Basic knowledge of assembly language (2) -debug

Basic knowledge of

Machine language is difficult to understand , And the length is long .
Assembly instruction is a writing format that is easy to memorize .
register ： Simply put, yes CPU A device that can store data in .
Assembly language consists of three instructions ：
（1） Assembly instruction ： Mnemonics for machine codes , There is a corresponding machine code .（ The core ）
（2） Pseudo instruction ： No corresponding machine code , By compiler , No corresponding machine code .
（3） Other symbols ： Such as +、-、*、/ etc. , Recognized by compiler , No corresponding machine code .
Memory chips can be divided into two categories in terms of read-write properties ：RAM（ Ram ） and ROM（ read-only memory ）.

register

Different CPU, The number of registers 、 The structure is different .
General registers ：AX、BX、CX、DX.
Physical address ： Physical address = Segment address $\times$+ offset
X Hexadecimal digits move one digit to the left , amount to $\times$X
The segment address is stored in four segment registers CS、DS、SS、ES.
CS：IP Access address instruction .
jmp Instructions , modify CSip.

Debug

I installed a xp Virtual machine to achieve access debug Function of .
（1） use R Command view 、 change CPU The contents of the register .
We already know that AX BX CX DX CS IP These six registers , Now take a look at them .

Modify the contents of the register .

In this figure ,CS：IP Point to ）0AE3:0100, The machine code stored here is 40, The corresponding assembly instructions are INC AX;
have access to r Command to cs and ip Make changes .

（2） use debug Of d Command to view the contents of memory
If we want to know 10000H The content of , have access to “d Segment address ： offset ” To view .

The data in the middle is the content stored in each address , On the left is the starting address of each line , On the right is the data in each memory unit that can be displayed ASCII code .
（3） use debug Of e Command to rewrite the contents of memory
-e Then add the address , Plus the number to be modified , Number customization

Or use -e You can also add addresses .

（4） use E Command to write machine code to memory , use U Command to view the meaning of machine code in memory , use T The command executes the machine code in memory .
-u Add address , Show assembly language ;

-t It can be done in one step .