my solution to lab5

lab/kern/syscall.c

@@ -55,6 +55,7 @@ sys_env_destroy(envid_t envid)
 
 	if ((r = envid2env(envid, &e, 1)) < 0)
 		return r;
+	
 	if (e == curenv)
 		cprintf("[%08x] exiting gracefully\n", curenv->env_id);
 	else
@@ -128,6 +129,38 @@ sys_env_set_status(envid_t envid, int status)
 	return 0;
 }
 
+// Set envid's trap frame to 'tf'.
+// tf is modified to make sure that user environments always run at code
+// protection level 3 (CPL 3), interrupts enabled, and IOPL of 0.
+//
+// Returns 0 on success, < 0 on error.  Errors are:
+//	-E_BAD_ENV if environment envid doesn't currently exist,
+//		or the caller doesn't have permission to change envid.
+static int
+sys_env_set_trapframe(envid_t envid, struct Trapframe *tf)
+{
+	// LAB 5: Your code here.
+	// Remember to check whether the user has supplied us with a good
+	// address!
+	struct Env *env;
+	int r;
+	if ( (r = envid2env(envid, &env, 1)) < 0)
+		return r;
+
+	// 什么时候会出现没有权限访问的问题？
+	user_mem_assert(env, tf, sizeof(struct Trapframe), PTE_U);
+	// 直接整个结构体也是可以赋值的
+	
+	// tf->tf_cs |= (GD_UT | 0x3); 
+	tf->tf_eflags |= FL_IF;
+	// 普通进程无I/O权限
+	tf->tf_eflags &=  ~FL_IOPL_MASK;
+	
+	env->env_tf = *tf;
+	return 0;
+	
+}
+
 // Set the page fault upcall for 'envid' by modifying the corresponding struct
 // Env's 'env_pgfault_upcall' field.  When 'envid' causes a page fault, the
 // kernel will push a fault record onto the exception stack, then branch to
@@ -436,6 +469,9 @@ syscall(uint32_t syscallno, uint32_t a1, uint32_t a2, uint32_t a3, uint32_t a4,
 		return sys_ipc_recv( (void *) a1);
 	case SYS_ipc_try_send:
 		return sys_ipc_try_send((envid_t) a1, (uint32_t) a2, (void *) a3, (int) a4);
+
+	case SYS_env_set_trapframe:
+		return sys_env_set_trapframe((envid_t) a1, (struct Trapframe *) a2);
 	case NSYSCALLS:
 		return -E_INVAL;