=/stdlib_test" "${image}" /stdlib_test
+}
+
+echo ""
+echo "Testing static linked user libraries and dynamic linked system libraries"
+build_args=(
+  --incompatible_enable_cc_toolchain_resolution
+  --platforms=//platforms:linux-x86_64
+  --extra_toolchains=@llvm_toolchain_with_sysroot//:cc-toolchain-x86_64-linux
+  --symlink_prefix=/
+  --color=yes
+  --show_progress_rate_limit=30
+)
+"${bazel}" --bazelrc=/dev/null build "${build_args[@]}" //tests:stdlib_test
+file "${binpath}" | tee /dev/stderr | grep -q ELF
+check_with_image "frolvlad/alpine-glibc" # Need glibc image for system libraries.
+
+echo ""
+echo "Testing static linked user and system libraries"
+build_args+=(
+  --features=fully_static_link
+)
+"${bazel}" --bazelrc=/dev/null build "${build_args[@]}" //tests:stdlib_test
+file "${binpath}" | tee /dev/stderr | grep -q ELF
+check_with_image "alpine"

toolchain/cc_toolchain_config.bzl

@@ -96,87 +96,101 @@ def cc_toolchain_config(
 
     is_xcompile = not (host_os == target_os and host_arch == target_arch)
 
+    # Default compiler flags:
+    compile_flags = [
+        "--target=" + target_system_name,
+        # Security
+        "-U_FORTIFY_SOURCE",  # https://github.com/google/sanitizers/issues/247
+        "-fstack-protector",
+        "-fno-omit-frame-pointer",
+        # Diagnostics
+        "-fcolor-diagnostics",
+        "-Wall",
+        "-Wthread-safety",
+        "-Wself-assign",
+    ]
+
+    dbg_compile_flags = ["-g", "-fstandalone-debug"]
+
+    opt_compile_flags = [
+        "-g0",
+        "-O2",
+        "-D_FORTIFY_SOURCE=1",
+        "-DNDEBUG",
+        "-ffunction-sections",
+        "-fdata-sections",
+    ]
+
+    link_flags = [
+        "--target=" + target_system_name,
+        "-lm",
+        "-no-canonical-prefixes",
+    ]
+
     # Linker flags:
     if host_os == "darwin" and not is_xcompile:
         # lld is experimental for Mach-O, so we use the native ld64 linker.
         use_lld = False
-        linker_flags = [
+        link_flags.extend([
             "-headerpad_max_install_names",
             "-undefined",
             "dynamic_lookup",
-        ]
+        ])
     else:
         # We prefer the lld linker.
         # Note that for xcompiling from darwin to linux, the native ld64 is
         # not an option because it is not a cross-linker, so lld is the
         # only option.
         use_lld = True
-        linker_flags = [
+        link_flags.extend([
             "-fuse-ld=lld",
             "-Wl,--build-id=md5",
             "-Wl,--hash-style=gnu",
             "-Wl,-z,relro,-z,now",
-        ]
+        ])
 
+    # Flags related to C++ standard.
     # The linker has no way of knowing if there are C++ objects; so we
     # always link C++ libraries.
-    if host_os == "linux" and not is_xcompile:
-        # For single-platform linux builds, we can statically link the bundled
-        # libraries.
-        linker_flags.extend([
-            "-L{}lib".format(toolchain_path_prefix),
-            "-l:libc++.a",
-            "-l:libc++abi.a",
-            "-l:libunwind.a",
-            # Compiler runtime features.
-            "-rtlib=compiler-rt",
-            # To support libunwind.
-            "-lpthread",
-            "-ldl",
-        ])
+    if not is_xcompile:
+        cxx_flags = [
+            "-std=c++17",
+            "-stdlib=libc++",
+        ]
+        if use_lld:
+            # For single-platform builds, we can statically link the bundled
+            # libraries.
+            link_flags.extend([
+                "-L{}lib".format(toolchain_path_prefix),
+                "-l:libc++.a",
+                "-l:libc++abi.a",
+                "-l:libunwind.a",
+                # Compiler runtime features.
+                "-rtlib=compiler-rt",
+                # To support libunwind.
+                "-lpthread",
+                "-ldl",
+            ])
+        else:
+            # TODO: Not sure how to achieve static linking of bundled libraries
+            # with ld64; maybe we don't really need it.
+            link_flags.extend([
+                "-lc++",
+                "-lc++abi",
+            ])
     else:
+        cxx_flags = [
+            "-std=c++17",
+            "-stdlib=libstdc++",
+        ]
+
         # For xcompile, we expect to pick up these libraries from the sysroot.
-        # TODO: For single-platform darwin builds, we can statically link the
-        # bundled libraries but I do not know the right flags to make it
-        # happen.
-        linker_flags.extend([
-            "-lc++",
-            "-lc++abi",
+        link_flags.extend([
+            "-l:libstdc++.a",
         ])
 
-    link_flags = [
-        "-lm",
-        "-no-canonical-prefixes",
-    ] + linker_flags
-
     opt_link_flags = ["-Wl,--gc-sections"] if target_os == "linux" else []
 
-    # Default compiler flags:
-    compile_flags = [
-        # Security
-        "-U_FORTIFY_SOURCE",  # https://github.com/google/sanitizers/issues/247
-        "-fstack-protector",
-        "-fno-omit-frame-pointer",
-        # Diagnostics
-        "-fcolor-diagnostics",
-        "-Wall",
-        "-Wthread-safety",
-        "-Wself-assign",
-    ]
-
-    dbg_compile_flags = ["-g", "-fstandalone-debug"]
-
-    opt_compile_flags = [
-        "-g0",
-        "-O2",
-        "-D_FORTIFY_SOURCE=1",
-        "-DNDEBUG",
-        "-ffunction-sections",
-        "-fdata-sections",
-    ]
-
-    cxx_flags = ["-std=c++17", "-stdlib=libc++"]
-
     # Coverage flags:
     coverage_compile_flags = ["-fprofile-instr-generate", "-fcoverage-mapping"]
     coverage_link_flags = ["-fprofile-instr-generate"]