linux内核分析第三周学习笔记

标签（空格分隔）： 20135328陈都

陈都 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

构造一个简单的Linux系统MenuOS

上周回顾：

• 计算机三大法宝

• 存储程序计算机

• 函数调用堆栈

• 中断

• 操作系统两把宝剑

• 中断上下文的切换

• 进程上下文的切换

Linux内核源码简介

我们关注的部分

• arch/x86目录下的代码
• init/main.c中start_kernel函数就相当于普通C程序的main函数
• kernel目录：存放linux内核最核心的代码，用于实现系统的核心模块，包括进程管理、进程调度器、中断处理、系统时钟管理、同步机制等

README

提供内核的各种编译方法、生成文件的查看方法。

• installing 如何安装内核源代码
• make mrproper 清理安装时生成的中间代码

启动Linux内核的三个参数：

• kernel
• initrd
• root所在分区、目录

需要知道的一行代码：qemu -kernel (文件名) -initrd (rootfs.img)

qemu -kernel linux-3.18.6/arch/x86/boot/bzImage -initrd rootfs.img -s -S

使用gdb跟踪调试内核

qemu -kernel linux-3.18.6/arch/x86/boot/bzImage -initrd rootfs.img -s

-S # 关于-s和-S选项的说明：

-S freeze CPU at startup (use ’c’ to start execution)

-s shorthand for -gdb tcp::1234 若不想使用1234端口，则可以使用-gdb

tcp:xxxx来取代-s选项

另开一个shell窗口

gdb （gdb）file linux-3.18.6/vmlinux # 在gdb界面中targe remote之前加载符号表

（gdb）target remote:1234 # 建立gdb和gdbserver之间的连接,按c 让qemu上的Linux继续运行

（gdb）break start_kernel # 断点的设置可以在target remote之前，也可以在之后

总结分析start_kernel

start_kernel：包括很多模块的初始化。

分析内核都会涉及到start_kernel，都会在init初始化。

详细分析从start_kernel到init进程启动的过程

start_kernel函数的执行代码在init目录下的main.c^[1]

500asmlinkage __visible void __init start_kernel(void)
501{
   char *command_line;
   char *after_dashes;
505    /*
    * Need to run as early as possible, to initialize the
    * lockdep hash:
    */
   lockdep_init();
   set_task_stack_end_magic(&init_task);     init_task即手工创建的PCB，0号进程即最终的idle进程。
   smp_setup_processor_id();
   debug_objects_early_init();
514    /*
    * Set up the the initial canary ASAP:
    */
   boot_init_stack_canary();
519    cgroup_init_early();
521    local_irq_disable();
   early_boot_irqs_disabled = true;
524/*
* 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 */
538    build_all_zonelists(NULL, NULL);
   page_alloc_init();
541    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);
551    jump_label_init();
553    /*
    * 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();   涉及到中断的初始化
   mm_init();
564    /*
    * 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();
600    kmem_cache_init_late();
602    /*
    * 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);
612    lockdep_info();
614    /*
    * 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();
621#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;
   }
629#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();
642#ifdef CONFIG_X86
   if (efi_enabled(EFI_RUNTIME_SERVICES))
       efi_enter_virtual_mode();
645#endif
646#ifdef CONFIG_X86_ESPFIX64
   /* Should be run before the first non-init thread is created */
   init_espfix_bsp();
649#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();
668    check_bugs();
670    sfi_init_late();
672    if (efi_enabled(EFI_RUNTIME_SERVICES)) {
       efi_late_init();
       efi_free_boot_services();
   }
677    ftrace_init();
679    /* Do the rest non-__init'ed, we're now alive */
   rest_init();
681}