diff options
Diffstat (limited to 'contrib/syslinux-4.02/mbr/isohdpfx.S')
| -rw-r--r-- | contrib/syslinux-4.02/mbr/isohdpfx.S | 263 |
1 files changed, 263 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/mbr/isohdpfx.S b/contrib/syslinux-4.02/mbr/isohdpfx.S new file mode 100644 index 0000000..0bf807e --- /dev/null +++ b/contrib/syslinux-4.02/mbr/isohdpfx.S @@ -0,0 +1,263 @@ +/* ----------------------------------------------------------------------- + * + * 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 |