/* ----------------------------------------------------------------------- * * Copyright 2007-2009 H. Peter Anvin - All Rights Reserved * Copyright 2009 Intel Corporation; author: H. Peter Anvin * * Permission is hereby granted, free of charge, to any person * obtaining a copy of this software and associated documentation * files (the "Software"), to deal in the Software without * restriction, including without limitation the rights to use, * copy, modify, merge, publish, distribute, sublicense, and/or * sell copies of the Software, and to permit persons to whom * the Software is furnished to do so, subject to the following * conditions: * * The above copyright notice and this permission notice shall * be included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. * * ----------------------------------------------------------------------- */ /* * Modified MBR code used on an ISO image in hybrid mode. * * This doesn't follow the El Torito spec at all -- it is just a stub * loader of a hard-coded offset, but that's good enough to load * ISOLINUX. */ #include "adjust.h" .code16 .text HYBRID_MAGIC = 0x7078c0fb isolinux_hybrid_signature = 0x7c00+64 isolinux_start_hybrid = 0x7c00+64+4 .globl bootsec /* Important: the top 6 words on the stack are passed to isolinux.bin */ stack = 0x7c00 partoffset = (stack-8) driveno = (stack-14) heads = (stack-16) sectors = (stack-18) ebios_flag = (stack-20) secpercyl = (stack-24) BIOS_kbdflags = 0x417 BIOS_page = 0x462 /* gas/ld has issues with doing this as absolute addresses... */ .section ".bootsec", "a", @nobits .globl bootsec bootsec: .space 512 .text .globl _start _start: .byte 0x33, 0xed /* xorw %bp, %bp */ nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop .byte 0x33, 0xed /* xorw %bp, %bp */ cli movw %bp, %ss movw $stack, %sp sti cld /* Check to see if we have a partition table entry */ xorl %ebx, %ebx xorl %ecx, %ecx #ifdef PARTITION_SUPPORT andw %si, %si /* %si == 0 -> no partition data */ jz 1f testb $0x7f, (%si) /* Invalid active flag field? */ jnz 1f cmpb %cl, 4(%si) /* Partition type zero == invalid? */ je 1f cmpl $0x58504721, %eax /* !GPT signature in EAX? */ jne 2f cmpb $0xed, 4(%si) /* EFI partition type? */ jne 2f /* We have GPT partition information */ movl (32+20)(%si), %ecx movl (36+20)(%si), %ebx jmp 1f /* We have non-GPT partition information */ 2: movl 8(%si), %ecx #endif 1: /* We have no partition information */ pushl %ebx /* -4: partoffset_hi */ pushl %ecx /* -8: partoffset_lo */ pushw %es /* -10: es:di -> $PnP header */ pushw %di /* -12: es:di -> $PnP header */ movw %bp, %ds movw %bp, %es ADJUST_DRIVE pushw %dx /* -14: dl -> drive number */ /* Copy down to 0:0x600 */ movw $0x7c00, %si movw $_start, %di movw $(512/2), %cx rep; movsw ljmpw $0, $next next: /* Check to see if we have EBIOS */ pushw %dx /* drive number */ movb $0x41, %ah /* %al == 0 already */ movw $0x55aa, %bx xorw %cx, %cx xorb %dh, %dh stc int $0x13 jc 1f cmpw $0xaa55, %bx jne 1f andw $1,%cx /* Bit 0 = fixed disk subset */ jz 1f /* We have EBIOS; patch in the following code at read_sector_cbios: movb $0x42, %ah ; jmp read_common */ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ (read_sector_cbios) jmp 1f 1: popw %dx pushw %cx /* EBIOS flag */ /* Get (C)HS geometry */ movb $0x08, %ah int $0x13 andw $0x3f, %cx /* Sector count */ popw %bx /* EBIOS flag */ pushw %cx /* -16: Save sectors on the stack */ movzbw %dh, %ax /* dh = max head */ incw %ax /* From 0-based max to count */ pushw %ax /* -18: Save heads on the stack */ mulw %cx /* Heads*sectors -> sectors per cylinder */ pushw %bx /* -20: EBIOS flag */ /* Save sectors/cylinder on the stack */ pushw %dx /* -22: High word */ pushw %ax /* -24: Low word */ /* * Load sectors. We do this one at a time mostly to avoid * pitfalls and to share code with the stock MBR code. */ movw $0x7c00, %bx movw $4, %cx /* Sector count */ movl (lba_offset), %eax 2: call read_sector jc disk_error incl %eax addb $(512 >> 8), %bh loopw 2b /* * Okay, that actually worked... update the stack pointer * and jump into isolinux.bin... */ cmpl $HYBRID_MAGIC,(isolinux_hybrid_signature) jne bad_signature cli movw $ebios_flag, %sp /* * Use a ljmpw here to work around a bug in some unknown version * of gas or ld when it comes to jumping to an absolute symbol... * * Look more closely into it if we ever are short on space. */ ljmpw $0, $isolinux_start_hybrid bad_signature: call error .ascii "isolinux.bin missing or corrupt.\r\n" /* * read_sector: read a single sector pointed to by %eax to %es:%bx. * CF is set on error. All registers saved. */ read_sector: pushal xorl %edx, %edx addl (partoffset), %eax adcl (partoffset+4), %edx pushl %edx /* MSW of LBA */ pushl %eax /* LSW of LBA */ pushw %es /* Buffer segment */ pushw %bx /* Buffer offset */ pushw $1 /* Sector count */ pushw $16 /* Size of packet */ movw %sp, %si /* This chunk is skipped if we have ebios */ /* Do not clobber %eax before this chunk! */ /* This also relies on %bx and %edx as set up above. */ read_sector_cbios: divl (secpercyl) shlb $6, %ah movb %ah, %cl movb %al, %ch xchgw %dx, %ax divb (sectors) movb %al, %dh orb %ah, %cl incw %cx /* Sectors are 1-based */ movw $0x0201, %ax read_common: movb (driveno), %dl int $0x13 leaw 16(%si), %sp /* Drop DAPA */ popal ret disk_error: call error .ascii "Operating system load error.\r\n" /* * Print error messages. This is invoked with "call", with the * error message at the return address. */ error: popw %si 2: lodsb movb $0x0e, %ah movb (BIOS_page), %bh movb $0x07, %bl int $0x10 /* May destroy %bp */ cmpb $10, %al /* Newline? */ jne 2b int $0x18 /* Boot failure */ die: hlt jmp die /* Address of pointer to isolinux.bin */ lba_offset = _start+432