armlinux内核启动过程(自解压后)的启动分析

1、内核启动过程分析* linux/arch/arm/kernel/head.s* copyright (c) 1994-2002 russell king* copyright (c) 2003 arm limited* all rights reserved* this program is free software; you can redistribute it and/or modify* it under the terms of the gnu general public license version 2 as* published by the free software f

2、oundation.* kernel startup code for all 32-bit cpus#include <linux/linkage.h>#include <linux/init.h>#include <asm/assembler.h>#include <asm/domain.h> #include <asm/ptrace<h> #include <asm/asm-offsets>h> #include <asm/memory.h> #include <asm/threadfo

3、.h>#include <asm/system>h> #if (phys_offset & oxoolfffff)#error '*phys_offset must be at an even 2mib boundary!n/boundary(分界线) #endif#define kernel_ram_vaddr#define kernel_ram_paddr(page.offset + text_offset) (phys_offset + text_offset)* swapper_pg_dir is the virtual address of t

4、he initial page* we place the page tables 16k below kernel_ram_vaddr therefore, we must* make sure that kernel_ram_vaddr is correctly set. currently, we expect* the least significant 16 bits to be 0x8000, but we could probably* relax this restriction to kernel_ram_vaddr >= page_offset + 0x4000.*/

5、 swapper_pg_d让是初始页表的虚拟地址我们将页表放在 kernel_ram_vaddr以下16k的空间中.因此我们必须保证kernel_ram_vaddr已经被正常设置.当前，我们期望的是这个地址的最后 16 bits为0x8000,但我们或许可以放宽这项限制到kernel_ram_vaddr >= page offset + 0x4000.#if (kernel_ram_vaddr & oxffff) != 0x8000#error kernel_ram_vaddr must start at 0xxxxx8000 内核的起始地址必须是 32k 对齐#endifglo

6、blequ 为 16kbkernel startup entry point.* 水这些参数同通常是由解压代码传进来的* this is normally called from the decompressor code. the requirements* are: mmu = off, d-cache = off，icache = dont care, ro = 0,* rl = machine nr, r2 = a tags pointer.* this code is mostly position independent, so if you link the kernel at*

7、 0xc0008000, you call this at pa(0xc0008000).* see linux/arch/arm/tools/mach-types for the complete list of machine* numbers for rlrl中放的是机器id* we're trying to keep crap to a minimum; do not add any machine specific* crap here thatfs what the boot loader (or in extreme 极度的，well justified 合理的* cir

8、cumstances事件，详细事件，zlmage) is for.不要随意的添加机器id,要和bootloard/swapper_pg_dir定义一个全局变量swapper_pg_dir, kernel_ram_vaddr 0x4000/*页表的起始地址，大小.macro pgtbl, rd/*定义一个宏，在建页表时用到*/ldr rd, =(kernel_ram_paddr 0x4000).endm#ifdef config_xip_kernel#define kernel start xip virt addr(config xip phys addr)#define kernel_end

9、_edataoc#else #define kernel_start kernel_ram_vaddr#define kernel.end _end /*内核镜像的结束地址(虚拟地址，在vmlinux.lds.s 中定义)*/#endif提供的相匹配。*/.section m.text.headn, maxn 定义一个.text.head段，段的属性a是允许段，x可执行v entry(stext) 入 口 点msr cpsr_c, #psr_f_bit | psr_i_bit | svc_mode ensure svc mode 管理模式 and irqs disabledmrc pl5, 0

10、, r9, co, co get processor id通过协处理器cpl5的寄存器co来获得bl _lookup_processor_type r5=procinfo r9=cpuid 判断内核是否支持处理器 cpu movs rlo, r5 invalid processor (r5=0)?beq _error_p yes，errorbl _lookup_machine_type r5=machinfo通过机器码判断是否支持单板movsr5 invalid machine (r5=0)?beq _error_a yes，error fafbl _vet_atags检查 atags 合法性

11、bl _create_page_tables创建页表* the following calls cpu specific code in a position independent* mannen see arch/arm/mm/proc-*<s for details. rlo = 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

12、 the cpu control register value.*/idr 13, _svvitch_data address to jump to after mmu has been enabledadr lr, _enable_mmu return (pic) addressadd pc, rlo, #procinfo_initfuncendproc(stext) get offset between vit&phys convert virt addresses to physical address space value, mask mask wanted bitslinu

13、x/arch/arm/kernel/head-common.s _lookup_processor_type: adr r3, 3f ldmda r3, r5 - r7 sub3,3, r7 add r5, r5, r3 add r6, r6, r31: idmia r5, r3, r4 sizeof(procnfoist)and r4 r4, r9 teq r3, r4 beq 2f add r5, r5, #proc_info_sz cmp r5, r6bio lbmov5, #02: mov pc, lr unknown processorendproc(lookup_processor

14、_type) linux/arch/arm/kernel/head-common.s 这段代码的定义地址3： longlong _arch_info_begin.long _arch_info_end_lookup_machine_type:adr r3, 3b r3中存放这标号3处的物理地址ldmia r3, r4, r5, r6 r4 中存放标号 3 处的虚拟地址，r5=_arch_info_begin 的虚 拟地址，r6存放的是_arch_info_end的虚拟地址sub r3, r3, r4 get offset between virt&phys物理地址与虚拟地址间的偏移量

15、add r5, r5, r3 convert virt addresses to r5 也变成了对应的物理地址add r6, r6, r3 physical address spacer6 也变成了对应的物理地址1: idr r3, r5, #machinfo_type get machine typeteq r3, rl matches loader number? 和内核传进的比较beq 2f found匹配了那么就返回head.sadd r5, r5, #sizeof_machine_desc next machine_desc cmp r5, r6比较看看是不是最后一个机器idbio

16、lbmov r5, #0 unknown machine2: mov pc, lrendproc(lookup machine type)#if defined(config_smp)entry (secondary _startup)/* common entry point for secondary cpus.* ensure that wefre in svc mode, and irqs are disabled. lookup* the processor type there is no need to check the machine type* as it has alre

17、ady been validated by the primary processormsr cpsr_c, #psr_f_bit | psr_i_bit | svc.modemrc pl5, 0, r9, co, co get processor idbl _lookup_processor_typemovs rlo, r5 invalid processor?moveq r0 #fpf yes, error 'pbeq _error* use the page tables supplied from _cpu_up.adr 珂 _secondary_dataidmia r4, r

18、5, r7, rl3 address to jump to aftersub r4, r4, r5 mmu has been enabledldr r4, r7, r4 get secondary_data.pgdiradr lr, _enable_mmu return addressadd pc, rlo, #procinfo_initfunc initialise processor (return control reg) endproc(secondary_startup)= & secondary_dataentry(_secondary_switched)ldr sp, r

19、7, #4 get secondary_data.stackmov fp, #0bsecondary _start_kernelendproc(secondary .switched).type_secondary_data, % object_secondary _data:long long secondary _datalong_secondary _switched#endif/setup common bits before finally enabling the mmu. essentially* this is just loading the page table point

20、er and domain access* registers.*/_enable_mmu:#ifdef config_alignment_traporr ro, r0, #cr_a/*使能地址对齐检查功能*/#elsebic ro, r0, #cr_a/*禁止地址对齐检査功能可#endif#ifdef config cpu dcache disable defined(config_smp) */#endif#ifdef config_cpu_bpredict_disablebic ro, ro, #cr_z#endif#ifdef config_cpu_icache_disablebic

21、ro, ro, #cr_i /*禁止指令的 cache*/#endifmov 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 pl5, 0, r5, c3, co, 0 load domain access register 把内核控制域存入 cpl5 的寄存器c3中mcr pl5, 0, r4,

22、 c2, co, 0 load page table pointer 把页表基址存入 cpl5 的寄存器 c2 中 b _turn_mmu_onendproc(_enable_mmu)严* 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 linuxarm-kern

23、el* mailing list archives before sending another post to the list.* r0 = cp#15 control register* rl3 = virtual* address to jump to upon completion* other registers depend on the function called upon completion*/.align 5 /*32k 对齐*/_turn_mmu_on:mov ro, r0mcr pl5, 0, ro, cl, co, 0 write control regmrc

24、pl5, 0, r3, co, co, 0 read id regmov r3, r3mov r3, r3/*为什么这里有两个nop,因为打开mmu操作之后要经过三个cycle之后才生效，这和arm的流水线有关*/mov pc, rl3endproc(_turn_mmu_on)amount which are required to get the kernel runnings which generally means mapping in the kernel code.* r8=machinfo* r9=cpuid* rlo =procinfo* returns:ro, r3, r6,

25、 r7 corrupted r4 = physical page table addresscreate_page_tables: page table addresspgtbl r4* clear the 16k level 1 swapper (交易者)page table*/mov ro, r4mov r3, #0add r6, ro, #0x4000 页表的结束地址1: str r3, ro, #4str r3, ro, #4str r3, ro, #4str r3, ro, #4teq ro, r6bne lb清空整个16k的页表idr r7, rlo, #procinfo_mm_m

26、muflagsj mm_mmuflags*define(procinfo_mm_mmuflags, offsetof(struct*_cpu_mm_mmu_flags);define in archarmkernel旬mov r6, pc, lsr #20 为物理地址orr r3,7, r6, isl #20str r3, r4, r6, lsl #2 个页表占4bit* create identity mapping for first mb of kernel to* cater (满足)for the mmu enable. this identity mapping* will be

27、removed by pagingnit()> we use our current program* counter to determine corresponding (相应的)section base address.*/ start of kernel section此时mmu还没有开启，所以pc flags + kernel base identity mapping填到对应的页表中区，lsl #2是因为一* now setup the pagetables for our kernel direct* mapped region.(地区，范围)*/add ro, r4, #

28、(kernel_start & oxffoooooo) » 18 str r3, ro, #(kernel_start & oxoofooooo) » 18!idr r6, =(kernel_end1) /*内核结束地址(虚拟地址)*/ add ro, ro, #4add r6, r4, r6, lsr #181: cmp ro, r6add3, r3, #1 « 20strls r3, ro, #4bls lb#ifdef config_xip_kernel/* map some ram to cover our data and bss are

29、as*/orr r3, r7, #(kernel_ram_paddr & oxffoooooo).if (kernel_ram_paddr & oxoofooooo)orr r3, r3, #(kernel_ram_paddr & oxoofooooo) endifadd ro, r4, #(kernel_ram_vaddr & oxffoooooo) » 18 str r3, ro, #(kernel_ram_vaddr & 0x00(x)0000) » 18! idr r6, =(_end 1)add ro, ro, #4add

30、f6,4,6, lsr #181: cmp ro, r6add r3, r3, #1 « 20strls r3, ro, #4bls lb#endif* then map first 1mb of ram in case it contains our boot params, add ro, r4, #page_offset » 18orr r6, r7, #(phys_offset & oxffoooooo).if (phys.offset & oxoofboooo)orr r6, i*6, #(phys_offset & oxoofooooo) .endifstr r6, ro#ifdef config debug llldr r7