From: Ben Pfaff <blp@cs.stanford.edu>
Date: Mon, 23 Apr 2007 00:05:33 +0000 (+0000)
Subject: Correctly initialize the esp0 pointer in the TSS for the initial
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=58ff179ed68e25b33037ca479b0f51f8fdbec7fe;p=pintos-anon

Correctly initialize the esp0 pointer in the TSS for the initial
kernel thread.  Shouldn't actually matter in practice, because that
pointer is only used on a user->kernel transition, and the initial
kernel thread never runs a user process.

Reported by Godmar Back.
---

diff --git a/src/userprog/process.c b/src/userprog/process.c
index 781cc5d..c0e5215 100644
--- a/src/userprog/process.c
+++ b/src/userprog/process.c
@@ -129,7 +129,7 @@ process_activate (void)
 
   /* Set thread's kernel stack for use in processing
      interrupts. */
-  tss_set_esp0 ((uint8_t *) t + PGSIZE);
+  tss_update ();
 }
 
 /* We load ELF binaries.  The following definitions are taken
diff --git a/src/userprog/tss.c b/src/userprog/tss.c
index f103823..569e8d1 100644
--- a/src/userprog/tss.c
+++ b/src/userprog/tss.c
@@ -82,9 +82,9 @@ tss_init (void)
      few fields of it are ever referenced, and those are the only
      ones we initialize. */
   tss = palloc_get_page (PAL_ASSERT | PAL_ZERO);
-  tss->esp0 = ptov(0x20000);
   tss->ss0 = SEL_KDSEG;
   tss->bitmap = 0xdfff;
+  tss_update ();
 }
 
 /* Returns the kernel TSS. */
@@ -95,10 +95,11 @@ tss_get (void)
   return tss;
 }
 
-/* Sets the ring 0 stack pointer in the TSS to ESP0. */
+/* Sets the ring 0 stack pointer in the TSS to point to the end
+   of the thread stack. */
 void
-tss_set_esp0 (uint8_t *esp0) 
+tss_update (void) 
 {
   ASSERT (tss != NULL);
-  tss->esp0 = esp0;
+  tss->esp0 = (uint8_t *) thread_current () + PGSIZE;
 }
diff --git a/src/userprog/tss.h b/src/userprog/tss.h
index fa8d47b..467bd19 100644
--- a/src/userprog/tss.h
+++ b/src/userprog/tss.h
@@ -6,6 +6,6 @@
 struct tss;
 void tss_init (void);
 struct tss *tss_get (void);
-void tss_set_esp0 (uint8_t *);
+void tss_update (void);
 
 #endif /* userprog/tss.h */