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2002-12-11 Yoshinori K. Okuji <okuji@enbug.org>

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Add a workaround for buggy BIOSes which don't pass boot drive
	correctly. The idea is that GRUB forces the fixed disk flag
	when booted from a hard disk. When BIOS loads GRUB directly,
	the boot drive must be either of 0x00 and 0x80, so this should
	work, if those BIOSes always pass zero to %dl. AFAIK, this
	assumption is always correct.

	* stage2/builtins.c (install_func): Store the fixed disk flag of
	the destination drive in BOOT_DRIVE_MASK in Stage 1.

	* stage1/stage1.h (STAGE1_BOOT_DRIVE_MASK): New macro.

	* stage1/stage1.S (boot_drive_mask): New variable. It is or'ed
	to %dl.
This commit is contained in:
okuji 2002-12-10 17:30:29 +00:00
parent 631d47d206
commit f8111d3b54
4 changed files with 37 additions and 2 deletions
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17
ChangeLog
View file

@ -1,3 +1,20 @@
2002-12-11 Yoshinori K. Okuji <okuji@enbug.org>
Add a workaround for buggy BIOSes which don't pass boot drive
correctly. The idea is that GRUB forces the fixed disk flag
when booted from a hard disk. When BIOS loads GRUB directly,
the boot drive must be either of 0x00 and 0x80, so this should
work, if those BIOSes always pass zero to %dl. AFAIK, this
assumption is always correct.
* stage2/builtins.c (install_func): Store the fixed disk flag of
the destination drive in BOOT_DRIVE_MASK in Stage 1.
* stage1/stage1.h (STAGE1_BOOT_DRIVE_MASK): New macro.
* stage1/stage1.S (boot_drive_mask): New variable. It is or'ed
to %dl.
2002-12-09 Yoshinori K. Okuji <okuji@enbug.org>
* stage2/char_io.c (init_page): Change the software name from

11
stage1/stage1.S
View file

@ -1,7 +1,7 @@
/* -*-Asm-*- */
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 1999,2000,2001 Free Software Foundation, Inc.
* Copyright (C) 1999,2000,2001,2002 Free Software Foundation, Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@ -107,6 +107,15 @@ after_BPB:
/* general setup */
cli /* we're not safe here! */
/*
* This is a workaround for buggy BIOSes which don't pass boot
* drive correctly. If GRUB is installed into a HDD, do
* "orb $0x80, %dl", otherwise "orb $0x00, %dl" (i.e. nop).
*/
.byte 0x80, 0xca
boot_drive_mask:
.byte 0x00
/*
* ljmp to the next instruction because some bogus BIOSes
* jump to 07C0:0000 instead of 0000:7C00.

5
stage1/stage1.h
View file

@ -1,6 +1,6 @@
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 1999, 2000 Free Software Foundation, Inc.
* Copyright (C) 1999,2000,2002 Free Software Foundation, Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
@ -51,6 +51,9 @@
/* The offset of STAGE2_SEGMENT. */
#define STAGE1_STAGE2_SEGMENT 0x48
/* The offset of BOOT_DRIVE_MASK. */
#define STAGE1_BOOT_DRIVE_MASK 0x4d
/* The offset of a magic number used by Windows NT. */
#define STAGE1_WINDOWS_NT_MAGIC 0x1b8

6
stage2/builtins.c
View file

@ -1916,6 +1916,12 @@ install_func (char *arg, int flags)
/* Set the "force LBA" flag. */
*((unsigned char *) (stage1_buffer + STAGE1_FORCE_LBA)) = is_force_lba;
/* Set the boot drive mask. This is a workaround for buggy BIOSes which
don't pass boot drive correctly. Instead, they pass 0x00 even when
booted from 0x80. */
*((unsigned char *) (stage1_buffer + STAGE1_BOOT_DRIVE_MASK))
= (dest_drive & BIOS_FLAG_FIXED_DISK);
/* Read the first sector of Stage 2. */
disk_read_hook = disk_read_savesect_func;