arm linux源代码分析(1)

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1、ARMLinux源代码分析(1)/*ARMLinux源代码分析(1)--head.STigerZ(tigerz@yeah.net)http://emblinux.org/1.分析环境   kernel:2.6.10   board:SMDK24101.32,64MSDRAM,128MSM卡2.head.S*//* *linux/arch/arm/kernel/head.S * * Copyright(C)1994-2002RussellKing * *Thisprogramisfreesoftware;youcanred

2、istributeitand/ormodify *itunderthetermsoftheGNUGeneralPublicLicenseversion2as *publishedbytheFreeSoftwareFoundation. * * Kernelstartupcodeforall32-bitCPUs */#include#include#include#include#include<

3、asm/mach-types.h>#include#include#include#ifndefCONFIG_XIP_KERNEL/*我在的平台,这个宏没有定义*//* *Weplacethepagetables16KbelowTEXTADDR. Therefore,wemustmakesure *thatTEXTADDRiscorrectlyset. Currently,weexpecttheleastsignificant 

4、*16bitstobe0x8000,butwecouldprobablyrelaxthisrestrictionto *TEXTADDR>=PAGE_OFFSET+0x4000 * *页表放在比TEXTADDR低16K的地方,所以我们必须要确认TEXTADDR被正确设定.目前, *我们希望低16位为0x8000,不过我们可以放松这个限制为 *TEXTADDR>=PAGE_OFFSET+0x4000 * *Notethatswapper_pg_diristhevirtualaddressofthepagetables,an

5、d *pgtblgivesusaposition-independentreferencetothesetables. Wecan *dothisbecausestext==TEXTADDR * *注意swapper_pg_dir是页表的虚拟地址,pgtbl给我们一个位置无关的页表地址,这是 *因为stext==TEXTADDR. */#if(TEXTADDR&0xffff)!=0x8000   #errorTEXTADDRmuststartat0xXXXX8000#endif   /*swapper_pg_dir=0x

6、30008000-0x4000*/   .globl swapper_pg_dir   .equ   swapper_pg_dir,TEXTADDR-0x4000   /*rd=stext-0x4000,这里stext==TEXTADDR*/   /*adr指令是在pc值上+/-一个标号的偏移得到的,所以得到的地址只跟pc和标号到    *pc的偏移相关,跟编译地址无关.在MMU打开前,代码要是地址无关的,会经常    *用到adr.    */   .macro pgtbl,rd,phys   adr    rd,s

7、text   sub    rd,rd,#0x4000   .endm#else/**XIPKernel:**Weplacethepagetables16KbelowDATAADDR. Therefore,wemustmakesure*thatDATAADDRiscorrectlyset. Currently,weexpecttheleastsignificant*16bitstobe0x8000,butwecouldprobablyrelaxthisrestrictionto*DATAADDR>=PAGE_OFFS

8、ET+0x4000**Notethatpgtblismeanttoreturnthephysicaladdressofswapper_pg_dir.*Wecan'tmakeitrelativetothekernelpositioninthiscasesince*thekernelcanphysicallybeanyw