linux内核分析之系统调用

在内核入口函数start_kernel中调用trap_init实现系统调用的初始化工作

void __init trap_init(void)
{
	...
	set_system_trap_gate(SYSCALL_VECTOR, &system_call);
	....
}

也就是IDT中0x80用来实现系统调用，实现系统调用的函数为system_call，为汇编实现

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)/*跳转到具体的系统调用函数*/
	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
 ........



具体的系统调用函数存放在sys_call_table表中，在调用system_call具体的系统调用号存放在eax寄存器中。