内核编写

8086 CPU（实模式）ROM 实模式显卡和显存寄存器标志寄存器FLAGS 相关工具 Bochs Netwide Assembler(NASM)dd Convert and copy a file 编程语言支持

加电复位后，ROM-BIOS将读取硬盘0面0道1扇区（主引导扇区Main Boot Sector，MBR），共512字节

8086 CPU（实模式）

20根地址线：0x00000~0xFFFFF

DRAM：0x00000~0x9FFFF

ROM：0xF0000~0xFFFFF

外围设备：0xA0000~0xEFFFF

起始地址

结束地址

大小

用途

FFFF0

FFFFF

16B

BIOS入口地址，此地址也属于BIOS区域

F0000

FFFEF

64KB-16B

BIOS区域

C8000

EFFFF

160KB

映射硬件适配器的ROM或内存映射式I/O

C0000

C7FFF

32KB

显示器适配BIOS

B8000

BFFFF

32KB

用于文本模式显示适配器

B0000

B7FFF

32KB

用于黑白显示器适配器

A0000

AFFFF

64KB

用于彩色显示器适配器

9FC00

9FFFF

1KB

EBDA，扩展BIOS区域

07E00

9FBFF

约608KB

可用区域

07C00

07DFF

512B

MBR被BIOS加载到此处

00500

07BFF

约30KB

可用区域

00400

004FF

256B

BIOS Data Area (BIOS数据区)

00000

003FF

1KB

interrupt Vector Table(中断向量表)

reset

CS=0xFFF IP=0x0000

指向物理地址：0xFFFF0 (ROM)

指令指向顺序：低地址到高地址推进

ROM

硬件诊断、检测和初始化。

提供一套软件例程，让人民不必了解硬件的细节的情况控制I/O设备

基本输入输出系统（Base Input & Output System，BIOS）

读取主引导扇区到 0x0000:0x7c00 (0x07c00) 并jmp

实模式

主引导扇区

512字节最后两个字节应当是0x55和0xAA

jmp 0x0000:0x7c00 ROM-BIOS将引导扇区加载到此处

显卡和显存

图形模式

文本模式（80x25 25行，80字符) 0xB8000~0xBFFFF

寄存器

标志寄存器FLAGS

相关工具

Bochs

Netwide Assembler(NASM)

是一款基于英特尔x86 架构的汇编与反汇编工具

nasm xx.asm -o xx.o 汇编文件编译成二进制文件

usage: nasm [-@ response file] [-o outfile] [-f format] [-l listfile]
            [options...] [--] filename
    or nasm -v   for version info

    -t          assemble in SciTech TASM compatible mode
    -g          generate debug information in selected format
    -E (or -e)  preprocess only (writes output to stdout by default)
    -a          don't preprocess (assemble only)
    -M          generate Makefile dependencies on stdout
    -MG         d:o, missing files assumed generated
    -MF <file>  set Makefile dependency file
    -MD <file>  assemble and generate dependencies
    -MT <file>  dependency target name
    -MQ <file>  dependency target name (quoted)
    -MP         emit phony target

    -Z<file>    redirect error messages to file
    -s          redirect error messages to stdout

    -F format   select a debugging format

    -I<path>    adds a pathname to the include file path
    -O<digit>   optimize branch offsets
                -O0: No optimization
                -O1: Minimal optimization
                -Ox: Multipass optimization (default)

    -P<file>    pre-includes a file
    -D<macro>[=<value>] pre-defines a macro
    -U<macro>   undefines a macro
    -X<format>  specifies error reporting format (gnu or vc)
    -w+foo      enables warning foo (equiv. -Wfoo)
    -w-foo      disable warning foo (equiv. -Wno-foo)

--prefix,--postfix
  this options prepend or append the given argument to all
  extern and global variables

Warnings:
    error                   treat warnings as errors (default off)
    macro-params            macro calls with wrong parameter count (default on)
    macro-selfref           cyclic macro references (default off)
    macro-defaults          macros with more default than optional parameters (default on)
    orphan-labels           labels alone on lines without trailing `:' (default on)
    number-overflow         numeric constant does not fit (default on)
    gnu-elf-extensions      using 8- or 16-bit relocation in ELF32, a GNU extension (default off)
    float-overflow          floating point overflow (default on)
    float-denorm            floating point denormal (default off)
    float-underflow         floating point underflow (default off)
    float-toolong           too many digits in floating-point number (default on)
    user                    %warning directives (default on)
    lock                    lock prefix on unlockable instructions (default on)
    hle                     invalid hle prefixes (default on)

response files should contain command line parameters, one per line.

For a list of valid output formats, use -hf.
For a list of debug formats, use -f <form> -y.