asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
{

}

void set_task_stack_end_magic(struct task_struct *tsk)
{
	unsigned long *stackend;
	//获取栈边界地址
	stackend = end_of_stack(tsk);
	*stackend = STACK_END_MAGIC;	/* for overflow detection */
}

	struct task_struct init_task = {
#ifdef CONFIG_THREAD_INFO_IN_TASK
	.thread_info	= INIT_THREAD_INFO(init_task),
	.stack_refcount	= REFCOUNT_INIT(1),
#endif
	.............................................................
	.stack		= init_stack,
	..............................................................
};

union thread_union {
#ifndef CONFIG_ARCH_TASK_STRUCT_ON_STACK
	struct task_struct task;
#endif
#ifndef CONFIG_THREAD_INFO_IN_TASK
	struct thread_info thread_info;
#endif
	unsigned long stack[THREAD_SIZE/sizeof(long)];
};

	/* x86 */
	struct thread_info {
		unsigned long		flags;		/* low level flags */
		u32			status;		/* thread synchronous flags */
	};

	/* ARM */
	struct thread_info {
		unsigned long		flags;		/* low level flags */
		int			preempt_count;	/* 0 => preemptable, <0 => bug */
		mm_segment_t		addr_limit;	/* address limit */
		struct task_struct	*task;		/* main task structure */
		… …
	};

	//X86_64
	void __init __weak smp_setup_processor_id(void)
	{
	}
	
	//ARM64
	void __init smp_setup_processor_id(void)
	{
		//获取CPU ID
		u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;
		set_cpu_logical_map(0, mpidr);
		/*
		 * clear __my_cpu_offset on boot CPU to avoid hang caused by
		 * using percpu variable early, for example, lockdep will
		 * access percpu variable inside lock_release
	 	*/
		set_my_cpu_offset(0);
		pr_info("Booting Linux on physical CPU 0x%010lx [0x%08x]\n",(unsigned long)mpidr, read_cpuid_id());
	}
	
	//ARM32
	void __init smp_setup_processor_id(void)
	{
		int i;
		//判断是否是smp系统,如果是则从arm协处理器读取当前cpuid,否则为0
		u32 mpidr = is_smp() ? read_cpuid_mpidr() & MPIDR_HWID_BITMASK : 0;
		//根据level确定cpu号，即cpu=(mpidr>>0)&0xff
		u32 cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);

		cpu_logical_map(0) = cpu;
		for (i = 1; i < nr_cpu_ids; ++i)
			cpu_logical_map(i) = i == cpu ? 0 : i;

		/*
		 * clear __my_cpu_offset on boot CPU to avoid hang caused by
		 * using percpu variable early, for example, lockdep will
		 * access percpu variable inside lock_release
		 */
		set_my_cpu_offset(0);

		pr_info("Booting Linux on physical CPU 0x%x\n", mpidr);
	}
	

/*
 * Called during early boot to initialize the hash buckets and link
 * the static object pool objects into the poll list. After this call
 * the object tracker is fully operational.
 */
void __init debug_objects_early_init(void)
{
	int i;

	for (i = 0; i < ODEBUG_HASH_SIZE; i++)
		raw_spin_lock_init(&obj_hash[i].lock);

	for (i = 0; i < ODEBUG_POOL_SIZE; i++)
		hlist_add_head(&obj_static_pool[i].node, &obj_pool);
}

	struct task_struct {
	.......
	#ifdef CONFIG_CGROUPS
	/* Control Group info protected by css_set_lock: */
	struct css_set __rcu		*cgroups;
	/* cg_list protected by css_set_lock and tsk->alloc_lock: */
	struct list_head		cg_list;
	#endif
	......
	}

	struct css_set {
	/*
	 * Set of subsystem states, one for each subsystem. This array is
	 * immutable after creation apart from the init_css_set during
	 * subsystem registration (at boot time).
	 * 存储一组指向 cgroup_subsys_state 的指针。一个cgroup_subsys_state 就是进程与一个特定子系统相关的信息。
	 * 通过这个指针数组，进程就可以获得相应的 cgroups 控制信息
	 */
	struct cgroup_subsys_state *subsys[CGROUP_SUBSYS_COUNT];

	/* reference count  css_set 的引用数，因为一个 css_set 可以被多个进程公用，只要这些进程的 cgroups 信息相同 */
	refcount_t refcount;

	/*
	 * For a domain cgroup, the following points to self.  If threaded,
	 * to the matching cset of the nearest domain ancestor.  The
	 * dom_cset provides access to the domain cgroup and its csses to
	 * which domain level resource consumptions should be charged.
	 */
	struct css_set *dom_cset;

	/* the default cgroup associated with this css_set */
	struct cgroup *dfl_cgrp;

	/* internal task count, protected by css_set_lock */
	int nr_tasks;

	/*
	 * Lists running through all tasks using this cgroup group.
	 * mg_tasks lists tasks which belong to this cset but are in the
	 * process of being migrated out or in.  Protected by
	 * css_set_rwsem, but, during migration, once tasks are moved to
	 * mg_tasks, it can be read safely while holding cgroup_mutex.
	 */
	struct list_head tasks;
	struct list_head mg_tasks;
	struct list_head dying_tasks;

	/* all css_task_iters currently walking this cset */
	struct list_head task_iters;

	/*
	 * On the default hierarhcy, ->subsys[ssid] may point to a css
	 * attached to an ancestor instead of the cgroup this css_set is
	 * associated with.  The following node is anchored at
	 * ->subsys[ssid]->cgroup->e_csets[ssid] and provides a way to
	 * iterate through all css's attached to a given cgroup.
	 */
	struct list_head e_cset_node[CGROUP_SUBSYS_COUNT];

	/* all threaded csets whose ->dom_cset points to this cset */
	struct list_head threaded_csets;
	struct list_head threaded_csets_node;

	/*
	 * List running through all cgroup groups in the same hash
	 * slot. Protected by css_set_lock
	 * 用于把所有 css_set 组织成一个 hash 表，这样内核可以快速查找特定的 css_set
	 */
	struct hlist_node hlist;

	/*
	 * List of cgrp_cset_links pointing at cgroups referenced from this
	 * css_set.  Protected by css_set_lock.
	 */
	struct list_head cgrp_links;

	....
};

struct cgroup_subsys_state {
	/* PI: the cgroup that this css is attached to */
	struct cgroup *cgroup;

	/* PI: the cgroup subsystem that this css is attached to */
	struct cgroup_subsys *ss;

	/* reference count - access via css_[try]get() and css_put() */
	struct percpu_ref refcnt;

	/* siblings list anchored at the parent's ->children */
	struct list_head sibling;
	struct list_head children;

	/* flush target list anchored at cgrp->rstat_css_list */
	struct list_head rstat_css_node;

	/*
	 * PI: Subsys-unique ID.  0 is unused and root is always 1.  The
	 * matching css can be looked up using css_from_id().
	 */
	int id;

	unsigned int flags;

	/*
	 * Monotonically increasing unique serial number which defines a
	 * uniform order among all csses.  It's guaranteed that all
	 * ->children lists are in the ascending order of ->serial_nr and
	 * used to allow interrupting and resuming iterations.
	 */
	u64 serial_nr;

	/*
	 * Incremented by online self and children.  Used to guarantee that
	 * parents are not offlined before their children.
	 */
	atomic_t online_cnt;

	/*
	 * PI: the parent css.	Placed here for cache proximity to following
	 * fields of the containing structure.
	 */
	struct cgroup_subsys_state *parent;
	};

int __init cgroup_init_early(void)
{
	static struct cgroup_fs_context __initdata ctx;
	struct cgroup_subsys *ss;
	int i;

	//初始化根cgroup
	ctx.root = &cgrp_dfl_root;
	init_cgroup_root(&ctx);
	cgrp_dfl_root.cgrp.self.flags |= CSS_NO_REF;
	//初始化css_set
	RCU_INIT_POINTER(init_task.cgroups, &init_css_set);
	//循环遍历所有子系统
	for_each_subsys(ss, i) {
		WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id,
		     "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p id:name=%d:%s\n",
		     i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free,
		     ss->id, ss->name);
		WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN,
		     "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]);

		ss->id = i;
		ss->name = cgroup_subsys_name[i];
		if (!ss->legacy_name)
			ss->legacy_name = cgroup_subsys_name[i];
		//该子系统是否需要初始化
		if (ss->early_init)
			cgroup_init_subsys(ss, true);
	}
	return 0;
}

#if IS_ENABLED(CONFIG_CPUSETS)
SUBSYS(cpuset)
#endif

#if IS_ENABLED(CONFIG_CGROUP_SCHED)
SUBSYS(cpu)
#endif

#if IS_ENABLED(CONFIG_CGROUP_CPUACCT)
SUBSYS(cpuacct)
#endif

#if IS_ENABLED(CONFIG_BLK_CGROUP)
SUBSYS(io)
#endif

#if IS_ENABLED(CONFIG_MEMCG)
SUBSYS(memory)
#endif

#if IS_ENABLED(CONFIG_CGROUP_DEVICE)
SUBSYS(devices)
#endif

#if IS_ENABLED(CONFIG_CGROUP_FREEZER)
SUBSYS(freezer)
#endif

#if IS_ENABLED(CONFIG_CGROUP_NET_CLASSID)
SUBSYS(net_cls)
#endif

#if IS_ENABLED(CONFIG_CGROUP_PERF)
SUBSYS(perf_event)
#endif

#if IS_ENABLED(CONFIG_CGROUP_NET_PRIO)
SUBSYS(net_prio)
#endif

#if IS_ENABLED(CONFIG_CGROUP_HUGETLB)
SUBSYS(hugetlb)
#endif

#if IS_ENABLED(CONFIG_CGROUP_PIDS)
SUBSYS(pids)
#endif

#if IS_ENABLED(CONFIG_CGROUP_RDMA)
SUBSYS(rdma)
#endif

/*
 * The following subsystems are not supported on the default hierarchy.
 */
#if IS_ENABLED(CONFIG_CGROUP_DEBUG)
SUBSYS(debug)
#endif

/*
 * Activate the first processor.
 */
void __init boot_cpu_init(void)
{
	//获取cpu id
	int cpu = smp_processor_id();

	/* Mark the boot cpu "present", "online" etc for SMP and UP case */
	//根据cpu id设置在线、激活 、present、possible
	set_cpu_online(cpu, true);
	set_cpu_active(cpu, true);
	set_cpu_present(cpu, true);
	set_cpu_possible(cpu, true);

#ifdef CONFIG_SMP
	__boot_cpu_id = cpu;
#endif
}

int __init early_security_init(void)
{
	int i;
	//初始化安全 lsm hook hlist_head;
	struct hlist_head *list = (struct hlist_head *) &security_hook_heads;
	struct lsm_info *lsm;

	for (i = 0; i < sizeof(security_hook_heads) / sizeof(struct hlist_head);
	     i++)
		INIT_HLIST_HEAD(&list[i]);
	//根据__start_early_lsm_info 、__end_early_lsm_info列表，初始化lsm，x86_64：__end_early_lsm_info-__start_early_lsm_info=0
	for (lsm = __start_early_lsm_info; lsm < __end_early_lsm_info; lsm++) {
		if (!lsm->enabled)
			lsm->enabled = &lsm_enabled_true;
		prepare_lsm(lsm);
		initialize_lsm(lsm);
	}

	return 0;
}

void __init setup_arch(char **cmdline_p)
{
	//保留_text 到 __end_of_kernel_reserve 之间内核占用的内存
	memblock_reserve(__pa_symbol(_text),
			 (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
	//保留 page 0
	memblock_reserve(0, PAGE_SIZE);
	//保留 ramdisk 内存，如果有的话
	early_reserve_initrd();
	//这个不是很了解，感觉像是保留和显示相关的内存
	olpc_ofw_detect();
	//初始化中断描述表b
	idt_setup_early_traps();
	//根据cpu_dev_register()注册的设备，填充cpu_devs[]，并填充boot_cpu_data结构信息
	early_cpu_init();
	//没太懂，初始化一个空操作指令数组，类似于延时？！占位？用于hook?
	arch_init_ideal_nops();
	//处理静态定义的jump label，执行跳转指令或是nop指令
	jump_label_init();
	//加载静态定义的跳转表,注册模块通知
	static_call_init();
	//函数用于初始化slot_virt[8] 数组，该数据用于管理2M虚拟地址空间，每个slot用于管理64 pages,每个page大小4K,并把这2M空间映射成PMD,再把PMD加入PTE表。
	early_ioremap_init();
	//把olpc加入pgd表
	setup_olpc_ofw_pgd();
	....
	//
	init_cache_modes();
	//KASLR是kernel address space layout randomization的缩写，直译过来就是内核地址空间布局随机化。
	//KASLR技术允许kernel image加载到VMALLOC区域的任何位置。当KASLR关闭的时候，kernel image都会映射到一个固定的链接地址.相对安全
	kernel_randomize_memory();
}