tons more work on modularizing the code
This commit is contained in:
319
include/fat32/fat32_sys.inc
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319
include/fat32/fat32_sys.inc
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; Copyright (c) 2024 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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%ifndef __INC_FAT32_SYS
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%include "partition_table.inc"
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%include "fat32/bpb_offset_bx.inc"
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%include "fat32/fat32_structures.inc"
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ALIGN 4, db 0x90
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InitFATDriver:
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__CDECL16_ENTRY
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.func:
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xor eax, eax
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mov dword [fat32_state + FAT32_State_t.active_cluster_32], eax
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mov dword [fat32_state + FAT32_State_t.active_FAT_cluster_32], eax
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mov dword [fat32_state + FAT32_State_t.first_root_dir_sector_32], eax
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mov dword [fat32_state + FAT32_State_t.active_dir_cluster_32], eax
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.calc_active_part:
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mov bx, [partition_offset_ptr]
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mov ax, [bx + 0]
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mov bx, ax
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mov ax, [bx + 0]
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mov dx, partition_table
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add dx, ax ; dx points to the partition that was booted from
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mov bx, dx ; set bx, should point at our partition
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mov eax, dword [bx + PartEntry_t.lba_start]
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mov dword [fat32_state + FAT32_State_t.active_drive_lba_32], eax
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.calc_first_fat:
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movzx eax, word [fat32_bpb + FAT32_bpb_t.reserved_sectors_16] ; first fat from start of partition
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add eax, dword [fat32_state + FAT32_State_t.active_drive_lba_32] ; calculate offset from start of drive
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mov dword [fat32_state + FAT32_State_t.first_fat_sector_32], eax
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.calc_total_fat:
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mov ebx, dword [fat32_ebpb + FAT32_ebpb_t.sectors_per_fat_32]
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movzx eax, byte [fat32_bpb + FAT32_bpb_t.fat_count_8]
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mul ebx ; result in EDX:EAX, CF set on > 32bit return value
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jc InitFATDriver.error ; as a catch for unhandled overflow, just error if value is greater than 32bits
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mov dword [fat32_state + FAT32_State_t.fat_size_32], eax
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.calc_first_data:
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mov edx, dword [fat32_state + FAT32_State_t.first_fat_sector_32]
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add eax, edx
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mov dword [fat32_state + FAT32_State_t.first_data_sector_32], eax
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.get_first_root_dir:
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; TODO
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jmp InitFATDriver.endp
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.error:
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ERROR STAGE2_FAT32_INIT_ERROR
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.endp:
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__CDECL16_EXIT
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ret
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; TODO: needs validation
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; this involves using the low memory buffer for the bios call and moving the file sector by sector to high memory
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;
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; SFN is a 8.3 file name, all uppercase, and padded with spaces
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; do not add a null byte to the end of the string
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; eg. kernel.bin == "KERNEL BIN"
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;
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; returns first cluster of file if found
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; halts/errors if file is not found
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; uint32_t SearchFATDIR(uint8_t* SFN);
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ALIGN 4, db 0x90
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SearchFATDIR:
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__CDECL16_ENTRY
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.file_lookup:
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.load_first_dir:
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mov eax, [fat32_ebpb + FAT32_ebpb_t.root_dir_cluster_32]
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mov dword [fat32_state + FAT32_State_t.active_dir_cluster_32], eax
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push dword eax ; cluster
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lea ax, [dir_buffer]
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push ax ; offset
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xor ax, ax
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push ax ; segment
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call ReadFATCluster ; uint8_t ReadFATCluster(uint16_t seg, uint16_t offset, uint32_t cluster)
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add sp, 0x8
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lea si, [dir_buffer]
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jmp SearchFATDIR.empty_dir_entry
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.load_next_dir:
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; if eax >= 0x0FFFFFF8 then there are no more clusters (end of chain)
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; if eax == 0x0FFFFFF7 then this is a cluster that is marked as bad
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mov eax, dword [fat32_state + FAT32_State_t.active_dir_cluster_32]
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push dword eax
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call NextCluster ; uint32_t NextCluster(uint32_t active_cluster);
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add sp, 0x4
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cmp eax, 0x0fff_fff7
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jb SearchFATDIR.load_next_dir_next_OK
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ERROR STAGE2_FAT32_END_OF_CHAIN
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.load_next_dir_next_OK:
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; load 512 bytes of directory entries from data sector
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mov eax, [fat32_state + FAT32_State_t.active_dir_cluster_32]
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push dword eax
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lea ax, [dir_buffer] ; cluster
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push ax ; offset
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xor ax, ax
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push ax ; segment
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call ReadFATCluster ; uint8_t ReadFATCluster(uint16_t seg, uint16_t offset, uint32_t cluster)
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sub sp, 0x8
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lea si, [dir_buffer]
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.empty_dir_entry:
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; check for 0x0 in first byte, if true then there are no more files
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; if true we did not find the file, we should error here
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cmp byte [si], 0
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jne SearchFATDIR.unused_dir_entry
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ERROR STAGE2_FAT32_NO_FILE
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.unused_dir_entry:
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; check for 0xe5 and 0x05 in first byte, if true then this entry is unused, but it is not the last entry.
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cmp byte [si], 0xe5
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je SearchFATDIR.next_entry
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cmp byte [si], 0x05
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je SearchFATDIR.next_entry
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jmp SearchFATDIR.parse_dir
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.next_entry:
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; increment offset by 32 bytes to read the next entry in this set of dir entries
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; if we are at the end of the buffer, then load the next buffer
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add si, 0x20 ; 32 bytes
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lea ax, [dir_buffer]
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add ax, 0x1FF ; 512 - 1 bytes
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cmp si, ax
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jae SearchFATDIR.load_next_dir
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jmp SearchFATDIR.empty_dir_entry
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.parse_dir:
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.lfn_check:
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; check for ATTR_READ_ONLY | ATTR_HIDDEN | ATTR_SYSTEM | ATTR_VOLUME_ID (0x0F) in offset 11
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; TODO: going to skip LFN for now, since all valid volumes will have SFN's
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cmp byte [si+11], 0x0F
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je SearchFATDIR.next_entry
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.sfn_file_name_check:
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push si
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push di
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mov cx, 0xA ; max of 11 filename length of 11 characters
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; si points to the start of the current directory entry
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lea di, [BootTarget_str] ; current memory location (8.3 name is at offset 0)
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repe cmpsb ; compare the strings
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pop di
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pop si
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jne SearchFATDIR.next_entry
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.sfn_entry_found:
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mov ax, [si + FAT32_SFN_t.cluster_16_high]
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shl eax, 16
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mov ax, [si + FAT32_SFN_t.cluster_16_low]
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; eax == first cluster of file
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.endp:
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__CDECL16_EXIT
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ret
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; uint32_t NextCluster(uint32_t active_cluster);
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; if eax >= 0x0FFFFFF8 then there are no more clusters (end of chain)
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; if eax == 0x0FFFFFF7 then this is a cluster that is marked as bad
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ALIGN 4, db 0x90
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NextCluster:
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__CDECL16_ENTRY
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.func:
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mov bx, [boot_drive_ptr]
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mov ax, [bx + 0]
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mov bx, ax
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movzx ax, byte [bx + 0] ; 67h override would probably work but this is the 16bit way to do it
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mov byte [bp - 2], al ; save boot drive as a local for easy access
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mov dword edx, [bp + 4]
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mov si, fat32_nc_data
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.calc_offset:
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; fat_offset = active_cluster * 4
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mov eax, 4
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mul edx
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mov dword [si + FAT32_NextClusterData_t.fat_offset], eax
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.calc_fat_sector:
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; fat_sector = first_fat_sector + (fat_offset / sector_size)
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; entry_offset = fat_offset % sector_size
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mov edx, 0xffff_0000
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and edx, eax
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shr edx, 16
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push si
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mov si, fat32_bpb
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mov cx, word [si + FAT32_bpb_t.bytes_per_sector_16]
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pop si
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div cx ; DX:AX / cx = fat_sector - first_fat_sector in AX
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; DX = remainder (fat_offset mod sector_size)
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mov ecx, 0x0000_ffff
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and edx, ecx
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mov dword [si + FAT32_NextClusterData_t.entry_offset], edx
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push si
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mov si, fat32_state
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mov ecx, dword [si + FAT32_State_t.first_fat_sector_32]
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pop si
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mov edx, 0x0000ffff
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and eax, edx
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add eax, ecx ; fat_sector + first_fat_sector
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mov dword [si + FAT32_NextClusterData_t.fat_sector], eax
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.load_fat_table:
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movzx ax, [bp - 2]
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push ax
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mov ax, 0x1
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push ax
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; load correct fat
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mov eax, dword [si + FAT32_NextClusterData_t.fat_sector]
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push dword eax
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mov ax, fat_buffer
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push ax
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xor ax, ax
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push ax
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call read_disk_raw
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add sp, 0xC
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; uint8_t read_stage2_raw(uint16_t buf_segment, uint16_t buf_offset,
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; uint32_t lba,
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; uint16_t count, uint16_t drive_num)
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.read_cluster:
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; next_cluster = fat_buffer[entry_offset]
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mov ebx, dword [si + FAT32_NextClusterData_t.entry_offset]
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mov si, fat_buffer
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mov eax, dword [bx+si+0]
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.endp:
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__CDECL16_EXIT
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ret
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; uint32_t ClusterToLBA(uint32_t cluster)
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ALIGN 4, db 0x90
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ClusterToLBA:
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__CDECL16_ENTRY
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.func:
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mov dword eax, [bp + 4]
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sub eax, 2
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movzx edx, byte [fat32_bpb + FAT32_bpb_t.sectors_per_cluster_8]
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mul edx
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add eax, dword [fat32_state + FAT32_State_t.first_data_sector_32]
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; eax contains the LBA now
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.endp:
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__CDECL16_EXIT
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ret
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; uint8_t ReadFATCluster(uint16_t seg, uint16_t offset, uint32_t cluster)
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ALIGN 4, db 0x90
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ReadFATCluster:
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__CDECL16_ENTRY
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.func:
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mov bx, [boot_drive_ptr]
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mov ax, [bx + 0]
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mov bx, ax
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movzx ax, byte [bx + 0] ; 67h override would probably work but this is the 16bit way to do it
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mov byte [bp - 2], al ; save boot drive as a local for easy access
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mov dword eax, [bp + 8]
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push dword eax
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call ClusterToLBA ; uint32_t ClusterToLBA(uint32_t cluster)
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add sp, 0x4 ; eax == LBA
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movzx ax, [bp - 2]
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push ax
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mov ax, 0x1
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push ax
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; load correct fat
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mov eax, dword [si + FAT32_NextClusterData_t.fat_sector]
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push dword eax
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mov ax, fat_buffer
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push ax
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xor ax, ax
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push ax
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call read_disk_raw
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add sp, 0xC
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.endp:
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__CDECL16_EXIT
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ret
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%endif
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%define __INC_FAT32_SYS
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