bazel构建使用clang工具链

最近使用clang工具构建bazel项目。官方文档给的step较为繁琐，这里暂时记录一下，以便后期可以直接去用。这里具体的规则不进行详细解释，具体看官方文档有关描述。

查看预定义变量列表，使用如下命令：

bazel info --show_make_env

类似效果如下图：

官方配置C++工具链

项目的整体结构为：

build-tool-chain
├── main
│   ├── BUILD
│   └── hello-world.cc
├── toolchain
│   ├── BUILD
│   └── cc_toolchain_config.bzl
│   
└── WORKSPACE
│   
└── .bazelrc

WORKSPACE里面内容为空，可根据需要填写你项目所需的外部依赖。

.bazelrc内容主要配置--crosstool_top,--cpu, --host_crosstool_top

# Use our custom-configured c++ toolchain.

build:clang_config --crosstool_top=//toolchain:clang_suite

# Use --cpu as a differentiator.

build:clang_config --cpu=k8

# Use the default Bazel C++ toolchain to build the tools used during the
# build.

build:clang_config --host_crosstool_top=@bazel_tools//tools/cpp:toolchain

toolchain/BUILD的内容主要为cc_toolchain_suite,文件组等

package(default_visibility = ["//visibility:public"])

load(":cc_toolchain_config.bzl", "cc_toolchain_config")

# filegroup(name = "clang_suite")

cc_toolchain_suite(
    name = "clang_suite",
    toolchains = {
        "k8": ":k8_toolchain",
    },
)

filegroup(name = "empty")

cc_toolchain(
    name = "k8_toolchain",
    toolchain_identifier = "k8-toolchain",
    toolchain_config = ":k8_toolchain_config",
    all_files = ":empty",
    compiler_files = ":empty",
    dwp_files = ":empty",
    linker_files = ":empty",
    objcopy_files = ":empty",
    strip_files = ":empty",
    supports_param_files = 0,
)

cc_toolchain_config(name = "k8_toolchain_config")
# filegroup(name = "cc_toolchain_config")

toolchain/cc_toolchain_config.bzl文件的内容，这里需要将对应的clang相关头文件搜索路径配置为你的搜索路径

# NEW
load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "ACTION_NAMES")
# NEW
load(
    "@bazel_tools//tools/cpp:cc_toolchain_config_lib.bzl",
    "feature",
    "flag_group",
    "flag_set",
    "tool_path",
)

all_link_actions = [ # NEW
    ACTION_NAMES.cpp_link_executable,
    ACTION_NAMES.cpp_link_dynamic_library,
    ACTION_NAMES.cpp_link_nodeps_dynamic_library,
]

def _impl(ctx):
    tool_paths = [
        tool_path(
            name = "gcc",
            path = "/home/wzy/app/llvm-build-13.0.1/bin/clang",
        ),
        tool_path(
            name = "g++",
            path = "/home/wzy/app/llvm-build-13.0.1/bin/clang++",
        ),
        tool_path(
            name = "ld",
            path = "/usr/bin/ld",
        ),
        tool_path(
            name = "ar",
            path = "/usr/bin/ar",
        ),
        tool_path(
            name = "cpp",
            path = "/home/wzy/app/llvm-build-13.0.1/bin/clang++",
        ),
        tool_path(
            name = "gcov",
            path = "/usr/bin/gcov",
        ),
        tool_path(
            name = "nm",
            path = "/usr/bin/nm",
        ),
        tool_path(
            name = "objdump",
            path = "/usr/bin/objdump",
        ),
        tool_path(
            name = "strip",
            path = "/usr/bin/strip",
        ),
    ]

    features = [ # NEW
        feature(
            name = "default_linker_flags",
            enabled = True,
            flag_sets = [
                flag_set(
                    actions = all_link_actions,
                    flag_groups = ([
                        flag_group(
                            flags = [
                                "-lstdc++",
                                "-lpthread",
                                "-lm",
                            ],
                        ),
                    ]),
                ),
            ],
        ),
    ]

    return cc_common.create_cc_toolchain_config_info(
        ctx = ctx,
        features = features, # NEW
        cxx_builtin_include_directories = [
            "/home/wzy/app/llvm-build-13.0.1/lib/clang/15.0.0/include",
            "/usr/include",
        ],
        toolchain_identifier = "local",
        host_system_name = "local",
        target_system_name = "local",
        target_cpu = "k8",
        target_libc = "unknown",
        compiler = "clang",
        abi_version = "unknown",
        abi_libc_version = "unknown",
        tool_paths = tool_paths,
    )

cc_toolchain_config = rule(
    implementation = _impl,
    attrs = {},
    provides = [CcToolchainConfigInfo],
)

剩下就是main包里面的示例配置了，这里也给出

main/BUILD

load("@rules_cc//cc:defs.bzl", "cc_binary")

cc_binary(
    name = "hello-world",
    srcs = ["hello-world.cc"],
)

示例代码hello-world.cc

#include <ctime>
#include <string>
#include <iostream>

std::string get_greet(const std::string& who) {
  return "Hello " + who;
}

void print_localtime() {
  std::time_t result = std::time(nullptr);
  std::cout << std::asctime(std::localtime(&result));
}

int main(int argc, char** argv) {
  std::string who = "world";
  if (argc > 1) {
    who = argv[1];
  }
  std::cout << get_greet(who) << std::endl;
  print_localtime();
  return 0;
}

使用配置工具链构建执行

bazel build -s --config=clang_config //main:hello-world --explain "log.txt" --verbose_explanations=true --worker_verbose=true

效果如下：

  bazel构建的信息，以及最后可执行文件执行