add comments on switch.S

labcodes/lab4/kern/process/switch.S

@@ -5,24 +5,24 @@ switch_to:                      # switch_to(from, to)
     # save from's registers
     movl 4(%esp), %eax          # eax points to from
     popl 0(%eax)                # save eip !popl
-    movl %esp, 4(%eax)
-    movl %ebx, 8(%eax)
-    movl %ecx, 12(%eax)
-    movl %edx, 16(%eax)
-    movl %esi, 20(%eax)
-    movl %edi, 24(%eax)
-    movl %ebp, 28(%eax)
+    movl %esp, 4(%eax)          # save esp::context of from
+    movl %ebx, 8(%eax)          # save ebx::context of from
+    movl %ecx, 12(%eax)         # save ecx::context of from
+    movl %edx, 16(%eax)         # save edx::context of from
+    movl %esi, 20(%eax)         # save esi::context of from
+    movl %edi, 24(%eax)         # save edi::context of from
+    movl %ebp, 28(%eax)         # save ebp::context of from
 
     # restore to's registers
     movl 4(%esp), %eax          # not 8(%esp): popped return address already
                                 # eax now points to to
-    movl 28(%eax), %ebp
-    movl 24(%eax), %edi
-    movl 20(%eax), %esi
-    movl 16(%eax), %edx
-    movl 12(%eax), %ecx
-    movl 8(%eax), %ebx
-    movl 4(%eax), %esp
+    movl 28(%eax), %ebp         # restore ebp::context of to
+    movl 24(%eax), %edi         # restore edi::context of to
+    movl 20(%eax), %esi         # restore esi::context of to
+    movl 16(%eax), %edx         # restore edx::context of to
+    movl 12(%eax), %ecx         # restore ecx::context of to
+    movl 8(%eax), %ebx          # restore ebx::context of to
+    movl 4(%eax), %esp          # restore esp::context of to
 
     pushl 0(%eax)               # push eip