/* ----------------------------------------------------------------------- * * 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. * * ----------------------------------------------------------------------- */ #include "adjust.h" .code16 .text .globl bootsec stack = 0x7c00 driveno = (stack-6) sectors = (stack-8) secpercyl = (stack-12) 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, 0xc0 /* xorw %ax, %ax */ cli movw %ax, %ds movw %ax, %ss movw $stack, %sp movw %sp, %si pushw %es /* es:di -> $PnP header */ pushw %di movw %ax, %es sti cld /* Copy down to 0:0x600 */ movw $_start, %di movw $(512/2), %cx rep; movsw ljmpw $0, $next next: ADJUST_DRIVE pushw %dx /* dl -> drive number */ /* 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 shrw %cx /* Bit 0 = fixed disk subset */ jnc 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) 1: popw %dx /* Get (C)HS geometry */ movb $0x08, %ah int $0x13 andw $0x3f, %cx /* Sector count */ pushw %cx /* Save sectors on the stack */ movzbw %dh, %ax /* dh = max head */ incw %ax /* From 0-based max to count */ mulw %cx /* Heads*sectors -> sectors per cylinder */ /* Save sectors/cylinder on the stack */ pushw %dx /* High word */ pushw %ax /* Low word */ xorl %eax, %eax /* Base */ cdq /* Root (%edx <- 0) */ call scan_partition_table /* If we get here, we have no OS */ missing_os: call error .ascii "Missing operating system.\r\n" /* * read_sector: read a single sector pointed to by %eax to 0x7c00. * CF is set on error. All registers saved. */ read_sector: pushal xorl %edx, %edx movw $bootsec, %bx 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 /* * read_partition_table: * Read a partition table (pointed to by %eax), and copy * the partition table into the ptab buffer. * * Clobbers %si, %di, and %cx, other registers preserved. * %cx = 0 on exit. * * On error, CF is set and ptab is overwritten with junk. */ ptab = _start+446 read_partition_table: call read_sector movw $bootsec+446, %si movw $ptab, %di movw $(16*4/2), %cx rep ; movsw ret /* * scan_partition_table: * Scan a partition table currently loaded in the partition table * area. Preserve all registers. * * On entry: * %eax - base (location of this partition table) * %edx - root (offset from MBR, or 0 for MBR) * * These get pushed into stack slots: * 28(%bp) - %eax - base * 20(%bp) - %edx - root */ scan_partition_table: pushal movw %sp, %bp /* Scan the primary partition table */ movw $ptab, %si movw $4, %cx /* Is it a primary partition table? */ andl %edx, %edx jnz 7f push %si push %cx 5: decb (partition) jz boot addw $16, %si loopw 5b popw %cx /* %cx <- 4 */ popw %si /* %si <- ptab */ /* No primary partitions found, look for extended/logical partitions */ 7: movb 4(%si), %al andb %al, %al jz 12f /* Not a valid partition */ cmpb $0x0f, %al /* 0x0f = Win9x extended */ je 8f andb $~0x80, %al /* 0x85 = Linux extended */ cmpb $0x05, %al /* 0x05 = MS-DOS extended */ jne 9f /* It is an extended partition. Read the extended partition and try to scan it. If the scan returns, re-load the current partition table and resume scan. */ 8: movl 8(%si), %eax /* Partition table offset */ addl %edx, %eax /* Compute location of new ptab */ andl %edx, %edx /* Is this the MBR? */ jnz 10f movl %eax, %edx /* Offset -> root if this was MBR */ 10: call read_partition_table jc 11f call scan_partition_table 11: /* This returned, so we need to reload the current partition table */ movl 28(%bp), %eax /* "Base" */ call read_partition_table /* fall through */ 9: /* Not an extended partition */ andl %edx, %edx /* Are we inside an extended part? */ jz 12f /* If so, this is a logical partition */ decb (partition) je boot 12: addw $16, %si loopw 7b /* Nothing found, return */ popal ret /* * boot: invoke the actual bootstrap. (%si) points to the partition * table entry, and 28(%bp) has the partition table base. */ boot: cmpb $0, 4(%si) je missing_os movl 8(%si), %eax addl 28(%bp), %eax movl %eax, 8(%si) /* Adjust in-memory partition table entry */ call read_sector jc disk_error cmpw $0xaa55, (bootsec+510) jne missing_os /* Not a valid boot sector */ movw $driveno, %sp /* driveno == bootsec-6 */ popw %dx /* dl -> drive number */ popw %di /* es:di -> $PnP vector */ popw %es cli jmpw *%sp /* %sp == bootsec */ 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 /* Location of the partition configuration byte */ partition = _start + 439