RPC知识杂项

操作系统

1. 新建一个fact函数
2. 代码如下：

#include "syscall.h"

int main()
{
int result;
result=Fact(6);

Halt();
}

3. syscall.h

#define SC_Fact 12

int Fact(int a);

4. start.s

加入下面代码

	.globl Fact
	.ent	Fact

Fact:
	addiu $2,$0,SC_Fact
	syscall
	j	$31
	.end Fact

5. 在exception.cc中加入下面内容，照猫画虎

   计算阶乘

   else if ((which == SyscallException) && (type == SC_Fact)) {
       int n = machine->ReadRegister(4);
       int result = 1;
   
       // 计算阶乘
       for (int i = 1; i <= n; ++i) {
           result *= i;
       }
   
       // 将结果存储在寄存器 2 中
       machine->WriteRegister(2, result);
   
       printf("\nsystem call Fact......\n");
   
       printf("n is %d\n", n);
       printf("Factorial of %d = %d\n\n", n, result);
   
       /* set previous program counter (debugging only) */
       machine->WriteRegister(PrevPCReg, machine->ReadRegister(PrevPCReg));
   
       /* set program counter to next instruction (all instructions are 4 bytes wide) */
       machine->WriteRegister(PCReg, machine->ReadRegister(PCReg) + 4);
   
       /* set next program counter for branch execution */
       machine->WriteRegister(NextPCReg, machine->ReadRegister(NextPCReg) + 4);
   
       return;
   }