MIT6.S081 Lab4: Trap

原 作者 佟亦凡 | 发表于 | 分类于 2020级

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;
}