MIT6.S081 Lab4: Trap

RISC-V assembly(easy)

1. a0-a7. a2

2. 无函数调用

3. 位于0x630

4. ra中是0x00

5. 输出为 He110 World，如果是大段存储，i应该为0x726c64，57616不需要改

Backtrace(moderate)

1. 在kernel/defs.h中添加函数声明void backtrace(void)

2. 在kernel/riscv.h中添加以下字段：

   // get frame pointer
   static inline uint64
   r_fp()
   {
       uint64 x;
       asm volatile("mv %0, s0" : "=r" (x));
       return x;
   }
   

3. 在kernel/printf.h中定义backtrace函数：

   void
   backtrace(void) {
       uint64 fp = r_fp();
       uint64 end = PGROUNDUP(fp); // end >= fp
   
       printf("backtrace:\n");
   
       while(fp != end) {
           printf("%p\n", *(uint64*)((char*)fp-8));
           fp = *(uint64*)((void*)fp-16);
       }
   }
   

4. 在kernel/sysproc.c的sys_sleep函数中增加字段：

   uint64
   sys_sleep(void)
       {
       int n;
       uint ticks0;
   
       backtrace(); // ←←←←←←←←
   
       if(argint(0, &n) < 0)
           return -1;
       acquire(&tickslock);
       ticks0 = ticks;
       while(ticks - ticks0 < n){
           if(myproc()->killed){
           release(&tickslock);
           return -1;
           }
           sleep(&ticks, &tickslock);
       }
       release(&tickslock);
       return 0;
   }
   

Alarm(Hard)

test0: invoke handler

1. 在Makefile中增加字段：

   UPROGS=\
       $U/_cat\
       $U/_echo\
       $U/_forktest\
       $U/_grep\
       $U/_init\
       $U/_kill\
       $U/_ln\
       $U/_ls\
       $U/_mkdir\
       $U/_rm\
       $U/_sh\
       $U/_stressfs\
       $U/_usertests\
       $U/_grind\
       $U/_wc\
       $U/_zombie\
       $U/_alarmtest\ # ←←←←←←←←
   

2. 在user/user.h中增加字段：

   int sigalarm(int, void (*)(void));
   int sigreturn(void);
   

3. 在user/usys.pl中增加字段：

   entry("sigalarm");
   entry("sigreturn");
   

4. 在kernel/syscall.h和kernel/syscall.c中增加字段：

   #define SYS_sigalarm 22
   #define SYS_sigreturn 23
   

   extern uint64 sys_sigalarm(void);
   extern uint64 sys_sigreturn(void);
   

   [SYS_sigalarm] sys_sigalarm,
   [SYS_sigreturn]  sys_sigreturn,
   

5. 给kernel/proc.h中的struct proc结构增加字段：

   int alarm;
   int count;
   uint64 callback;
   

6. 在kernel/proc.c中给allocproc函数增加字段：

   p->alarm = 0;
   p->count = 0;
   p->callback = 0;
   

7. 在kernel/sysproc.c中增加sigalarm和sigreturn函数定义：

   uint64 sys_sigalarm(void) {
       int arg1;
       uint64 arg2;
       struct proc* p = myproc();
       if(argint(0, &arg1) < 0)
           return -1;
       if(argaddr(1, &arg2) < 0)
           return -1;
       
       p->alarm = arg1;
       p->callback = arg2;
   
       return 0;
   }
   
   uint64 sys_sigreturn(void) {
       return 0;
   }
   

8. 在kernel/trap.c中增加字段：

   if(r_scause() == 8){
       // system call
   
       if(p->killed)
           exit(-1);
   
       // sepc points to the ecall instruction,
       // but we want to return to the next instruction.
       p->trapframe->epc += 4;
   
       // an interrupt will change sstatus &c registers,
       // so don't enable until done with those registers.
       intr_on();
   
       syscall();
   } else if((which_dev = devintr()) != 0){
       // ok
       // ↓↓↓↓↓↓↓↓
       if(which_dev == 2) {
           if(p->alarm) {
               p->count = (p->count+1) % p->alarm;
               if(!p->count){
                   p->trapframe->epc = p->callback;
               }
           }
       }
       // ↑↑↑↑↑↑↑↑
   } else {
       printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid);
       printf("            sepc=%p stval=%p\n", r_sepc(), r_stval());
       p->killed = 1;
   }
   

test1/test2(): resume interrupted code

1. 在kernel/def.h增加函数声明void savetrapframe(struct trapframe*, struct trapframe*)，声明结构体struct trapframe

2. 在kernel/trap.c中增加函数定义：

   void savetrapframe(struct trapframe* dst, struct trapframe* src) {
       dst->epc = src->epc;
       dst->kernel_hartid = src->kernel_hartid;
       dst->kernel_satp = src->kernel_satp;
       dst->kernel_sp = src->kernel_sp;
       dst->kernel_trap = src->kernel_trap;
       dst->a0 = src->a0;
       dst->a1 = src->a1;
       dst->a2 = src->a2;
       dst->a3 = src->a3;
       dst->a4 = src->a4;
       dst->a5 = src->a5;
       dst->a6 = src->a6;
       dst->a7 = src->a7;
       dst->ra = src->ra;
       dst->sp = src->sp;
       dst->gp = src->gp;
       dst->tp = src->tp;
       dst->t0 = src->t0;
       dst->t1 = src->t1;
       dst->t2 = src->t2;
       dst->t3 = src->t3;
       dst->t4 = src->t4;
       dst->t5 = src->t5;
       dst->t6 = src->t6;
       dst->s0 = src->s0;
       dst->s1 = src->s1;
       dst->s2 = src->s2;
       dst->s3 = src->s3;
       dst->s4 = src->s4;
       dst->s5 = src->s5;
       dst->s6 = src->s6;
       dst->s7 = src->s7;
       dst->s8 = src->s8;
       dst->s9 = src->s9;
       dst->s10 = src->s10;
       dst->s11 = src->s11;
   }
   

3. 给kernel/proc.h中的struct proc结构增加字段：

   struct trapframe *trapframe_dup; // a context copy
   int callback_once_flag;
   

4. 给kernel/proc.c中的allocproc和freeproc函数增加字段：

   // Allocate a trapframe_dup page.
   if((p->trapframe_dup = (struct trapframe *)kalloc()) == 0){
       release(&p->lock);
       return 0;
   }
   
   p->callback_once_flag = 0;
   

   if(p->trapframe_dup)
       kfree((void*)p->trapframe_dup);
   p->trapframe_dup = 0;
   

5. 修改sigreturn和usertrap函数：

   uint64 sys_sigreturn(void) {
       struct proc* p = myproc();
   
       savetrapframe(p->trapframe, p->trapframe_dup);
       p->callback_once_flag = 0;
       
       return 0;
   }
   

   if(r_scause() == 8){
       // system call
   
       if(p->killed)
           exit(-1);
   
       // sepc points to the ecall instruction,
       // but we want to return to the next instruction.
       p->trapframe->epc += 4;
   
       // an interrupt will change sstatus &c registers,
       // so don't enable until done with those registers.
       intr_on();
   
       syscall();
   } else if((which_dev = devintr()) != 0){
       // ok
       if(which_dev == 2) {
           if(p->alarm && !p->callback_once_flag) {
               p->count = (p->count+1) % p->alarm;
               if(!p->count){
                   savetrapframe(p->trapframe_dup, p->trapframe);
                   p->callback_once_flag = 1;
                   p->trapframe->epc = p->callback;
               }
           }
       }
   } else {
       printf("usertrap(): unexpected scause %p pid=%d\n", r_scause(), p->pid);
       printf("            sepc=%p stval=%p\n", r_sepc(), r_stval());
       p->killed = 1;
   }