Android arm linux kernel启动流程

__lookup_processor_type: adr r3, 3f ldmda r3, {r5 - r7} sub r3, r3, r7 @ get offset between virt&phys add r5, r5, r3 @ convert virt addresses to add r6, r6, r3 @ physical address space 1: ldmia r5, {r3, r4} @ value, mask and r4, r4, r9 @ mask wanted bits teq r3, r4 beq 2f add r5, r5, #PROC_INFO_SZ @ sizeof(proc_info_list) cmp r5, r6 blo 1b mov r5, #0 @ unknown processor 2: mov pc, lr ENDPROC(__lookup_processor_type)

他这里的执行过程其实比较简单就是在__proc_info_begin和__proc_info_end这个段里面里面去读取我们注册在里面的 proc_info_list这个结构体，这个结构体的定义在arch/arm/include/asm/procinfo.h，具体实现根据你使用的 cpu的架构在arch/arm/mm/里面找到具体的实现，这里我们使用的ARM11是proc-v6.S，我们可以看看这个结构体：

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1. .section".proc.info.init",#alloc,#execinstr
2. /*
3. *MatchanyARMv6processorcore.
4. */
5. .type__v6_proc_info,#object
6. _proc_info:
7. .long0x0007b000
8. .long0x0007f000
9. .longPMD_TYPE_SECT|/
10. PMD_SECT_BUFFERABLE|/
11. PMD_SECT_CACHEABLE|/
12. PMD_SECT_AP_WRITE|/
13. PMD_SECT_AP_READ
14. .longPMD_TYPE_SECT|/
15. PMD_SECT_XN|/
16. PMD_SECT_AP_WRITE|/
17. PMD_SECT_AP_READ
18. b__v6_setup
19. .longcpu_arch_name
20. .longcpu_elf_name
21. .longHWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_JAVA
22. .longcpu_v6_name
23. .longv6_processor_functions
24. .longv6wbi_tlb_fns
25. .longv6_user_fns
26. .longv6_cache_fns
27. .size__v6_proc_info,.-__v6_proc_info

.section ".proc.info.init", #alloc, #execinstr /* * Match any ARMv6 processor core. */ .type __v6_proc_info, #object __v6_proc_info: .long 0x0007b000 .long 0x0007f000 .long PMD_TYPE_SECT | / PMD_SECT_BUFFERABLE | / PMD_SECT_CACHEABLE | / PMD_SECT_AP_WRITE | / PMD_SECT_AP_READ .long PMD_TYPE_SECT | / PMD_SECT_XN | / PMD_SECT_AP_WRITE | / PMD_SECT_AP_READ b __v6_setup .long cpu_arch_name .long cpu_elf_name .long HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_JAVA .long cpu_v6_name .long v6_processor_functions .long v6wbi_tlb_fns .long v6_user_fns .long v6_cache_fns .size __v6_proc_info, . - __v6_proc_info

对着.h我们就知道各个成员变量的含义了，他这里lookup的过程实际上是先求出这个proc_info_list的实际物理地址，并将其内容读出，然后将其中的mask也就是我们这里的0x007f000与寄存器与之后与0x007b00进行比较，如果一样的话呢就校验成功了，如果不一样呢就会读下一个proc_info的信息，因为proc一般都是只有一个的，所以这里一般不会循环，如果检测正确寄存器就会将正确的proc_info_list的物理地址赋给寄存器，如果检测不到就会将寄存器值赋0，然后通过LR返回。

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1. bl__lookup_machine_type@r5=machinfo
2. movsr8,r5@invalidmachine(r5=0)?
3. beq__error_a@yes,errora

bl __lookup_machine_type @ r5=machinfo movs r8, r5 @ invalid machine (r5=0)? beq __error_a @ yes, error a

检测完proc_info_list以后就开始检测machine_type了，这个函数的实现也在head－common.S里面，我们看看它具体的实现：

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1. __lookup_machine_type:
2. adrr3,3b
3. ldmiar3,{r4,r5,r6}
4. subr3,r3,r4@getoffsetbetweenvirt&phys
5. addr5,r5,r3@convertvirtaddressesto
6. addr6,r6,r3@physicaladdressspace
7. 1:ldrr3,[r5,#MACHINFO_TYPE]@getmachinetype
8. teqr3,r1@matchesloadernumber?
9. beq2f@found
10. addr5,r5,#SIZEOF_MACHINE_DESC@nextmachine_desc
11. cmpr5,r6
12. blo1b
13. movr5,#0@unknownmachine
14. 2:movpc,lr
15. ENDPROC(__lookup_machine_type)

__lookup_machine_type: adr r3, 3b ldmia r3, {r4, r5, r6} sub r3, r3, r4 @ get offset between virt&phys add r5, r5, r3 @ convert virt addresses to add r6, r6, r3 @ physical address space 1: ldr r3, [r5, #MACHINFO_TYPE] @ get machine type teq r3, r1 @ matches loader number? beq 2f @ found add r5, r5, #SIZEOF_MACHINE_DESC @ next machine_desc cmp r5, r6 blo 1b mov r5, #0 @ unknown machine 2: mov pc, lr ENDPROC(__lookup_machine_type)

这里的过程基本上是同proc的检查是一样的，这里主要检查芯片的类型，比如我们现在的芯片是MSM7X27FFA，这也