rk3399 源码下查找交叉编译工具链

原因

小伙伴突然问到 android 下交叉编译链在哪个位置，一脸发懵，所以记录一下

硬件环境

平台	Android版本	内核版本
rk3399	android 7.1	4.4

kernel 和android 的编译时分为两部分所以我们需要分为两份查看

1.kernel

rk的编译命令基本是：

  cd kernel/
  make ARCH=arm64 rockchip_defconfig
  make ARCH=arm64 rk3399-box-rev2.img -j

所以我们从kernel的Makefile入手即可


      VERSION = 4  #kernel版本号
      PATCHLEVEL = 4
      SUBLEVEL = 103
      EXTRAVERSION =
      ...
       ifeq ($(ARCH),arm64)
      ifneq ($(wildcard $(srctree)/../prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9),)
      CROSS_COMPILE   ?= $(srctree)/../prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-android-
      endif
      endif
      ifeq ($(ARCH),arm)
      ifneq ($(wildcard $(srctree)/../prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9),)
      CROSS_COMPILE   ?= $(srctree)/../prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/bin/arm-linux-androidkernel-
      endif
      endif

即kerenel的交叉编译链在 prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-android-

2.Android

android 也是使用Makefile编译的，但里面改的太多，所以不从这儿入手。
在android 编译模块时我们通常

      source build/envsetup.sh
      lunch 22
      mmm 模块

所以从build/envsetup.sh入手

...

function setpaths()
{
    ....
    # and in with the new
    prebuiltdir=$(getprebuilt)
    gccprebuiltdir=$(get_abs_build_var ANDROID_GCC_PREBUILTS)

    # defined in core/config.mk
    targetgccversion=$(get_build_var TARGET_GCC_VERSION)
    targetgccversion2=$(get_build_var 2ND_TARGET_GCC_VERSION)
    export TARGET_GCC_VERSION=$targetgccversion

    # The gcc toolchain does not exists for windows/cygwin. In this case, do not reference it.
    export ANDROID_TOOLCHAIN=
    export ANDROID_TOOLCHAIN_2ND_ARCH=
    local ARCH=$(get_build_var TARGET_ARCH)
    case $ARCH in
        x86) toolchaindir=x86/x86_64-linux-android-$targetgccversion/bin
            ;;
        x86_64) toolchaindir=x86/x86_64-linux-android-$targetgccversion/bin
            ;;
        arm) toolchaindir=arm/arm-linux-androideabi-$targetgccversion/bin
            ;;
        arm64) toolchaindir=aarch64/aarch64-linux-android-$targetgccversion/bin;
               toolchaindir2=arm/arm-linux-androideabi-$targetgccversion2/bin
            ;;
        mips|mips64) toolchaindir=mips/mips64el-linux-android-$targetgccversion/bin
            ;;
        *)
            echo "Can't find toolchain for unknown architecture: $ARCH"
            toolchaindir=xxxxxxxxx
            ;;
    esac
      if [ -d "$gccprebuiltdir/$toolchaindir" ]; then
         export ANDROID_TOOLCHAIN=$gccprebuiltdir/$toolchaindir
      fi
      ...
}
...

所以Android的交叉编译链在$gccprebuiltdir/$toolchaindir 也就是 prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-$targetgccversion/bin

其中的$gccprebuiltdir和$targetgccversion 的变量可以从上下文赋值得到
或者在命令行使用命令得到：

~/RK3399_7.1$ get_build_var TARGET_GCC_VERSION
4.9

~/RK3399_7.1$ get_build_var ANDROID_GCC_PREBUILTS
prebuilts/gcc/linux-x86

由上面可以看到ANDROID_TOOLCHAIN也就是android toolchain的位置

使用命令行也可以直接得到

~/RK3399_7.1$get_build_var ANDROID_TOOLCHAIN    
/***/RK3399_7.1/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin
~/RK3399_7.1$

3.查看Android编译环境变量多使用 get_build_var get_abs_build_var

下面时命令实现

105 # Get the exact value of a build variable.
 106 function get_build_var()
 107 {
 108     if [ "$BUILD_VAR_CACHE_READY" = "true" ]
 109     then
 110         eval echo "${var_cache_$1}"
 111     return
 112     fi
 113 
 114     T=$(gettop)
 115     if [ ! "$T" ]; then
 116         echo "Couldn't locate the top of the tree.  Try setting TOP." >&2
 117         return
 118     fi
 119     (cd $T; CALLED_FROM_SETUP=true BUILD_SYSTEM=build/core 
 120       command make --no-print-directory -f build/core/config.mk dumpvar-$1)
 121 }