Linux|Kernel啟動(dòng)流程源碼分析

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內(nèi)核生命周期

uboot 打印完 Starting kernel . . .，就完成了自己的使命，控制權(quán)便交給了 kernel 的第一條指令，也就是下面這個(gè)函數(shù)。

init/main.c

????asmlinkage?__visible?void?__init?start_kernel(void)
????{
?????...
?????rest_init();
????}

start_kernel 相當(dāng)于內(nèi)核的 main 函數(shù)，內(nèi)核的生命周期就是從執(zhí)行這個(gè)函數(shù)的第一條語句開始的，直到最后一個(gè)函數(shù) reset_init()，內(nèi)核將不再?gòu)倪@個(gè)函數(shù)中返回，而是陷入這個(gè)函數(shù)里面的一個(gè) while(1) 死循環(huán)，這個(gè)死循環(huán)被作為 idle 進(jìn)程，也就是 0 號(hào)進(jìn)程。

所以，內(nèi)核的生命周期，就是一個(gè)完整的 start_kernel 函數(shù)。始于 start_kernel 函數(shù)的第一條語句，停留在最后的死循環(huán)。

init 進(jìn)程

kernel 會(huì)創(chuàng)建眾多內(nèi)核線程，來持續(xù)致力于內(nèi)存、磁盤、CPU 的管理，其中有兩個(gè)內(nèi)核線程比較重要，需要我們重點(diǎn)講解，那就是 1 號(hào)內(nèi)核線程 kernel_init 和 2 號(hào)內(nèi)核線程 kthreadd。1 號(hào)內(nèi)核線程最終會(huì)被用戶的第一個(gè)進(jìn)程 init 代替，也就成了 1 號(hào)進(jìn)程。如下：

????#?ps
????PID???USER?????COMMAND
????????1?root?????init
????????2?root?????[kthreadd]
????????3?root?????[rcu_gp]
????????4?root?????[rcu_par_gp]
????????7?root?????[kworker/u4:0-ev]
????????8?root?????[mm_percpu_wq]
????????9?root?????[ksoftirqd/0]
????...

COMMAND 這一列，帶中括號(hào)的是內(nèi)核線程，不帶中括號(hào)的是用戶進(jìn)程。從 PID 統(tǒng)一編址就可以看出，它倆地位是一樣的。
下面我們深入分析一下從 start_kernel 到最終運(yùn)行 init 進(jìn)程，kernel 都經(jīng)歷了什么

打印

添加打印，是分析流程的好方法。

????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();
????
????????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?and?entropy?after?arch
?????????*?and?after?adding?latent?and?command?line?entropy.
?????????*/
????????add_latent_entropy();
????????add_device_randomness(command_line,?strlen(command_line));
????????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?*/
????????boot_cpu_hotplug_init();
????
????????build_all_zonelists(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);
????????vfs_caches_init_early();
????????sort_main_extable();
????????trap_init();
????????mm_init();
????
????????ftrace_init();
????
????????/*?trace_printk?can?be?enabled?here?*/
????????early_trace_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();
????????radix_tree_init();
????
????????/*
?????????*?Set?up?housekeeping?before?setting?up?workqueues?to?allow?the?unbound
?????????*?workqueue?to?take?non-housekeeping?into?account.
?????????*/
????????housekeeping_init();
????
????????/*
?????????*?Allow?workqueue?creation?and?work?item?queueing/cancelling
?????????*?early.??Work?item?execution?depends?on?kthreads?and?starts?after
?????????*?workqueue_init().
?????????*/
????????workqueue_init_early();
????
????????rcu_init();
????
????????/*?Trace?events?are?available?after?this?*/
????????trace_init();
????
????????if?(initcall_debug)
?????????initcall_debug_enable();
????
????????context_tracking_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_safe_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();
????
????printk("##?start_kernel()?-->?console_init()\n");
????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();
????
????????/*
?????????*?This?needs?to?be?called?before?any?devices?perform?DMA
?????????*?operations?that?might?use?the?SWIOTLB?bounce?buffers.?It?will
?????????*?mark?the?bounce?buffers?as?decrypted?so?that?their?usage?will
?????????*?not?cause?"plain-text"?data?to?be?decrypted?when?accessed.
?????????*/
????????mem_encrypt_init();
????
????#ifdef?CONFIG_BLK_DEV_INITRD
????if?(initrd_start?&&?!initrd_below_start_ok?&&
????page_to_pfn(virt_to_page((void?_)initrd_start))?????pr_crit("initrd?overwritten?(0x%08lx?,
????page_to_pfn(virt_to_page((void?_)initrd_start)),
????min_low_pfn);
????initrd_start?=?0;
????}
????#endif
????page_ext_init();
????kmemleak_init();
????debug_objects_mem_init();
????setup_per_cpu_pageset();
????numa_policy_init();
????acpi_early_init();
????if?(late_time_init)
????late_time_init();
????calibrate_delay();
????pid_idr_init();
????anon_vma_init();
????#ifdef?CONFIG_X86
????if?(efi_enabled(EFI_RUNTIME_SERVICES))
????efi_enter_virtual_mode();
????#endif
????thread_stack_cache_init();
????cred_init();
????fork_init();
????proc_caches_init();
????uts_ns_init();
????buffer_init();
????key_init();
????security_init();
????dbg_late_init();
????vfs_caches_init();
????pagecache_init();
????signals_init();
????seq_file_init();
????proc_root_init();
????nsfs_init();
????cpuset_init();
????cgroup_init();
????taskstats_init_early();
????delayacct_init();
????
????????check_bugs();
????
????????acpi_subsystem_init();
????????arch_post_acpi_subsys_init();
????????sfi_init_late();
????
????????if?(efi_enabled(EFI_RUNTIME_SERVICES))?{
?????????efi_free_boot_services();
????????}
????
????printk("##?run?rest_init()\n");
????/_?Do?the?rest?non-\_\_init'ed,?we're?now?alive?_/
????rest_init();
????printk("##?after?rest_init()\n");
????}
????

一開始嘗試在函數(shù)剛開始就添加 printk 打印，結(jié)果發(fā)現(xiàn)添加完 printk 后內(nèi)核起不來，最后保守起見，在 131 行 console_init(); 后才開始添加打印。

????
????Starting?kernel?...
????
????[?0.000000]?Booting?Linux?on?physical?CPU?0x0
????[?0.000000]?Linux?version?4.18.12?(liyongjun@Box)?(gcc?version?9.3.0?(Buildroot?2021.05))?#14?SMP?Thu?Nov?25?00:37:30?CST?2021
????[?0.000000]?CPU:?ARMv7?Processor?[410fc074]?revision?4?(ARMv7),?cr=10c5387d
????[?0.000000]?CPU:?div?instructions?available:?patching?division?code
????[?0.000000]?CPU:?PIPT?/?VIPT?nonaliasing?data?cache,?VIPT?aliasing?instruction?cache
????[?0.000000]?OF:?fdt:?Machine?model:?LeMaker?Banana?Pi
????[?0.000000]?Memory?policy:?Data?cache?writealloc
????[?0.000000]?cma:?Reserved?16?MiB?at?0x7ec00000
????[?0.000000]?psci:?probing?for?conduit?method?from?DT.
????[?0.000000]?psci:?Using?PSCI?v0.1?Function?IDs?from?DT
????[?0.000000]?random:?get_random_bytes?called?from?start_kernel+0xa0/0x430?with?crng_init=0
????[?0.000000]?percpu:?Embedded?16?pages/cpu?@(ptrval)?s34444?r8192?d22900?u65536
????[?0.000000]?Built?1?zonelists,?mobility?grouping?on.?Total?pages:?260202
????[?0.000000]?Kernel?command?line:?console=ttyS0,57600?earlyprintk?root=/dev/mmcblk0p2?rootwait
????[?0.000000]?Dentry?cache?hash?table?entries:?131072?(order:?7,?524288?bytes)
????[?0.000000]?Inode-cache?hash?table?entries:?65536?(order:?6,?262144?bytes)
????[?0.000000]?Memory:?1011460K/1046952K?available?(6144K?kernel?code,?418K?rwdata,?1524K?rodata,?1024K?init,?240K?bss,?19108K?reserved,?16384K?cma-reserved,?244136K?highmem)
????[?0.000000]?Virtual?kernel?memory?layout:
????[?0.000000]?vector?:?0xffff0000?-?0xffff1000?(?4?kB)
????[?0.000000]?fixmap?:?0xffc00000?-?0xfff00000?(3072?kB)
????[?0.000000]?vmalloc?:?0xf0800000?-?0xff800000?(?240?MB)
????[?0.000000]?lowmem?:?0xc0000000?-?0xf0000000?(?768?MB)
????[?0.000000]?pkmap?:?0xbfe00000?-?0xc0000000?(?2?MB)
????[?0.000000]?modules?:?0xbf000000?-?0xbfe00000?(?14?MB)
????[?0.000000]?.text?:?0x(ptrval)?-?0x(ptrval)?(7136?kB)
????[?0.000000]?.init?:?0x(ptrval)?-?0x(ptrval)?(1024?kB)
????[?0.000000]?.data?:?0x(ptrval)?-?0x(ptrval)?(?419?kB)
????[?0.000000]?.bss?:?0x(ptrval)?-?0x(ptrval)?(?241?kB)
????[?0.000000]?SLUB:?HWalign=64,?Order=0-3,?MinObjects=0,?CPUs=2,?Nodes=1
????[?0.000000]?Hierarchical?RCU?implementation.
????[?0.000000]?RCU?restricting?CPUs?from?NR_CPUS=8?to?nr_cpu_ids=2.
????[?0.000000]?RCU:?Adjusting?geometry?for?rcu_fanout_leaf=16,?nr_cpu_ids=2
????[?0.000000]?NR_IRQS:?16,?nr_irqs:?16,?preallocated?irqs:?16
????[?0.000000]?GIC:?Using?split?EOI/Deactivate?mode
????[?0.000000]?arch_timer:?cp15?timer(s)?running?at?24.00MHz?(phys).
????[?0.000000]?clocksource:?arch_sys_counter:?mask:?0xffffffffffffff?max_cycles:?0x588fe9dc0,?max_idle_ns:?440795202592?ns
????[?0.000007]?sched_clock:?56?bits?at?24MHz,?resolution?41ns,?wraps?every?4398046511097ns
????[?0.000021]?Switching?to?timer-based?delay?loop,?resolution?41ns
????[?0.000334]?clocksource:?timer:?mask:?0xffffffff?max_cycles:?0xffffffff,?max_idle_ns:?79635851949?ns
????[?0.000586]?clocksource:?hstimer:?mask:?0xffffffff?max_cycles:?0xffffffff,?max_idle_ns:?6370868154?ns
????[?0.000822]?Console:?colour?dummy?device?80x30
????[?0.000844]?##?start_kernel()?-->?console_init()?//?132?行的打印
????
??

可是，發(fā)現(xiàn)在 console_init() 之前就有不少打印了，這個(gè)地方還是有些不解。猜測(cè)要么是在 console_init() 之前就已經(jīng)可以打印了；要么是在 console_init() 之前先將打印緩存著，等初始化之后再打印。這點(diǎn)以后再研究吧。先插個(gè)眼??。

接著看打印

????[????0.000844]?##?start_kernel()?-->?console_init()
????[????0.000872]?Calibrating?delay?loop?(skipped),?value?calculated?using?timer?frequency..?48.00?BogoMIPS?(lpj=240000)
????[????0.000886]?pid_max:?default:?32768?minimum:?301
????[????0.001054]?Mount-cache?hash?table?entries:?2048?(order:?1,?8192?bytes)
????[????0.001070]?Mountpoint-cache?hash?table?entries:?2048?(order:?1,?8192?bytes)
????[????0.001727]?CPU:?Testing?write?buffer?coherency:?ok
????[????0.001779]?##?run?rest_init()
????

從 133 行到 206 行，代碼不少，打印卻只有寥寥 5 行。少就說明不重要，那就不分析了，哈哈??。
看下面的代碼，乖乖，就剩一句了：rest_init();，并且第 210 行的 printk 等到系統(tǒng)完全起來都沒有打印，說明 rest_init() 就沒返回。看來是個(gè)扛把子。

????static?noinline?void?__ref?rest_init(void)
????{
?????struct?task_struct?*tsk;
?????int?pid;
????printk("##?rcu_scheduler_starting()\n");
?????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.
??????*/
?????pid?=?kernel_thread(kernel_init,?NULL,?CLONE_FS);
?????/*
??????*?Pin?init?on?the?boot?CPU.?Task?migration?is?not?properly?working
??????*?until?sched_init_smp()?has?been?run.?It?will?set?the?allowed
??????*?CPUs?for?init?to?the?non?isolated?CPUs.
??????*/
?????rcu_read_lock();
?????tsk?=?find_task_by_pid_ns(pid,?&init_pid_ns);
?????set_cpus_allowed_ptr(tsk,?cpumask_of(smp_processor_id()));
?????rcu_read_unlock();
????printk("##?bb\n");
?????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();
????printk("##?cc\n");
?????/*
??????*?Enable?might_sleep()?and?smp_processor_id()?checks.
??????*?They?cannot?be?enabled?earlier?because?with?CONFIG_PREEMPT=y
??????*?kernel_thread()?would?trigger?might_sleep()?splats.?With
??????*?CONFIG_PREEMPT_VOLUNTARY=y?the?init?task?might?have?scheduled
??????*?already,?but?it's?stuck?on?the?kthreadd_done?completion.
??????*/
?????system_state?=?SYSTEM_SCHEDULING;
????printk("##?dd\n");
?????complete(&kthreadd_done);
????
????????/*
?????????*?The?boot?idle?thread?must?execute?schedule()
?????????*?at?least?once?to?get?things?moving:
?????????*/
????
????printk("##?ee\n");
????schedule_preempt_disabled();
????printk("##?ff\n");
????/_?Call?into?cpu_idle?with?preempt?disabled?_/
????cpu_startup_entry(CPUHP_ONLINE);
????//?printk("##?ff\n");
????}
????
????

對(duì)應(yīng)打印如下：

???[????0.001779]?##?run?rest_init()
????[????0.001786]?##?rcu_scheduler_starting()
????[????0.002030]?##?bb
????[????0.002089]?##?cc
????[????0.002097]?##?dd
????[????0.002104]?##?ee
????[????0.002150]?##?kernel_init()
????[????0.002199]?/cpus/cpu@0?missing?clock-frequency?property
????[????0.002214]?/cpus/cpu@1?missing?clock-frequency?property
????[????0.002228]?CPU0:?thread?-1,?cpu?0,?socket?0,?mpidr?80000000
????[????0.002799]?Setting?up?static?identity?map?for?0x40100000?-?0x40100060
????[????0.002972]?Hierarchical?SRCU?implementation.
????[????0.003776]?smp:?Bringing?up?secondary?CPUs?...
????[????0.014335]?##?ff
????

打印了 kernel_init()，是因?yàn)檎{(diào)用了 schedule_preempt_disabled()，其內(nèi)部調(diào)用了 schedule() 執(zhí)行進(jìn)程切換，進(jìn)入睡眠。當(dāng)然，在當(dāng)前進(jìn)程被喚醒時(shí)，程序也是從這個(gè)斷點(diǎn)開始運(yùn)行。

???void?__sched?schedule_preempt_disabled(void)
????{
?????sched_preempt_enable_no_resched();
?????schedule();
?????preempt_disable();
????}
????

執(zhí)行進(jìn)程切換后，kernel_init() 才有機(jī)會(huì)運(yùn)行

???static?int?__ref?kernel_init(void?*unused)
????{
?????int?ret;
????printk("##?kernel_init()\n");
?????kernel_init_freeable();
?????/*?need?to?finish?all?async?__init?code?before?freeing?the?memory?*/
?????async_synchronize_full();
????
????????ftrace_free_init_mem();
????
????????jump_label_invalidate_initmem();
????????free_initmem();
????
????printk("##?2.\n");
????mark_readonly();
????printk("##?3.\n");
????system_state?=?SYSTEM_RUNNING;
????numa_default_policy();
????
????????rcu_end_inkernel_boot();
????
????printk("##?4.\n");
????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"))?{
????
????printk("##?kernel_init()?-->?/sbin/init\n");
????return?0;
????}
????
????????panic("No?working?init?found.??Try?passing?init=?option?to?kernel.?"
??????????????"See?Linux?Documentation/admin-guide/init.rst?for?guidance.");
????
????}
????
????

對(duì)應(yīng)打印如下：

????[????0.002150]?##?kernel_init()
????[????0.002199]?/cpus/cpu@0?missing?clock-frequency?property
????[????0.002214]?/cpus/cpu@1?missing?clock-frequency?property
????[????0.002228]?CPU0:?thread?-1,?cpu?0,?socket?0,?mpidr?80000000
????[????0.002799]?Setting?up?static?identity?map?for?0x40100000?-?0x40100060
????[????0.002972]?Hierarchical?SRCU?implementation.
????[????0.003776]?smp:?Bringing?up?secondary?CPUs?...
????[????0.014335]?##?ff
????[????0.014540]?CPU1:?thread?-1,?cpu?1,?socket?0,?mpidr?80000001
????[????0.014681]?smp:?Brought?up?1?node,?2?CPUs
????[????0.014697]?SMP:?Total?of?2?processors?activated?(96.00?BogoMIPS).
????[????0.014704]?CPU:?All?CPU(s)?started?in?HYP?mode.
????[????0.014709]?CPU:?Virtualization?extensions?available.
????[????0.015730]?devtmpfs:?initialized
????[????0.015786]?##?11.
????[????0.015802]?##?22.
????[????0.015811]?##?33.
????[????0.015820]?##?44.
????[????0.015825]?##?55.
????[????0.015918]?##?66.
????[????0.015999]?##?77.
????[????0.016006]?##?88.
????[????0.016058]?##?99.
????[????0.021654]?##?AA.
????[????0.021836]?###?AAA.
????[????0.022450]?VFP?support?v0.3:?implementor?41?architecture?2?part?30?variant?7?rev?4
????[????0.022721]?clocksource:?jiffies:?mask:?0xffffffff?max_cycles:?0xffffffff,?max_idle_ns:?19112604462750000?ns
????[????0.022747]?futex?hash?table?entries:?512?(order:?3,?32768?bytes)
????[????0.023540]?pinctrl?core:?initialized?pinctrl?subsystem
????[????0.024726]?NET:?Registered?protocol?family?16
????[????0.026025]?DMA:?preallocated?256?KiB?pool?for?atomic?coherent?allocations
????[????0.027158]?hw-breakpoint:?found?5?(+1?reserved)?breakpoint?and?4?watchpoint?registers.
????[????0.027173]?hw-breakpoint:?maximum?watchpoint?size?is?8?bytes.
????[????0.042711]?reg-fixed-voltage?gmac-3v3:?could?not?find?pctldev?for?node?/soc@1c00000/pinctrl@1c20800/gmac_power_pin@0,?deferring?probe
????[????0.043233]?SCSI?subsystem?initialized
????[????0.043811]?usbcore:?registered?new?interface?driver?usbfs
????[????0.043864]?usbcore:?registered?new?interface?driver?hub
????[????0.043933]?usbcore:?registered?new?device?driver?usb
????[????0.044199]?pps_core:?LinuxPPS?API?ver.?1?registered
????[????0.044209]?pps_core:?Software?ver.?5.3.6?-?Copyright?2005-2007?Rodolfo?Giometti?
????[????0.044230]?PTP?clock?support?registered
????[????0.044563]?Advanced?Linux?Sound?Architecture?Driver?Initialized.
????[????0.045501]?clocksource:?Switched?to?clocksource?arch_sys_counter
????[????0.046238]?simple-framebuffer?7fe79000.framebuffer:?framebuffer?at?0x7fe79000,?0x178e00?bytes,?mapped?to?0x(ptrval)
????[????0.046258]?simple-framebuffer?7fe79000.framebuffer:?format=x8r8g8b8,?mode=656x536x32,?linelength=2880
????[????0.052472]?Console:?switching?to?colour?frame?buffer?device?82x33
????[????0.058369]?simple-framebuffer?7fe79000.framebuffer:?fb0:?simplefb?registered!
????[????0.066686]?NET:?Registered?protocol?family?2
????[????0.067281]?tcp_listen_portaddr_hash?hash?table?entries:?512?(order:?0,?6144?bytes)
????[????0.067316]?TCP?established?hash?table?entries:?8192?(order:?3,?32768?bytes)
????[????0.067395]?TCP?bind?hash?table?entries:?8192?(order:?4,?65536?bytes)
????[????0.067522]?TCP:?Hash?tables?configured?(established?8192?bind?8192)
????[????0.067655]?UDP?hash?table?entries:?512?(order:?2,?16384?bytes)
????[????0.067722]?UDP-Lite?hash?table?entries:?512?(order:?2,?16384?bytes)
????[????0.067964]?NET:?Registered?protocol?family?1
????[????0.068567]?RPC:?Registered?named?UNIX?socket?transport?module.
????[????0.068583]?RPC:?Registered?udp?transport?module.
????[????0.068590]?RPC:?Registered?tcp?transport?module.
????[????0.068596]?RPC:?Registered?tcp?NFSv4.1?backchannel?transport?module.
????[????0.069204]?hw?perfevents:?no?interrupt-affinity?property?for?/pmu,?guessing.
????[????0.069499]?hw?perfevents:?enabled?with?armv7_cortex_a7?PMU?driver,?5?counters?available
????[????0.071072]?workingset:?timestamp_bits=30?max_order=18?bucket_order=0
????[????0.077754]?NFS:?Registering?the?id_resolver?key?type
????[????0.077803]?Key?type?id_resolver?registered
????[????0.077812]?Key?type?id_legacy?registered
????[????0.079006]?bounce:?pool?size:?64?pages
????[????0.079106]?Block?layer?SCSI?generic?(bsg)?driver?version?0.4?loaded?(major?248)
????[????0.079119]?io?scheduler?noop?registered
????[????0.079127]?io?scheduler?deadline?registered
????[????0.079295]?io?scheduler?cfq?registered?(default)
????[????0.079307]?io?scheduler?mq-deadline?registered
????[????0.079315]?io?scheduler?kyber?registered
????[????0.080074]?sun4i-usb-phy?1c13400.phy:?could?not?find?pctldev?for?node?/soc@1c00000/pinctrl@1c20800/usb0_id_detect_pin@0,?deferring?probe
????[????0.083501]?sun4i-pinctrl?1c20800.pinctrl:?initialized?sunXi?PIO?driver
????[????0.140590]?Serial:?8250/16550?driver,?8?ports,?IRQ?sharing?disabled
????[????0.143240]?console?[ttyS0]?disabled
????[????0.163431]?1c28000.serial:?ttyS0?at?MMIO?0x1c28000?(irq?=?48,?base_baud?=?1500000)?is?a?U6_16550A
????[????1.630962]?console?[ttyS0]?enabled
????[????1.661099]?1c28c00.serial:?ttyS1?at?MMIO?0x1c28c00?(irq?=?49,?base_baud?=?1500000)?is?a?U6_16550A
????[????1.702024]?1c29c00.serial:?ttyS2?at?MMIO?0x1c29c00?(irq?=?50,?base_baud?=?1500000)?is?a?U6_16550A
????[????1.723737]?sun4i-backend?1e60000.display-backend:?Couldn't?find?matching?frontend,?frontend?features?disabled
????[????1.744080]?sun4i-drm?display-engine:?bound?1e60000.display-backend?(ops?0xc07482cc)
????[????1.759592]?sun4i-backend?1e40000.display-backend:?Couldn't?find?matching?frontend,?frontend?features?disabled
????[????1.779827]?sun4i-drm?display-engine:?bound?1e40000.display-backend?(ops?0xc07482cc)
????[????1.795785]?sun4i-drm?display-engine:?No?panel?or?bridge?found...?RGB?output?disabled
????[????1.811456]?sun4i-drm?display-engine:?bound?1c0c000.lcd-controller?(ops?0xc074724c)
????[????1.827130]?sun4i-drm?display-engine:?No?panel?or?bridge?found...?RGB?output?disabled
????[????1.842825]?sun4i-drm?display-engine:?bound?1c0d000.lcd-controller?(ops?0xc074724c)
????[????1.858540]?sun4i-drm?display-engine:?bound?1c16000.hdmi?(ops?0xc0748cd0)
????[????1.872123]?[drm]?Supports?vblank?timestamp?caching?Rev?2?(21.10.2013).
????[????1.885344]?[drm]?No?driver?support?for?vblank?timestamp?query.
????[????1.897182]?fb:?switching?to?sun4i-drm-fb?from?simple
????[????1.907391]?Console:?switching?to?colour?dummy?device?80x30
????[????2.418984]?[drm]?Cannot?find?any?crtc?or?sizes
????[????2.428711]?[drm]?Initialized?sun4i-drm?1.0.0?20150629?for?display-engine?on?minor?0
????[????2.545528]?ahci-sunxi?1c18000.sata:?controller?can't?do?PMP,?turning?off?CAP_PMP
????[????2.560532]?ahci-sunxi?1c18000.sata:?SSS?flag?set,?parallel?bus?scan?disabled
????[????2.574817]?ahci-sunxi?1c18000.sata:?AHCI?0001.0100?32?slots?1?ports?3?Gbps?0x1?impl?platform?mode
????[????2.592721]?ahci-sunxi?1c18000.sata:?flags:?ncq?sntf?stag?pm?led?clo?only?pio?slum?part?ccc
????[????2.610642]?scsi?host0:?ahci-sunxi
????[????2.617874]?ata1:?SATA?max?UDMA/133?mmio?[mem?0x01c18000-0x01c18fff]?port?0x100?irq?36
????[????2.635546]?libphy:?Fixed?MDIO?Bus:?probed
????[????2.643735]?CAN?device?driver?interface
????[????2.652152]?sun7i-dwmac?1c50000.ethernet:?PTP?uses?main?clock
????[????2.663680]?sun7i-dwmac?1c50000.ethernet:?no?reset?control?found
????[????2.676345]?ehci_hcd:?USB?2.0?'Enhanced'?Host?Controller?(EHCI)?Driver
????[????2.689416]?ehci-platform:?EHCI?generic?platform?driver
????[????2.700248]?ohci_hcd:?USB?1.1?'Open'?Host?Controller?(OHCI)?Driver
????[????2.712647]?ohci-platform:?OHCI?generic?platform?driver
????[????2.725114]?sunxi-rtc?1c20d00.rtc:?registered?as?rtc0
????[????2.735252]?sunxi-rtc?1c20d00.rtc:?RTC?enabled
????[????2.744274]?i2c?/dev?entries?driver
????[????2.752374]?axp20x-i2c?1-0034:?AXP20x?variant?AXP209?found
????[????2.778365]?input:?axp20x-pek?as?/devices/platform/soc@1c00000/1c2ac00.i2c/i2c-1/1-0034/axp20x-pek/input/input0
????[????2.799556]?ldo1:?supplied?by?regulator-dummy
????[????2.808582]?ldo2:?supplied?by?regulator-dummy
????[????2.818392]?ldo3:?supplied?by?regulator-dummy
????[????2.827795]?ldo4:?supplied?by?regulator-dummy
????[????2.836730]?ldo5:?supplied?by?regulator-dummy
????[????2.846544]?dcdc2:?supplied?by?regulator-dummy
????[????2.856093]?dcdc3:?supplied?by?regulator-dummy
????[????2.866705]?axp20x-i2c?1-0034:?AXP20X?driver?loaded
????[????2.877918]?Registered?IR?keymap?rc-empty
????[????2.886099]?rc?rc0:?sunxi-ir?as?/devices/platform/soc@1c00000/1c21800.ir/rc/rc0
????[????2.900854]?input:?sunxi-ir?as?/devices/platform/soc@1c00000/1c21800.ir/rc/rc0/input1
????[????2.916966]?sunxi-ir?1c21800.ir:?initialized?sunXi?IR?driver
????[????2.930370]?sunxi-wdt?1c20c90.watchdog:?Watchdog?enabled?(timeout=16?sec,?nowayout=0)
????[????2.949908]?sunxi-mmc?1c0f000.mmc:?Got?CD?GPIO
????[????2.957174]?ata1:?SATA?link?down?(SStatus?0?SControl?300)
????[????2.984443]?sunxi-mmc?1c0f000.mmc:?base:0x(ptrval)?irq:30
????[????2.996403]?sun4i-ss?1c15000.crypto-engine:?Die?ID?0
????[????3.008208]?usbcore:?registered?new?interface?driver?usbhid
????[????3.019411]?usbhid:?USB?HID?core?driver
????[????3.028477]?random:?fast?init?done
????[????3.038082]?sun4i-codec?1c22c00.codec:?ASoC:?Failed?to?create?component?debugfs?directory
????[????3.055988]?sun4i-codec?1c22c00.codec:?Codec?<->?1c22c00.codec?mapping?ok
????[????3.070975]?NET:?Registered?protocol?family?17
????[????3.079931]?can:?controller?area?network?core?(rev?20170425?abi?9)
????[????3.092458]?NET:?Registered?protocol?family?29
????[????3.101361]?can:?raw?protocol?(rev?20170425)
????[????3.109908]?can:?broadcast?manager?protocol?(rev?20170425?t)
????[????3.121240]?can:?netlink?gateway?(rev?20170425)?max_hops=1
????[????3.132444]?Key?type?dns_resolver?registered
????[????3.141113]?Registering?SWP/SWPB?emulation?handler
????[????3.155150]?mmc0:?host?does?not?support?reading?read-only?switch,?assuming?write-enable
????[????3.162888]?sun7i-dwmac?1c50000.ethernet:?PTP?uses?main?clock
????[????3.182777]?sun7i-dwmac?1c50000.ethernet:?no?reset?control?found
????[????3.194864]?mmc0:?new?high?speed?SDHC?card?at?address?59b4
????[????3.206939]?mmcblk0:?mmc0:59b4?USD00?7.32?GiB
????[????3.217882]??mmcblk0:?p1?p2
????[????3.305735]?sun7i-dwmac?1c50000.ethernet:?Version?ID?not?available
????[????3.318137]?sun7i-dwmac?1c50000.ethernet:????DWMAC1000
????[????3.328068]?sun7i-dwmac?1c50000.ethernet:?DMA?HW?capability?register?supported
????[????3.342498]?sun7i-dwmac?1c50000.ethernet:?Normal?descriptors
????[????3.353804]?sun7i-dwmac?1c50000.ethernet:?Ring?mode?enabled
????[????3.372879]?libphy:?stmmac:?probed
????[????3.379711]?mdio_bus?stmmac-0:00:?attached?PHY?driver?[unbound]?(mii_bus:phy_addr=stmmac-0:00,?irq=POLL)
????[????3.398646]?mdio_bus?stmmac-0:01:?attached?PHY?driver?[unbound]?(mii_bus:phy_addr=stmmac-0:01,?irq=POLL)
????[????3.437826]?ehci-platform?1c14000.usb:?EHCI?Host?Controller
????[????3.449048]?ehci-platform?1c14000.usb:?new?USB?bus?registered,?assigned?bus?number?1
????[????4.445622]?[drm]?Cannot?find?any?crtc?or?sizes
????[????4.454972]?ehci-platform?1c14000.usb:?irq?32,?io?mem?0x01c14000
????[????4.495500]?ehci-platform?1c14000.usb:?USB?2.0?started,?EHCI?1.00
????[????4.508602]?hub?1-0:1.0:?USB?hub?found
????[????4.516156]?hub?1-0:1.0:?1?port?detected
????[????4.524842]?ehci-platform?1c1c000.usb:?EHCI?Host?Controller
????[????4.536034]?ehci-platform?1c1c000.usb:?new?USB?bus?registered,?assigned?bus?number?2
????[????4.551813]?ehci-platform?1c1c000.usb:?irq?37,?io?mem?0x01c1c000
????[????4.585504]?ehci-platform?1c1c000.usb:?USB?2.0?started,?EHCI?1.00
????[????4.598505]?hub?2-0:1.0:?USB?hub?found
????[????4.606055]?hub?2-0:1.0:?1?port?detected
????[????4.614695]?ohci-platform?1c14400.usb:?Generic?Platform?OHCI?controller
????[????4.627974]?ohci-platform?1c14400.usb:?new?USB?bus?registered,?assigned?bus?number?3
????[????4.643687]?ohci-platform?1c14400.usb:?irq?33,?io?mem?0x01c14400
????[????4.730281]?hub?3-0:1.0:?USB?hub?found
????[????4.737832]?hub?3-0:1.0:?1?port?detected
????[????4.746524]?ohci-platform?1c1c400.usb:?Generic?Platform?OHCI?controller
????[????4.759793]?ohci-platform?1c1c400.usb:?new?USB?bus?registered,?assigned?bus?number?4
????[????4.775542]?ohci-platform?1c1c400.usb:?irq?38,?io?mem?0x01c1c400
????[????4.860311]?hub?4-0:1.0:?USB?hub?found
????[????4.867876]?hub?4-0:1.0:?1?port?detected
????[????4.876658]?usb_phy_generic?usb_phy_generic.0.auto:?usb_phy_generic.0.auto?supply?vcc?not?found,?using?dummy?regulator
????[????4.898584]?musb-hdrc?musb-hdrc.1.auto:?MUSB?HDRC?host?driver
????[????4.910112]?musb-hdrc?musb-hdrc.1.auto:?new?USB?bus?registered,?assigned?bus?number?5
????[????4.926629]?hub?5-0:1.0:?USB?hub?found
????[????4.934193]?hub?5-0:1.0:?1?port?detected
????[????4.942801]?sunxi-rtc?1c20d00.rtc:?setting?system?clock?to?1970-01-01?00:00:11?UTC?(11)
????[????4.959189]?vcc3v0:?disabling
????[????4.965121]?vcc5v0:?disabling
????[????4.971086]?usb0-vbus:?disabling
????[????4.977556]?ALSA?device?list:
????[????4.983479]???#0:?sun4i-codec
????[????4.989417]?###?BBB.
????[????4.997149]?EXT4-fs?(mmcblk0p2):?INFO:?recovery?required?on?readonly?filesystem
????[????5.011809]?EXT4-fs?(mmcblk0p2):?write?access?will?be?enabled?during?recovery
????[????5.029755]?EXT4-fs?(mmcblk0p2):?recovery?complete
????[????5.090424]?EXT4-fs?(mmcblk0p2):?mounted?filesystem?with?ordered?data?mode.?Opts:?(null)
????[????5.106669]?VFS:?Mounted?root?(ext4?filesystem)?readonly?on?device?179:2.
????[????5.121202]?devtmpfs:?mounted
????[????5.127186]?##?111.
????[????5.132783]?Freeing?unused?kernel?memory:?1024K
????[????5.141851]?##?2.
????
????

可以看到從第 5 行到第 12 行區(qū)區(qū)幾個(gè)函數(shù)，竟然打印了那么多，而且還看到了眾多驅(qū)動(dòng)相關(guān)的打印，如 usb、Console、Key、io、pinctrl、Serial、CAN、RTC、input、mmc、mdio_bus，說明我們整天開發(fā)的驅(qū)動(dòng)，是在這個(gè)階段初始化的呀。這里我直接給出調(diào)用關(guān)系，可以看到，驅(qū)動(dòng)相關(guān)的打印是在 do_initcalls() 中產(chǎn)生的

kernel_init()
kernel_init_freeable()
do_basic_setup()
printk("###?AAA.\n");
do_initcalls();
printk("###?BBB.\n");????

static?void?__init?do_initcalls(void)
{
??int?level;

??for?(level?=?0;?level?????do_initcall_level(level);
}
????

驅(qū)動(dòng)初始化完，內(nèi)核也就接近尾聲了

????[????4.989417]?###?BBB.
????[????4.997149]?EXT4-fs?(mmcblk0p2):?INFO:?recovery?required?on?readonly?filesystem
????[????5.011809]?EXT4-fs?(mmcblk0p2):?write?access?will?be?enabled?during?recovery
????[????5.029755]?EXT4-fs?(mmcblk0p2):?recovery?complete
????[????5.090424]?EXT4-fs?(mmcblk0p2):?mounted?filesystem?with?ordered?data?mode.?Opts:?(null)
????[????5.106669]?VFS:?Mounted?root?(ext4?filesystem)?readonly?on?device?179:2.
????[????5.121202]?devtmpfs:?mounted
????[????5.127186]?##?111.
????[????5.132783]?Freeing?unused?kernel?memory:?1024K
????[????5.141851]?##?2.
????[????5.145862]?##?3.
????[????5.149703]?##?4.
????[????5.162188]?##?kernel_init()?-->?/sbin/init
????##?init_main()
????[????5.232554]?EXT4-fs?(mmcblk0p2):?re-mounted.?Opts:?(null)
????Starting?syslogd:?OK
????Starting?klogd:?OK
????Running?sysctl:?OK
????Initializing?random?number?generator:?OK
????Saving?random?seed:?[????5.377468]?random:?dd:?uninitialized?urandom?read?(512?bytes?read)
????OK
????Starting?network:?OK
????
????Welcome?to?Bananapi?M1
????buildroot?login:
????
????

• 掛載根文件系統(tǒng)
• 內(nèi)核收尾工作
• kernel_init 內(nèi)核線程調(diào)用 do_execve 函數(shù)，去執(zhí)行 init 程序，產(chǎn)生 init 進(jìn)程（1 號(hào)進(jìn)程）。該內(nèi)核線程終結(jié)。

rest_init() 函數(shù)的最后一句 cpu_startup_entry(CPUHP_ONLINE); 最終變成了 idle 進(jìn)程（0 號(hào)進(jìn)程）。

???void?cpu_startup_entry(enum?cpuhp_state?state)
????{
?????/*
??????*?This?#ifdef?needs?to?die,?but?it's?too?late?in?the?cycle?to
??????*?make?this?generic?(ARM?and?SH?have?never?invoked?the?canary
??????*?init?for?the?non?boot?CPUs!).?Will?be?fixed?in?3.11
??????*/
????#ifdef?CONFIG_X86
?????/*
??????*?If?we're?the?non-boot?CPU,?nothing?set?the?stack?canary?up
??????*?for?us.?The?boot?CPU?already?has?it?initialized?but?no?harm
??????*?in?doing?it?again.?This?is?a?good?place?for?updating?it,?as
??????*?we?wont?ever?return?from?this?function?(so?the?invalid
??????*?canaries?already?on?the?stack?wont?ever?trigger).
??????*/
?????boot_init_stack_canary();
????#endif
?????arch_cpu_idle_prepare();
?????cpuhp_online_idle(state);
?????while?(1)
??????do_idle();
????}
????

而在 kernel_init 同期稍晚創(chuàng)建的 kthreadd 內(nèi)核線程，則一直存在，成為 2 號(hào)進(jìn)程

    # ps    PID   USER     COMMAND        1 root     init        2 root     [kthreadd]        3 root     [rcu_gp]        4 root     [rcu_par_gp]        7 root     [kworker/u4:0-ev]        8 root     [mm_percpu_wq]        9 root     [ksoftirqd/0]    ...