2018-2019-1 20189221《Linux核心原理與分析》第四周作業

教材學習：《庖丁解牛Linux核心分析》

第 3 章 MenuOS的構造

計算機三大法寶：儲存程式計算機，函式呼叫堆疊，中斷
作業系統兩把寶劍：中斷上下文，程序上下文

Linux核心原始碼：

Linux核心使用的是第二週時下載的Linux-2.6版本
Linux核心目錄：

init目錄下的main.c函式：

start_kernel()：

init_task()：

rest_init()：

隨書學習很有收穫，也算是為實驗操作做了很多準備。

實驗報告：實驗 3 跟蹤分析Linux核心的啟動過程

實驗流程

使用實驗樓的虛擬機器開啟shell，核心啟動完成後進入menu程式

使用gdb跟蹤除錯核心

gdb
（gdb）file linux-3.18.6/vmlinux # 在gdb介面中targe remote之前載入符號表
（gdb）target remote:1234 # 建立gdb和gdbserver之間的連線,按c 讓qemu上的Linux繼續執行
（gdb）break start_kernel # 斷點的設定可以在target remote之前，也可以在之後

設定斷點：

使用list檢視斷點臨近程式碼：

除錯過程中：

程式碼分析

start_kernel()程式碼：

asmlinkage __visible void __init start_kernel(void)
{
    char *command_line;
    char *after_dashes;

    lockdep_init();
    set_task_stack_end_magic(&init_task);
    smp_setup_processor_id();
    debug_objects_early_init();
    boot_init_stack_canary();
    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);
    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();

    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 /*與x86硬體相關程式碼 如果主機板支援EFI的話*/
    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();

    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(); 
}
 

start_kernel()分析：

lockdep_init(); //死鎖檢測模組初始化
debug_objects_early_init(); //初始化堆疊 此堆疊有額外的越界保護功能
page_address_init(); //初始化頁表地址
pidhash_init(); //給新程序分配程序號
mm_init(); //初始化記憶體管理
sched_init(); //啟動排程器
radix_tree_init(); //init some links before init_ISA_irqs() //初始化中斷

rest_init()函式：

static noinline void __init_refok rest_init(void)
{
    int pid; 

    rcu_scheduler_starting();
    /*
     * We need to spawn init first so that it obtains pid 1, however
     * the init task will end up wanting to create kthreads, which, if
     * we schedule it before we create kthreadd, will OOPS.
     */
    kernel_thread(kernel_init, NULL, CLONE_FS); 
    numa_default_policy();
    pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
    rcu_read_lock();
    kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
    rcu_read_unlock();
    complete(&kthreadd_done);

    /*
     * The boot idle thread must execute schedule()
     * at least once to get things moving:
     */
    init_idle_bootup_task(current); /*idle初始化*/
    schedule_preempt_disabled();
    /* Call into cpu_idle with preempt disabled */
    cpu_startup_entry(CPUHP_ONLINE);
}

rest_init()分析：

int pid; //定義程序號
kernel_thread(kernel_init, NULL, CLONE_FS); //初始化核心執行緒

本週小結

• 這周學習時間上按照計劃完成，較之之前兩週都輕鬆許多
• 這周遇到的問題不確定是怎樣的問題：
  問題一：一開始實驗時，QEMU視窗無反應，點選則實驗樓的實驗環境宕機
  
  解決：個人認為是實驗樓的原因，因為第二天我再次進行實驗時：
  
  兩個小時之後再次嘗試實驗樓才恢復正常