Date: Fri, 13 Oct 1995 15:30:25 +0200 (UKR) From: Sergey Shkonda <serg@bcs1.bcs.zaporizhzhe.ua> To: martin@innovus.com, hackers@freebsd.org Subject: netboot patch Message-ID: <199510131330.AA09369@bcs1.bcs.zaporizhzhe.ua>
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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 */
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