at&t版启动引导初步

BOOTSEG        = 0x07c0        /* original address of boot-sector */
SYSSEG        = 0x1000        /* historical load address >> 4 */
    .code16

    .global bootsect_start
bootsect_start:

    # Normalize the start address
    ljmp    $BOOTSEG, $start2

start2:
    movw    %cs, %ax  /* make all the register to zero*/
    movw    %ax, %ds
    movw    %ax, %es
    movw    %ax, %ss
    xorw    %sp, %sp  /* zero the sp*/
    sti
    cld


msg_loop:
    movw    $bugger_off_msg, %ax
    movw     %ax, %bp
    movw     $16, %cx
    movw     $0x1301, %ax
    movw    $0x00c, %bx
    int    $0x10
    jmp    msg_loop

bugger_off_msg:
    .ascii "hello os world!!!"
    .org 510
    .word 0xaa55

Makefile

cc = gcc
ld = ld
as = as
ld_flag = -Ttext 0x0 -s --oformat binary 
c_flag = -E -traditional-cpp

all:a.img
a.img: boot.bin
    dd if=boot.bin of=a.img bs=512 conv=notrunc #用 bin file 生成对应的镜像文件
boot.bin:boot.o
    $(ld) $(ld_flag) $^ -o $@
boot.o:boot.s
    $(as) $^ -o $@
boot.s:boot.S
    $(cc) $(c_flag) $^ -o $@
clean:
    rm a.img boot.s boot.o boo.bin 

这样一个简单的在bios POST后，打印hello os world的程序就完成了，相对于intel版的代码，在编译阶段相对来说复杂的多，但是复杂也就意味着更自由，继续学习。