diff options
Diffstat (limited to 'purgatory/arch/i386/entry32-16.S')
| -rw-r--r-- | purgatory/arch/i386/entry32-16.S | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/purgatory/arch/i386/entry32-16.S b/purgatory/arch/i386/entry32-16.S new file mode 100644 index 0000000..c051aab --- /dev/null +++ b/purgatory/arch/i386/entry32-16.S @@ -0,0 +1,165 @@ +/* + * kexec: Linux boots Linux + * + * Copyright (C) 2003,2004 Eric Biederman (ebiederm@xmission.com) + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation (version 2 of the License). + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +#undef i386 + .text + .globl entry16, entry16_regs + .arch i386 + .balign 16 +entry16: + .code32 + /* Compute where I am running at (assumes esp valid) */ + call 1f +1: popl %ebx + subl $(1b - entry16), %ebx + + /* Fixup my real mode segment */ + movl %ebx, %eax + shrl $4, %eax + movw %ax, (2 + realptr - entry16)(%ebx) + + /* Fixup the gdt */ + leal (gdt - entry16)(%ebx), %eax + movl %eax, (0x02 + gdt - entry16)(%ebx) + + movl %ebx, %eax + shll $16, %eax + + movl %ebx, %ecx + shrl $16, %ecx + andl $0xff, %ecx + + movl %ebx, %edx + andl $0xff000000, %edx + orl %edx, %ecx + + orl %eax, (0x08 + gdt - entry16)(%ebx) + orl %ecx, (0x0c + gdt - entry16)(%ebx) + orl %eax, (0x10 + gdt - entry16)(%ebx) + orl %ecx, (0x14 + gdt - entry16)(%ebx) + + + /* Setup the classic BIOS interrupt table at 0x0 */ + lidt (idtptr - entry16)(%ebx) + + /* Provide us with 16bit segments that we can use */ + lgdt (gdt - entry16)(%ebx) + + /* Note we don't disable the a20 line, (this shouldn't be required) + * The code to do it is in kexec_test and it is a real pain. + * I will worry about that when I need it. + */ + + /* Load 16bit data segments, to ensure the segment limits are set */ + movl $0x10, %eax + movl %eax, %ds + movl %eax, %es + movl %eax, %ss + movl %eax, %fs + movl %eax, %gs + + /* switch to 16bit mode */ + ljmp $0x08, $1f - entry16 +1: + .code16 + /* Disable Paging and protected mode */ + /* clear the PG & PE bits of CR0 */ + movl %cr0,%eax + andl $~((1 << 31)|(1<<0)),%eax + movl %eax,%cr0 + + /* make intersegment jmp to flush the processor pipeline + * and reload %cs:%eip (to clear upper 16 bits of %eip). + */ + ljmp *(realptr - entry16) +3: + /* we are in real mode now + * set up the real mode segment registers : %ds, $ss, %es + */ + /* Setup the data segment */ + movw %cs, %ax + movw %ax, %ds + + /* Load the registers */ + movl eax - entry16, %eax + movl ebx - entry16, %ebx + movl ecx - entry16, %ecx + movl edx - entry16, %edx + movl esi - entry16, %esi + movl edi - entry16, %esi + movl esp - entry16, %esp + movl ebp - entry16, %ebp + movw es - entry16, %es + movw ss - entry16, %ss + movw fs - entry16, %fs + movw gs - entry16, %gs + movw ds - entry16, %ds + + /* Jump to the kernel entrypoint */ + ljmp %cs:*(realdest - entry16) + + .balign 4 +entry16_regs: +eax: .long 0x00000000 +ebx: .long 0x00000000 +ecx: .long 0x00000000 +edx: .long 0x00000000 +esi: .long 0x00000000 +edi: .long 0x00000000 +esp: .long 0x00000000 +ebp: .long 0x00000000 +ds: .word 0x0000 +es: .word 0x0000 +ss: .word 0x0000 +fs: .word 0x0000 +gs: .word 0x0000 +realdest: +ip: .word 0x0000 +cs: .word 0x0000 +pad: .word 0x0000 + .size entry16_regs, . - entry16_regs + + .balign 16 +realptr: + .word 3b - entry16 + .word 0x0000 + + .data + .balign 16 + +idtptr: + /* 256 entry idt at 0 */ + .word 0x400 - 1 + .word 0, 0 + + .balign 16 +gdt: + /* 0x00 unusable segment so used as the gdt ptr */ + .word gdt_end - gdt - 1 + .long 0 /* gdt */ + .word 0 + + /* 0x08 16 bit real mode code segment */ + .word 0xffff, 0x0000 + .byte 0x00, 0x9b, 0x00, 0x00 + + /* 0x10 16 bit real mode data segment */ + .word 0xffff, 0x0000 + .byte 0x00, 0x93, 0x00, 0x00 +gdt_end: |