PA3 : lazy allocation

trap.c

@@ -14,6 +14,9 @@ extern uint vectors[];  // in vectors.S: array of 256 entry pointers
 struct spinlock tickslock;
 uint ticks;
 
+int mappages(pde_t *pgdir, void *va, uint size, uint pa, int perm);
+
+
 void
 tvinit(void)
 {
@@ -36,6 +39,7 @@ idtinit(void)
 void
 trap(struct trapframe *tf)
 {
+  char * mem;
   if(tf->trapno == T_SYSCALL){
     if(myproc()->killed)
       exit();
@@ -77,9 +81,24 @@ trap(struct trapframe *tf)
             cpuid(), tf->cs, tf->eip);
     lapiceoi();
     break;
-
+  case T_PGFLT:
+    mem = kalloc();
+    uint addr = PGROUNDDOWN(rcr2());
+    if(mem == 0){
+      cprintf("out of memory during alloc\n");
+      break;
+    }
+    memset(mem, 0, PGSIZE);
+    if(mappages(myproc()->pgdir, (char*) addr, PGSIZE, V2P(mem), PTE_W | PTE_U) < 0)
+    {
+      cprintf("out of memory during alloc\n");
+      kfree(mem);
+      break;
+    }
+    break;
   //PAGEBREAK: 13
-  default:
+
+   default:
     if(myproc() == 0 || (tf->cs&3) == 0){
       // In kernel, it must be our mistake.
       cprintf("unexpected trap %d from cpu %d eip %x (cr2=0x%x)\n",