[src/trunk]: src/sys/arch/i386/i386 Add some comments on lgdt().

[mycroft <mycroft%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/0ab88eb0f868
branches:  trunk
changeset: 525292:0ab88eb0f868
user:      mycroft <mycroft%NetBSD.org@localhost>
date:      Tue Apr 09 16:22:22 2002 +0000

description:
Add some comments on lgdt().
Also, reload %fs and %gs, since they are now set to the kernel data descriptor.

diffstat:

 sys/arch/i386/i386/locore.s |  14 +++++++++-----
 1 files changed, 9 insertions(+), 5 deletions(-)

diffs (40 lines):

diff -r c37b3edaa914 -r 0ab88eb0f868 sys/arch/i386/i386/locore.s
--- a/sys/arch/i386/i386/locore.s       Tue Apr 09 16:16:32 2002 +0000
+++ b/sys/arch/i386/i386/locore.s       Tue Apr 09 16:22:22 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: locore.s,v 1.251 2002/04/09 16:16:32 mycroft Exp $     */
+/*     $NetBSD: locore.s,v 1.252 2002/04/09 16:22:22 mycroft Exp $     */
 
 /*-
  * Copyright (c) 1998, 2000 The NetBSD Foundation, Inc.
@@ -1583,22 +1583,26 @@
 
 /*
  * void lgdt(struct region_descriptor *rdp);
- * Change the global descriptor table.
- * XXX should there be an MD section 9 man page for this?
- *     or even just a better comment? --Perry, May 7, 2001
+ * Load a new GDT pointer (and do any necessary cleanup).
+ * XXX It's somewhat questionable whether reloading all the segment registers
+ * is necessary, since the actual descriptor data is not changed except by
+ * process creation and exit, both of which clean up via task switches.  OTOH,
+ * this only happens at run time when the GDT is resized.
  */
 /* LINTSTUB: Func: void lgdt(struct region_descriptor *rdp) */
 NENTRY(lgdt)
        /* Reload the descriptor table. */
        movl    4(%esp),%eax
        lgdt    (%eax)
-       /* Flush the prefetch q. */
+       /* Flush the prefetch queue. */
        jmp     1f
        nop
 1:     /* Reload "stale" selectors. */
        movl    $GSEL(GDATA_SEL, SEL_KPL),%eax
        movw    %ax,%ds
        movw    %ax,%es
+       movw    %ax,%fs
+       movw    %ax,%gs
        movw    %ax,%ss
        /* Reload code selector by doing intersegment return. */
        popl    %eax