Fix implementation of clone and exec. Now the init process can load and execute the pci driver

kernel/elf.rs

@@ -61,8 +61,11 @@ impl<'a> Elf<'a> {
             let mut context = context_lock.write();
 
             // Unmap previous image and stack
+            println!("Clear image");
             context.image.clear();
+            println!("Drop heap");
             drop(context.heap.take());
+            println!("Drop stack");
             drop(context.stack.take());
 
             for segment in self.segments() {
@@ -112,6 +115,7 @@ impl<'a> Elf<'a> {
         }
 
         // Go to usermode
+        println!("Execute {:X}", self.entry());
         unsafe { usermode(self.entry(), arch::USER_STACK_OFFSET + arch::USER_STACK_SIZE - 256); }
     }
 }