.code16
.section ".bstext", "ax"
.global bootsect_start
bootsect_start:
cli
movw %cs, %ax#ax = code section address
movw%ax, %ds#ds = code section address
movw%ax, %es#es = code section address
movw0x4000, %ax#toplimit of stack
movw%ax, %ss#ss = toplimit of stack
xorw%sp, %sp#sp = 0
movw0xB800, %ax
movw%ax, %es#es = address of VGA
xorw%di, %di#di = 0, initial address
movw0x0000, %ax#ax = black space
movw0x0250, %bx#the destination of loop
cloop:stosw#store, di automatically + 2
cmp%di, %bx#check if arrive the destination
jb cloop
xorw%di, %di#di = 0, initial print address
movw$output, %si#si = output addr, init hello word addr
movw0x004C, %bx#the destination of loop
ploop:
lodsb#al -> word, si automatically + 1
movb0x07, %ah#ah -> white word
stosw#print word in colour
cmp%di, %bx
jb ploop
eloop:
jmp eloop
.section ".bsdata", "ax" #data section
output: .ascii "helloworld by whitestarmeow, PB15111598"
length:
.int 2000
strlen:
.int 39
.section ".signature", "a"
.globl sig
sig: .word 0xAA55

gcc -c -m32 start16_hello.S -o start16_hello.o
ld -T start16_hello.ld start16_hello.o -o start16_hello.elf
objcopy -O binary start16_hello.elf start16_hello.bin
dd if=/dev/zero of=a_start16_hello.img bs=512 count=2880
sudo losetup /dev/loop4 a_start16_hello.img
sudo dd if=start16_hello.bin of=/dev/loop4 bs=512 count=1
sudo losetup -d /dev/loop4
qemu-system-i386 -fda a_start16_hello.img

start16_hello.ld
/*
* start16.ld
*
* Linker script for the i386 bootsect code
*/
OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
OUTPUT_ARCH(i386)
ENTRY(bootsect_start)
SECTIONS
{
. = 0x7C00;
.bstext: { *(.bstext) }
.bsdata: { *(.bsdata) }
. = 0x7C00 + 510;
.signature: { *(.signature) }
}