Drivers code doesn't seem to work about os-tutorial HOT 5 OPEN

Talk is cheap, Show me the code
                                     ---- Linus Torvalds

[bits 16]
load_kernel:
    mov bx, MSG_LOAD_KERNEL
    call print
    call print_nl

    mov bx, KERNEL_OFFSET ; Read from disk and store in 0x1000
    mov dh, 8 ; number of sectors (512 bytes per sector)        <======This line======
    mov dl, [BOOT_DRIVE]
    call disk_load
    ret

$ make debug
qemu-system-i386 -s -fda os-image.bin &
/usr/local/i386elfgcc/bin/i386-elf-gdb -ex "target remote localhost:1234" -ex "symbol-file kernel.elf"
GNU gdb (GDB) 8.2
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "--host=x86_64-apple-darwin18.2.0 --target=i386-elf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word".
/Users/lewisxy/.gdbinit:1: Error in sourced command file:
No symbol table is loaded.  Use the "file" command.
WARNING: Image format was not specified for 'os-image.bin' and probing guessed raw.
         Automatically detecting the format is dangerous for raw images, write operations on block 0 will be restricted.
         Specify the 'raw' format explicitly to remove the restrictions.
Remote debugging using localhost:1234
warning: No executable has been specified and target does not support
determining executable automatically.  Try using the "file" command.
0xfffecf4c in ?? ()
Reading symbols from kernel.elf...done.
(gdb) b main
Breakpoint 1 at 0x1007: file kernel/kernel.c, line 3.
(gdb) c
Continuing.

Breakpoint 1, main () at kernel/kernel.c:3
3	void main() {
(gdb) s
4	    clear_screen();
(gdb) s
clear_screen () at drivers/screen.c:108
108	    int screen_size = MAX_COLS * MAX_ROWS;
(gdb) s
110	    char *screen = VIDEO_ADDRESS;
(gdb) s
112	    for (i = 0; i < screen_size; i++) {
(gdb) s
113	        screen[i*2] = ' ';
(gdb) s
114	        screen[i*2+1] = WHITE_ON_BLACK;
(gdb) s
112	    for (i = 0; i < screen_size; i++) {
(gdb) b 116
Breakpoint 2 at 0x13ca: file drivers/screen.c, line 116.
(gdb) c
Continuing.

Breakpoint 2, clear_screen () at drivers/screen.c:116
116	    set_cursor_offset(get_offset(0, 0));
(gdb) s
get_offset (col=0, row=0) at drivers/screen.c:120
120	int get_offset(int col, int row) { return 2 * (row * MAX_COLS + col); }
(gdb) s
get_offset_row (offset=5078) at drivers/screen.c:121
121	int get_offset_row(int offset) { return offset / (2 * MAX_COLS); }
(gdb) s

Breakpoint 1, main () at kernel/kernel.c:3
3	void main() {
(gdb)