""" This file specifies a clang toolchain that can run on a Linux host which does depend on any installed packages from the host machine. See build_toolchain.bzl for more details on the creation of the toolchain. It uses the usr subfolder of the built toolchain as a sysroot It follows the example of: - https://docs.bazel.build/versions/4.2.1/tutorial/cc-toolchain-config.html - https://github.com/emscripten-core/emsdk/blob/7f39d100d8cd207094decea907121df72065517e/bazel/emscripten_toolchain/crosstool.bzl """ load( "@bazel_tools//tools/cpp:cc_toolchain_config_lib.bzl", "action_config", "feature", "flag_group", "flag_set", "tool", "variable_with_value", ) load("@bazel_tools//tools/build_defs/cc:action_names.bzl", "ACTION_NAMES") # The location of the created clang toolchain. EXTERNAL_TOOLCHAIN = "external/clang_linux_amd64" def _clang_impl(ctx): action_configs = _make_action_configs() features = [] features += _make_default_flags() features += _make_diagnostic_flags() # https://docs.bazel.build/versions/main/skylark/lib/cc_common.html#create_cc_toolchain_config_info # Note, this rule is defined in Java code, not Starlark # https://cs.opensource.google/bazel/bazel/+/master:src/main/java/com/google/devtools/build/lib/starlarkbuildapi/cpp/CcModuleApi.java return cc_common.create_cc_toolchain_config_info( ctx = ctx, features = features, abi_libc_version = "unknown", abi_version = "unknown", action_configs = action_configs, # This is important because the linker will complain if the libc shared libraries are not # under this directory. Because we extract the libc libraries to # EXTERNAL_TOOLCHAIN/lib, and the various headers and shared libraries to # EXTERNAL_TOOLCHAIN/usr, we make the top level folder the sysroot so the linker can # find the referenced libraries (e.g. EXTERNAL_TOOLCHAIN/usr/lib/x86_64-linux-gnu/libc.so # is just a text file that refers to "/lib/x86_64-linux-gnu/libc.so.6" and # "/lib64/ld-linux-x86-64.so.2" which will use the sysroot as the root). builtin_sysroot = EXTERNAL_TOOLCHAIN, compiler = "clang", host_system_name = "local", target_cpu = "k8", # It is unclear if target_libc matters. target_libc = "glibc-2.31", target_system_name = "local", toolchain_identifier = "clang-toolchain", ) provide_clang_toolchain_config = rule( attrs = {}, provides = [CcToolchainConfigInfo], implementation = _clang_impl, ) def _make_action_configs(): """ This function sets up the tools needed to perform the various compile/link actions. Bazel normally restricts us to referring to (and therefore running) executables/scripts that are in this directory (That is EXEC_ROOT/toolchain). However, the executables we want to run are brought in via WORKSPACE.bazel and are located in EXEC_ROOT/external/clang.... Therefore, we make use of "trampoline scripts" that will call the binaries from the toolchain directory. These action_configs also let us dynamically specify arguments from the Bazel environment if necessary (see cpp_link_static_library_action). """ # https://cs.opensource.google/bazel/bazel/+/master:tools/cpp/cc_toolchain_config_lib.bzl;l=435;drc=3b9e6f201a9a3465720aad8712ab7bcdeaf2e5da clang_tool = tool(path = "clang_trampoline.sh") lld_tool = tool(path = "lld_trampoline.sh") ar_tool = tool(path = "ar_trampoline.sh") # https://cs.opensource.google/bazel/bazel/+/master:tools/cpp/cc_toolchain_config_lib.bzl;l=488;drc=3b9e6f201a9a3465720aad8712ab7bcdeaf2e5da assemble_action = action_config( action_name = ACTION_NAMES.assemble, tools = [clang_tool], ) c_compile_action = action_config( action_name = ACTION_NAMES.c_compile, tools = [clang_tool], ) cpp_compile_action = action_config( action_name = ACTION_NAMES.cpp_compile, tools = [clang_tool], ) linkstamp_compile_action = action_config( action_name = ACTION_NAMES.linkstamp_compile, tools = [clang_tool], ) preprocess_assemble_action = action_config( action_name = ACTION_NAMES.preprocess_assemble, tools = [clang_tool], ) cpp_link_dynamic_library_action = action_config( action_name = ACTION_NAMES.cpp_link_dynamic_library, tools = [lld_tool], ) cpp_link_executable_action = action_config( action_name = ACTION_NAMES.cpp_link_executable, # Bazel assumes it is talking to clang when building an executable. There are # "-Wl" flags on the command: https://releases.llvm.org/6.0.1/tools/clang/docs/ClangCommandLineReference.html#cmdoption-clang-Wl tools = [clang_tool], ) cpp_link_nodeps_dynamic_library_action = action_config( action_name = ACTION_NAMES.cpp_link_nodeps_dynamic_library, tools = [lld_tool], ) # This is the same rule as # https://github.com/emscripten-core/emsdk/blob/7f39d100d8cd207094decea907121df72065517e/bazel/emscripten_toolchain/crosstool.bzl#L143 # By default, there are no flags or libraries passed to the llvm-ar tool, so # we need to specify them. The variables mentioned by expand_if_available are defined # https://docs.bazel.build/versions/main/cc-toolchain-config-reference.html#cctoolchainconfiginfo-build-variables cpp_link_static_library_action = action_config( action_name = ACTION_NAMES.cpp_link_static_library, flag_sets = [ flag_set( flag_groups = [ flag_group( # https://llvm.org/docs/CommandGuide/llvm-ar.html # replace existing files or insert them if they already exist, # create the file if it doesn't already exist # symbol table should be added # Deterministic timestamps should be used flags = ["rcsD", "%{output_execpath}"], # Despite the name, output_execpath just refers to linker output, # e.g. libFoo.a expand_if_available = "output_execpath", ), ], ), flag_set( flag_groups = [ flag_group( iterate_over = "libraries_to_link", flag_groups = [ flag_group( flags = ["%{libraries_to_link.name}"], expand_if_equal = variable_with_value( name = "libraries_to_link.type", value = "object_file", ), ), flag_group( flags = ["%{libraries_to_link.object_files}"], iterate_over = "libraries_to_link.object_files", expand_if_equal = variable_with_value( name = "libraries_to_link.type", value = "object_file_group", ), ), ], expand_if_available = "libraries_to_link", ), ], ), flag_set( flag_groups = [ flag_group( flags = ["@%{linker_param_file}"], expand_if_available = "linker_param_file", ), ], ), ], tools = [ar_tool], ) action_configs = [ assemble_action, c_compile_action, cpp_compile_action, cpp_link_dynamic_library_action, cpp_link_executable_action, cpp_link_nodeps_dynamic_library_action, cpp_link_static_library_action, linkstamp_compile_action, preprocess_assemble_action, ] return action_configs def _make_default_flags(): """Here we define the flags for certain actions that are always applied.""" cxx_compile_includes = flag_set( actions = [ ACTION_NAMES.c_compile, ACTION_NAMES.cpp_compile, ], flag_groups = [ flag_group( flags = [ # THIS ORDER MATTERS GREATLY. If these are in the wrong order, the # #include_next directives will fail to find the files, causing a compilation # error (or, without -no-canonical-prefixes, a mysterious case where files # are included with an absolute path and fail the build). "-isystem", EXTERNAL_TOOLCHAIN + "/include/c++/v1", "-isystem", EXTERNAL_TOOLCHAIN + "/usr/include", "-isystem", EXTERNAL_TOOLCHAIN + "/lib/clang/13.0.0/include", "-isystem", EXTERNAL_TOOLCHAIN + "/usr/include/x86_64-linux-gnu", # We do not want clang to search in absolute paths for files. This makes # Bazel think we are using an outside resource and fail the compile. "-no-canonical-prefixes", ], ), ], ) cpp_compile_includes = flag_set( actions = [ ACTION_NAMES.cpp_compile, ], flag_groups = [ flag_group( flags = [ # http://g/skia-staff/bhPPBV4YdeU/5oyG5GRgBQAJ "-std=c++14", "-Wno-c++17-extensions", "-Wno-psabi", # noisy ], ), ], ) link_exe_flags = flag_set( actions = [ACTION_NAMES.cpp_link_executable], flag_groups = [ flag_group( flags = [ "-fuse-ld=lld", # We chose to use the llvm runtime, not the gcc one because it is already # included in the clang binary "--rtlib=compiler-rt", "-std=c++14", # We statically include these libc++ libraries so they do not need to be # on a developer's machine (they can be tricky to get). EXTERNAL_TOOLCHAIN + "/lib/libc++.a", EXTERNAL_TOOLCHAIN + "/lib/libc++abi.a", EXTERNAL_TOOLCHAIN + "/lib/libunwind.a", # Dynamically Link in the other parts of glibc (not needed in glibc 2.34+) "-lpthread", "-lm", "-ldl", ], ), ], ) return [feature( "default_flags", enabled = True, flag_sets = [ cxx_compile_includes, cpp_compile_includes, link_exe_flags, ], )] def _make_diagnostic_flags(): """Here we define the flags that can be turned on via features to yield debug info.""" cxx_diagnostic = flag_set( actions = [ ACTION_NAMES.c_compile, ACTION_NAMES.cpp_compile, ], flag_groups = [ flag_group( flags = [ "--trace-includes", "-v", ], ), ], ) link_diagnostic = flag_set( actions = [ACTION_NAMES.cpp_link_executable], flag_groups = [ flag_group( flags = [ "-Wl,--verbose", "-v", ], ), ], ) link_search_dirs = flag_set( actions = [ACTION_NAMES.cpp_link_executable], flag_groups = [ flag_group( flags = [ "--print-search-dirs", ], ), ], ) return [ # Running a Bazel command with --features diagnostic will cause the compilation and # link steps to be more verbose. feature( "diagnostic", enabled = False, flag_sets = [ cxx_diagnostic, link_diagnostic, ], ), # Running a Bazel command with --features print_search_dirs will cause the link to fail # but directories searched for libraries, etc will be displayed. feature( "print_search_dirs", enabled = False, flag_sets = [ link_search_dirs, ], ), ]