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6b1e1df5c9
- Multiboot support added back in FreeLdr MSVC builds so that it can be booted using e.g. GRUB. See CORE-15563. - Re-introduce the disk drive mapper code.
179 lines
4.3 KiB
ArmAsm
179 lines
4.3 KiB
ArmAsm
/*
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* FreeLoader
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* Copyright (C) 1998-2002 Brian Palmer <brianp@sginet.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include <asm.inc>
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#include <arch/pc/x86common.h>
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#include <multiboot.h>
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/* Multiboot support
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*
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* Allows freeldr to be loaded as a "multiboot kernel" by
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* other boot loaders like GRUB.
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* This code is not referenced from anywhere. GRUB searches for
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* the header signature and uses the header to load it.
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*/
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#define MB_INFO_FLAGS_OFFSET 0
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#define MB_INFO_BOOT_DEVICE_OFFSET 12
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#define MB_INFO_COMMAND_LINE_OFFSET 16
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#define CMDLINE_SIZE 256
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/*
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* We want to execute at FREELDR_BASE (to be compatible with
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* bootsector loading), but GRUB only allows loading of
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* multiboot kernels above 1MB. So we let GRUB load us
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* there and then relocate ourself to FREELDR_BASE.
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*/
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#define INITIAL_BASE HEX(200000)
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#ifdef _USE_ML
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EXTERN __bss_start__:DWORD
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EXTERN __bss_end__:DWORD
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#endif
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#ifdef _USE_ML
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.MBDATA SEGMENT PUBLIC 'DATA'
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ASSUME nothing
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#endif
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/* Align to 32 bits boundary */
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.align 4
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/* Multiboot header */
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MultibootHeader:
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/* magic */
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.long MULTIBOOT_HEADER_MAGIC
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/* flags */
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.long MULTIBOOT_HEADER_FLAGS
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/* checksum */
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.long -(MULTIBOOT_HEADER_MAGIC + MULTIBOOT_HEADER_FLAGS)
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/* header_addr */
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.long MultibootHeader + INITIAL_BASE - FREELDR_BASE
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/* load_addr */
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.long INITIAL_BASE
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/* load_end_addr */
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.long 0
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/* bss_end_addr */
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.long 0
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/* entry_addr */
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.long MultibootEntry + INITIAL_BASE - FREELDR_BASE
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#ifdef _USE_ML
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.MBDATA ENDS
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#endif
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.code32
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ASSUME ES:NOTHING, FS:NOTHING, GS:NOTHING
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MultibootEntry:
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cld
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/* Check for valid multiboot signature */
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cmp eax, MULTIBOOT_BOOTLOADER_MAGIC
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jne mbfail
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/* Save command line */
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test dword ptr ds:[ebx + MB_INFO_FLAGS_OFFSET], MB_INFO_FLAG_COMMAND_LINE
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jz mb2
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mov esi, dword ptr ds:[ebx + MB_INFO_COMMAND_LINE_OFFSET]
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mov edi, offset cmdline + INITIAL_BASE - FREELDR_BASE
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mov ecx, CMDLINE_SIZE - 1
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mb1:
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lodsb
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stosb
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test al, al
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jz mb2
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dec ecx
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jnz mb1
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mb2:
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/* See if the boot device was passed in */
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test dword ptr ds:[ebx + MB_INFO_FLAGS_OFFSET], MB_INFO_FLAG_BOOT_DEVICE
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/* If no boot device known, assume first partition of first harddisk */
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mov dx, HEX(0180)
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jz mb3
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/* Load boot drive into DL, boot partition into DH */
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mov edx, dword ptr ds:[ebx + MB_INFO_BOOT_DEVICE_OFFSET]
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bswap edx
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inc dh
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mb3:
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/* Relocate itself to lower address */
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mov esi, INITIAL_BASE
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mov edi, FREELDR_BASE
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mov ecx, offset __bss_start__ - FREELDR_BASE
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shr ecx, 2
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rep movsd
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/* Load segment registers for real-address mode */
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#ifdef _USE_ML
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lgdt fword ptr ds:[gdtptr]
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#else
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lgdt ds:[gdtptr]
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#endif
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mov ax, HEX(10)
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mov ds, ax
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mov es, ax
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mov fs, ax
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mov gs, ax
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mov ss, ax
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/* Jump to relocated code */
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ljmp HEX(08), mb4
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mbfail:
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int 3
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mbstop:
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jmp short mbstop /* We should never get here */
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.code16
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mb4:
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/* Disable protected mode */
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mov eax, cr0
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and eax, CR0_PE_CLR
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mov cr0, eax
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/* Jump to real entry point */
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ljmp16 0, FREELDR_BASE
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.endcode16
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/* Force 8-byte alignment */
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.align 8
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gdt:
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.word HEX(0000), HEX(0000), HEX(0000), HEX(0000) /* 00: NULL descriptor */
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.word HEX(FFFF), HEX(0000), HEX(9B00), HEX(008F) /* 08: 16-bit flat CS (!) */
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.word HEX(FFFF), HEX(0000), HEX(9300), HEX(0000) /* 10: 16-bit real mode DS */
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/* GDT table pointer */
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gdtptr:
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.word HEX(17) /* Limit */
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.long gdt /* Base Address */
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PUBLIC cmdline
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cmdline:
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.space CMDLINE_SIZE
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END
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