林亮生 + 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
1.gdb跟踪调试内核 qemu -kernel linux-3.18.6/arch/x86/boot/bzImage -initrd rootfs.img -s -S 此时进入调试模式，显示为一片黑屏。 2.gdb (gdb) file linux-3.18.6/vmlinux #将文件加载进来 (gdb) target remote:1234 #建立连接 (gdb) break start-kernel #设置断点 (gdb) c #Continue (gdb) list #查看代码 (gdb) rest_init (gdb) c (gdb) list 进入gdb调试界面 连接调试，打断点在start_kernel，并让程序执行 程序执行后会在start_kernel停下，这是停下后的界面 程序执行到rest_init停下的界面 程序执行结束界面 3.内核源码 start_kernel asmlinkage __visible void __init start_kernel(void) { char *command_line; char *after_dashes; 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(); boot_cpu_state_init(); 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, NULL, &unknown_bootoption); if (!IS_ERR_OR_NULL(after_dashes)) parse_args("Setting init args", after_dashes, NULL, 0, -1, -1, NULL, 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(); /* trace_printk() and trace points may be used after this */ trace_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(); printk_nmi_init(); 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 (0xlx < 0xlx) - disabling it.\n", page_to_pfn(virt_to_page((void *)initrd_start)), min_low_pfn); initrd_start = 0; } #endif page_ext_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_stack_cache_init(); cred_init(); fork_init(); proc_caches_init(); buffer_init(); key_init(); security_init(); dbg_late_init(); vfs_caches_init(); signals_init(); /* rootfs populating might need page-writeback */ page_writeback_init(); proc_root_init(); nsfs_init(); cpuset_init(); cgroup_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(); } 比较关心的几个地方： set_task_stack_end_magic(&init_task); 创建了0号进程 trap_init(); 中断的初始化 mm_init(); 内存管理的初始化 sched_init(); 调度的初始化 rest_init(); 其它的初始化 rest_init方法体 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); } 其中 kernel_thread(kernel_init, NULL, CLONE_FS); kernel_init是个方法，方法体为 static int __ref kernel_init(void *unused) { int ret; kernel_init_freeable(); /* need to finish all async __init code before freeing the memory */ async_synchronize_full(); free_initmem(); mark_rodata_ro(); system_state = SYSTEM_RUNNING; numa_default_policy(); flush_delayed_fput(); if (ramdisk_execute_command) { ret = run_init_process(ramdisk_execute_command); if (!ret) return 0; pr_err("Failed to execute %s (error %d)\n", ramdisk_execute_command, ret); } /* * We try each of these until one succeeds. * * The Bourne shell can be used instead of init if we are * trying to recover a really broken machine. */ if (execute_command) { ret = run_init_process(execute_command); if (!ret) return 0; panic("Requested init %s failed (error %d).", execute_command, ret); } if (!try_to_run_init_process("/sbin/init") || !try_to_run_init_process("/etc/init") || !try_to_run_init_process("/bin/init") || !try_to_run_init_process("/bin/sh")) return 0; panic("No working init found. Try passing init= option to kernel. " "See Linux Documentation/init.txt for guidance."); } 其中 ret = run_init_process(ramdisk_execute_command); 而init_process就是Linux系统中的1号进程，也是第一个用户态进程；ramdisk_execute_command表明了根目录下的程序，找不到会继续往sbin，etc等目录下去寻找。 pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); 创建内核线程 cpu_startup_entry(CPUHP_ONLINE); 里面是一个while(1)的死循环，当系统没有进程需要执行时就调度到该idle进程。