diff options
| -rw-r--r-- | src/entry.asm | 88 |
1 files changed, 69 insertions, 19 deletions
diff --git a/src/entry.asm b/src/entry.asm index 4ab54ac..34d11cf 100644 --- a/src/entry.asm +++ b/src/entry.asm @@ -24,12 +24,13 @@ %define EXT2_SIG_OFFSET 0x38 ; Signature offset in superblock %define EXT2_TABLE_OFFSET 0x08 ; Inode table offset after superblock %define EXT2_NEW_TABLE 0x1000 ; New inode table location in memory -%define EXT2_INODE_SIZE 0x80 ; Single inode size %define EXT2_ROOT_INODE 0x02 ; Root directory inode -%define EXT2_ROOT_DIR EXT2_NEW_TABLE + (EXT2_ROOT_INODE - 1) * EXT2_INODE_SIZE +%define EXT2_INODE_SIZE 0x80 ; Single inode size +%define EXT2_GET_ADDRESS(inode) (EXT2_NEW_TABLE + (inode - 1) * EXT2_INODE_SIZE) %define EXT2_TYPE_OFFSET 0x00 ; Inode offset of filetype and rights %define EXT2_COUNT_OFFSET 0x1c ; Inode offset of number of data blocks %define EXT2_POINTER_OFFSET 0x28 ; Inode offset of first data pointer +%define EXT2_INODE_OFFSET 0x00 ; Dirent offset of inode number %define EXT2_FILENAME_OFFSET 0x08 ; Dirent offset of file name %define EXT2_ENTRY_LENGTH_OFFSET 0x04 ; Dirent offset of entry length %define EXT2_SIG 0xef53 ; Signature @@ -44,6 +45,8 @@ bits 16 org LOCATION +; This is the first stage. It prints some things, checks some things +; and jumps to the second stage. Nothing special. global _start _start: ; Clear screen @@ -113,9 +116,13 @@ stage_two_msg db "Stage2 loaded", NEWLINE, RETURN, NULL disk_success_msg db "Disk is valid", NEWLINE, RETURN, NULL inode_table_msg db "Found inode table", NEWLINE, RETURN, NULL boot_dir_msg db "Found boot directory", NEWLINE, RETURN, NULL +drive db 0 + +; Filenames boot_dir_name db "boot", NULL boot_dir_name_len equ $ - boot_dir_name -drive db 0 +kernel_file_name db "kernel.bin", NULL +kernel_file_name_len equ $ - kernel_file_name ; Data packet: @@ -134,6 +141,12 @@ lba: times 510 - ($ - $$) db 0 dw 0xAA55 +; This is the second stage. It tries to load '/boot/kernel.bin' into memory. +; To do this, it first checks the integrity of the ext2 fs. Then it has to loop +; through every directory in the root until the 'boot' directory is found. +; The same procedure follows, searching for the kernel.bin file. +; After this is finished, the stage can jump into the protected mode, enable the +; A20 line and finally jump to the kernel! ez stage_two: mov si, stage_two_msg call print ; yay! @@ -147,8 +160,7 @@ stage_two: ; Load inode table mov ax, [superblock + EXT2_SB_SIZE + EXT2_TABLE_OFFSET] ; Inode table - mov cx, 2 - mul cx ; ax = cx * ax + shl ax, 1 ; Multiply ax by 2 mov [lba], ax ; Sector mov ax, 2 mov [count], ax ; Read 1024 bytes @@ -159,51 +171,89 @@ stage_two: call print ; Load root dir - mov bx, EXT2_ROOT_DIR ; First block - mov ax, [bx + EXT2_TYPE_OFFSET] ; Filetype + mov bx, EXT2_GET_ADDRESS(EXT2_ROOT_INODE) ; First block + mov ax, [bx + EXT2_TYPE_OFFSET] ; Get filetype and ax, EXT2_DIR ; AND with directory cmp ax, EXT2_DIR ; Check if it's a directory jne disk_error ; Not a directory! - mov cx, [bx + EXT2_COUNT_OFFSET] ; Number of sectors for inode + ;mov cx, [bx + EXT2_COUNT_OFFSET] ; Number of sectors for inode - TODO later! mov ax, [bx + EXT2_POINTER_OFFSET] ; Address of first block pointer - mov dx, 2 - mul dx + shl ax, 1 ; Multiply ax by 2 mov [lba], ax mov bx, 0x5000 mov [dest], bx call disk_read - ; TODO: Fix endless loop when not found ; Find boot directory - .file_loop: + ; TODO: Fix endless loop when not found + .boot_dir_loop: mov si, bx ; First comparison string add si, EXT2_FILENAME_OFFSET ; Set pointer to filename mov di, boot_dir_name ; Second comparison string mov cx, boot_dir_name_len ; String length rep cmpsb ; Compare strings je .found_boot ; Found correct dirent! - add bx, [bx + EXT2_ENTRY_LENGTH_OFFSET] ; Add dirent struct size - jmp .file_loop ; Jump to next dirent! + add bx, EXT2_ENTRY_LENGTH_OFFSET ; Add dirent struct size + jmp .boot_dir_loop ; Jump to next dirent! .found_boot: mov si, boot_dir_msg call print ; Show happy message! + + ; Find kernel! + ; First, get the 'boot' directory block pointer + ; Second, loop through the files until 'kernel.bin' is found + ; (EXT2_NEW_TABLE + (inode - 1) * EXT2_INODE_SIZE) ; This only works with constant inodes + mov ax, [bx + EXT2_INODE_OFFSET] ; Get inode number + jne disk_error + dec ax ; Decrement inode: (inode - 1) + mov cx, EXT2_INODE_SIZE ; Prepare for multiplication + mul cx ; Multiply inode number + mov bx, ax ; Move for effective address calculations + mov bx, [bx + EXT2_NEW_TABLE] ; Yay - bx is now at the inodes start! + mov ax, [bx + EXT2_TYPE_OFFSET] ; Get filetype + and ax, EXT2_DIR ; AND with directory + cmp ax, EXT2_DIR ; Check if it's a directory + jne disk_error ; Well, 'boot' isn't a directory - what do you want? + ; Read first block + mov ax, [bx + EXT2_POINTER_OFFSET] ; Address of first block pointer + shl ax, 1 ; Multiply ax by 2 + mov [lba], ax + mov bx, 0x5000 + mov [dest], bx + call disk_read + + ; Find kernel + .kernel_file_loop: + mov si, bx ; First comparison string + add si, EXT2_FILENAME_OFFSET ; Set pointer to filename + mov di, kernel_file_name ; Second comparison string + mov cx, kernel_file_name_len ; String length + rep cmpsb ; Compare strings + je .found_kernel ; Found correct dirent! + add bx, EXT2_ENTRY_LENGTH_OFFSET ; Add dirent struct size + jmp .kernel_file_loop ; Jump to next dirent! + + .found_kernel: + mov si, bx ; First comparison string + add si, EXT2_FILENAME_OFFSET ; Set pointer to filename + call print + jmp $ mov bx, 0x5000 mov [dest + 2], bx mov bx, 0 ; Inode location = 0xF0000 mov [dest], bx - call stage_three_load + call kernel_load jmp protected_mode_enter -stage_three_load: +kernel_load: xor ax, ax ; Clear ax mov dx, ax ; Clear dx mov ax, [di] ; Set ax = block pointer - mov dx, 2 ; Mul 2 for sectors - mul dx ; ax = dx * ax + shl ax, 1 ; Multiply ax by 2 mov [lba], ax mov [dest], bx @@ -213,7 +263,7 @@ stage_three_load: add bx, 1024 ; 1kb increase add di, 0x4 ; Move to next block pointer sub cx, 2 ; Read 2 blocks - jnz stage_three_load + jnz kernel_load ret nop |