这个函数实现在system/core/init/selinux.cpp中。主要就是启动SElinux， 然后成功后进入到SecondStageMain。

int SetupSelinux(char** argv) {
    MountMissingSystemPartitions();

    SelinuxSetupKernelLogging();

    LOG(INFO) << "Opening SELinux policy";

    // Read the policy before potentially killing snapuserd.
    std::string policy;
    ReadPolicy(&policy);

    LoadSelinuxPolicy(policy);
    const char* path = "/system/bin/init";
    const char* args[] = {path, "second_stage", nullptr};
    execv(path, const_cast(args));
}