diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/entry.asm | 39 |
1 files changed, 38 insertions, 1 deletions
diff --git a/src/entry.asm b/src/entry.asm index 667d721..4b8b247 100644 --- a/src/entry.asm +++ b/src/entry.asm @@ -43,6 +43,8 @@ %define EXT2_GET_ADDRESS(inode) (EXT2_INODE_TABLE_LOC + (inode - 1) * EXT2_INODE_SIZE) %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_IND_POINTER_OFFSET 0x2c ; Inode offset of singly indirect data pointer +%define EXT2_DIRECT_POINTER_COUNT 0x0c ; Direct pointer count %define EXT2_SIG 0xef53 ; Signature ; MMAP constants @@ -284,7 +286,7 @@ stage_two: ; Load kernel mov bx, EXT2_GET_ADDRESS(EXT2_KERNEL_INODE) ; First block - mov cx, [bx + EXT2_COUNT_OFFSET] ; Number of sectors for inode + mov cx, [bx + EXT2_COUNT_OFFSET] ; Number of blocks for inode lea di, [bx + EXT2_POINTER_OFFSET] ; Address of first block pointer mov bx, 0x5000 ; Load to this address mov [dest + 2], bx @@ -308,14 +310,49 @@ stage_two: kernel_load: xor ax, ax ; Clear ax mov dx, ax ; Clear dx + + cmp cx, EXT2_DIRECT_POINTER_COUNT ; Indirect pointer needed? + jge .indirect ; Singly indirect pointer + mov ax, [di] ; Set ax = block pointer shl ax, 1 ; Multiply ax by 2 + mov [lba], ax + mov [dest], bx + call disk_read + jmp .end + +.indirect: + push di + push bx + push cx + + xor ebx, ebx + + mov bx, EXT2_GET_ADDRESS(EXT2_KERNEL_INODE) ; First block + lea di, [bx + EXT2_IND_POINTER_OFFSET] ; Address of singly indirect pointer + mov bx, 0x3000 ; Arbitrary address + mov ax, [di] ; Set ax = block pointer + shl ax, 1 ; Multiply ax by 2 mov [lba], ax mov [dest], bx + call disk_read + + sub cx, EXT2_DIRECT_POINTER_COUNT + lea di, [ebx + 4 * ecx] + mov bx, 0x4000 ; Arbitrary address + mov ax, [di] + shl ax, 1 + mov [lba], ax + mov [dest], bx call disk_read + pop cx + pop bx + pop di + +.end: add bx, 0x400 ; 1kb increase add di, 0x4 ; Move to next block pointer sub cx, 0x2 ; Read 2 blocks |