体系调用是os操作体系供给的服务,用户程序经过各种体系调用,来引证内核供给的各种服务,体系调用的履行让用户程序堕入内核,该堕入动作由swi软中止完结.
At91rm9200处理器对应的linux2.4.19内核体系调用对应的软中止界说如下:
#if defined(__thumb__) //thumb形式
#define __syscall(name)/
“push {r7}/n/t” /
“mov r7, #” __sys1(__NR_##name) “/n/t” /
“swi 0/n/t” /
“pop {r7}”
#else //arm形式
#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
举一个比如来说:open体系调用,库函数终究会调用__syscall (open),宏打开之后为swi #__NR_open,即,swi #0x900005触发中止,中止号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]地址中的中止号,之后查询arch/arm/kernel/entry-common.S中的sys_call_table体系调用表,该表内容在arch/arm/kernel/calls.S中界说,__NR_open在表中对应的次序号为
__syscall_start:
…
.long SYMBOL_NAME(sys_open) //第5个
…
将sys_call_table[5]中内容传给pc,体系进入sys_open函数,处理本质的open动作
注:用到的一些函数数据地点文件,如下所示
arch/arm/kernel/calls.S声明晰体系调用函数
include/asm-arm/unistd.h界说了体系调用的调用号规矩
vector_swi界说在arch/arm/kernel/entry-common.S
vector_IRQ界说在arch/arm/kernel/entry-armv.S
vector_FIQ界说在arch/arm/kernel/entry-armv.S
arch/arm/kernel/entry-common.S中对sys_call_table进行了界说:
.type sys_call_table, #object
ENTRY(sys_call_table)
#include “calls.S” //将calls.S中的内容次序链接到这儿
源程序：
ENTRY(vector_swi)
save_user_regs
zero_fp
get_scno //将[lr,#-4]中的中止号转储到scno(r7)
arm710_bug_check scno, ip
#ifdef CONFIG_ALIGNMENT_TRAP
ldr ip, __cr_alignment
ldr ip, [ip]
mcr p15, 0, ip, c1, c0 @ update control register
#endif
enable_irq ip
str r4, [sp, #-S_OFF]! @ push fifth arg
get_current_task tsk
ldr ip, [tsk, #TSK_PTRACE] @ check for syscall tracing
bic scno, scno, #0xff000000 @ mask off SWI op-code
//#define OS_NUMBER 9[entry-header.S]
//所以关于上面示例中open体系调用号scno=0x900005
//eor scno,scno,#0x900000
//之后scno=0x05
eor 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 pointer
tst ip, #PT_TRACESYS @ are we tracing syscalls?
bne __sys_trace
adrsvc al, lr, ret_fast_syscall @ return address
cmp scno, #NR_syscalls @ check upper syscall limit
//履行sys_open函数
ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine
add r1, sp, #S_OFF
2: mov why, #0 @ no longer a real syscall
cmp scno, #ARMSWI_OFFSET
eor r0, scno, #OS_NUMBER << 20 @ put OS number back
bcs 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_OFF
mov 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, label
adr/cond /reg, /label
.endm
//对应反汇编:
//add lr, pc, #16 ; lr = __sys_trace_return
*/
adrsvc al, lr, __sys_trace_return @ return address
add r1, sp, #S_R0 + S_OFF @ pointer to regs
cmp scno, #NR_syscalls @ check upper syscall limit
ldmccia r1, {r0 – r3} @ have to reload r0 – r3
ldrcc pc, [tbl, scno, lsl #2] @ call sys_* routine
b 2b
__sys_trace_return:
str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
mov r1, sp
mov r0, #1 @ trace exit [IP = 1]
bl SYMBOL_NAME(syscall_trace)
b ret_disable_irq
.align 5
#ifdef CONFIG_ALIGNMENT_TRAP
.type __cr_alignment, #object
__cr_alignment:
.word SYMBOL_NAME(cr_alignment)
#endif
.type sys_call_table, #object
ENTRY(sys_call_table)
#include “calls.S”
