changed extention from .s to .nasm
This commit is contained in:
225
src/vbr/vbr.nasm
Executable file
225
src/vbr/vbr.nasm
Executable file
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; Copyright (c) 2023 Elaina Claus
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;
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; Permission is hereby granted, free of charge, to any person obtaining a copy
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; of this software and associated documentation files (the "Software"), to deal
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; in the Software without restriction, including without limitation the rights
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; to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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; copies of the Software, and to permit persons to whom the Software is
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; furnished to do so, subject to the following conditions:
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;
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; The above copyright notice and this permission notice shall be included in all
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; copies or substantial portions of the Software.
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;
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; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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; AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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; OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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; SOFTWARE.
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[BITS 16]
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[ORG 0x7C00]
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[CPU KATMAI]
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jmp short init
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nop
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bpb_start:
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; fill BPB area with 0x00 since we skip writing this part to disk
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; but we need it for the 'jmp short entry; nop' above
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times 33 db 0x00
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ebpb_start:
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; fill BPB area with 0x00 since we skip writing this part to disk
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; but we need it for the 'jmp short entry; nop' above
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times 54 db 0x00
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%include "entry.inc"
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init:
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cli ; We do not want to be interrupted
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xor ax, ax ; 0 AX
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mov ds, ax ; Set segment registers to 0
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mov es, ax ; *
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mov ss, ax ; Set Stack Segment to 0
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mov sp, STACK_START ; Setup stack
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mov bp, sp ; base ptr = stack ptr
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mov bx, VBR_ENTRY ; move BP to the new start of the initial boot sector
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jmp 0:main ; fix up cs:ip just in case and jump to relocated code
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%include "config.inc"
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%include "errors.inc"
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%include "memory.inc"
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%include "partition_table.inc"
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%include "fat32/bpb.inc"
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main:
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sti ; all done with inital setup and relocation, reenable interupts
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mov [bsDriveNumber], dl ; BIOS passes drive number in DL
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mov [partition_offset], si ; save passed partition entry offset
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.check_FAT_size:
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cmp dword [bsSectorHuge], 0 ; SectorsHuge will not be set if FAT12/16
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ja main.load_stage2
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ERROR VBR_ERROR_WRONG_FAT_SIZE
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; read sectors 1-63 to stage2 entry point
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.load_stage2:
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push bp
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mov bp, sp
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;uint8_t read_disk_raw(size_t count, uint16_t buf_segment, uint16_t buf_offset,
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; uint16_t lower_lower_lba, uint16_t upper_lower_lba)
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xor ax, ax
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push ax ; upper_lower_lba = 0
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mov ax , 1
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push ax ; lower_lower_lba = 1
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xor ax, ax
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push ax ; offset = 0
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; 07E0:0
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mov ax, STAGE2_ENTRY
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shr ax, 4
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push ax ; segment = 7E0
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mov ax, STAGE2_SECTOR_COUNT
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push ax
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call read_disk_raw
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leave
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.check_sig:
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mov ax, 0x7E0
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mov fs, ax
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cmp dword [fs:0x7FFC], 0xDEADBEEF
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je main.sig_ok
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ERROR VBR_ERROR_NO_SIGNATURE ; no signature present in stage2
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.sig_ok:
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push bp
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mov bp, sp
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mov ax, fat32_bpb_SIZE ; size in byte
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push ax
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mov ax, bpb_start ; start of bpb
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push ax
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mov ax, fat32_bpb ; defined in memory.inc, destination
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push ax
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call kmemcpy ; copy bpb to memory
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leave
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push bp
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mov bp, sp
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mov ax, fat32_ebpb_SIZE ; 72 bytes of data
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push ax
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mov ax, ebpb_start ; start of ebpb
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push ax
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mov ax, fat32_ebpb ; defined in memory.inc, destination
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push ax
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call kmemcpy ; copy ebpb to memory
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leave
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mov si, [partition_offset]
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mov dl, [bsDriveNumber]
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jmp 0:0x7E00
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stop:
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hlt
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jmp short stop
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; Wrapper for AH=0x42 INT13h (Extended Read)
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;
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; BIOS call details
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; AH = 42h
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; DL = drive number
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; DS:SI -> disk address packet
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;
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; Return:
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; CF clear if successful
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; AH = 00h
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; CF set on error
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; AH = error code
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; disk address packet's block count field set to number of blocks
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; successfully transferred
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;
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;
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; uint8_t read_disk_raw(uint16_t buf_segment, uint16_t buf_offset, uint16_t lower_lower_lba, uint16_t upper_lower_lba)
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; bp-0 = call frame
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; bp-2 = upper_lower_lba
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; bp-4 = lower_lower_lba
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; bp-6 = offset
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; bp-8 = segment
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; bp-10 = count
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; bp-12 = ret ptr
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read_disk_raw:
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push si
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; uint8_t* kmemset(void* dest, uint8_t val, size_t len);
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push bp
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mov bp, sp
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mov ax, 0x10
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push ax ; len = 16 bytes
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xor ax, ax
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push ax ; val = 0
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mov ax, lba_packet
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push ax ; dest = lba_packet address
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call kmemset
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leave
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mov byte [lba_packet + LBAPkt_t.size], 0x10
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mov word [lba_packet + LBAPkt_t.xfer_size], STAGE2_SECTOR_COUNT
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mov ax, [bp-2]
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shl eax, 16
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mov ax, [bp-4]
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mov dword [lba_packet + LBAPkt_t.lower_lba], eax
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mov ax, [bp-6]
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mov word [lba_packet + LBAPkt_t.offset], ax
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mov ax, [bp-8]
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mov word [lba_packet + LBAPkt_t.segment], ax
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mov si, lba_packet
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mov ah, 0x42
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mov dl, byte [bsDriveNumber]
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int 0x13
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jnc read_disk_raw.endf
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ERROR VBR_ERROR_DISK_READ_ERR
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.endf:
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pop si
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ret
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; Data
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; #############
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;
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; Locals
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;
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; #############
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; offset from the begining of sector 0 to the active partition.
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partition_offset:
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dw 0x0000
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%assign bytes_remaining (420 - ($ - $$))
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%warning VBR has bytes_remaining bytes remaining for code (MAX: 420 bytes)
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times (510 - ($ - $$)) nop ; Fill the rest of sector with nop
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BootSig:
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dw 0xAA55 ; Add boot signature at the end of bootloader
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