Android O 编译探析

根目录下的Makefile

include build/core/main.mk

build/core/main.mk

host_prebuilts := linux-x86

.PHONY: run_soong_ui
run_soong_ui:
    +@prebuilts/build-tools/$(host_prebuilts)/bin/makeparallel --ninja build/soong/soong_ui.bash --make-mode $(MAKECMDGOALS)

.PHONY: $(MAKECMDGOALS)
$(sort $(MAKECMDGOALS)) : run_soong_ui
    @#empty

MAKECMDGOALS

The targets given to make on the command line. Setting this variable has no effect on the operation of make.

根据build/envsetup.sh,MAKECMDGOALS会被mm/mmm/mma/mmma设置,结构大致是MODULES-IN-$DIR, 执行make/m时为空

prebuilts/build-tools/linux-x86/bin/makeparallel

file prebuilts/build-tools/linux-x86/bin/makeparallel

prebuilts/build-tools/linux-x86/bin/makeparallel: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24, stripped

源代码位置 build/make/tools/makeparallel,是用C++编写的,可以自行执行make编译

makeparallel.cpp

int main(int argc, char* argv[]) {
    解析参数
    pid = fork();
  if (pid < 0) {
    error(errno, errno, "fork failed");
  } else if (pid == 0) {
    // child
    unsetenv("MAKEFLAGS");
    unsetenv("MAKELEVEL");

    // make 3.81 sets the stack ulimit to unlimited, which may cause problems
    // for child processes
    struct rlimit rlim{};
    if (getrlimit(RLIMIT_STACK, &rlim) == 0 && rlim.rlim_cur == RLIM_INFINITY) {
      rlim.rlim_cur = 8*1024*1024;
      setrlimit(RLIMIT_STACK, &rlim);
    }

    // 执行 build/soong/soong_ui.bash --make-mode XXX
    int ret = execvp(path, args.data());
    if (ret < 0) {
      error(errno, errno, "exec %s failed", path);
    }
    abort();
  }
  // 父进程等待子进程退出
}

build/soong/soong_ui.bash

...
run_go "$@"

核心是执行函数run_go

function run_go
{
    # Increment when microfactory changes enough that it cannot rebuild itself.
    # For example, if we use a new command line argument that doesn't work on older versions.
    local mf_version=2

    local mf_src="${TOP}/build/soong/cmd/microfactory"

    local out_dir="${OUT_DIR-}"
    if [ -z "${out_dir}" ]; then
        if [ "${OUT_DIR_COMMON_BASE-}" ]; then
            out_dir="${OUT_DIR_COMMON_BASE}/$(basename ${TOP})"
        else
            out_dir="${TOP}/out"
        fi
    fi

    local mf_bin="${out_dir}/microfactory_$(uname)"
    local mf_version_file="${out_dir}/.microfactory_$(uname)_version"
    local soong_ui_bin="${out_dir}/soong_ui"
    local from_src=1

    if [ -f "${mf_bin}" ] && [ -f "${mf_version_file}" ]; then
        if [ "${mf_version}" -eq "$(cat "${mf_version_file}")" ]; then
            from_src=0
        fi
    fi

    // 第一次直接运行go文件并生成可执行文件microfactory_Linux,之后直接执行microfactory_Linux
    local mf_cmd
    if [ $from_src -eq 1 ]; then
        mf_cmd="${GOROOT}/bin/go run ${mf_src}/microfactory.go"
    else
        mf_cmd="${mf_bin}"
    fi

   // 为了生成soong_ui
    ${mf_cmd} -s "${mf_src}" -b "${mf_bin}" \
            -pkg-path "android/soong=${TOP}/build/soong" -trimpath "${TOP}/build/soong" \
            -o "${soong_ui_bin}" android/soong/cmd/soong_ui

    if [ $from_src -eq 1 ]; then
        echo "${mf_version}" >"${mf_version_file}"
    fi

 // 执行soong_ui
    exec "${out_dir}/soong_ui" "$@"
}

build/soong/cmd/microfactory/microfactory.go

省略

build/soong/cmd/soong_ui/main.go

func main() {
      ......
      build.Build(buildCtx, config, build.BuildAll)
}

build/soong/ui/build/build.go

const (
    BuildNone          = iota
    BuildProductConfig = 1 << iota
    BuildSoong         = 1 << iota
    BuildKati          = 1 << iota
    BuildNinja         = 1 << iota
    BuildAll           = BuildProductConfig | BuildSoong | BuildKati | BuildNinja
)

func Build(ctx Context, config Config, what int)
根据之前what值决定执行哪些操作，根据上面的代码，可以看到调用的是build.BuildAll
下面看一下每项操作具体做了哪些工作

BuildProductConfig

>runMakeProductConfig(ctx, config)

build/soong/ui/build/make.go
核心操作是执行了make -f build/core/config.mk，解析命令执行结果获得变量/值的集合，同步环境变>量。为config设置KATI_GOALS、NINJA_GOALS,其实就是之前的MAKECMDGOALS。

BuildSoong

runSoongBootstrap(ctx, config)
runSoong(ctx, config)

runSoongBootstrap
核心逻辑是执行build/soong/bootstrap.bash

build/soong/bootstrap.bash
输出模板build/soong/soong.bootstrap.in到out/soong/.soong.bootstrap,执行build/blueprint/bootstrap.bash,建立软链接out/soong/soong指向build/soong/soong.bash
$ cat out/soong/.soong.bootstrap 
BUILDDIR="out/soong"
SRCDIR_FROM_BUILDDIR="../.."
PREBUILTOS="linux-x86"
build/blueprint/bootstrap.bash
输出模板build/soong/build.ninja.in到out/soong/.minibootstrap/build.ninja,变量存储到out/soong/.blueprint.bootstrap
$ cat out/soong/.blueprint.bootstrap
BOOTSTRAP="./bootstrap.bash"
BOOTSTRAP_MANIFEST="./build/soong/build.ninja.in"
runSoong
执行out/soong/soong(build/soong/soong.bash)

build/soong/soong.bash
BUILDDIR=out/soong NINJA="prebuilts/build-tools/linux-x86/bin/ninja" build/blueprint/blueprint.bash $@
build/blueprint/blueprint.bash
# Build minibp and the primary build.ninja
"${NINJA}" -w dupbuild=err -f "${BUILDDIR}/.minibootstrap/build.ninja"

# Build the primary builder and the main build.ninja
"${NINJA}" -w dupbuild=err -f "${BUILDDIR}/.bootstrap/build.ninja"

# SKIP_NINJA can be used by wrappers that wish to run ninja themselves.
if [ -z "$SKIP_NINJA" ]; then
   "${NINJA}" -w dupbuild=err -f "${BUILDDIR}/build.ninja" "$@"
else
   exit 0
fi

BuildKati

runKati(ctx, config)

- build/soong/ui/build/kati.go
  runKati 核心是执行ckati命令。ckati的源码位于build/kati下，通过make执行

// 生成KatiSuffix，后面会需要
genKatiSuffix(ctx, config)
executable := "prebuilts/build-tools/" + config.HostPrebuiltTag() + "/bin/ckati"
args := []string{
        "--ninja",
        "--ninja_dir=" + config.OutDir(),
        "--ninja_suffix=" + config.KatiSuffix(),
        "--regen",
        "--ignore_optional_include=" + filepath.Join(config.OutDir(), "%.P"),
        "--detect_android_echo",
        "--color_warnings",
        "--gen_all_targets",
        "-f", "build/core/main.mk",
    }

- build/kati/main.cc

跟踪main函数，先进行Init()，初始化了一些东西，先不care。把参数做个备份保存到orig_args（不知道什么意图）。把参数拿去解析(flags.cc)，解析完存放结构体Flags中。
FindFirstMakefie寻找第一个makefile，上面已经通过-f指定了makefile，未指定则顺序寻找当前目录下的GNUmakefile、makefile、Makefile。
然后进入Run函数。根据之前参数需要生成Ninja文件。NeedsRegen判断是否需要重新生成ninja文件。函数IsMissingOutputs判断GetNinjaFilename/GetNinjaShellScriptFilename是否存在，涉及到config.ninja_suffix，也就是KatiSuffix上面已备注。