simonhancrew / gn-build

Basic //build directory for use with Chromium's GN

//build directory for GN-based projects

This project provides a work-in-progress standalone version of the toolchains and configs used by the Chromium project.

Supported platforms

The toolchains have been tested on the following platforms:

• Windows (MSVC 2013/2015/2017/2019, Clang 3.8)
• FreeBSD (GCC 6, Clang 11)
• Linux (GCC 6, Clang 3.8)
• OS X (Xcode 7.3.1)

The testsrc branch contains the test/example project used by the CI tests.

Reference

Basic variables

All variables described here are build args and can be overridden in the user's args.gn file.

//build/config/BUILDCONFIG.gn

(these variables are available everywhere)

• is_debug (default: true): Toggle between debug and release builds.
• is_clang (default: false): Favor Clang over the platform default (GCC/MSVC).
• is_official_build (default: !is_debug): Set to enable the official build level of optimization. This enables an additional level of optimization above release (!is_debug).
• external (default: "//external"): Label of the external projects directory. By convention, all 3rd-party projects should end up in this directory, so they can depend on each other (e.g. $external/mysql_connector -> $external/zlib)

//build/toolchain/clang.gni

• use_lld (default: false): Use the new LLD linker. This requires is_clang to be true.
• clang_base_path (default: ""): The path of your Clang installation folder (without /bin). If you use Clang on Windows, you are required to set this, as the Clang installation isn't automatically detected.

//build/toolchain/compiler_version.gni

• gcc_version (default: auto-detected): Version of the GCC compiler. Note: Auto-detection is toolchain-specific and happens only if GCC is the active compiler.
  Format: major * 10000 + minor * 100 + patchlevel
• clang_version (default: auto-detected): Version of the Clang compiler. Note: Auto-detection is toolchain-specific and happens only if Clang is the active compiler.
  Format: major * 10000 + minor * 100 + patchlevel
• msc_ver (default: auto-detected): Value of the _MSC_VER variable. See https://msdn.microsoft.com/en-us/library/b0084kay.aspx. Note: Auto-detection happens only when targeting Windows.
• msc_full_ver (default: auto-detected): Value of the _MSC_FULL_VER variable. See https://msdn.microsoft.com/en-us/library/b0084kay.aspx. Note: Auto-detection happens only when targeting Windows.

Windows toolchain

//build/toolchain/win/settings.gni

• visual_studio_version (default: "latest"): Desired version of Visual Studio. If visual_studio_path is set, this must be the version of the VS installation at the visual_studio_path.

  Use "2013" for Visual Studio 2013 or "latest" for automatically choosing the highest version (visual_studio_path must be unset in this case).

• visual_studio_path (default: auto-detected): The path of your MSVC installation. If this is set you must set visual_studio_version as well. Autodetected based on visual_studio_version.

• windows_sdk_version (default: auto-detected): Windows SDK version to use. Can either be a full Windows 10 SDK number (e.g. 10.0.10240.0), "8.1" for the Windows 8.1 SDK or "default" for the default SDK selected by VS.

• clang_msc_ver (default: auto-detected): MSVC version clang-cl will report in _MSC_VER.

POSIX toolchain

This is the default toolchain for POSIX operating systems, which is used for all POSIX systems that don't have special toolchains.

//build/toolchain/posix/settings.gni

• gcc_cc (default: gcc): Path of the GCC C compiler executable. Does not have to be absolute.
• gcc_cxx (default: g++): Path of the GCC C++ compiler executable. Does not have to be absolute.
• clang_cc (default: clang): Path of the Clang C compiler executable. Does not have to be absolute. Note: If clang_base_path is set, the default will be clang_base_path/bin/clang.
• clang_cxx (default: clang++): Path of the Clang C++ compiler executable. Does not have to be absolute. Note: If clang_base_path is set, the default will be clang_base_path/bin/clang++.

Mac/iOS toolchain

//build/toolchain/mac/settings.gni

• use_system_xcode (default: true): Use the system install of Xcode for tools like ibtool, libtool, etc. This does not affect the compiler. When this variable is false, targets will instead use a hermetic install of Xcode.
• hermetic_xcode_path (default: ""): The path to the hermetic install of Xcode. Only relevant when use_system_xcode = false.
• use_xcode_clang (default: true): Compile with Xcode version of clang instead of hermetic version shipped with the build. If true, clang_base_path needs to be set.
• enable_dsyms (default: true): Produce dSYM files for targets that are configured to do so. dSYM generation is controlled globally as it is a linker output (produced via the //build/toolchain/mac/linker_driver.py. Enabling this will result in all shared library, loadable module, and executable targets having a dSYM generated.
• enable_stripping (default: is_official_build): Strip symbols from linked targets by default. If this is enabled, the //build/config/mac:strip_all config will be applied to all linked targets. If custom stripping parameters are required, remove that config from a linked target and apply custom -Wcrl,strip flags. See //build/toolchain/mac/linker_driver.py for more information.

//build/toolchain/mac/mac_sdk.gni

• mac_sdk_min (default: "10.10"): Minimum supported version of the Mac SDK.
• mac_deployment_target (default: "10.9"): Minimum supported version of OSX.
• mac_sdk_path (default: ""): Path to a specific version of the Mac SDK, not including a slash at the end. If empty, the path to the lowest version greater than or equal to mac_sdk_min is used.
• mac_sdk_name (default: "macosx"): The SDK name as accepted by xcodebuild.

//build/toolchain/mac/ios_sdk.gni

• ios_sdk_path (default: ""): Path to a specific version of the iOS SDK, not including a slash at the end. When empty this will use the default SDK based on the value of use_ios_simulator.

  SDK properties (required when ios_sdk_path is non-empty):

  • ios_sdk_name: The SDK name as accepted by xcodebuild.
  • ios_sdk_version
  • ios_sdk_platform
  • ios_sdk_platform_path
  • xcode_version
  • xcode_build
  • machine_os_build

• ios_deployment_target (default: "9.0"): Minimum supported version of OSX.

Android toolchain

//build/toolchain/android/settings.gni

• android_ndk_root (default: "$external/android_tools/ndk"): Path of the Android NDK.
• android_ndk_version (default: "r12b"): NDK Version string.
• android_ndk_major_version (default: 12): NDK Major version.
• android_sdk_root (default: "$external/android_tools/sdk"): Path of the Android SDK.
• android_sdk_version (default: "24"): Android SDK version.
• android_sdk_build_tools_version (default: "24.0.2"): Version of the Build Tools contained in the SDK.
• android_libcpp_lib_dir (default: ""): Libc++ library directory. Override to use a custom libc++ binary.
• use_order_profiling (default: false): Adds intrumentation to each function. Writes a file with the order that functions are called at startup.

Recommended workflow

Fork this repo and add it as a submodule/subtree/DEPS-entry to your project. This way you can modify every part of the //build directory while still being able to easily merge upstream changes (e.g. support for new GN features that you don't want to implement yourself.)

To ease sharing/composition of projects using this //build repo, it is recommended that you refrain from modifying large parts of the toolchains/configs. If changes are necessary, consider contributing them back ;)

For more complex projects, it might be feasible to use a custom build-config file that just import()s //build/config/BUILDCONFIG.gn and then overrides the defaults set inside BUILDCONFIG.gn. There's also GN's default_args scope, which can be used to provide project-specific argument overrides.