| /* ----------------------------------------------------------------------- |
| * |
| * 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 |
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| nop |
| nop |
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| 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 |
