浅析Arm Linux操作系统调用流程详细解析

#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

....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

ENTRY(vector_swi)    save_user_regs    zero_fp    get_scno                                        //将[lr,#-4]中的中断号转储到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]//所以对于上面示例中open系统调用号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//执行sys_open函数    ldrcc    pc, [tbl, scno, lsl #2]                @ call sys_* routine    add    r1, sp, #S_OFF2:  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. We're 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, #objectENTRY(sys_call_table)#include "calls.S"