常用的buildroot配置项有哪些呢

概述

buildroot用于嵌入式开发的整体编译环境，可以根据用户的配置，编译kernel，uboot，rootfs，用户的app等。并通过包含外部的Config.in，获取外部自定义的编译规则，进行编译。
网上大多数资料，均是在buildroot内部配置kernel、uboot、app，实际情况是，为了和buildroot源码独立开，自己的、或公司的代码均需要放在buildroot源码外部，本文即说明如果在buidlroot外部放置自己的代码及编译规则，并通过buildroot单编或整编。
配置

添加配置文件

法1：在configs下添加以_defconfig结尾的文件
编译: make xxx_defconfig
法2：直接拷贝自己的buildroot.config到buildroot/.config
编译：make
常用配置项说明

以下为常用的buildroot配置项：
1、BR2_TARGET_ROOTFS_XXXX:指定文件系统类型
例如BR2_TARGET_ROOTFS_JFFS2、BR2_TARGET_ROOTFS_EXT2
2、BR2_ROOTFS_OVERLAY：rootfs覆盖
该目录存放自己定制的rootfs，在buildroot制作完rootfs后，将拷贝overlay目录替换output下的部分文件。
3、BR2_TOOLCHAIN_EXTERNAL_PATH：指定交叉编译链路径
编译buildroot目录外的代码

目的：
创建两个目录：app, platform
APP目录

app：存放buildroot，和平台无关的应用程序。
app目录结构体：

app$ tree -L 1
.
├── buildroot
├── build.sh
├── Config.in
├── external.desc
├── external.mk
├── my_package
├── my_source
├── prebuilts
└── rootfs_overlay
buildroot: buildroot源码
build.sh：提供给外部调用(platform)，最终进入buildroot make
my_package: 放置自己包的编译规则
my_source: 放置自己包的源码
buildroot编译放在它的目录之外的源码时，需要提供以下几个文件：
external.desc、external.desc、external.mk
external.desc

指定外部编译的顶层目录

book@suns:~/ss_sdk/app$ cat external.desc
name: MY_APP
desc: my app external tree


其中，name是必须写出的，external.desc将导致buildroot/.config生成BR2_EXTERNAL_MY_APP_PATH
BR2_EXTERNAL_MY_APP_PATH的值，是由：在app目录下执行:
make -C ./buildroot/ BR2_EXTERNAL=/home/book/ss_sdk/app
得到的，即最终.config会写入：
BR2_EXTERNAL_MY_APP_PAT
Config.in

包含子目录的Config.in

book@suns:~/ss_sdk/app$ cat ./Config.in
source "$BR2_EXTERNAL_MY_APP_PATH/my_package/sstest/Config.in"


external.mk

包含子目录的编译规则

book@suns:~/ss_sdk/app$ cat external.mk
include $(sort $(wildcard $(BR2_EXTERNAL_MY_APP_PATH)/my_package/*/*.mk))


my_package

包含自己的包的编译规则
该目录下的子目录名字，必须buildroot.config中的BR2_PACKAGE_XXXX中的XXXX一致(大写变小写)
目录结构：

book@suns:~/ss_sdk/app/my_package$ tree
.
└── sstest
    ├── Config.in
    └── sstest.mk


1 directory, 2 files


其中，sstest文件夹是我们需要添加的一个进程对应的编译规则。
Config.in:
告诉buildroot，本目录是BR2_PACKAGE_SSTEST对应的编译规则的目录。

book@suns:~/ss_sdk/app/koal_package/sstest$ cat Config.in
config BR2_PACKAGE_SSTEST
        bool "sstest"
        help
          ss test module


.mk
book@suns:~/ss_sdk/app/koal_package/sstest$ cat sstest.mk
################################################################################
#
# SSTEST
#
################################################################################


SSTEST_VERSION = 1.0
SSTEST_SITE_METHOD = local
SSTEST_SITE = $(BR2_EXTERNAL_MY_APP_PATH)/my_source/sstest


SSTEST_LICENSE = Custom
SSTEST_LICENSE_FILES = license.txt
# Installs only a static library and a header file
SSTEST_INSTALL_STAGING = YES
SSTEST_INSTALL_TARGET = NO


define SSTEST_BUILD_CMDS
        $(TARGET_MAKE_ENV) $(MAKE) -C $(@D)
endef


define SSTEST_INSTALL_STAGING_CMDS
        $(TARGET_CONFIGURE_OPTS) $(MAKE) PREFIX=$(STAGING_DIR) -C $(@D) install
endef


$(eval $(generic-package))


my_source

该目录下的子目录名字，必须buildroot.config中的BR2_PACKAGE_XXXX中的XXXX一致(大写变小写)
目录结构：

book@suns:~/ss_sdk/app/koal_source$ tree
.
└── sstest
    ├── main.c
    └── Makefile


1 directory, 2 files


platform目录

存放平台相关的代码，例如工具链、kernel、uboot的patch文件及配置文件等等。
外部交叉编译工具链

目的：使用外部的已经制作好的交叉编译工具链。
将工具链放在platfrom文件夹中，在buildroot配置文件中配置工具链。
buildroot配置

需要根据toolchain的规格进行配置，例如是glibc(较省flash)还是libc，工具链版本等等。

#
# Toolchain
#
BR2_TOOLCHAIN=y
BR2_TOOLCHAIN_USES_GLIBC=y
# BR2_TOOLCHAIN_BUILDROOT is not set
BR2_TOOLCHAIN_EXTERNAL=y


#
# Toolchain External Options
#
# BR2_TOOLCHAIN_EXTERNAL_CODESOURCERY_MIPS is not set
# BR2_TOOLCHAIN_EXTERNAL_CODESCAPE_MTI_MIPS is not set
# BR2_TOOLCHAIN_EXTERNAL_MUSL_CROSS is not set
BR2_TOOLCHAIN_EXTERNAL_CUSTOM=y
# BR2_TOOLCHAIN_EXTERNAL_DOWNLOAD is not set
BR2_TOOLCHAIN_EXTERNAL_PREINSTALLED=y
BR2_TOOLCHAIN_EXTERNAL_PATH="$(TOPDIR)/../prebuilts/toolchains/mips-gcc520-glibc222"
BR2_TOOLCHAIN_EXTERNAL_CUSTOM_PREFIX="mips-linux-gnu"
BR2_TOOLCHAIN_EXTERNAL_PREFIX="mips-linux-gnu"
BR2_TOOLCHAIN_EXTERNAL_GLIBC=y
# BR2_TOOLCHAIN_EXTERNAL_GCC_6 is not set
BR2_TOOLCHAIN_EXTERNAL_GCC_5=y
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_9 is not set
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_8 is not set
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_7 is not set
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_6 is not set
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_5 is not set
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_4 is not set
# BR2_TOOLCHAIN_EXTERNAL_GCC_4_3 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_8 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_7 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_6 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_5 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_4 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_3 is not set
BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_2=y
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_1 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_0 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_19 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_18 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_17 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_16 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_15 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_14 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_13 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_12 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_11 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_10 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_9 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_8 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_7 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_6 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_5 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_4 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_3 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_2 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_1 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_3_0 is not set
# BR2_TOOLCHAIN_EXTERNAL_HEADERS_REALLY_OLD is not set
# BR2_TOOLCHAIN_EXTERNAL_CUSTOM_UCLIBC is not set
BR2_TOOLCHAIN_EXTERNAL_CUSTOM_GLIBC=y
# BR2_TOOLCHAIN_EXTERNAL_CUSTOM_MUSL is not set
BR2_TOOLCHAIN_EXTERNAL_HAS_SSP=y
BR2_TOOLCHAIN_EXTERNAL_INET_RPC=y
BR2_TOOLCHAIN_EXTERNAL_CXX=y
# BR2_TOOLCHAIN_EXTERNAL_FORTRAN is not set
BR2_TOOLCHAIN_EXTRA_EXTERNAL_LIBS=""
# BR2_TOOLCHAIN_EXTERNAL_GDB_SERVER_COPY is not set
注意：
1、BR2_TOOLCHAIN_EXTERNAL_GCC_5：gcc版本号5开头，根据自己实际去配置
2、BR2_TOOLCHAIN_EXTERNAL_HAS_SSP：堆栈粉碎保护(Stack Smashing Protection)
3、BR2_TOOLCHAIN_EXTERNAL_INET_RPC：是否支持RPC，远程过程调用，主要用于NFS
kernel源码编译

目的，使用外部的kernel源码进行编译。
kernel配置文件放在外部。
主要包括：
1、修改buildroot中kernel相关的配置项
2、开始进入buildroot编译前，将kernel源码拷贝到dl目录下
buildroot中对kernel的配置

buildroot.conf中kernel相关的配置如下:

#
# Kernel
#
BR2_LINUX_KERNEL=y
# BR2_LINUX_KERNEL_LATEST_VERSION is not set
BR2_LINUX_KERNEL_CUSTOM_VERSION=y
# BR2_LINUX_KERNEL_CUSTOM_TARBALL is not set
# BR2_LINUX_KERNEL_CUSTOM_GIT is not set
# BR2_LINUX_KERNEL_CUSTOM_HG is not set
# BR2_LINUX_KERNEL_CUSTOM_SVN is not set
BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="linux"
BR2_LINUX_KERNEL_VERSION="3.10.14"
BR2_LINUX_KERNEL_PATCH="n"
# BR2_LINUX_KERNEL_USE_DEFCONFIG is not set
# BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG is not set
BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="../../platform/configs/kernel.config"
BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES=""
BR2_LINUX_KERNEL_UBOOT_IMAGE=y
BR2_LINUX_KERNEL_UIMAGE=y
# BR2_LINUX_KERNEL_VMLINUX_BIN is not set
# BR2_LINUX_KERNEL_VMLINUX is not set
# BR2_LINUX_KERNEL_VMLINUZ is not set
# BR2_LINUX_KERNEL_VMLINUZ_BIN is not set
# BR2_LINUX_KERNEL_IMAGE_TARGET_CUSTOM is not set
# BR2_LINUX_KERNEL_GZIP is not set
# BR2_LINUX_KERNEL_LZ4 is not set
# BR2_LINUX_KERNEL_LZMA is not set
# BR2_LINUX_KERNEL_LZO is not set
# BR2_LINUX_KERNEL_XZ is not set
# BR2_LINUX_KERNEL_DTS_SUPPORT is not set
# BR2_LINUX_KERNEL_USE_INTREE_DTS is not set
# BR2_LINUX_KERNEL_USE_CUSTOM_DTS is not set
BR2_LINUX_KERNEL_INTREE_DTS_NAME=""
# BR2_LINUX_KERNEL_INSTALL_TARGET is not set
其中：
BR2_LINUX_KERNEL：决定是否编译kernel
BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE：指定外部配置文件路径
BR2_LINUX_KERNEL_UIMAGE：编译出uImage
BR2_LINUX_KERNEL_VERSION: 必须指定kernel版本号
BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE：该值-版本号就是dl下kernel源码包的名字，buildroot根据这个名字去dl下找源码包，并解压编译。
自定义编译规则

kernel的编译规则在buildroot/linux/linux.mk文件中指定
修改源码包的压缩格式

在linux.mk中找LINUX_SOURCE修改后缀。
uboot源码编译

待续。。。。