| """ |
| 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, |
| ], |
| ), |
| ] |