Arm Linux系统调用流程详细解析SWI

务,用户程序通过各种系统调用,来引用内核提供的各种服务,系统调用的执行让用户程序陷入内核,该陷入动作由swi软中断完成.

At91rm9200处理器对应的linux2.4.19内核系统调用对应的软中断定义如下:

#if defined(__thumb__)                             //thumb模式#define __syscall(name)                          \"push    {r7}\n\t"                           \"mov    r7, #" __sys1(__NR_##name) "\n\t"    \"swi    0\n\t"                               \"pop    {r7}"#else                                              //arm模式#define __syscall(name) "swi\t" __sys1(__NR_##name) "\n\t"#endif#define __sys2(x) #x#define __sys1(x) __sys2(x)#define __NR_SYSCALL_BASE    0x900000               //此为OS_NUMBER < 20运算值#define __NR_open            (__NR_SYSCALL_BASE+ 5) //0x900005 

举一个例子来说:open系统调用,库函数最终会调用__syscall(open),宏展开之后为swi #__NR_open,即,swi #0x900005触发中断,中断号0x900005存放在[lr,#-4]地址中,处理器跳转到arch/arm/kernel/entry-common.S中vector_swi读取[lr,#-4]地址中的中断号,之后查询arch/arm/kernel/entry-common.S中的sys_call_table系统调用表,该表内容在arch/arm/kernel/calls.S中定义,__NR_open在表中对应的顺序号为

__syscall_start:

.long    SYMBOL_NAME(sys_open)                     //第5个...将sys_call_table[5]中内容传给pc,系统进入sys_open函数,处理实质的open动作注:用到的一些函数数据所在文件,如下所示arch/arm/kernel/calls.S声明了系统调用函数include/asm-arm/unistd.h定义了系统调用的调用号规则vector_swi定义在arch/arm/kernel/entry-common.Svector_IRQ定义在arch/arm/kernel/entry-armv.Svector_FIQ定义在arch/arm/kernel/entry-armv.Sarch/arm/kernel/entry-common.S中对sys_call_table进行了定义:.type    sys_call_table, #objectENTRY(sys_call_table)#include "calls.S"                                 //将calls.S中的内容顺序链接到这里

源程序：

ENTRY(vector_swi)save_user_regszero_fpget_scno                                        //将[lr,#-4]中的中断号转储到scno(r7)arm710_bug_check scno, ip#ifdef CONFIG_ALIGNMENT_TRAPldr    ip, __cr_alignmentldr    ip, [ip]mcr    p15, 0, ip, c1, c0                       @ update control register#endifenable_irq ipstr    r4, [sp, #-S_OFF]!                       @ push fifth argget_current_task tskldr    ip, [tsk, #TSK_PTRACE]                   @ check for syscall tracingbic    scno, scno, #0xff000000                  @ mask off SWI op-code//#define OS_NUMBER    9[entry-header.S]//所以对于上面示例中open系统调用号scno=0x900005//eor scno,scno,#0x900000//之后scno=0x05eor    scno, scno, #OS_NUMBER < 20             @ check OS number//sys_call_table项为calls.S的内容adr    tbl, sys_call_table                      @ load syscall table pointertst    ip, #PT_TRACESYS                         @ are we tracing syscalls?bne    __sys_traceadrsvc    al, lr, ret_fast_syscall              @ return addresscmp    scno, #NR_syscalls                       @ check upper syscall limit//执行sys_open函数ldrcc    pc, [tbl, scno, lsl #2]                @ call sys_* routineadd    r1, sp, #S_OFF2:  mov    why, #0                                  @ no longer a real syscallcmp    scno, #ARMSWI_OFFSETeor    r0, scno, #OS_NUMBER < 20               @ put OS number backbcs    SYMBOL_NAME(arm_syscall)    b    SYMBOL_NAME(sys_ni_syscall)                @ not private func/** This is the really slow path. Were going to be doing* context switches, and waiting for our parent to respond.*/__sys_trace:add    r1, sp, #S_OFFmov    r0, #0                                   @ trace entry [IP = 0]bl    SYMBOL_NAME(syscall_trace)/*//2007-07-01 gliethttp [entry-header.S]//Like adr, but force SVC mode (if required).macro adrsvc, cond, reg, labeladr\cond \reg, \label.endm//对应反汇编://add l