Armlinux内核移植及系统初始化过程分析

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1、Arm linux 内核移植及系统初始化过程分析Edwin. Rong edwinrongmxic 本文主要介绍内核移植过程中涉及文件的分布及其用途，以及简单介绍系统的初始化过程。整个arm linux内核的启动可分为三个阶段：第一阶段主要是进行cpu和体系结构的检查、cpu本身的初始化以及页表的建立等；第二阶段主要是对系统中的一些根底设施进行初始化；最后那么是更高层次的初始化，如根设备和外部设备的初始化。了解系统的初始化过程，有益于更好地移植内核。1. 内核移植涉及文件分布介绍1.1. 内核移植涉及的头文件/linux-2.6.18.8/includerootlocalhost includ

2、e# tree -L 1.|- Kbuild|- acpi|- asm - asm-arm|- asm-alpha|- asm-arm -(1)|- asm-sparc|- asm-sparc64|- config|- keys|- linux-(2)|- math-emu|- media|- mtd|- net|- pcmcia|- rdma|- rxrpc|- scsi|- sound- video内核移植过程中涉及到的头文件包括处理器相关的头文件(1)和处理器无关的头文件(2)。1.2. 内核移植涉及的源文件/linux-2.6.18.8/arch/armrootlocalhost ar

3、m# tree -L 1.|- Kconfig|- Kconfig-nommu|- Kconfig.debug|- Makefile|- boot -(2)|- common|- configs|- kernel -(3)|- lib|- mach-at91rm9200|- mach-omap1|- mach-omap2|- mach-realview|- mach-rpc|- mach-s3c2410 -(4)|- mach-sa1100|- mach-versatile|- mm -(5)|- nwfpe|- oprofile|- plat-omap|- tools -(1)- vfp(1

4、)/linux-2.6.18.8/arch/arm/toolsrootlocalhost tools# tree -L 1.|- Makefile|- gen-mach-types- mach-typesMach-types 文件定义了不同系统平台的系统平台号。移植linux内核到新的平台上需要对新的平台登记系统平台号。Mach-types文件格式如下：# machine_is_xxxCONFIG_xxxxMACH_TYPE_xxxnumbers3c2410ARCH_S3C2410S3C2410 182smdk2410ARCH_SMDK2410SMDK2410 193之所以需要这些信息，是因为

5、脚本文件linux/arch/arm/tools/gen-mach-types需要linux/arch/tools/mach-types来产生linux/include/asm-arm/mach-types.h文件，该文件中设置了一些宏定义，需要这些宏定义来为目标系统选择适宜的代码。(2)linux-2.6.18.8/arch/arm/boot/compressedrootlocalhost compressed# tree -L 1.|- Makefile|- Makefile.debug|- big-endian.S|- head-at91rm9200.S|- head.S|- ll_ch

6、ar_wr.S|- misc.c|- ofw-shark.c|- piggy.S- vmlinux.lds.inHead.s 是内核映像的入口代码，是自引导程序。自引导程序包含一些初始化程序，这些程序都是体系结构相关的。在对系统作完初始化设置工作后，调用misc.c文件中的decompress_kernel()函数解压缩内核映像到指定的位置，然后跳转到kernel的入口地址。Vmlinux.lds.in用来生成内核映像的内存配置文件。(3)linux-2.6.18.8/arch/arm/kernelrootlocalhost kernel# tree -L 1.|- Makefile|- ap

7、m.c|- armksyms.c|- arthur.c|- asm-offsets.c|- bios32.c|- calls.S|- dma.c|- ecard.c|- entry-armv.S|- entry-common.S|- entry-header.S|- fiq.c|- head-common.S|- head-nommu.S|- head.S|- init_task.c|- io.c|- irq.c|- isa.c|- module.c|- process.c|- ptrace.c|- ptrace.h|- semaphore.c|- setup.c|- smp.c|- sys_

8、arm.c|- time.c|- traps.c- vmlinux.lds.S内核入口处也是由一段汇编语言实现的，由head.s和head-common.s两个文件组成。Head.s 是内核的入口文件， 在head.s的末尾处 #include head-common.S。 经过一系列的初始化后，跳转到linux-2.6.18.8/init/main.c中的start_kernel()函数中，开始内核的根本初始化过程。/linux-2.6.18.8/initrootlocalhost init# tree.|- Kconfig|- Makefile|- calibrate.c|- do_mou

9、nts.c|- do_mounts.h|- do_mounts_initrd.c|- do_mounts_md.c|- do_mounts_rd.c|- initramfs.c|- main.c- version.c(4)/linux-2.6.18.8/arch/arm/mach-s3c2410rootlocalhost mach-s3c2410# tree -L 1.|- Kconfig|- Makefile|- Makefile.boot|- bast-irq.c|- bast.h|- clock.c|- clock.h|- common-smdk.c|- common-smdk.h|-

10、cpu.c|- cpu.h|- devs.c|- devs.h|- dma.c|- gpio.c|- irq.c|- irq.h|- mach-anubis.c|- mach-smdk2410.c|- pm-simtec.c|- pm.c|- pm.h|- s3c2400-gpio.c|- s3c2400.h|- s3c2410-clock.c|- s3c2410-gpio.c|- s3c2410.c|- s3c2410.h|- sleep.S|- time.c|- usb-simtec.c- usb-simtec.h这个目录中的文件都是板级相关的，其中比拟重要是如下几个：linux/arch

11、/arm/mach-s3c2410/cpu.c linux/arch/arm/mach-s3c2410/common-smdk.clinux/arch/arm/mach-s3c2410/devs.clinux/arch/arm/mach-s3c2410/mach-smdk2410.clinux/arch/arm/mach-s3c2410/Makefile.bootlinux/arch/arm/mach-s3c2410/s3c2410.c2. 处理器和设备这里主要介绍处理器和设备的描述和操作过程。设备描述在linux/arch/arm/mach-s3c2410/devs.c和linux/arch

12、/arm/mach-s3c2410/common-smdk.c中实现。最后以nand flash为例具体介绍。2.1. 处理器、设备描述设备描述主要两个结构体完成：struct resource和struct platform_device。先来看看着两个结构体的定义：struct resource resource_size_t start;resource_size_t end;const char *name;unsigned long flags;struct resource *parent, *sibling, *child;Resource结构体主要是描述了设备在系统中的起止地址

13、、名称、标志以及为了链式描述方便指向本结构体类型的指针。Resource定义的实例将被添加到platform_device结构体对象中去。struct platform_device const char* name;u32id;struct devicedev;u32num_resources;struct resource* resource;Platform_device结构体包括结构体的名称、ID号、平台相关的信息、设备的数目以及上面定义的resource信息。Platform_device结构对象将被直接通过设备操作函数注册导系统中去。具体注册和注销过程在下一节介绍。2.2. 处理器

14、、设备操作(1) int platform_device_register(struct platform_device * pdev)； 注册设备(2) void platform_device_unregister(struct platform_device * pdev)； 注销设备(3) int platform_add_devices(struct platform_device *devs, int num)；添加设备，通过调用上面两个函数实现。2.3. 添加Nand flash设备下面以nand flash 设备的描述为例，具体介绍下设备的描述和注册过程。/ resource结

15、构体实例s3c_nand_resource 对nand flash 控制器描述，包括控制器的起止地址和标志。static struct resource s3c_nand_resource = 0 = .start = S3C2410_PA_NAND,.end = S3C2410_PA_NAND + S3C24XX_SZ_NAND - 1,.flags = IORESOURCE_MEM,;/platform_device结构体实例s3c_device_nand定义了设备的名称、ID号并把resource对象作为其成员之一。struct platform_device s3c_device_na

16、nd = .name = s3c2410-nand,.id = -1,.num_resources = ARRAY_SIZE(s3c_nand_resource),.resource = s3c_nand_resource,;/ nand flash 的分区情况，由mtd_partition结构体定义。static struct mtd_partition smdk_default_nand_part = 0 = .name= Boot Agent,.size= SZ_16K,.offset= 0,1 = .name= S3C2410 flash partition 1,.offset = 0

17、,.size= SZ_2M,2 = .name= S3C2410 flash partition 2,.offset = SZ_4M,.size= SZ_4M,3 = .name= S3C2410 flash partition 3,.offset= SZ_8M,.size= SZ_2M,4 = .name= S3C2410 flash partition 4,.offset = SZ_1M * 10,.size= SZ_4M,5 = .name= S3C2410 flash partition 5,.offset= SZ_1M * 14,.size= SZ_1M * 10,6 = .name

18、= S3C2410 flash partition 6,.offset= SZ_1M * 24,.size= SZ_1M * 24,7 = .name= S3C2410 flash partition 7,.offset = SZ_1M * 48,.size= SZ_16M,;static struct s3c2410_nand_set smdk_nand_sets = 0 = .name= NAND,.nr_chips= 1,.nr_partitions= ARRAY_SIZE(smdk_default_nand_part),.partitions= smdk_default_nand_pa

19、rt,;/* choose a set of timings which should suit most 512Mbit * chips and beyond.*/static struct s3c2410_platform_nand smdk_nand_info = .tacls= 20,.twrph0= 60,.twrph1= 20,.nr_sets= ARRAY_SIZE(smdk_nand_sets),.sets= smdk_nand_sets,;/* devices we initialise */ 最后将nand flash 设备参加到系统即将注册的设备集合中。 static s

20、truct platform_device _initdata *smdk_devs = &s3c_device_nand,&smdk_led4,&smdk_led5,&smdk_led6,&smdk_led7,;然后通过smdk_machine_init()函数，调用设备添加函数platform_add_devices(smdk_devs, ARRAY_SIZE(smdk_devs) 完成设备的注册。具体过程参见系统初始化的相关局部。3. 系统初始化3.1. 系统初始化的主干线Start_kernel() setup_arch() reset_init() kernel_thread(ini

21、t ) init() do_basic_setup() driver_init() do_initcall()Start_kernel()函数负责初始化内核各个子系统，最后调用reset_init()，启动一个叫做init的内核线程，继续初始化。Start_kernel()函数在init/main.c中实现。asmlinkage void _init start_kernel(void)char * command_line;extern struct kernel_param _start_param, _stop_param;smp_setup_processor_id();/* * Ne

22、ed to run as early as possible, to initialize the * lockdep hash: */lockdep_init();local_irq_disable();early_boot_irqs_off();early_init_irq_lock_class();/* * Interrupts are still disabled. Do necessary setups, then * enable them */lock_kernel();boot_cpu_init();page_address_init();printk(KERN_NOTICE)

23、;printk(linux_banner);setup_arch(&command_line); /setup processor and machine and destinate some pointers for do_initcalls() functions / for example init_machine pointer is initialized with smdk_machine_init() function , and /init_machine() function is called by customize_machine(), and the function

24、 is processed by /arch_initcall(fn). Therefore smdk_machine_init() is issured. by edwinsetup_per_cpu_areas();smp_prepare_boot_cpu();/* arch-specific boot-cpu hooks */* * Set up the scheduler prior starting any interrupts (such as the * timer interrupt). Full topology setup happens at smp_init() * ti

25、me - 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();build_all_zonelists();page_alloc_init();printk(KERN_NOTICE Kernel command line: %sn, saved_com

26、mand_line);parse_early_param();parse_args(Booting kernel, command_line, _start_param, _stop_param - _start_param, &unknown_bootoption);sort_main_extable();unwind_init();trap_init();rcu_init();init_IRQ();pidhash_init();init_timers();hrtimers_init();softirq_init();timekeeping_init();time_init();profil

27、e_init();if (!irqs_disabled()printk(start_kernel(): bug: interrupts were enabled earlyn);early_boot_irqs_on();local_irq_enable();/* * HACK ALERT! This is early. Were enabling the console before * weve done PCI setups etc, and console_init() must be aware of * this. But we do want output early, in ca

28、se something goes wrong. */console_init();if (panic_later)panic(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_INITRDif (initrd_start & !

29、initrd_below_start_ok &initrd_start min_low_pfn PAGE_SHIFT) printk(KERN_CRIT initrd overwritten (0x%08lx 0x%08lx) - disabling it.n,initrd_start,min_low_pfn 18) & 0xfffc,.boot_params= S3C2410_SDRAM_PA + 0x100,.map_io= smdk2410_map_io,.init_irq= s3c24xx_init_irq,.init_machine= smdk_machine_init,.timer

30、= &s3c24xx_timer,MACHINE_END由此可见在.arch.info.init段内存放了_desc_mach_desc_SMDK2410结构体。初始化了相应的初始化函数指针。问题又来了， 这些初始化指针函数是什么时候被调用的呢？分析发现，不一而同。如s3c24xx_init_irq()函数是通过start_kernel()里的init_IRQ()函数调用init_arch_irq()实现的。因为在MACHINE_START结构体中 .init_irq= s3c24xx_init_irq，而在setup_arch()函数中init_arch_irq = mdesc-init_i

31、rq， 所以调用init_arch_irq()就相当于调用了s3c24xx_init_irq()。又如smdk_machine_init()函数的初始化。在MACHINE_START结构体中，函数指针赋值，.init_machine= smdk_machine_init。而init_machine()函数被linux/arch/arm/kernel/setup.c文件中的customize_machine()函数调用并被arch_initcall(Fn)宏处理，arch_initcall(customize_machine)。 被arch_initcall(Fn)宏处理过函数将linux/in

32、it/main.cdo_initcalls()函数调用。 具体参看下边的局部。void _init setup_arch(char *cmdline_p)struct tag *tags = (struct tag *)&init_tags;struct machine_desc *mdesc;char *from = default_command_line;setup_processor();mdesc = setup_machine(machine_arch_type);/machine_arch_type =SMDK2410 by edwinmachine_name = mdesc-n

33、ame;if (mdesc-soft_reboot)reboot_setup(s);if (mdesc-boot_params)tags = phys_to_virt(mdesc-boot_params);/* * If we have the old style parameters, convert them to * a tag list. */if (tags-hdr.tag != ATAG_CORE)convert_to_tag_list(tags);if (tags-hdr.tag != ATAG_CORE)tags = (struct tag *)&init_tags;if (m

34、desc-fixup)mdesc-fixup(mdesc, tags, &from, &meminfo);if (tags-hdr.tag = ATAG_CORE) if (meminfo.nr_banks != 0)squash_mem_tags(tags);parse_tags(tags);init_mm.start_code = (unsigned long) &_text;init_mm.end_code = (unsigned long) &_etext;init_mm.end_data = (unsigned long) &_edata;init_mm.brk = (unsigne

35、d long) &_end;memcpy(saved_command_line, from, COMMAND_LINE_SIZE);saved_command_lineCOMMAND_LINE_SIZE-1 = 0;parse_cmdline(cmdline_p, from);paging_init(&meminfo, mdesc);request_standard_resources(&meminfo, mdesc);#ifdef CONFIG_SMPsmp_init_cpus();#endifcpu_init();/* * Set up various architecture-speci

36、fic pointers */init_arch_irq = mdesc-init_irq;system_timer = mdesc-timer;init_machine = mdesc-init_machine;#ifdef CONFIG_VT#if defined(CONFIG_VGA_CONSOLE)conswitchp = &vga_con;#elif defined(CONFIG_DUMMY_CONSOLE)conswitchp = &dummy_con;#endif#endif3.3. rest_init()函数分析下面我们来分析下rest_init()函数。Start_kerne

37、l()函数负责初始化内核各子系统，最后调用reset_init()，启动一个叫做init的内核线程，继续初始化。在init内核线程中，将执行以下init()函数的程序。Init()函数负责完成根文件系统的挂接、初始化设备驱动程序和启动用户空间的init进程等重要工作。static void noinline rest_init(void)_releases(kernel_lock)kernel_thread(init, NULL, CLONE_FS | CLONE_SIGHAND);numa_default_policy();unlock_kernel();/* * The boot idle

38、 thread must execute schedule() * at least one to get things moving: */preempt_enable_no_resched();schedule();preempt_disable();/* Call into cpu_idle with preempt disabled */cpu_idle();static int init(void * unused)lock_kernel();/* * init can run on any cpu. */set_cpus_allowed(current, CPU_MASK_ALL)

39、;/* * Tell the world that were going to be the grim * reaper of innocent orphaned children. * * We dont want people to have to make incorrect * assumptions about where in the task array this * can be found. */child_reaper = current;smp_prepare_cpus(max_cpus);do_pre_smp_initcalls();smp_init();sched_i

40、nit_smp();cpuset_init_smp();/* * Do this before initcalls, because some drivers want to access * firmware files. */populate_rootfs(); /挂接根文件系统do_basic_setup(); /初始化设备驱动程序/* * check if there is an early userspace init. If yes, let it do all * the work /启动用户空间的init进程 */if (!ramdisk_execute_command)ram

41、disk_execute_command = /init;if (sys_access(const char _user *) ramdisk_execute_command, 0) != 0) ramdisk_execute_command = NULL;prepare_namespace();/* * Ok, we have completed the initial bootup, and * were essentially up and running. Get rid of the * initmem segments and start the user-mode stuff.

42、*/free_initmem();unlock_kernel();mark_rodata_ro();system_state = SYSTEM_RUNNING;numa_default_policy();if (sys_open(const char _user *) /dev/console, O_RDWR, 0) = 0) sys_write(fd, (char *)initrd_start,initrd_end - initrd_start);sys_close(fd);free_initrd();#elseprintk(KERN_INFO Unpacking initramfs.);e

43、rr = unpack_to_rootfs(char *)initrd_start,initrd_end - initrd_start, 0);if (err)panic(err);printk( donen);free_initrd();#endif#endif3.3.2. 初始化设备驱动程序linux/init/main.cstatic void _init do_basic_setup(void)/* drivers will send hotplug events */init_workqueues();usermodehelper_init();driver_init(); /* 初

44、始化驱动程序模型。调用驱动初始化函数初始化子系统。 */#ifdef CONFIG_SYSCTLsysctl_init();#endifdo_initcalls();linux/init/main.cextern initcall_t _initcall_start, _initcall_end;static void _init do_initcalls(void)initcall_t *call;int count = preempt_count();for (call = _initcall_start; call _initcall_end; call+) char *msg = NULL;char msgbuf40;int result;if (initcall_debug) printk(Calling initcall 0x%p, *call);print_fn_descriptor_symbol(: %s(),(unsigned long) *call);printk(n);result = (*call)();/* Make sure there is no pending stuff from the initcall sequence */flush_scheduled_work();分析上面一段代码可以看出，设备的初始化是通过do_b