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Add some comments on lgdt().

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Also, reload %fs and %gs, since they are now set to the kernel data descriptor.
This commit is contained in:
mycroft 2002-04-09 16:22:22 +00:00
parent 745cd2197b
commit e7dc129161
1 changed files with 9 additions and 5 deletions
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14
sys/arch/i386/i386/locore.s
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@ -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 @@ ENTRY(subyte)
/*
* 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