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Diffstat (limited to 'examples/custom_toolchain/BUILD')
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diff --git a/examples/custom_toolchain/BUILD b/examples/custom_toolchain/BUILD new file mode 100644 index 0000000..371fdfd --- /dev/null +++ b/examples/custom_toolchain/BUILD @@ -0,0 +1,118 @@ +# Copyright 2021 The Bazel Authors. All rights reserved. +# +# Licensed under the Apache License, Version 2.0 (the "License"); +# you may not use this file except in compliance with the License. +# You may obtain a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, +# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +# See the License for the specific language governing permissions and +# limitations under the License. + +# Proof-of-concept example showing how to write a custom C++ toolchain. +# +# Important documentation: +# +# - https://docs.bazel.build/versions/master/platforms-intro.html#c +# - https://docs.bazel.build/versions/master/tutorial/cc-toolchain-config.html +# - https://docs.bazel.build/versions/master/be/c-cpp.html#cc_toolchain +# +# There are two ways to select C++ toolchains: +# +# - NEW (USE IF POSSIBLE): with the --platforms flag +# - LEGACY: with the --crosstool_top and --cpu flags +# +# See https://docs.bazel.build/versions/master/platforms-intro.html#c for details. +# +# This example demonstrates both approaches. + +load("@rules_cc//cc:defs.bzl", "cc_library", "cc_toolchain", "cc_toolchain_suite") + +# Load the Starlark logic defining the toolchain's behavior. For example: what +# program runs to compile a source file and how its command line is +# constructed. See toolchain_config.bzl for details. +load(":toolchain_config.bzl", "cc_toolchain_config") + +# The library we want to build. Building this calls two C++ actions: compile (.cc -> +# .o) and archive (.o -> .a). +cc_library( + name = "buildme", + srcs = ["buildme.cc"], +) + +# This example intentionally makes the cc_toolchain_config definition +# simple. You could alternative add attributes to support multiple +# cc_toolchain_config targets with finer customization. +cc_toolchain_config( + name = "toolchain_semantics", +) + +# Register the toolchain with Bazel. Most of these attribute just tell Bazel +# where to find the files needed to run C++ commands. The toolchain_config +# attribute registers the behavior specification declared above. +cc_toolchain( + name = "my_custom_toolchain", + all_files = ":toolchain_files", + ar_files = ":toolchain_files", + compiler_files = ":toolchain_files", + dwp_files = ":toolchain_files", + linker_files = ":toolchain_files", + objcopy_files = ":toolchain_files", + strip_files = ":toolchain_files", + toolchain_config = ":toolchain_semantics", +) + +filegroup( + name = "toolchain_files", + srcs = [ + "sample_compiler", + "sample_linker", + ], +) + +# Implements legacy toolchain selection. +# +# Setting --crosstool_top here registers the set of available +# toolchains. Setting --cpu to one of the toolchain attribute's keys selects a +#toolchain. +cc_toolchain_suite( + name = "legacy_selector", + toolchains = { + "x86": ":my_custom_toolchain", + }, +) + +# Implements platform-based (recommended) toolchain selection. +# +# See https://docs.bazel.build/versions/master/platforms-intro.html. The main +# differences are: +# +# 1. --cpu / --crosstool_top are replaced by a platform() definition with +# much more customizable properties. For example, a platform can specify +# OS, device type (server, phone, tablet) or custom hardware extensions. +# 2. All languages can support platform-based toolchains. A single --platforms +# value can choose C++, Python, Scala, and all other toolchains in your +# build. This is especially useful for multi-language builds. +# 3. Platforms support features like incompatible target skipping: +# https://docs.bazel.build/versions/master/platforms.html#skipping-incompatible-targets. +toolchain( + name = "platform_based_toolchain", + # Trigger this toolchain for x86-compatible platforms. + # See https://github.com/bazelbuild/platforms. + target_compatible_with = ["@platforms//cpu:x86_64"], + # Register this toolchain with platforms. + toolchain = ":my_custom_toolchain", + # The public interface for all C++ toolchains. Starlark rules that use C++ + # access the toolchain through this interface. + toolchain_type = "@bazel_tools//tools/cpp:toolchain_type", +) + +# Define a platform matching any x86-compatible toolchain. See +# https://docs.bazel.build/versions/master/platforms.html. +platform( + name = "x86_platform", + constraint_values = ["@platforms//cpu:x86_64"], +) |