Chromium Arm平臺編譯配置
- 以下內容以Chromium67爲準。
- Chromium支持多平臺編譯,如Linux、android、MAC。在編譯時,可以指定cpu類型,如
current_cpu="arm"
# 或
current_cpu="arm64"
- 當指定cpu類型時,chromium的gn編譯系統便會根據指定的CPU類型,進行設置。
- 這裏,分析以下當cpu類型爲arm時,chromium的bulid/config模塊,所做的配置。
Arm Config for build
- 源碼路徑:
src/build/config/arm.gni - Chromium官網鏈接: https://chromium.googlesource.com/chromium/src/+/master/build/config/arm.gni
- 內容如下:
# Copyright 2014 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.
import("//build/config/v8_target_cpu.gni")
# These are primarily relevant in current_cpu == "arm" contexts, where
# ARM code is being compiled. But they can also be relevant in the
# other contexts when the code will change its behavior based on the
# cpu it wants to generate code for.
if (current_cpu == "arm" || v8_current_cpu == "arm") {
declare_args() {
# Version of the ARM processor when compiling on ARM. Ignored on non-ARM
# platforms.
arm_version = 7
# The ARM architecture. This will be a string like "armv6" or "armv7-a".
# An empty string means to use the default for the arm_version.
arm_arch = ""
# The ARM floating point hardware. This will be a string like "neon" or
# "vfpv3". An empty string means to use the default for the arm_version.
arm_fpu = ""
# The ARM floating point mode. This is either the string "hard", "soft", or
# "softfp". An empty string means to use the default one for the
# arm_version.
arm_float_abi = ""
# The ARM variant-specific tuning mode. This will be a string like "armv6"
# or "cortex-a15". An empty string means to use the default for the
# arm_version.
arm_tune = ""
# Whether to use the neon FPU instruction set or not.
arm_use_neon = ""
# Whether to enable optional NEON code paths.
arm_optionally_use_neon = false
# Thumb is a reduced instruction set available on some ARM processors that
# has increased code density.
arm_use_thumb = true
}
assert(arm_float_abi == "" || arm_float_abi == "hard" ||
arm_float_abi == "soft" || arm_float_abi == "softfp")
if (arm_use_neon == "") {
if (current_os == "linux" && target_cpu != v8_target_cpu) {
# Don't use neon on V8 simulator builds as a default.
arm_use_neon = false
} else {
arm_use_neon = true
}
}
if (arm_version == 6) {
if (arm_arch == "") {
arm_arch = "armv6"
}
if (arm_tune != "") {
arm_tune = ""
}
if (arm_float_abi == "") {
arm_float_abi = "softfp"
}
if (arm_fpu == "") {
arm_fpu = "vfp"
}
arm_use_thumb = false
arm_use_neon = false
} else if (arm_version == 7) {
if (arm_arch == "") {
arm_arch = "armv7-a"
}
if (arm_tune == "") {
arm_tune = "generic-armv7-a"
}
if (arm_float_abi == "") {
if (current_os == "android" || target_os == "android") {
arm_float_abi = "softfp"
} else if (current_os == "linux" && target_cpu != v8_target_cpu) {
# Default to the same as Android for V8 simulator builds.
arm_float_abi = "softfp"
} else {
arm_float_abi = "hard"
}
}
if (arm_fpu == "") {
if (arm_use_neon) {
arm_fpu = "neon"
} else {
arm_fpu = "vfpv3-d16"
}
}
} else if (arm_version == 8) {
if (arm_arch == "") {
arm_arch = "armv8-a"
}
if (arm_tune == "") {
arm_tune = "generic-armv8-a"
}
if (arm_float_abi == "") {
if (current_os == "android" || target_os == "android") {
arm_float_abi = "softfp"
} else {
arm_float_abi = "hard"
}
}
if (arm_fpu == "") {
if (arm_use_neon) {
arm_fpu = "neon"
} else {
arm_fpu = "vfpv3-d16"
}
}
}
} else if (current_cpu == "arm64" || v8_current_cpu == "arm64") {
# arm64 supports only "hard".
arm_float_abi = "hard"
arm_use_neon = true
}
- 分析:
- 首先,如果當前cpu類型爲arm,或者v8當前cpu類型爲arm。定義一系列參數,這些參數爲默認參數。如果之前定義過,便不再定義(比如在編譯時,指定了arm_float_abi(軟/硬浮點))。
declare_args() {
# Version of the ARM processor when compiling on ARM. Ignored on non-ARM
# platforms.
arm_version = 7
# The ARM architecture. This will be a string like "armv6" or "armv7-a".
# An empty string means to use the default for the arm_version.
arm_arch = ""
# The ARM floating point hardware. This will be a string like "neon" or
# "vfpv3". An empty string means to use the default for the arm_version.
arm_fpu = ""
# The ARM floating point mode. This is either the string "hard", "soft", or
# "softfp". An empty string means to use the default one for the
# arm_version.
arm_float_abi = ""
# The ARM variant-specific tuning mode. This will be a string like "armv6"
# or "cortex-a15". An empty string means to use the default for the
# arm_version.
arm_tune = ""
# Whether to use the neon FPU instruction set or not.
arm_use_neon = ""
# Whether to enable optional NEON code paths.
arm_optionally_use_neon = false
# Thumb is a reduced instruction set available on some ARM processors that
# has increased code density.
arm_use_thumb = true
}
- 之後,就是一系列判斷,對arm類型所要使用的編譯參數進行判斷。關於這些編譯參數的具體含義,可自行百度。
# 軟浮點或硬浮點
arm_float_abi
# arm架構
arm_arch
# 是否使用neno
arm_use_neon
# 是否使用thumb
arm_use_thumb
# fpu類型
arm_fpu
- 在定義好一系列編譯參數後,使用arm編譯器進行編譯。
GNI文件,並非編譯文件,而且模板文件。編譯系統如何使用它?
答:在.gn文件中,通過import引入模板文件(有點類型C++的頭文件)中的定義。
- 例:src/v8/BUILD.gn,在該gn文件開頭,我們可以看到import了arm.gni文件。
# Copyright 2014 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.
import("//build/config/android/config.gni")
import("//build/config/arm.gni")
import("//build/config/dcheck_always_on.gni")
import("//build/config/host_byteorder.gni")
import("//build/config/jumbo.gni")
import("//build/config/mips.gni")
import("//build/config/sanitizers/sanitizers.gni")
.....