Clarify function comment.

[pintos-anon] / src / userprog / pagedir.c

diff --git a/src/userprog/pagedir.c b/src/userprog/pagedir.c
index 4604ca2ddf94b24e97f31fbd5d553b06ab3ff7c1..5e7fa9293f2850eb16cc876d2b728deaad42c222 100644 (file)
--- a/src/userprog/pagedir.c
+++ b/src/userprog/pagedir.c
@@ -88,6 +88,8 @@ lookup_page (uint32_t *pd, const void *vaddr, bool create)
 /* Adds a mapping from user virtual page UPAGE to kernel virtual
    address KPAGE in page directory PD.
    UPAGE must not already be mapped.
+   KPAGE should probably be a page obtained from the user pool
+   with palloc_get_page() .
    If WRITABLE is true, the new page is read/write;
    otherwise it is read-only.
    Returns true if successful, false if memory allocation
@@ -223,7 +225,7 @@ pagedir_activate (uint32_t *pd)
      aka PDBR (page directory base register).  This activates our
      new page tables immediately.  See [IA32-v2a] "MOV--Move
      to/from Control Registers" and [IA32-v3] 3.7.5. */
-  asm volatile ("mov %%cr3, %0" :: "r" (vtop (pd)));
+  asm volatile ("movl %0, %%cr3" :: "r" (vtop (pd)));
 }
 
 /* Returns the currently active page directory. */
@@ -235,7 +237,7 @@ active_pd (void)
      See [IA32-v2a] "MOV--Move to/from Control Registers" and
      [IA32-v3] 3.7.5. */
   uintptr_t pd;
-  asm volatile ("mov %0, %%cr3" : "=r" (pd));
+  asm volatile ("movl %%cr3, %0" : "=r" (pd));
   return ptov (pd);
 }