system call return values

initialize 2nd cpu's idt

defs.h

@@ -17,7 +17,8 @@ void sleep(void *);
 void wakeup(void *);
 
 // trap.c
-void tinit(void);
+void tvinit(void);
+void idtinit(void);
 
 // string.c
 void * memcpy(void *dst, void *src, unsigned n);

main.c

@@ -25,6 +25,7 @@ main()
     cprintf("an application processor\n");
     release_spinlock(&kernel_lock);
     acquire_spinlock(&kernel_lock);
+    idtinit();
     lapic_init(cpu());
     curproc[cpu()] = &proc[0]; // XXX
     swtch();
@@ -37,7 +38,8 @@ main()
 
   mp_init(); // multiprocessor
   kinit(); // physical memory allocator
-  tinit(); // traps and interrupts
+  tvinit(); // trap vectors
+  idtinit(); // CPU's idt
   pic_init();
 
   // create fake process zero

proc.c

@@ -73,6 +73,7 @@ newproc()
   // set up kernel stack to return to user space
   np->tf = (struct Trapframe *) (np->kstack + KSTACKSIZE - sizeof(struct Trapframe));
   *(np->tf) = *(op->tf);
+  np->tf->tf_regs.reg_eax = 0; // so fork() returns 0 in child
   sp = (unsigned *) np->tf;
   *(--sp) = (unsigned) &trapret;  // for return from swtch()
   *(--sp) = 0;  // previous bp for leave in swtch()

syscall.c

@@ -42,13 +42,16 @@ fetcharg(int argno, int *ip)
   return fetchint(curproc[cpu()], esp + 8 + 4*argno, ip);
 }
 
-void
+int
 sys_fork()
 {
-  newproc();
+  struct proc *np;
+
+  np = newproc();
+  return np->pid;
 }
 
-void
+int
 sys_exit()
 {
   struct proc *p;
@@ -67,14 +70,16 @@ sys_exit()
       p->pid = 1;
 
   swtch();
+
+  return 0;
 }
 
-void
+int
 sys_wait()
 {
   struct proc *p;
   struct proc *cp = curproc[cpu()];
-  int any;
+  int any, pid;
 
   cprintf("waid pid %d ppid %d\n", cp->pid, cp->ppid);
 
@@ -84,53 +89,57 @@ sys_wait()
       if(p->state == ZOMBIE && p->ppid == cp->pid){
         kfree(p->mem, p->sz);
         kfree(p->kstack, KSTACKSIZE);
+        pid = p->pid;
         p->state = UNUSED;
         cprintf("%x collected %x\n", cp, p);
-        return;
+        return pid;
       }
       if(p->state != UNUSED && p->ppid == cp->pid)
         any = 1;
     }
     if(any == 0){
       cprintf("%x nothing to wait for\n", cp);
-      return;
+      return -1;
     }
     sleep(cp);
   }
 }
 
-void
+int
 sys_cons_putc()
 {
   int c;
 
   fetcharg(0, &c);
   cons_putc(c & 0xff);
+  return 0;
 }
 
 void
 syscall()
 {
   struct proc *cp = curproc[cpu()];
   int num = cp->tf->tf_regs.reg_eax;
+  int ret = -1;
 
   cprintf("%x sys %d\n", cp, num);
   switch(num){
   case SYS_fork:
-    sys_fork();
+    ret = sys_fork();
     break;
   case SYS_exit:
-    sys_exit();
+    ret = sys_exit();
     break;
   case SYS_wait:
-    sys_wait();
+    ret = sys_wait();
     break;
   case SYS_cons_putc:
-    sys_cons_putc();
+    ret = sys_cons_putc();
     break;
   default:
     cprintf("unknown sys call %d\n", num);
     // XXX fault
     break;
   }
+  cp->tf->tf_regs.reg_eax = ret;
 }

trap.c

@@ -14,14 +14,19 @@ extern void trapenter();
 extern void trapenter1();
 
 void
-tinit()
+tvinit()
 {
   int i;
 
   for(i = 0; i < 256; i++){
     SETGATE(idt[i], 1, SEG_KCODE << 3, vectors[i], 0);
   }
   SETGATE(idt[T_SYSCALL], T_SYSCALL, SEG_KCODE << 3, vectors[48], 3);
+}
+
+void
+idtinit()
+{
   asm volatile("lidt %0" : : "g" (idt_pd.pd_lim));
 }
 

user1.c

@@ -1,4 +1,4 @@
-void
+int
 fork()
 {
   asm("mov $1, %eax");
@@ -12,19 +12,25 @@ cons_putc(int c)
   asm("int $48");
 }
 
-void
+int
 puts(char *s)
 {
   int i;
 
   for(i = 0; s[i]; i++)
     cons_putc(s[i]);
+  return i;
 }
 
 main()
 {
-  // fork();
-  puts("hello!\n");
+  int pid;
+  pid = fork();
+  if(pid == 0){
+    cons_putc('C');
+  } else {
+    cons_putc('P');
+  }
   while(1)
     ;
 }