网站设计怎么收费,社交网站源代码,网站链接只显示到文件夹怎么做的,网站大全app下载对Linux-Android系统的启动做了一些分析#xff0c;下面的一篇文章侧重讲述Linux启动过程中函数Start_kernel()被调用之前的一些分析#xff0c;同时也对函数Start_kernel()之后的代码流程作了概述#xff0c;我希望关于Linux-Android系统的启动的专题能够继续地写下去… 对Linux-Android系统的启动做了一些分析下面的一篇文章侧重讲述Linux启动过程中函数Start_kernel()被调用之前的一些分析同时也对函数Start_kernel()之后的代码流程作了概述我希望关于Linux-Android系统的启动的专题能够继续地写下去哈哈。如果有不正确或者不完善的地方欢迎前来拍砖留言或者发邮件到guopeixin126.com进行讨论现行谢过。 一. 内核自引导程序
1. 内核zimage自解压 这部分代码在arch/${arch}/boot/compressed/head.S中该文件的代码在zimage的生成过程中将会被打包到zimage中。 head.S会首先初始化自解压相关的如内存等环境接下来就去调用decompress_kernel去解压并调用call_kernel函数去启动vmlinux。 去下面仅仅列举一下head.S文件中最重要的部分----------------------------------------------------------------/* * Were not in danger of overwriting ourselves. Do this the simple way. * * r4 kernel execution address * r7 architecture ID */wont_overwrite: mov r0, r4 mov r3, r7 bl decompress_kernel b call_kernel...call_kernel: bl cache_clean_flush bl cache_off mov r0, #0 must be zero mov r1, r7 restore architecture number mov r2, r8 restore atags pointer mov pc, r4 call kernel---------------------------------------------------------------- 其中函数decompress_kernel在arch/${arch}/boot/compressed/misc.c中实现功能就是完成zimage镜像的自解压显然该自解压的过程需
要配置相应的解压地址等这部分代码如下----------------------------------------------------------------ulgdecompress_kernel(ulg output_start, ulg free_mem_ptr_p, ulg free_mem_ptr_end_p, int arch_id){ output_data (uch *)output_start; /* Points to kernel start */ free_mem_ptr free_mem_ptr_p; /* 显然这个地址是从通过寄存器传进来的 */ free_mem_end_ptr free_mem_ptr_end_p; __machine_arch_type arch_id; arch_decomp_setup(); makecrc(); putstr(Uncompressing Linux...); gunzip(); putstr( done, booting the kernel./n); return output_ptr;}---------------------------------------------------------------- 调用call_kernel后首先关闭cache然后就跳转到vmlinux入口去执行并将系统的控制权交给了vmlinux。
2. 内核vmlinux入口 vmlinux的编译简单描述 因为这里会牵扯到两个文件head.S和head-nommu.S,所以下面简单的描述一下vmlinux的生成过程。来看一下/arch/${arch}/kernel/makefile
在该文件的最后脚本如下----------------------------------------------------------------## Makefile for the linux kernel.#
AFLAGS_head.o : -DTEXT_OFFSET$(TEXT_OFFSET)
ifdef CONFIG_DYNAMIC_FTRACECFLAGS_REMOVE_ftrace.o -pgendif
# Object file lists.
obj-y : compat.o elf.o entry-armv.o entry-common.o irq.o / process.o ptrace.o setup.o signal.o / sys_arm.o stacktrace.o time.o traps.o
obj-$(CONFIG_ISA_DMA_API) dma.oobj-$(CONFIG_ARCH_ACORN) ecard.o obj-$(CONFIG_FIQ) fiq.oobj-$(CONFIG_MODULES) armksyms.o module.oobj-$(CONFIG_ARTHUR) arthur.oobj-$(CONFIG_ISA_DMA) dma-isa.oobj-$(CONFIG_PCI) bios32.o isa.oobj-$(CONFIG_SMP) smp.oobj-$(CONFIG_DYNAMIC_FTRACE) ftrace.oobj-$(CONFIG_KEXEC) machine_kexec.o relocate_kernel.oobj-$(CONFIG_KPROBES) kprobes.o kprobes-decode.oobj-$(CONFIG_ATAGS_PROC) atags.oobj-$(CONFIG_OABI_COMPAT) sys_oabi-compat.oobj-$(CONFIG_ARM_THUMBEE) thumbee.oobj-$(CONFIG_KGDB) kgdb.o
obj-$(CONFIG_CRUNCH) crunch.o crunch-bits.oAFLAGS_crunch-bits.o : -Wa,-mcpuep9312
obj-$(CONFIG_CPU_XSCALE) xscale-cp0.oobj-$(CONFIG_CPU_XSC3) xscale-cp0.oobj-$(CONFIG_IWMMXT) iwmmxt.oAFLAGS_iwmmxt.o : -Wa,-mcpuiwmmxt
ifneq ($(CONFIG_ARCH_EBSA110),y) obj-y io.oendif
head-y : head$(MMUEXT).oobj-$(CONFIG_DEBUG_LL) debug.o
extra-y : $(head-y) init_task.o vmlinux.lds---------------------------------------------------------------- 可以看到文件的结束位置有一行代码“head-y : head$(MMUEXT).o”其中MMUEXT在/arch/${arch}/makefile中
定义实际上对于没有mmu的处理器MMUEXT就是nommu而对于包含mmu的处理器它的值是空参照MMUEXT在/arch/${arch}/makefile中的相关代码
如下----------------------------------------------------------------# defines filename extension depending memory manement type.ifeq ($(CONFIG_MMU),)MMUEXT : -nommuendif---------------------------------------------------------------- 所以对于诸如S3C6410之类的包含MMU的处理器实际上最终vmlinux开始位置的代码就是/arch/${arch}/kernel/head.S. head.S文件的分析 需要注意的是对于该文件的描述一般的书籍上可能是仅仅对老版本的linux系统进行了分析就是说该文件结束位置直接调用了
start_kernel 函数至此开始执行c代码。其实并不是这样的。 下面简单的列写一下head.S的内容----------------------------------------------------------------/* * Kernel startup entry point. * --------------------------- * * This is normally called from the decompressor code. The requirements * are: MMU off, D-cache off, I-cache dont care, r0 0, * r1 machine nr, r2 atags pointer. * * This code is mostly position independent, so if you link the kernel at * 0xc0008000, you call this at __pa(0xc0008000). * * See linux/arch/arm/tools/mach-types for the complete list of machine * numbers for r1. * * Were trying to keep crap to a minimum; DO NOT add any machine specific * crap here - thats what the boot loader (or in extreme, well justified * circumstances, zImage) is for. */ .section .text.head, axENTRY(stext) msr cpsr_c, #PSR_F_BIT | PSR_I_BIT | SVC_MODE ensure svc mode and irqs disabled mrc p15, 0, r9, c0, c0 get processor id bl __lookup_processor_type r5procinfo r9cpuid movs r10, r5 invalid processor (r50)? beq __error_p yes, error p bl __lookup_machine_type r5machinfo movs r8, r5 invalid machine (r50)? beq __error_a yes, error a bl __vet_atags bl __create_page_tables /* * The following calls CPU specific code in a position independent * manner. See arch/arm/mm/proc-*.S for details. r10 base of * xxx_proc_info structure selected by __lookup_machine_type * above. On return, the CPU will be ready for the MMU to be * turned on, and r0 will hold the CPU control register value. */ ldr r13, __switch_data address to jump to after mmu has been enabled adr lr, __enable_mmu return (PIC) address add pc, r10, #PROCINFO_INITFUNCENDPROC(stext)
#if defined(CONFIG_SMP)ENTRY(secondary_startup) /* * Common entry point for secondary CPUs. * * Ensure that were in SVC mode, and IRQs are disabled. Lookup * the processor type - there is no need to check the machine type * as it has already been validated by the primary processor. */ msr cpsr_c, #PSR_F_BIT | PSR_I_BIT | SVC_MODE mrc p15, 0, r9, c0, c0 get processor id bl __lookup_processor_type movs r10, r5 invalid processor? moveq r0, #p yes, error p beq __error /* * Use the page tables supplied from __cpu_up. */ adr r4, __secondary_data ldmia r4, {r5, r7, r13} address to jump to after sub r4, r4, r5 mmu has been enabled ldr r4, [r7, r4] get secondary_data.pgdir adr lr, __enable_mmu return address add pc, r10, #PROCINFO_INITFUNC initialise processor (return control reg)ENDPROC(secondary_startup) /* * r6 secondary_data */ENTRY(__secondary_switched) ldr sp, [r7, #4] get secondary_data.stack mov fp, #0 b secondary_start_kernelENDPROC(__secondary_switched) .type __secondary_data, %object__secondary_data: .long . .long secondary_data .long __secondary_switched#endif /* defined(CONFIG_SMP) */
/* * Setup common bits before finally enabling the MMU. Essentially * this is just loading the page table pointer and domain access * registers. */__enable_mmu:#ifdef CONFIG_ALIGNMENT_TRAP orr r0, r0, #CR_A#else bic r0, r0, #CR_A#endif#ifdef CONFIG_CPU_DCACHE_DISABLE bic r0, r0, #CR_C#endif#ifdef CONFIG_CPU_BPREDICT_DISABLE bic r0, r0, #CR_Z#endif#ifdef CONFIG_CPU_ICACHE_DISABLE bic r0, r0, #CR_I#endif mov r5, #(domain_val(DOMAIN_USER, DOMAIN_MANAGER) | / domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) | / domain_val(DOMAIN_TABLE, DOMAIN_MANAGER) | / domain_val(DOMAIN_IO, DOMAIN_CLIENT)) mcr p15, 0, r5, c3, c0, 0 load domain access register mcr p15, 0, r4, c2, c0, 0 load page table pointer b __turn_mmu_onENDPROC(__enable_mmu)
/* * Enable the MMU. This completely changes the structure of the visible * memory space. You will not be able to trace execution through this. * If you have an enquiry about this, *please* check the linux-arm-kernel * mailing list archives BEFORE sending another post to the list. * * r0 cp#15 control register * r13 *virtual* address to jump to upon completion * * other registers depend on the function called upon completion */ .align 5__turn_mmu_on: mov r0, r0 mcr p15, 0, r0, c1, c0, 0 write control reg mrc p15, 0, r3, c0, c0, 0 read id reg mov r3, r3 mov r3, r3 mov pc, r13ENDPROC(__turn_mmu_on)
#include head-common.S---------------------------------------------------------------- 可能大家注意到上面有大段的文字是secondary_startup以及CONFIG_SMP等其实这个是对于SMP系统才会采用的代码。众所周知SMP是对
称多处理的简称是指系统中使用了一组处理器各CPU之间共享内存子系统和总线结构对应的有非对称多处理嵌入式设备上我们并不会使用到
SMP的功能。 乍一看无论如何也调用不到网上所谓的start_kernel函数中大家注意看“ldr r13, __switch_data”这里就是将函数__switch_data的
地址保存到r13并在函数__enable_mmu--__turn_mmu_on结束位置的“mov pc, r13”中将__switch_data调用起来。而函数__switch_data是实
现在/arch/${arch}/kernel/head-common.S中的一个函数而函数start_kernel就是由__switch_data调用起来的。 你一定在奇怪那么函数__enable_mmu是怎么调用起来的呢呵呵你简直是太聪明、太细心了。那赶紧听我跟你说吧代码“add pc,
r10, #PROCINFO_INITFUNC”将会跳转到/arch/${arch}/mm/proc-arn-926.S中的初始化函数__arm926_setup中并在该函数结束的位置以“mov pc,
lr”的方式调用__enable_mmu千万别告诉我你忘记了前面提到的__enable_mmu的值保存在lr中哦。 至于为什么代码“add pc, r10, #PROCINFO_INITFUNC”将会跳转到/arch/${arch}/mm/proc-arn-926.S中的初始化函数__arm926_setup
中我这里就不列举了。可以参照后面我转载的一篇文章。---------------------------------------------------------------- .type __arm926_setup, #function__arm926_setup: mov r0, #0 mcr p15, 0, r0, c7, c7 invalidate I,D caches on v4 mcr p15, 0, r0, c7, c10, 4 drain write buffer on v4#ifdef CONFIG_MMU mcr p15, 0, r0, c8, c7 invalidate I,D TLBs on v4#endif
#ifdef CONFIG_CPU_DCACHE_WRITETHROUGH mov r0, #4 disable write-back on caches explicitly mcr p15, 7, r0, c15, c0, 0#endif adr r5, arm926_crval ldmia r5, {r5, r6} mrc p15, 0, r0, c1, c0 get control register v4 bic r0, r0, r5 orr r0, r0, r6#ifdef CONFIG_CPU_CACHE_ROUND_ROBIN orr r0, r0, #0x4000 .1.. .... .... ....#endif mov pc, lr---------------------------------------------------------------- 好了终于调用到start_kernel了,这是任何版本的linux内核通用的初始化函数。
3. Linux系统初始化 前面已经提到函数start_kernel是任何版本的linux内核通用的初始化函数也是汇编代码执行结束后的第一个c函数它实现在
init/main.c中。 有关start_kernel的代码很长初始化了很多东西比如调用了setup_arch()、timer_init()、init_IRQ、console_init()、
pgtable_cache_init()、security_init()、signals_init()和rest_init()等这里只对rest_init()做简单的分析。 下面首先列写一下rest_init()的代码----------------------------------------------------------------/* * We need to finalize in a non-__init function or else race conditions * between the root thread and the init thread may cause start_kernel to * be reaped by free_initmem before the root thread has proceeded to * cpu_idle. * * gcc-3.4 accidentally inlines this function, so use noinline. */
static noinline void __init_refok rest_init(void) __releases(kernel_lock){ int pid; kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND); numa_default_policy(); pid kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES); kthreadd_task find_task_by_pid_ns(pid, init_pid_ns); unlock_kernel(); /* * The boot idle thread must execute schedule() * at least once to get things moving: */ init_idle_bootup_task(current); rcu_scheduler_starting(); preempt_enable_no_resched(); schedule(); preempt_disable(); /* Call into cpu_idle with preempt disabled */ cpu_idle();}---------------------------------------------------------------- 可以看到函数rest_init()首先会去创建线程kernel_init注意这里和网上或者相关书籍中描述的也不一样可能是Linux版本的问题
有些文档中描述这里创建的是Init线程虽然名字不一致但是具体的实现是基本一致的基本上都是完成根文件系统的挂载、初始化所有Linux的
设备驱动就是调用驱动的初始化函数类似于CE/Mobile中的Device Manager对设备驱动的初始化以及启动用户空间Init进程。 由于手中的rest_init进程和网上描述的都是不一致的所以这里也进行了简要的列举代码如下----------------------------------------------------------------static int __init kernel_init(void * unused){ lock_kernel(); /* * init can run on any cpu. */ set_cpus_allowed_ptr(current, CPU_MASK_ALL_PTR); /* * 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. */ init_pid_ns.child_reaper current; cad_pid task_pid(current); smp_prepare_cpus(setup_max_cpus); do_pre_smp_initcalls(); start_boot_trace(); smp_init(); sched_init_smp(); cpuset_init_smp(); do_basic_setup(); /* * check if there is an early userspace init. If yes, let it do all * the work */ if (!ramdisk_execute_command) ramdisk_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.. */ init_post(); return 0;}
static noinline int init_post(void){ /* need to finish all async __init code before freeing the memory */ async_synchronize_full(); 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) printk(KERN_WARNING Warning: unable to open an initial console./n); (void) sys_dup(0); (void) sys_dup(0); current-signal-flags | SIGNAL_UNKILLABLE; if (ramdisk_execute_command) { run_init_process(ramdisk_execute_command); printk(KERN_WARNING Failed to execute %s/n, ramdisk_execute_command); } /* * 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) { run_init_process(execute_command); printk(KERN_WARNING Failed to execute %s. Attempting defaults.../n, execute_command); } run_init_process(/sbin/init); run_init_process(/etc/init); run_init_process(/bin/init); run_init_process(/bin/sh); panic(No init found. Try passing init option to kernel.);}---------------------------------------------------------------- 可以看到和网络上相关的描述不一样的是这里首先会去初始化设备驱动而不是像网上或者数据上所描述的一样首先去加载跟文件系
统难道不存在初始化的时候需要访问文件的驱动了或者以前的做法纯属一种安全的考虑 这些问题就留到以后对LinuxAndroid有深入地了解之后再去考虑吧! 好了,搞定!!!
