mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-09-24 22:02:23 +01:00
Dana Jansens
db88edfa1e
This reduces object sizes which is desirable for linking speed. zygoloid did some analysis to determine if any of our code requires RTTI for `dynamic_cast` here: https://github.com/carbon-language/carbon-lang/pull/7532#discussion_r3611196721: > The only thing I found is that libc++ requires dynamic_cast in order for std::print to correctly write Unicode to terminals on Windows We use `llvm::print` functionality, not `std::print`, so this doesn't affect our toolchain. Note that libc++ and libc++abi are built with RTTI enabled. It is explicitly allowed to use different compiler flags when building these libraries even though they share some headers with users of the libraries, so this does not cause ODR violations.
305 lines
11 KiB
Python
305 lines
11 KiB
Python
# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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# Exceptions. See /LICENSE for license information.
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# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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"""Definitions of general C++ `cc_toolchain_config` features."""
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load("@rules_cc//cc:action_names.bzl", "ACTION_NAMES", "ACTION_NAME_GROUPS")
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load(
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"@rules_cc//cc:cc_toolchain_config_lib.bzl",
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"feature",
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"flag_group",
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"flag_set",
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"with_feature_set",
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)
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load(
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":cc_toolchain_actions.bzl",
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"preprocessor_compile_actions",
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)
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clang_feature = feature(
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name = "clang",
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enabled = True,
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flag_sets = [
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_compile_actions + ACTION_NAME_GROUPS.all_cc_link_actions,
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flag_groups = [
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flag_group(flags = [
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"-no-canonical-prefixes",
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"-fcolor-diagnostics",
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]),
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flag_group(
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expand_if_available = "sysroot",
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flags = ["--sysroot=%{sysroot}"],
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),
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],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_compile_actions,
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flag_groups = [
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flag_group(flags = [
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# Compile actions shouldn't link anything.
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"-c",
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]),
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# Flags controlling the production of specific outputs from
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# compile actions.
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flag_group(
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expand_if_available = "output_assembly_file",
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flags = ["-S"],
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),
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flag_group(
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expand_if_available = "output_preprocess_file",
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flags = ["-E"],
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),
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flag_group(
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expand_if_available = "dependency_file",
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flags = ["-MD", "-MF", "%{dependency_file}"],
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),
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flag_group(
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expand_if_available = "output_file",
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flags = ["-frandom-seed=%{output_file}"],
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),
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],
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),
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flag_set(
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# Flags specific to compiling C++ sources.
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actions = ACTION_NAME_GROUPS.all_cpp_compile_actions,
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flag_groups = [flag_group(flags = [
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"-fno-exceptions",
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"-fno-rtti",
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"-std=c++20",
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])],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_compile_actions,
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flag_groups = [flag_group(flags = [
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"-ffunction-sections",
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"-fdata-sections",
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])],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_compile_actions,
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flag_groups = [flag_group(
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expand_if_available = "pic",
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flags = ["-fPIC"],
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)],
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),
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flag_set(
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actions = preprocessor_compile_actions,
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flag_groups = [
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flag_group(flags = [
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# Disable a warning and override builtin macros to
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# ensure a hermetic build.
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"-Wno-builtin-macro-redefined",
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"-D__DATE__=\"redacted\"",
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"-D__TIMESTAMP__=\"redacted\"",
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"-D__TIME__=\"redacted\"",
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]),
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flag_group(
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flags = ["-D%{preprocessor_defines}"],
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iterate_over = "preprocessor_defines",
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),
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flag_group(
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expand_if_available = "includes",
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flags = ["-include", "%{includes}"],
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iterate_over = "includes",
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),
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flag_group(
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flags = ["-iquote", "%{quote_include_paths}"],
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iterate_over = "quote_include_paths",
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),
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flag_group(
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flags = ["-I%{include_paths}"],
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iterate_over = "include_paths",
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),
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flag_group(
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flags = ["-isystem", "%{system_include_paths}"],
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iterate_over = "system_include_paths",
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),
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],
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),
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flag_set(
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actions = [
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ACTION_NAMES.cpp_link_dynamic_library,
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ACTION_NAMES.cpp_link_nodeps_dynamic_library,
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],
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flag_groups = [flag_group(flags = ["-shared"])],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_link_actions,
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flag_groups = [
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flag_group(
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expand_if_available = "strip_debug_symbols",
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flags = ["-Wl,-S"],
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),
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flag_group(
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expand_if_available = "library_search_directories",
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flags = ["-L%{library_search_directories}"],
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iterate_over = "library_search_directories",
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),
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flag_group(
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expand_if_available =
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"runtime_library_search_directories",
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iterate_over = "runtime_library_search_directories",
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flags = [
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"-Wl,-rpath,$ORIGIN/%{runtime_library_search_directories}",
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],
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),
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],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_link_actions,
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flag_groups = [
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flag_group(
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flags = [
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"-fuse-ld=lld",
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# Force the C++ standard library and runtime libraries
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# to be statically linked. This works even with libc++
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# and libunwind despite the names, provided libc++ is
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# built with the CMake option:
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# - `-DCMAKE_POSITION_INDEPENDENT_CODE=ON`
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"-static-libstdc++",
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"-static-libgcc",
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# Link with Clang's runtime library. This is always
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# linked statically.
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"-rtlib=compiler-rt",
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# Link with pthread.
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"-lpthread",
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],
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),
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],
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with_features = [with_feature_set(["linux_target"])],
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),
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flag_set(
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actions = [ACTION_NAMES.cpp_link_executable],
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flag_groups = [flag_group(
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expand_if_available = "force_pic",
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flags = ["-pie"],
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)],
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with_features = [with_feature_set([
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"linux_target",
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"freebsd_target",
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])],
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),
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flag_set(
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actions = [ACTION_NAMES.cpp_link_executable],
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flag_groups = [flag_group(
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expand_if_available = "force_pic",
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flags = ["-fpie"],
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)],
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with_features = [with_feature_set(["macos_target"])],
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),
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],
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)
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clang_warnings_feature = feature(
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name = "clang_warnings",
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enabled = True,
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flag_sets = [flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_compile_actions,
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flag_groups = [flag_group(flags = [
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"-Werror",
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"-Wall",
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"-Wextra",
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"-Wthread-safety",
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"-Wself-assign",
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"-Wimplicit-fallthrough",
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"-Wctad-maybe-unsupported",
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"-Wextra-semi",
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"-Wmissing-prototypes",
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"-Wzero-as-null-pointer-constant",
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"-Wdelete-non-virtual-dtor",
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# TODO: Regression that warns on anonymous unions; remove depending
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# on fix.
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"-Wno-missing-designated-field-initializers",
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])],
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)],
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)
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# Libc++ HARDENING_MODE has 4 possible values:
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# https://libcxx.llvm.org/Hardening.html#notes-for-users
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#
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# Do not enable DEBUG hardening mode, even for -c dbg, because its performance
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# impact on llvm-symbolizer is too severe -- this flag results in symbolization
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# becoming quadratic in the number of debug symbols, in practice meaning it
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# never completes.
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_libcpp_debug_flags = [
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"-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_EXTENSIVE",
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]
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_libcpp_release_flags = [
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"-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_FAST",
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]
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def libcxx_feature(llvm_bindir = None, clang_bindir = None):
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"""Builds a libc++ feature.
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Returns:
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The feature for use with `cc_toolchain_config`.
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Args:
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llvm_bindir: Optional LLVM installation `bin` directory, causes the
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feature to look for adjacent installed libraries.
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clang_bindir: Optional Clang installation `bin` directory, causes the
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feature to look for adjacent installed libraries if different from
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`llvm_bindir`.
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"""
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# Explicitly add LLVM libs to the search path to preempt the
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# detected GCC installation's library paths. Those might have a
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# system installed libc++ and we want to find the one next to
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# our Clang.
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extra_link_flags = []
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if llvm_bindir:
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extra_link_flags.append("-L" + llvm_bindir + "/../lib")
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if clang_bindir and clang_bindir != llvm_bindir:
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extra_link_flags.append("-L" + clang_bindir + "/../lib")
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return feature(
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name = "libcxx",
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enabled = True,
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flag_sets = [
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cpp_compile_actions + ACTION_NAME_GROUPS.all_cc_link_actions,
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flag_groups = [flag_group(flags = [
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"-stdlib=libc++",
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])],
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with_features = [
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# libc++ is only used on non-Windows platforms.
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with_feature_set(not_features = ["windows_target"]),
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],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cpp_compile_actions,
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flag_groups = [flag_group(flags = _libcpp_debug_flags)],
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with_features = [with_feature_set(not_features = ["opt"])],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cpp_compile_actions,
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flag_groups = [flag_group(flags = _libcpp_release_flags)],
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with_features = [with_feature_set(features = ["opt"])],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_link_actions,
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flag_groups = [flag_group(flags = [
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"-unwindlib=libunwind",
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])],
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with_features = [
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# libc++ is only used on non-Windows platforms.
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with_feature_set(not_features = ["windows_target"]),
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],
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),
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flag_set(
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actions = ACTION_NAME_GROUPS.all_cc_link_actions,
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flag_groups = [flag_group(flags = extra_link_flags + [
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# Force linking the static libc++abi archive here. This
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# *should* be linked automatically, but not every release of
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# LLVM correctly sets the CMake flags to do so.
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"-l:libc++abi.a",
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])],
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with_features = [with_feature_set(["linux_target"])],
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),
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],
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)
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