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BUILDCONFIG.gn
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BUILDCONFIG.gn
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# Copyright (c) 2013 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
# =============================================================================
# WHAT IS THIS FILE?
# =============================================================================
#
# This is the master GN build configuration. This file is loaded after the
# build args (args.gn) for the build directory and after the toplevel ".gn"
# file (which points to this file as the build configuration).
#
# This file will be executed and the resulting context will be used to execute
# every other file in the build. So variables declared here (that don't start
# with an underscore) will be implicitly global.
# =============================================================================
# PLATFORM SELECTION
# =============================================================================
#
# There are two main things to set: "os" and "cpu". The "toolchain" is the name
# of the GN thing that encodes combinations of these things.
#
# Users typically only set the variables "target_os" and "target_cpu" in "gn
# args", the rest are set up by our build and internal to GN.
#
# There are three different types of each of these things: The "host"
# represents the computer doing the compile and never changes. The "target"
# represents the main thing we're trying to build. The "current" represents
# which configuration is currently being defined, which can be either the
# host, the target, or something completely different (like nacl). GN will
# run the same build file multiple times for the different required
# configuration in the same build.
#
# This gives the following variables:
# - host_os, host_cpu, host_toolchain
# - target_os, target_cpu, default_toolchain
# - current_os, current_cpu, current_toolchain.
#
# Note the default_toolchain isn't symmetrical (you would expect
# target_toolchain). This is because the "default" toolchain is a GN built-in
# concept, and "target" is something our build sets up that's symmetrical with
# its GYP counterpart. Potentially the built-in default_toolchain variable
# could be renamed in the future.
#
# When writing build files, to do something only for the host:
# if (current_toolchain == host_toolchain) { ...
if (target_os == "") {
target_os = host_os
}
if (target_cpu == "") {
if (target_os == "android") {
# If we're building for Android, we should assume that we want to
# build for ARM by default, not the host_cpu (which is likely x64).
# This allows us to not have to specify both target_os and target_cpu
# on the command line.
target_cpu = "arm"
} else {
target_cpu = host_cpu
}
}
if (current_cpu == "") {
current_cpu = target_cpu
}
if (current_os == "") {
current_os = target_os
}
# =============================================================================
# BUILD FLAGS
# =============================================================================
#
# This block lists input arguments to the build, along with their default
# values.
#
# If a value is specified on the command line, it will overwrite the defaults
# given in a declare_args block, otherwise the default will be used.
#
# YOU SHOULD ALMOST NEVER NEED TO ADD FLAGS TO THIS FILE. GN allows any file in
# the build to declare build flags. If you need a flag for a single component,
# you can just declare it in the corresponding BUILD.gn file.
#
# - If your feature is a single target, say //components/foo, you can put
# a declare_args() block in //components/foo/BUILD.gn and use it there.
# Nobody else in the build needs to see the flag.
#
# - Defines based on build variables should be implemented via the generated
# build flag header system. See //build/buildflag_header.gni. You can put
# the buildflag_header target in the same file as the build flag itself. You
# should almost never set "defines" directly.
#
# - If your flag toggles a target on and off or toggles between different
# versions of similar things, write a "group" target that forwards to the
# right target (or no target) depending on the value of the build flag. This
# group can be in the same BUILD.gn file as the build flag, and targets can
# depend unconditionally on the group rather than duplicating flag checks
# across many targets.
#
# - If a semi-random set of build files REALLY needs to know about a define and
# the above pattern for isolating the build logic in a forwarding group
# doesn't work, you can put the argument in a .gni file. This should be put
# in the lowest level of the build that knows about this feature (which should
# almost always be outside of the //build directory!).
#
# Other flag advice:
#
# - Use boolean values when possible. If you need a default value that expands
# to some complex thing in the default case (like the location of the
# compiler which would be computed by a script), use a default value of -1 or
# the empty string. Outside of the declare_args block, conditionally expand
# the default value as necessary.
#
# - Use a name like "use_foo" or "is_foo" (whatever is more appropriate for
# your feature) rather than just "foo".
#
# - Write good comments directly above the declaration with no blank line.
# These comments will appear as documentation in "gn args --list".
#
# - Don't call exec_script inside declare_args. This will execute the script
# even if the value is overridden, which is wasteful. See first bullet.
declare_args() {
# Set to enable the official build level of optimization. This has nothing
# to do with branding, but enables an additional level of optimization above
# release (!is_debug). This might be better expressed as a tri-state
# (debug, release, official) but for historical reasons there are two
# separate flags.
is_official_build = false
# Set to true when compiling with the Clang compiler.
is_clang = false
# Allows the path to a custom target toolchain to be injected as a single
# argument, and set as the default toolchain.
custom_toolchain = ""
# This should not normally be set as a build argument. It's here so that
# every toolchain can pass through the "global" value via toolchain_args().
host_toolchain = ""
# 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 -> $external/zlib)
external = "//external"
# DON'T ADD MORE FLAGS HERE. Read the comment above.
}
declare_args() {
# Debug build. Enabling official builds automatically sets is_debug to false.
is_debug = !is_official_build
}
assert(!(is_debug && is_official_build), "Can't do official debug builds")
# ==============================================================================
# TOOLCHAIN SETUP
# ==============================================================================
#
# Here we set the default toolchain, as well as the variable host_toolchain
# which will identify the toolchain corresponding to the local system when
# doing cross-compiles. When not cross-compiling, this will be the same as the
# default toolchain.
#
# We do this before anything else to make sure we complain about any
# unsupported os/cpu combinations as early as possible.
if (host_toolchain == "") {
# This should only happen in the top-level context.
# In a specific toolchain context, the toolchain_args()
# block should have propagated a value down.
# TODO(dpranke): Add some sort of assert here that verifies that
# no toolchain omitted host_toolchain from its toolchain_args().
if (host_os == "mac") {
host_toolchain = "//build/toolchain/mac:clang_$host_cpu"
} else if (host_os == "win") {
# On Windows always use the target CPU for host builds. On the
# configurations we support this will always work and it saves build steps.
if (is_clang) {
host_toolchain = "//build/toolchain/win:clang_$target_cpu"
} else {
host_toolchain = "//build/toolchain/win:$target_cpu"
}
} else {
if (target_os != host_os) {
# TODO(dpranke) - is_clang normally applies only to the target
# build, and there is no way to indicate that you want to override
# it for both the target build *and* the host build. Do we need to
# support this?
host_toolchain = "//build/toolchain/posix:clang_$host_cpu"
} else if (is_clang) {
host_toolchain = "//build/toolchain/posix:clang_$host_cpu"
} else {
host_toolchain = "//build/toolchain/posix:$host_cpu"
}
}
}
_default_toolchain = ""
if (target_os == "android") {
if (is_clang) {
_default_toolchain = "//build/toolchain/android:android_clang_$target_cpu"
} else {
_default_toolchain = "//build/toolchain/android:android_$target_cpu"
}
} else if (target_os == "ios") {
_default_toolchain = "//build/toolchain/mac:ios_clang_$target_cpu"
} else if (target_os == "mac") {
assert(host_os == "mac", "Mac cross-compiles are unsupported.")
_default_toolchain = host_toolchain
} else if (target_os == "win") {
# On Windows we use the same toolchain for host and target by default.
assert(target_os == host_os, "Win cross-compiles only work on win hosts.")
if (is_clang) {
_default_toolchain = "//build/toolchain/win:clang_$target_cpu"
} else {
_default_toolchain = "//build/toolchain/win:$target_cpu"
}
} else if (target_os == "winuwp") {
# Only target WinUWP on for a Windows store application and only
# x86, x64 and arm are supported target CPUs.
assert(target_cpu == "x86" || target_cpu == "x64" || target_cpu == "arm" ||
target_cpu == "arm64")
_default_toolchain = "//build/toolchain/win:uwp_$target_cpu"
} else {
if (is_clang) {
_default_toolchain = "//build/toolchain/posix:clang_$target_cpu"
} else {
_default_toolchain = "//build/toolchain/posix:$target_cpu"
}
}
# If a custom toolchain has been set in the args, set it as default. Otherwise,
# set the default toolchain for the platform (if any).
if (custom_toolchain != "") {
set_default_toolchain(custom_toolchain)
} else if (_default_toolchain != "") {
set_default_toolchain(_default_toolchain)
}
# =============================================================================
# OS DEFINITIONS
# =============================================================================
#
# We set these various is_FOO booleans for convenience in writing OS-based
# conditions.
#
# - is_android, is_freebsd, is_ios, and is_win should be obvious.
# - is_mac is set only for desktop Mac. It is not set on iOS.
# - is_posix is true for mac and any Unix-like system (basically everything
# except Windows).
# - is_linux is true for desktop Linux, but not Android (which is
# generally too different despite being based on the Linux kernel).
if (current_os == "win" || current_os == "winuwp") {
is_android = false
is_ios = false
is_linux = false
is_mac = false
is_posix = false
is_win = true
is_freebsd = false
} else if (current_os == "mac") {
is_android = false
is_ios = false
is_linux = false
is_mac = true
is_posix = true
is_win = false
is_freebsd = false
} else if (current_os == "android") {
is_android = true
is_ios = false
is_linux = false
is_mac = false
is_posix = true
is_win = false
is_freebsd = false
} else if (current_os == "ios") {
is_android = false
is_ios = true
is_linux = false
is_mac = false
is_posix = true
is_win = false
is_freebsd = false
} else if (current_os == "linux") {
is_android = false
is_ios = false
is_linux = true
is_mac = false
is_posix = true
is_win = false
is_freebsd = false
} else if (current_os == "freebsd") {
is_android = false
is_ios = false
is_linux = false
is_mac = false
is_posix = true
is_win = false
is_freebsd = true
}
# =============================================================================
# TARGET DEFAULTS
# =============================================================================
#
# Set up the default configuration for every build target of the given type.
# The values configured here will be automatically set on the scope of the
# corresponding target. Target definitions can add or remove to the settings
# here as needed.
# Holds all configs used for running the compiler.
default_compiler_configs = [
"//build/config:extra_flags",
"//build/config:afdo",
"//build/config:compiler",
"//build/config:pthread",
"//build/config:stackrealign",
"//build/config:compiler_arm_fpu",
"//build/config:compiler_arm_thumb",
"//build/config:default_optimization",
"//build/config:default_stack_frames",
"//build/config:default_symbols",
"//build/config:c++11",
"//build/config:rtti",
"//build/config:exceptions",
"//build/config:runtime_library",
"//build/config:symbol_visibility_hidden",
]
if (is_win) {
default_compiler_configs += [
"//build/config/win:default_crt",
"//build/config/win:lean_and_mean",
"//build/config/win:nominmax",
"//build/config/win:winver",
"//build/config/win:vs_code_analysis",
"//build/config/win:unicode",
]
}
if (is_android) {
default_compiler_configs +=
[ "//build/config/android:default_cygprofile_instrumentation" ]
}
# Debug/release-related defines.
if (is_debug) {
default_compiler_configs += [ "//build/config:debug" ]
} else {
default_compiler_configs += [ "//build/config:release" ]
}
# Static libraries and source sets use only the compiler ones.
set_defaults("static_library") {
configs = default_compiler_configs
}
set_defaults("source_set") {
configs = default_compiler_configs
}
# Compute the set of configs common to all linked targets (shared libraries,
# loadable modules, executables) to avoid duplication below.
if (is_win) {
# Windows linker setup for EXEs and DLLs.
# Many targets remove these configs, so they are not contained within
# //build/config:executable_config for easy removal.
_linker_configs = [
"//build/config/win:default_incremental_linking",
# Default to console-mode apps. Most of our targets are tests and such
# that shouldn't use the windows subsystem.
"//build/config/win:console",
]
} else if (is_mac || is_ios) {
_linker_configs = [ "//build/config/mac:strip_all" ]
} else {
_linker_configs = []
}
# Executable defaults.
default_executable_configs = default_compiler_configs + [
"//build/config:default_libs",
"//build/config:executable_config",
] + _linker_configs
set_defaults("executable") {
configs = default_executable_configs
}
# Shared library and loadable module defaults (also for components in component
# mode).
default_shared_library_configs = default_compiler_configs + [
"//build/config:default_libs",
"//build/config:shared_library_config",
] + _linker_configs
set_defaults("shared_library") {
configs = default_shared_library_configs
}
set_defaults("loadable_module") {
configs = default_shared_library_configs
}