Android启动流程分析之三：内核启动过程2--start_kernel

http://blog.csdn.net/ly890700/article/details/54586484

start_kernel是内核启动后执行的第一个C语言函数，位于kernel/init/main.c中

一 start_kernel上半段

kernel/init/main.c  Collapse source

asmlinkage __visible  void  __init start_kernel( void )
{
    char  *command_line;
    char  *after_dashes;
    /*
     * Need to run as early as possible, to initialize the
     * lockdep hash:
     */
    lockdep_init();
    set_task_stack_end_magic(&init_task);
    smp_setup_processor_id();
    debug_objects_early_init();
    cgroup_init_early();
    local_irq_disable();
    early_boot_irqs_disabled =  true ;
/*
 * Interrupts are still disabled. Do necessary setups, then
 * enable them
 */
    boot_cpu_init();
    page_address_init();
    pr_notice( "%s" , linux_banner);
    setup_arch(&command_line);
    /*
     * Set up the the initial canary ASAP:
     */
    boot_init_stack_canary();
    mm_init_cpumask(&init_mm);
    setup_command_line(command_line);
    setup_nr_cpu_ids();
    setup_per_cpu_areas();
    smp_prepare_boot_cpu();  /* arch-specific boot-cpu hooks */
    build_all_zonelists(NULL, NULL);
    page_alloc_init();
    pr_notice( "Kernel command line: %s\n" , boot_command_line);
    parse_early_param();
    after_dashes = parse_args( "Booting kernel" ,
                  static_command_line, __start___param,
                  __stop___param - __start___param,
                  -1, -1, &unknown_bootoption);
    if  (!IS_ERR_OR_NULL(after_dashes))
        parse_args( "Setting init args" , after_dashes, NULL, 0, -1, -1,
               set_init_arg);
    jump_label_init();
    /*
     * These use large bootmem allocations and must precede
     * kmem_cache_init()
     */
    setup_log_buf(0);
    pidhash_init();
    vfs_caches_init_early();
    sort_main_extable();
    trap_init();
    mm_init();
    /*
     * Set up the scheduler prior starting any interrupts (such as the
     * timer interrupt). Full topology setup happens at smp_init()
     * time - but meanwhile we still have a functioning scheduler.
     */
    sched_init();
    /*
     * Disable preemption - early bootup scheduling is extremely
     * fragile until we cpu_idle() for the first time.
     */
    preempt_disable();
    if  (WARN(!irqs_disabled(),
         "Interrupts were enabled *very* early, fixing it\n" ))
        local_irq_disable();
    idr_init_cache();
    rcu_init();
    context_tracking_init();
    radix_tree_init();
    /* init some links before init_ISA_irqs() */
    early_irq_init();
    init_IRQ();
    tick_init();
    rcu_init_nohz();
    init_timers();
    hrtimers_init();
    softirq_init();
    timekeeping_init();
    time_init();
    sched_clock_postinit();
    perf_event_init();
    profile_init();
    call_function_init();
    WARN(!irqs_disabled(),  "Interrupts were enabled early\n" );
    early_boot_irqs_disabled =  false ;
    local_irq_enable();

在start_kernel上半段中会调用一系列初始化函数来完成内核的初始化工作：

1 lockdep_init();  初始化内核死锁检测机制的哈希表

2 smp_setup_processor_id();  返回cpu号，单核cpu返回0

3 debug_objects_early_init();  对调试对象进行早期的初始化

4 local_irq_disable();  关闭当前cpu的中断

5 boot_cpu_init();  设置当前cpu位激活状态

6 page_address_init();   初始化高端内存的

7 setup_arch(&command_line);  执行内核架构相关初始化函数

8 boot_init_stack_canary();  初始化栈canary值，canary值用于防止栈溢出攻击的堆栈的保护字

9 build_all_zonelists(NULL, NULL);  建立系统内存页区(zone)链表

10 page_alloc_init();  内存页初始化

11 在parse_args函数中解析cmdline中的启动参数

12 etup_log_buf(0);  使用memblock_alloc分配一个启动时log缓冲区

13 pidhash_init();  初始化pid散列表

14 vfs_caches_init_early();  初始化dentry和inode的hashtable

15 sort_main_extable();  对内核异常向量表进行排序

16 trap_init();  对内核陷阱异常进行初始化，arm没有用到

17 mm_init();  初始化内核内存分配器，过度到伙伴系统，启动slab机制，初始化非连续内存区

18 sched_init();  初始化进程调度器

19 local_irq_disable();  关闭本地中断

20 rcu_init();  初始化rcu机制

21 init_IRQ();  初始化中断lockdep_init

22 tick_init();  初始化时钟滴答控制器

23 init_timers();  初始化内核定时器

24 softirq_init();  初始化软中断

25 time_init();  时钟初始化

26 profile_init();   对内核的一个性能测试工具profile进行初始化

27 local_irq_enable();  使能当前cpu中断

 

二 start_kernel下半段

 

 

 

kernel/init/main.c  Collapse source

    kmem_cache_init_late();
    /*
     * HACK ALERT! This is early. We're enabling the console before
     * we've done PCI setups etc, and console_init() must be aware of
     * this. But we do want output early, in case something goes wrong.
     */
    console_init();
    if  (panic_later)
        panic( "Too many boot %s vars at `%s'" , panic_later,
              panic_param);
    lockdep_info();
    /*
     * Need to run this when irqs are enabled, because it wants
     * to self-test [hard/soft]-irqs on/off lock inversion bugs
     * too:
     */
    locking_selftest();
#ifdef CONFIG_BLK_DEV_INITRD
    if  (initrd_start && !initrd_below_start_ok &&
        page_to_pfn(virt_to_page(( void  *)initrd_start)) < min_low_pfn) {
        pr_crit( "initrd overwritten (0x%08lx < 0x%08lx) - disabling it.\n" ,
            page_to_pfn(virt_to_page(( void  *)initrd_start)),
            min_low_pfn);
        initrd_start = 0;
    }
#endif
    page_cgroup_init();
    debug_objects_mem_init();
    kmemleak_init();
    setup_per_cpu_pageset();
    numa_policy_init();
    if  (late_time_init)
        late_time_init();
    sched_clock_init();
    calibrate_delay();
    pidmap_init();
    anon_vma_init();
    acpi_early_init();
#ifdef CONFIG_X86
    if  (efi_enabled(EFI_RUNTIME_SERVICES))
        efi_enter_virtual_mode();
#endif
#ifdef CONFIG_X86_ESPFIX64
    /* Should be run before the first non-init thread is created */
    init_espfix_bsp();
#endif
    thread_info_cache_init();
    cred_init();
    fork_init(totalram_pages);
    proc_caches_init();
    buffer_init();
    key_init();
    security_init();
    dbg_late_init();
    vfs_caches_init(totalram_pages);
    signals_init();
    /* rootfs populating might need page-writeback */
    page_writeback_init();
    proc_root_init();
    cgroup_init();
    cpuset_init();
    taskstats_init_early();
    delayacct_init();
    check_bugs();
    acpi_subsystem_init();
    sfi_init_late();
    if  (efi_enabled(EFI_RUNTIME_SERVICES)) {
        efi_late_init();
        efi_free_boot_services();
    }
    ftrace_init();
    /* Do the rest non-__init'ed, we're now alive */
    rest_init();
}

 

在下半段中主要完成：

 

1 kmem_cache_init_late();  初始化slab分配器的缓存机制

 

2 console_init(); 初始化控制台

 

3 lockdep_info();  打印锁的依赖信息

 

4 locking_selftest();  死锁检测

5 page_cgroup_init();  为page_cgroup相关结构分配存储空间

6 debug_objects_mem_init();  创建debug_obj的slab高速缓存

7