From eae0475758d2945884808df951d8748f9300cbe2 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Tue, 23 Apr 2019 16:14:41 -0700
Subject: [PATCH] Seemingly implement system calls (still appears to have a
 bug).

---
 kern/syscall.c | 30 +++++++++++++++++++++++++++---
 kern/trap.c    |  7 +++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/kern/syscall.c b/kern/syscall.c
index 414d489..59adfa7 100644
--- a/kern/syscall.c
+++ b/kern/syscall.c
@@ -19,8 +19,25 @@ sys_cputs(const char *s, size_t len)
 {
 	// Check that the user has permission to read memory [s, s+len).
 	// Destroy the environment if not.
+	const char* bottom = ROUNDDOWN(s, PGSIZE);
+	size_t aligned_count = ROUNDUP(len, PGSIZE) / PGSIZE;
+	while(aligned_count--) {
+		if (!(curenv->env_pgdir[PDX(bottom)] & PTE_P)) {
+			cprintf("[%08x] Tried to print unmapped address\n", curenv->env_id);
+			env_destroy(curenv);
+			return;
+		}
 
-	// LAB 3: Your code here.
+		pde_t pgdir_allowed = curenv->env_pgdir[PDX(bottom)] & PTE_U;
+		pde_t pt_allowed = *pgdir_walk(curenv->env_pgdir, bottom, 0) & PTE_U;
+		if(((curenv->env_tf.tf_cs & 0b11) > 1) && !(pt_allowed & pgdir_allowed)) {
+			cprintf("[%08x] Tried to print forbidden memory\n", curenv->env_id); 
+			env_destroy(curenv);
+			return;
+		}
+
+		bottom += PGSIZE;
+	}
 
 	// Print the string supplied by the user.
 	cprintf("%.*s", len, s);
@@ -70,9 +87,16 @@ syscall(uint32_t syscallno, uint32_t a1, uint32_t a2, uint32_t a3, uint32_t a4,
 	// Return any appropriate return value.
 	// LAB 3: Your code here.
 
-	panic("syscall not implemented");
-
 	switch (syscallno) {
+	case SYS_cputs:
+		sys_cputs((const char*) a1, a2);
+		return 0;
+	case SYS_cgetc:
+		return sys_cgetc();
+	case SYS_getenvid:
+		return sys_getenvid();
+	case SYS_env_destroy:
+		return sys_env_destroy(a1);
 	default:
 		return -E_INVAL;
 	}
diff --git a/kern/trap.c b/kern/trap.c
index e7b6a1a..2a4abef 100644
--- a/kern/trap.c
+++ b/kern/trap.c
@@ -200,6 +200,13 @@ trap_dispatch(struct Trapframe *tf)
 		page_fault_handler(tf);
 	} else if (tf->tf_trapno == T_BRKPT) {
 		monitor(tf);
+	} else if (tf->tf_trapno == T_SYSCALL) {
+		syscall(tf->tf_regs.reg_eax,
+				tf->tf_regs.reg_edx,
+				tf->tf_regs.reg_ecx,
+				tf->tf_regs.reg_ebx,
+				tf->tf_regs.reg_edi,
+				tf->tf_regs.reg_esi);
 	}
 
 	// Unexpected trap: The user process or the kernel has a bug.