实验三：gdb跟踪调试内核从start_kernel到init进程启动

原创作品转载请注明出处《Linux内核分析》MOOC课程http://mooc.study.163.com/course/USTC-1000029000

如果我写的不好或者有误的地方请留言

• 题目自拟，内容围绕Linux内核的启动过程，即从start_kernel到init进程启动；
• 博客中需要使用实验截图
• 博客内容中需要仔细分析start_kernel函数的执行过程
• 总结部分需要阐明自己对“Linux系统启动过程”的理解，尤其是idle进程、1号进程是怎么来的。

实验报告：

在实验楼里跑了一下gdb 没有多大印象 印象就是卡 这是卡吗 下面分析换自己的虚拟机

先来个宏观认识：

从start_kernel()中可以看到最后一条语句是rest_init();

 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();

     /*
      * Set up the the initial canary ASAP:
      */
     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,
                   -, -, &unknown_bootoption);
     if (!IS_ERR_OR_NULL(after_dashes))
         parse_args("Setting init args", after_dashes, NULL, , -, -,
                set_init_arg);

     jump_label_init();

     /*
      * These use large bootmem allocations and must precede
      * kmem_cache_init()
      */
     setup_log_buf();
     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 = ;
     }
 #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();

     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

 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);
     schedule_preempt_disabled();
     /* Call into cpu_idle with preempt disabled */
     cpu_startup_entry(CPUHP_ONLINE);
 }

rest_init

咱们需要知道的东西如下：

在start_kernel中：

init_task:手工创建的PCB 0号进程即最终的idle进程
trap_init:初始化中断管理模块
mm_init:初始化内存管理模块
sched_init:初始化调度模块

在rest_init中：

run_init_process:linux系统中的1号进程 第一个用户态进程

注意：

1.我们需要首先初始化获得pid=1的进程 如果初始化最终创建了ktheads

我们在创建kthreadd之前调度它 Linux系统将会OOPS

2.启动空闲线程必须至少执行一次schedule()