arm linux内核启动过程自解压后的启动分析文档格式.docx
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PHYS_OFFSETmustbeataneven2MiBboundary!
"
//boundary(分界线)
#endif
#defineKERNEL_RAM_VADDR(PAGE_OFFSET+TEXT_OFFSET)
#defineKERNEL_RAM_PADDR(PHYS_OFFSET+TEXT_OFFSET)
*swapper_pg_diristhevirtualaddressoftheinitialpage
*Weplacethepagetables16KbelowKERNEL_RAM_VADDR.Therefore,wemust
*makesurethatKERNEL_RAM_VADDRiscorrectlyset.Currently,weexpect
*theleastsignificant16bitstobe0x8000,butwecouldprobably
*relaxthisrestrictiontoKERNEL_RAM_VADDR>
=PAGE_OFFSET+0x4000.
*/swapper_pg_dir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16bits为0x8000,但我们或许可以放宽这项限制到KERNEL_RAM_VADDR>
#if(KERNEL_RAM_VADDR&
0xffff)!
=0x8000
#errorKERNEL_RAM_VADDRmuststartat0xXXXX8000//内核的起始地址必须是32k对齐
.globlswapper_pg_dir//定义一个全局变量
.equswapper_pg_dir,KERNEL_RAM_VADDR-0x4000/*页表的起始地址,大小为16kb*/
.macropgtbl,rd/*定义一个宏,在建页表时用到*/
ldr\rd,=(KERNEL_RAM_PADDR-0x4000)
.endm
#ifdefCONFIG_XIP_KERNEL
#defineKERNEL_STARTXIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
#defineKERNEL_END_edata_loc
#else
#defineKERNEL_STARTKERNEL_RAM_VADDR
#defineKERNEL_END_end/*内核镜像的结束地址(虚拟地址,在vmlinux.lds.S中定义)*/
*Kernelstartupentrypoint.
*---------------------------
*这些参数同通常是由解压代码传进来的
*Thisisnormallycalledfromthedecompressorcode.Therequirements
*are:
MMU=off,D-cache=off,I-cache=dontcare,r0=0,
*r1=machinenr,r2=atagspointer.
*Thiscodeismostlypositionindependent,soifyoulinkthekernelat
*0xc0008000,youcallthisat__pa(0xc0008000).
*Seelinux/arch/arm/tools/mach-typesforthecompletelistofmachine
*numbersforr1.r1中放的是机器ID
*We'
retryingtokeepcraptoaminimum;
DONOTaddanymachinespecific
*craphere-that'
swhatthebootloader(orinextreme极度的,welljustified合理的
*circumstances事件,详细事件,zImage)isfor.不要随意的添加机器ID,要和bootloard提供的相匹配。
.section"
.text.head"
"
ax"
@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
msrcpsr_c,#PSR_F_BIT|PSR_I_BIT|SVC_MODE@ensuresvcmode管理模式
@andirqsdisabled
mrcp15,0,r9,c0,c0@getprocessorid通过协处理器cp15的寄存器c0来获得
bl__lookup_processor_type@r5=procinfor9=cpuid判断内核是否支持处理器cpu
movsr10,r5@invalidprocessor(r5=0)?
beq__error_p@yes,error'
p'
bl__lookup_machine_type@r5=machinfo通过机器码判断是否支持单板
movsr8,r5@invalidmachine(r5=0)?
beq__error_a@yes,error'
a'
bl__vet_atags//检查atags合法性
bl__create_page_tables//创建页表
*ThefollowingcallsCPUspecificcodeinapositionindependent
*manner.Seearch/arm/mm/proc-*.Sfordetails.r10=baseof
*xxx_proc_infostructureselectedby__lookup_machine_type
*above.Onreturn,theCPUwillbereadyfortheMMUtobe
*turnedon,andr0willholdtheCPUcontrolregistervalue.
ldrr13,__switch_data@addresstojumptoafter
@mmuhasbeenenabled
adrlr,__enable_mmu@return(PIC)address
addpc,r10,#PROCINFO_INITFUNC
ENDPROC(stext)
linux/arch/arm/kernel/head-common.S
__lookup_processor_type:
adrr3,3f
ldmdar3,{r5-r7}
subr3,r3,r7@getoffsetbetweenvirt&
phys
addr5,r5,r3@convertvirtaddressesto
addr6,r6,r3@physicaladdressspace
1:
ldmiar5,{r3,r4}@value,mask
andr4,r4,r9@maskwantedbits
teqr3,r4
beq2f
addr5,r5,#PROC_INFO_SZ@sizeof(proc_info_list)
cmpr5,r6
blo1b
movr5,#0@unknownprocessor
2:
movpc,lr
ENDPROC(__lookup_processor_type)
linux/arch/arm/kernel/head-common.S这段代码的定义地址
3:
.long
.long__arch_info_begin
.long__arch_info_end
__lookup_machine_type:
adrr3,3b@r3中存放这标号3处的物理地址
ldmiar3,{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
subr3,r3,r4@getoffsetbetweenvirt&
phys物理地址与虚拟地址间的偏移量
addr5,r5,r3@convertvirtaddressestor5也变成了对应的物理地址
addr6,r6,r3@physicaladdressspacer6也变成了对应的物理地址
ldrr3,[r5,#MACHINFO_TYPE]@getmachinetype
teqr3,r1@matchesloadernumber?
和内核传进的比较
beq2f@found匹配了那么就返回head.S
addr5,r5,#SIZEOF_MACHINE_DESC@nextmachine_desc
cmpr5,r6@比较看看是不是最后一个机器ID
movr5,#0@unknownmachine
ENDPROC(__lookup_machine_type)
#ifdefined(CONFIG_SMP)
ENTRY(secondary_startup)
/*
*CommonentrypointforsecondaryCPUs.
*Ensurethatwe'
reinSVCmode,andIRQsaredisabled.Lookup
*theprocessortype-thereisnoneedtocheckthemachinetype
*asithasalreadybeenvalidatedbytheprimaryprocessor.
msrcpsr_c,#PSR_F_BIT|PSR_I_BIT|SVC_MODE
mrcp15,0,r9,c0,c0@getprocessorid
bl__lookup_processor_type
movsr10,r5@invalidprocessor?
moveqr0,#'
@yes,error'
beq__error
*Usethepagetablessuppliedfrom__cpu_up.
adrr4,__secondary_data
ldmiar4,{r5,r7,r13}@addresstojumptoafter
subr4,r4,r5@mmuhasbeenenabled
ldrr4,[r7,r4]@getsecondary_data.pgdir
adrlr,__enable_mmu@returnaddress
addpc,r10,#PROCINFO_INITFUNC@initialiseprocessor
@(returncontrolreg)
ENDPROC(secondary_startup)
*r6=&
secondary_data
ENTRY(__secondary_switched)
ldrsp,[r7,#4]@getsecondary_data.stack
movfp,#0
bsecondary_start_kernel
ENDPROC(__secondary_switched)
.type__secondary_data,%object
__secondary_data:
.long.
.longsecondary_data
.long__secondary_switched
#endif/*defined(CONFIG_SMP)*/
*SetupcommonbitsbeforefinallyenablingtheMMU.Essentially
*thisisjustloadingthepagetablepointeranddomainaccess
*registers.
__enable_mmu:
#ifdefCONFIG_ALIGNMENT_TRAP
orrr0,r0,#CR_A/*使能地址对齐检查功能*/
bicr0,r0,#CR_A/*禁止地址对齐检查功能*/
#ifdefCONFIG_CPU_DCACHE_DISABLE
bicr0,r0,#CR_C/*禁止数据的cache*/
#ifdefCONFIG_CPU_BPREDICT_DISABLE
bicr0,r0,#CR_Z
#ifdefCONFIG_CPU_ICACHE_DISABLE
bicr0,r0,#CR_I/*禁止指令的cache*/
movr5,#(domain_val(DOMAIN_USER,DOMAIN_MANAGER)|\
domain_val(DOMAIN_KERNEL,DOMAIN_MANAGER)|\
domain_val(DOMAIN_TABLE,DOMAIN_MANAGER)|\
domain_val(DOMAIN_IO,DOMAIN_CLIENT))
mcrp15,0,r5,c3,c0,0@loaddomainaccessregister把内核控制域存入cp15的寄存器c3中
mcrp15,0,r4,c2,c0,0@loadpagetablepointer把页表基址存入cp15的寄存器c2中
b__turn_mmu_on
ENDPROC(__enable_mmu)
*EnabletheMMU.Thiscompletelychangesthestructureofthevisible
*memoryspace.Youwillnotbeabletotraceexecutionthroughthis.
*Ifyouhaveanenquiryaboutthis,*please*checkthelinux-arm-kernel
*mailinglistarchivesBEFOREsendinganotherposttothelist.
*r0=cp#15controlregister
*r13=*virtual*addresstojumptouponcompletion
*otherregistersdependonthefunctioncalleduponcompletion
.align5/*32k对齐*/
__turn_mmu_on:
movr0,r0
mcrp15,0,r0,c1,c0,0@writecontrolreg
mrcp15,0,r3,c0,c0,0@readidreg
movr3,r3
movr3,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*/
movpc,r13
ENDPROC(__turn_mmu_on)
*Setuptheinitialpagetables.Weonlysetupthebarest
*amountwhicharerequiredtogetthekernelrunning,which
*generallymeansmappinginthekernelcode.
*r8=machinfo
*r9=cpuid
*r10=procinfo
*Returns:
*r0,r3,r6,r7corrupted
*r4=physicalpagetableaddress
__create_page_tables:
pgtblr4@pagetableaddress
*Clearthe16Klevel1swapper(交易者)pagetable
movr0,r4
movr3,#0
addr6,r0,#0x4000@页表的结束地址
strr3,[r0],#4
teqr0,r6
bne1b@清空整个16k的页表
ldrr7,[r10,#PROCINFO_MM_MMUFLAGS]@mm_mmuflags
/*
*DEFINE(PROCINFO_MM_MMUFLAGS,offsetof(structproc_info_list,*__cpu_mm_mmu_flags));
defineinarch\arm\kernel
*/
*CreateidentitymappingforfirstMBofkernelto
*cater(满足)fortheMMUenable.Thisidentitymapping
*willberemovedbypaging_init().Weuseourcurrentprogram
*countertodeterminecorresponding(相应的)sectionbaseaddress.
movr6,pc,lsr#20@startofkernelsection此时mmu还没有开启,所以pc为物理地址
orrr3,r7,r6,lsl#20@flags+kernelbase
strr3,[r4,r6,lsl#2]@identitymapping填到对应的页表中区,lsl#2是因为一个页表占4bit
*Nowsetupthepagetablesforourkerneldirect
*mappedregion.(地区,范围)
addr0,r4,#(KERNEL_START&
0xff000000)>
>
18
strr3,[r0,#(KERNEL_START&
0x00f00000)>
18]!
ldrr6,=(KERNEL_END-1)/*内核结束地址(虚拟地址)*/
addr0,r0,#4
addr6,r4,r6,lsr#18
cmpr0,r6
addr3,r3,#1<
<
20
strlsr3,[r0],#4
bls1b
*Mapsomeramtocoverour.dataand.bssareas.
orrr3,r7,#(KERNEL_RAM_PADDR&
0xff000000)
.if(KERNEL_RAM_PADDR&
0x00f00000)
orrr3,r3,#(KERNEL_RAM_PADDR&
.endif
addr0,r4,#(KERNEL_RAM_VADDR&
strr3,[r0,#(KERNEL_RAM_VADDR&
ldrr6,=(_end-1)
*Thenmapfirst1MBofr