MIT6.S081 Lab4: Trap

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我是靠谱客的博主英勇滑板，最近开发中收集的这篇文章主要介绍MIT6.S081 Lab4: Trap，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

RISC-V assembly(easy)

a0-a7. a2
无函数调用
位于0x630
ra中是0x00
输出为 He110 World，如果是大段存储，i应该为0x726c64，57616不需要改

Backtrace(moderate)

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

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;
}

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("%pn", *(uint64*)((char*)fp-8));
fp = *(uint64*)((void*)fp-16);
}
}

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

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 # ←←←←←←←←

在user/user.h中增加字段：

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

在user/usys.pl中增加字段：
```
entry("sigalarm");
entry("sigreturn");
```

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,

给kernel/proc.h中的struct proc结构增加字段：
```
int alarm;
int count;
uint64 callback;
```

在kernel/proc.c中给allocproc函数增加字段：

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

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;
}

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=%dn", r_scause(), p->pid);
printf("
sepc=%p stval=%pn", r_sepc(), r_stval());
p->killed = 1;
}

test1/test2(): resume interrupted code

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

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;
}

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;

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;

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=%dn", r_scause(), p->pid);
printf("
sepc=%p stval=%pn", r_sepc(), r_stval());
p->killed = 1;
}