more userspace stuff

kernel/common.S

@@ -20,8 +20,8 @@ io_wait:
 liftoff:
     cli
 
-    mov 4(%esp), %ecx
-    mov 8(%esp), %ebx
+    mov 4(%esp), %ecx 
+    mov 8(%esp), %ebx  
 
     mov $0x23, %ax
     mov %ax, %ds
@@ -29,15 +29,20 @@ liftoff:
     mov %ax, %fs
     mov %ax, %gs
 
-    push $0x23           
-    push %ebx
-    push $0x202
-    push $0x1B
-    push %ecx
+    pushl $0x23         # User Data Segment (SS)
+    pushl %ebx          # User Stack Pointer (ESP)
+    pushl $0x202        # EFLAGS (Interrupts enabled, bit 1 standard)
+    pushl $0x1B         # User Code Segment (CS)
+    pushl %ecx          # User Entry Point (EIP)
 
     xor %eax, %eax
+    xor %ebx, %ebx
+    xor %ecx, %ecx
     xor %edx, %edx
-    
+    xor %esi, %esi
+    xor %edi, %edi
+    xor %ebp, %ebp
+
     iret
 
 .global outb
@@ -121,5 +126,3 @@ outsw:
 fetch_cr3: 
     mov %cr3, %eax 
     ret
-
-.global set_cr3