bochs use linux boot program debugging helloword

1. Environment Tools

ubuntu 18.04.1

NASM

bochs

2.nasm安装:sudo apt-get install nasm

Bochs installation dependencies compiled library: sudo apt-get install vgabios xorg-dev bochs-sdl bochs bochs-x bochsbios bochs-doc libgtk2.0-dev

Download bochs source, http: //bochs.sourceforge.net/, download the latest version bochs-2.4.6.tar.gz

Extract the source package, unzip and enter the directory bochs-2.6.9, execution

./configure --enable-disasm --enable-debugger

make && make install

3. Write a master boot sector code execution boot.asm, and compiled with the command

nasm boot.asm -o boot.bin

    org 07c00h; tells the compiler that the program is loaded into memory address 07c00h 
    mov AX, cs 
    mov ds, AX 
    mov es, AX 
    Call DispStr; call display string subroutine 
    jmp $; infinite loop 
DispStr: 
    mov AX, bootmessage 
    mov BP, AX; es: bp = string address 
    MOV CX, 16; CX = string length 
    MOV AX, 01301h; AH = 13H, Al = 01h 
    MOV BX, 000CH; page number is 0 (bh = 0) black red (bl = 0Ch , highlighted) 
    mov DL, 0 
    int 10h; interrupt 10h No. 
    RET 

bootmessage : db "the Hello, OS World!" 
Times 510 - ($ - $$) db 0; fill the remaining space, so that the generated binary code exactly 512 bytes 
DW 0xaa55; end mark the MBR

4. boot.bin dd command written in the floppy disk image disk.img first sector

dd if=boot.bin of=disk.img bs=512 count=1 conv=notrunc

5. Create a configuration file bochsrc bochs start, as follows:

romimage: file=/usr/share/bochs/BIOS-bochs-latest
megs: 32
vgaromimage: file=/usr/share/bochs/VGABIOS-lgpl-latest
floppya:1_44=disk.img, status=inserted

boot:floppy

log: bochsout.txt
mouse: enabled=0

6. Run bochs -f bochsrc, pauses in the BIOS, waiting for debugging

At this point, you can set breakpoints, physical address 0x7c00, bochs use various debugging command to view the operation, the command will be mentioned later

Finally, the interface will appear red string "Hello, OS World!"

7.bochs basic commands roughly divided into the following categories

(1) Breakpoint setting command

vb / vbreak up: Offset

Set instruction breakpoint on a virtual address, which can be in seg and offset 0x hexadecimal number beginning, or decimal, octal, or is the beginning of the 0

lb/lbreak addr

Set breakpoints, addr above the linear address

b/break/pb/pbreak addr

Set a breakpoint on a physical address

info break

Displays current information about all breakpoints

d / of / delete n

Delete a breakpoint

(2) The execution control command

c/cont/continue

Continuous execution

s/step/stepi [count]

Execute count instructions, default is one, will follow the content and interrupt function calls

p/n/next [count]

Execute count instructions, default is 1, but skip function and interrupt call

Ctrl+C

Stop the execution, and return to the command prompt

q/quit/exit

Exit debugging and execution

(3) memory operation command

x /nuf addr

Check the content in memory at a linear address addr

xp /nuf addr

Check the content in memory at the physical address addr

其中参数n,u,f分别表示:

n为显示内存单元的计数值,默认为1

u表示单元大小,默认值为w

b(bytes)　　　　1字节

h(halfwords)　　 2字节

w(words)　　　 4字节

g(gaintwords)　 8字节

f为显示格式,默认值为x

　　x(hex)　　　　显示为16进制数

　　d(decimal)　　显示为10进制数

　　u(unsigned)　显示为无符号10进制数

　　o(octal)　　显示为8进制数

　　t(binary)　　显示为2进制数

　　c(char)　　　显示为对应的字符

(4)信息显示和CPU寄存器操作命令

r/reg/regs/registers

显示cpu寄存器及其内容

set $reg=val

修改寄存器的内容,除了段寄存器和标志寄存器以外,其它寄存器都可以修改.

creg

所有CR0-CR4寄存器

sreg

CPU全部状态信息,包括各个段选择子(cs,ds等),ldtr,gdtr等

print-stack

打印堆栈情况

info tab

显示页表

(5)反汇编命令

u/disasm/disassemble start end,反汇编给定线性地址范围的指令

u /10反汇编从当前地址开始的10条指令.

bochs的调试功能可以直接看到cup的执行情况，以及各个寄存器和内存单元的内容，对于掌握程序的运行情况是很有好处的。

bochs use linux boot program debugging helloword

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