/* ----------------------------------------------------------------------- * * 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: cli xorw %bp, %bp 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