标签：linux内核 系统调用 实现 getpid sys_call_table
......
# system call handler stub
ENTRY(system_call)
RING0_INT_FRAME # can't unwind into user space anyway
pushl %eax # save orig_eax
CFI_ADJUST_CFA_OFFSET 4
SAVE_ALL
GET_THREAD_INFO(%ebp)
# system call tracing in operation / emulation
testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%ebp)
jnz syscall_trace_entry
cmpl $(nr_syscalls), %eax
jae syscall_badsys
syscall_call:
call *sys_call_table(,%eax,4) //此处执行相应的系统调用
movl %eax,PT_EAX(%esp) # store the return value
syscall_exit:
LOCKDEP_SYS_EXIT
DISABLE_INTERRUPTS(CLBR_ANY) # make sure we don't miss an interrupt
# setting need_resched or sigpending
# between sampling and the iret
TRACE_IRQS_OFF
movl TI_flags(%ebp), %ecx
testl $_TIF_ALLWORK_MASK, %ecx # current->work
jne syscall_exit_work
......
$ cat ./arch/x86/include/asm/unistd.h #ifdef __KERNEL__ # ifdef CONFIG_X86_32 # include "unistd_32.h" # else # include "unistd_64.h" # endif #else # ifdef __i386__ # include "unistd_32.h" # else # include "unistd_64.h" # endif #endif
# cat arch/x86/include/asm/unistd_32.h #ifndef _ASM_X86_UNISTD_32_H #define _ASM_X86_UNISTD_32_H /* * This file contains the system call numbers. */ #define __NR_restart_syscall 0 #define __NR_exit 1 #define __NR_fork 2 #define __NR_read 3 #define __NR_write 4 #define __NR_open 5 #define __NR_close 6 #define __NR_waitpid 7 #define __NR_creat 8 #define __NR_link 9 #define __NR_unlink 10 #define __NR_execve 11 #define __NR_chdir 12 #define __NR_time 13 #define __NR_mknod 14 #define __NR_chmod 15 #define __NR_lchown 16 #define __NR_break 17 #define __NR_oldstat 18 #define __NR_lseek 19 #define __NR_getpid 20 #define __NR_mount 21 ......
ENTRY(sys_call_table) .long sys_restart_syscall /* 0 - old "setup()" system call, used for restarting */ .long sys_exit .long ptregs_fork .long sys_read .long sys_write .long sys_open /* 5 */ .long sys_close .long sys_waitpid .long sys_creat .long sys_link .long sys_unlink /* 10 */ .long ptregs_execve ...... .long sys_timerfd_settime /* 325 */ .long sys_timerfd_gettime .long sys_signalfd4 .long sys_eventfd2 .long sys_epoll_create1 .long sys_dup3 /* 330 */ .long sys_pipe2 .long sys_inotify_init1 .long sys_preadv .long sys_pwritev .long sys_rt_tgsigqueueinfo /* 335 */ .long sys_perf_event_open
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int main(int argc, const char *argv[])
{
pid_t pid;
asm volatile (
"mov $0, %%ebx\n\t"
"mov $20, %%eax\n\t" //把系统调用号20放入eax寄存器中，20对应于SYS_getpid()系统调用
"int $0x80\n\t" //0x80中断
"mov %%eax, %0\n\t" //将执行结果存放在pid变量中
:"=m"(pid)
);
printf("int PID: %d\n", pid);
printf("api PID: %d\n", getpid());
return 0;
}#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/syscall.h>
int main(int argc, const char *argv[])
{
pid_t pid, pidt;
pid = getpid();
pidt = syscall(SYS_getpid);
printf("getpid: %d\n", pid);
printf("SYS_getpid: %d\n", pidt);
return 0;
}系统调用在内核有一个实现函数，以getpid为例，其在内核实现为：/**
* sys_getpid - return the thread group id of the current process
*
* Note, despite the name, this returns the tgid not the pid. The tgid and
* the pid are identical unless CLONE_THREAD was specified on clone() in
* which case the tgid is the same in all threads of the same group.
*
* This is SMP safe as current->tgid does not change.
*/
SYSCALL_DEFINE0(getpid)
{
return task_tgid_vnr(current);
}
asmlinkage long sys_getpid(void)
{
return current->tpid;
}版权声明：本文为博主原创文章，未经博主允许不得转载。
标签：linux内核 系统调用 实现 getpid sys_call_table
原文地址：http://blog.csdn.net/shallnet/article/details/47113753
