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Siddhartha Bagaria
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Add a test for darwin to linux cross-compilation (#99)
Two changes were needed to make cross-compilation actually work: 1. The target triple needed to be provided. 2. C++ standard flags needed to be revised. The test checks both linkstatic and fully_static modes. Fixes #20.
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‎.github/workflows/tests.yml‎

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

‎platforms/BUILD.bazel‎

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

‎tests/BUILD.bazel‎

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

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

‎toolchain/cc_toolchain_config.bzl‎

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Original file line numberDiff line numberDiff line change
@@ -96,87 +96,101 @@ def cc_toolchain_config(
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is_xcompile = not (host_os == target_os and host_arch == target_arch)
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# Default compiler flags:
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compile_flags = [
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"--target=" + target_system_name,
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# Security
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"-U_FORTIFY_SOURCE", # https://github.com/google/sanitizers/issues/247
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"-fstack-protector",
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"-fno-omit-frame-pointer",
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# Diagnostics
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"-fcolor-diagnostics",
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"-Wall",
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"-Wthread-safety",
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"-Wself-assign",
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]
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dbg_compile_flags = ["-g", "-fstandalone-debug"]
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opt_compile_flags = [
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"-g0",
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"-O2",
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"-D_FORTIFY_SOURCE=1",
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"-DNDEBUG",
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"-ffunction-sections",
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"-fdata-sections",
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]
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link_flags = [
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"--target=" + target_system_name,
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"-lm",
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"-no-canonical-prefixes",
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]
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# Linker flags:
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if host_os == "darwin" and not is_xcompile:
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# lld is experimental for Mach-O, so we use the native ld64 linker.
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use_lld = False
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linker_flags = [
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link_flags.extend([
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"-headerpad_max_install_names",
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"-undefined",
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"dynamic_lookup",
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]
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])
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else:
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# We prefer the lld linker.
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# Note that for xcompiling from darwin to linux, the native ld64 is
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# not an option because it is not a cross-linker, so lld is the
112143
# only option.
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use_lld = True
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linker_flags = [
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link_flags.extend([
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"-fuse-ld=lld",
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"-Wl,--build-id=md5",
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"-Wl,--hash-style=gnu",
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"-Wl,-z,relro,-z,now",
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]
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])
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# Flags related to C++ standard.
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# The linker has no way of knowing if there are C++ objects; so we
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# always link C++ libraries.
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if host_os == "linux" and not is_xcompile:
124-
# For single-platform linux builds, we can statically link the bundled
125-
# libraries.
126-
linker_flags.extend([
127-
"-L{}lib".format(toolchain_path_prefix),
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"-l:libc++.a",
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"-l:libc++abi.a",
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"-l:libunwind.a",
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# Compiler runtime features.
132-
"-rtlib=compiler-rt",
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# To support libunwind.
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"-lpthread",
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"-ldl",
136-
])
155+
if not is_xcompile:
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cxx_flags = [
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"-std=c++17",
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"-stdlib=libc++",
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]
160+
if use_lld:
161+
# For single-platform builds, we can statically link the bundled
162+
# libraries.
163+
link_flags.extend([
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"-L{}lib".format(toolchain_path_prefix),
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"-l:libc++.a",
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"-l:libc++abi.a",
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"-l:libunwind.a",
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# Compiler runtime features.
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"-rtlib=compiler-rt",
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# To support libunwind.
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"-lpthread",
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"-ldl",
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])
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else:
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# TODO: Not sure how to achieve static linking of bundled libraries
176+
# with ld64; maybe we don't really need it.
177+
link_flags.extend([
178+
"-lc++",
179+
"-lc++abi",
180+
])
137181
else:
182+
cxx_flags = [
183+
"-std=c++17",
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"-stdlib=libstdc++",
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]
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# For xcompile, we expect to pick up these libraries from the sysroot.
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# TODO: For single-platform darwin builds, we can statically link the
140-
# bundled libraries but I do not know the right flags to make it
141-
# happen.
142-
linker_flags.extend([
143-
"-lc++",
144-
"-lc++abi",
188+
link_flags.extend([
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"-l:libstdc++.a",
145190
])
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147-
link_flags = [
148-
"-lm",
149-
"-no-canonical-prefixes",
150-
] + linker_flags
151-
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opt_link_flags = ["-Wl,--gc-sections"] if target_os == "linux" else []
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# Default compiler flags:
155-
compile_flags = [
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# Security
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"-U_FORTIFY_SOURCE", # https://github.com/google/sanitizers/issues/247
158-
"-fstack-protector",
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"-fno-omit-frame-pointer",
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# Diagnostics
161-
"-fcolor-diagnostics",
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"-Wall",
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"-Wthread-safety",
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"-Wself-assign",
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]
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dbg_compile_flags = ["-g", "-fstandalone-debug"]
168-
169-
opt_compile_flags = [
170-
"-g0",
171-
"-O2",
172-
"-D_FORTIFY_SOURCE=1",
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"-DNDEBUG",
174-
"-ffunction-sections",
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"-fdata-sections",
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]
177-
178-
cxx_flags = ["-std=c++17", "-stdlib=libc++"]
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# Coverage flags:
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coverage_compile_flags = ["-fprofile-instr-generate", "-fcoverage-mapping"]
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coverage_link_flags = ["-fprofile-instr-generate"]

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