Linux内核及ARM的内存管理 .

2009-12-16 09:40 1220人阅读 评论(0)收藏 举报

arch/arm/kernel/head.S

该文件末尾包含了语句：#include "head-common.S"，__lookup_processor_type函数在arch/arm/kernel/head-common.S中定义。

关键数据结构：struct proc_info_list，在arch/arm/include/asm/procinfo.h文件中定义，Cortex对此数据结构的填充在arch/arm/mm/proc-v7.s文件中定义。

head.s中，kernel的关键入口如下：

ENTRY(stext)

 ARM( msr cpsr_c, #PSR_F_BIT | PSR_I_BIT | SVC_MODE ) @ ensure svc mode

 THUMB( mov r9, #PSR_F_BIT | PSR_I_BIT | SVC_MODE )

 THUMB( msr cpsr_c, r9 ) @ ensure svc mode

@ and irqs disabled

mrc p15, 0, r9, c0, c0 @ get processor id

bl __lookup_processor_type @ r5=procinfo r9=cpuid

movs r10, r5 @ invalid processor (r5=0)?

beq __error_p @ yes, error 'p'

bl __lookup_machine_type @ r5=machinfo

movs r8, r5 @ invalid machine (r5=0)?

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

badr lr, __enable_mmu @ return (PIC) address

 ARM( add pc, r10, #PROCINFO_INITFUNC )

 THUMB( add r12, r10, #PROCINFO_INITFUNC )

 THUMB( mov pc, r12 )

ENDPROC(stext)

语句“add pc, r10, #PROCINFO_INITFUNC”通过查表调用proc-v7.s中__v7_setup函数，该函数末尾通过将lr寄存器赋给pc，导致对__enable_mmu的调用，完成使能mmu的操作，之后将r13寄存器值赋给pc，调用__switch_data数据结构中的第一个函数__mmap_switched，该函数指向最后的初始化函数，定义在head-common.s文件中，该函数最终调用init/main.c文件中的start_kernel函数。

语句“mrc p15, 0, r9, c0, c0”将协处理器寄存器CP15读入寄存器r9，此寄存器保存CPUID；之后调用函数__lookup_processor_type查找处理器类型；