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Fixed restoring segment descriptors in prot_to_real(). The descriptors

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must have limit 0xffff and attribute G = 0 (byte granularity) as well
as other properties that they already had (see e.g., the Intel i486
manual section 22.5).  Not restoring them broke Ctrl-Alt-Del in the
bootstrap for my ASUS P55TP4XE system, probably because the Award BIOS
does anti-tracing stuff involving inaccessible %esp's.

asm.S:
Don't use lret in prot_to_real().  This reduces the risk of using an
incompletely intialized stack segment and saves space.

Submitted by:	"K.Higashino" <a00303@cc.hc.keio.ac.jp> (on 13 Jan 1995!)
		reworked by me
This commit is contained in:
Bruce Evans 1996-03-08 05:15:54 +00:00
parent e522d8a28f
commit c50f3ecf5a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=14412
2 changed files with 13 additions and 12 deletions
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21
sys/i386/boot/biosboot/asm.S
View File

@ -24,7 +24,7 @@
* the rights to redistribute these changes.
*
* from: Mach, Revision 2.2 92/04/04 11:34:13 rpd
* $Id: asm.S,v 1.5 1994/10/06 09:41:01 rgrimes Exp $
* $Id: asm.S,v 1.6 1995/01/25 21:37:36 bde Exp $
*/
@ -116,16 +116,17 @@ xprot:
ENTRY(prot_to_real)
/* set up a dummy stack frame for the second seg change. */
movw $BOOTSEG, %ax
pushw %ax
movw $xreal, %ax /* gas botches pushw $xreal, extra bytes 0, 0 */
pushw %ax /* decode to add %al, (%eax) (%al usually 0) */
/* Prepare %ax while we're still in a mode that gas understands. */
movw $0x30, %ax
/* Change to use16 mode. */
ljmp $0x28, $x16
x16:
mov %ax, %ds
mov %ax, %ss
mov %ax, %es
/* clear the PE bit of CR0 */
mov %cr0, %eax
data32
@ -134,12 +135,12 @@ x16:
/*
* make intersegment jmp to flush the processor pipeline
* using the fake stack frame set up earlier
* and reload CS register
*/
lret
data32
ljmp $BOOTSEG, $xreal
xreal:
/*
* we are in real mode now
* set up the real mode segment registers : DS, SS, ES

4
sys/i386/boot/biosboot/table.c
View File

@ -24,7 +24,7 @@
* the rights to redistribute these changes.
*
* from: Mach, Revision 2.2 92/04/04 11:36:43 rpd
* $Id: table.c,v 1.7 1995/05/30 07:58:36 rgrimes Exp $
* $Id: table.c,v 1.8 1995/06/25 14:02:57 joerg Exp $
*/
/*
@ -86,9 +86,9 @@ struct seg_desc Gdt[] = {
{0xFFFF, RUN, RUN, 0x9E, 0x40, 0x0}, /* 0x18 : boot code */
{0xFFFF, RUN, RUN, 0x92, 0x40, 0x0}, /* 0x20 : boot data */
{0xFFFF, RUN, RUN, 0x9E, 0x0, 0x0}, /* 0x28 : boot code, 16 bits */
{0xFFFF, 0x0, 0x0, 0x92, 0x0, 0x0}, /* 0x30 : boot data, 16 bits */
#ifdef BDE_DEBUGGER
/* More for bdb. */
{}, /* BIOS_CS_INDEX = 6 : null */
{}, /* BIOS_TMP_INDEX = 7 : null */
{}, /* TSS_INDEX = 8 : null */
{0xFFFF, 0x0, 0x0, 0xB2, 0x40, 0x0}, /* DS_286_INDEX = 9 */