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From: Sergey Shkonda <serg@bcs1.bcs.zaporizhzhe.ua>
Message-Id: <199510131330.AA09369@bcs1.bcs.zaporizhzhe.ua>
Subject: netboot patch
To: martin@innovus.com, hackers@freebsd.org
Date: Fri, 13 Oct 1995 15:30:25 +0200 (UKR)
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     There are error in first patch. Need be another function
for switching to real mode at exit.

--
Sergey Shkonda,     serg@bcs1.bcs.zaporizhzhe.ua


*** start2.S.OO	Fri Oct 13 15:16:52 1995
--- start2.S	Fri Oct 13 15:29:48 1995
***************
*** 3,9 ****
  #define KERN_CODE_SEG	0x08
  #define KERN_DATA_SEG	0x10
  #define REAL_MODE_SEG	0x18
! #define REAL_MODE_DATA  0x20
  #define CR0_PE		1
  
  #define opsize		.byte 0x66
--- 3,10 ----
  #define KERN_CODE_SEG	0x08
  #define KERN_DATA_SEG	0x10
  #define REAL_MODE_SEG	0x18
! #define REAL_MODE_CODE	0x20
! #define REAL_MODE_DATA  0x28
  #define CR0_PE		1
  
  #define opsize		.byte 0x66
***************
*** 89,95 ****
  	call	_main
  	.globl	_exit
  _exit:
! 	call	_prot_to_real
  #ifdef BOOTROM
  	xor	%eax,%eax
  	mov	%ax,%ds
--- 90,96 ----
  	call	_main
  	.globl	_exit
  _exit:
! 	call	_quit_prot
  #ifdef BOOTROM
  	xor	%eax,%eax
  	mov	%ax,%ds
***************
*** 281,288 ****
  	pop	%eax
  	sub	$RELOC,%eax		/* Adjust return address */
  	push	%eax
  	sub	$RELOC,%esp		  /* Adjust stack pointer */
! 	ljmp	$REAL_MODE_SEG, $1f-RELOC /* jump to a 16 bit segment */
  1:
  	cli
  	mov	$REAL_MODE_DATA, %ax	/* load selector in shadow */
--- 282,324 ----
  	pop	%eax
  	sub	$RELOC,%eax		/* Adjust return address */
  	push	%eax
+ 	sub	$RELOC,%esp		/* Adjust stack pointer */
+ 	ljmp	$REAL_MODE_SEG, $1f	/* jump to a 16 bit segment */
+ 1:
+ 	cli
+ 	/* clear the PE bit of CR0 */
+ 	mov	%cr0, %eax
+ 	opsize
+ 	andl 	$0!CR0_PE, %eax
+ 	mov	%eax, %cr0
+ 
+ 	/* make intersegment jmp to flush the processor pipeline
+ 	 * and reload CS register
+ 	 */
+ 	opsize
+ 	ljmp	$(RELOC)>>4, $2f-RELOC
+ 2:
+ 	/* we are in real mode now
+ 	 * set up the real mode segment registers : DS, SS, ES
+ 	 */
+ 	mov	%cs, %ax
+ 	mov	%ax, %ds
+ 	mov	%ax, %es
+ 	mov	%ax, %ss
+ 	sti
+ 	opsize
+ 	ret
+ 
+ /**************************************************************************
+ QUIT_PROT - Quit from Protected Mode
+ **************************************************************************/
+ 	.globl	_quit_prot
+ _quit_prot:
+ 	pop	%eax
+ 	sub	$RELOC,%eax		/* Adjust return address */
+ 	push	%eax
  	sub	$RELOC,%esp		  /* Adjust stack pointer */
! 	ljmp	$REAL_MODE_CODE, $1f-RELOC /* jump to a 16 bit segment */
  1:
  	cli
  	mov	$REAL_MODE_DATA, %ax	/* load selector in shadow */
***************
*** 330,335 ****
--- 366,375 ----
  	.word	0xffff, 0
  	.byte	0, 0x93, 0xcf, 0
  
+ 	/* 16 bit real mode */
+ 	.word	0xffff, 0
+ 	.byte	0, 0x9b, 0x0f, 0
+ 
  	/* 16 bit real mode code segment */
  	.word	0xffff, RELOC&0xffff
  	.byte	(RELOC)>>16, 0x9b, 0x00, 0
***************
*** 340,344 ****
  
  	.align	4
  gdtarg:
! 	.word	0x27			/* limit */
  	.long	gdt			/* addr */
--- 380,384 ----
  
  	.align	4
  gdtarg:
! 	.word	0x2f			/* limit */
  	.long	gdt			/* addr */