# IdeFun

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# Build assembly language development environment under Windows 10

## Foreword

This semester school has arranged the assembly language course, and you need to build your own assembly language development environment. Hereby write down this article to record the construction process.

I have also found a lot of tutorials on setting up an assembly language development environment, but I am still at a loss after reading it.After I have explored, and combined with online tutorials, I want to write this easy-to-understand article.

Tool introduction: DOSBox is a DOS simulation program. Because it uses the SDL library, it can be easily ported to other platforms. At present, DOSBox has been supported on Windows, Linux, Mac OS X, BeOS, palmOS, Android, webOS , OS/2 and other systems. Many games under DOS can be run directly on this platform.

Tool official website:

Tool official website

Project homepage:

Project homepage

Screenshot of assembly tool

## Installation tutorial

### 1. Install DOSBox

Double-click to run the DOSBox installer

Click next

Click next

Select the installation location (I choose D:\DOSBox) and click install

Remember the installation location and use it later

### 2. Create a working directory

After installation, create a working directory (directory location and directory name can be customized)

Mine is in D:/DOSBox/Debug

Then create two folders ASM (put your own assembler) and MASM (put assembly tool) under Debug

Put the assembly tool into the MASM folder

### 3. Mount the working directory

Open the DOSBox installation directory (mine is in D:\DOSBox)

After opening, find the batch file DOSBox 0.74 Options.bat

Just double-click to run it and a notepad will appear

Use the shortcut key Ctrl+F to find the [autoexec] part (usually at the end of the file)

Add the following content to the file and save

Command explanation:

If you don’t add ‘cls’, it will be like this when you open it

With ‘cls’, it will be like this when opened (I think it is more beautiful, according to personal preference)

Note: Without this configuration, you need to manually enter the above command every time you open DOSBox, which is very troublesome

## Instructions for use

### DOSBox commonly used shortcut keys

Shortcut key Function
Alt+Enter Toggle full screen
Ctr+F1 Change keyboard mapping
Alt+Pause Pause simulation
Ctrl+Alt+F5 Start/Stop video recording
Ctrl+F4 Exchange the mounted disk image, that is, update the disk file
Ctrl+F5 Screenshot
Ctrl+F6 Start/Stop recording sound
Ctrl+F7 Reduce frame skipping
Ctrl+F8 Increase frame skip
Ctrl+F9 Close DOSBOX
Ctrl+F10 Capture/Release the mouse
Ctrl+F11 Simulate deceleration
Ctrl+F12 Speed up simulation
Alt+F12 Do not lock the speed

Note: I have not tested all of the above shortcut keys. For more detailed information, see README.txt (in the Documentation in the DOSBox installation directory)

The initial interface is very small, and the interface cannot be stretched directly, so if you need it, you can adjust it according to the following method
Double click to open DOSBox 0.74 Options.bat

Use the shortcut key Ctrl+F to find the windowresolution field

will

To

Note: No need to delete the original sentence, just add # in front of the comment.

After saving, restart DOSBox to take effect

### Create and edit files

Regarding creating and editing files, if your working directory (mounting directory) has an EDIT.COM file (in the assembly toolkit I provided), then you can create and edit the file in DOSBox. If not, please use me The provided toolkit or look down patiently.

Open DOSBox and use the following commands to create and edit the test.asm file

Press Enter and enter the following interface to edit (note: the mouse arrow can only be active in the editor, if you want to exit the mouse, you can use the Ctrl+F10 key combination to exit)

#### Use Notepad to create and edit files (other editors are also available)

Create the test.asm file in this way below

Create a new text document, copy the following code into it and save

Rename it to test.asm afterwards

### Compile and debug

Open DOSBox and enter the following command

After you press Enter, you will be asked for the file name, and it is recommended to press Enter directly

The compiler prompts to enter the name of the cross-reference file. This file is the same as the list file. It is an intermediate result produced by the compiler in the process of compiling the source program into the target file. You can let the compiler not generate this file, just press the Enter key.

You can enter the file name separately like the above picture, and open ASM to view the following

Open the ASM folder and view as follows

Continue to enter the command

After running, check the ASM folder

Continue to execute the following commands

### Simple use of debug

debug is a debugging tool for real mode (8086 mode) programs provided by Dos and Windows

• You can view the contents of various registers of the CPU
• You can check the status of the memory
• Can track the operation of the program at the machine code level
Command Function
R command View and change the contents of CPU registers
D command View the contents of the memory (in the form of machine instructions) (displayed in hexadecimal)
E command Rewrite the content in the memory, that is, provide instructions (using machine instructions), which are used less, mostly A commands
U command View the contents of the memory (convert the form of machine instructions to the form of assembly instructions) (decompilation)
T command Execute an assembly (machine) instruction (that is, execute the instruction in the current instruction buffer)
A command Compared with E, write a machine instruction in the memory in the form of assembly instruction
P command When the assembly instruction is int xx, use the p instruction to end (otherwise the CPU will point to an unknown address segment)
G command After executing the exe run result display
Q command Exit debug
? Command View command help

#### R command

##### View the contents of CPU registers

Tag name set reset
Overflow (whether) OV NV
To Direction (decrease/increase) DN UP
Sign (negative positive) NG PL
Zero (yes) ZR NZ
Auxiliary Carry (yes) AC NA
Parity (even odd) PE PO
Carry Carry (whether) CY NC
##### Change the content of the CPU register
###### Change the value of the register

If you want to modify the value in a register, such as the value in AX, you can add the register name after the R command, enter “r ax” and press the Enter key, and “:” will appear as an input prompt. Enter the value to be written later After the data, press the Enter key (press Enter directly to exit the modification), that is, the modification of the content in AX is completed. If you want to see the modified result, you can use the R command to view it again (there is no need between the R command and the register name). Spaces)

#### D command

Using the D command, you can view the contents of the memory, and debug will output 3 parts:

1. The middle is the content of 128 memory cells starting from the specified address, output in hexadecimal format, the output of each line starts from the address of an integer multiple of 16, and the content of up to 16 cells is output. Note that in each line There is a “-“ in the middle, which divides the output of each line into two parts, so that it is easy to view
2. On the left is the starting address of each line
3. On the right are the displayable ASCII characters corresponding to the data in each memory unit. If there is no corresponding displayable ASCII character, debug will use “.” instead

Note that the content of the memory we see is different in different computers, and it may be used every time
Debug sees different content, because what we see with Debug is the content that was originally in the memory, which is affected by the system environment that may change at any time. Of course, we can also change the memory and registers Content in

After entering the debug, use the D command to view it directly, and the content at the address preset by the debug will be listed

Use d segment address: offset address view (take d 1000:0 as an example)

After using “d segment address: offset address”, then use the D command to list the subsequent content

You can also specify the viewing range of the D command. At this time, use the format of “d segment address: start offset address end offset address”

If the input address is not a multiple of 16, the output effect is like this

#### E command

Rewrite the contents of the memory, but in the form of machine instructions

Write the contents of the memory unit 1000:0-1000:9 as 0, 1, 2, 3…., 9, and you can use the format of “e segment address: starting address data data data $\cdots$” To proceed

Use the E command to modify the contents of the memory unit starting from a certain address one by one by asking questions

• The red part is the modified data entered by the user. When it reaches a certain memory unit, you can choose to modify (enter the value to be modified) or not to modify (press the space directly). After processing a memory unit, press the space To continue processing the next memory unit; after all processing is complete, press enter

You can use the E command to write characters to the memory

You can also use the E command to write a string to the memory

#### U command

For the machine code disassembly display, the display output of the U command is divided into 3 parts, the address of each machine instruction, the machine instruction, and the assembly instruction corresponding to the machine instruction

The command starts from the specified address and disassembles 32 bytes. If the address is omitted, 32 bytes are displayed starting from the next unit of the last instruction of the previous U command

#### T command

##### Use the T command to execute the command pointed to by CS:IP

First use the E command to write 8 bytes of machine code to the memory unit starting from 1000:0

Machine code Corresponding assembly instructions
b80100 mov ax,0001
b90200 mov cx,0002

Then use the R command to view the status of the registers in the CPU, you can see that CS=0740H, IP=0100H, pointing to memory 0740:0100

If you want to use the T command to control the CPU to execute the instructions we wrote to 1000:0, you must first make CS:IP point to 1000:0; then use the R command to modify the contents of CS and IP so that CS:IP points to 1000:0

After completing the above steps, we can use the T command to execute the instructions we wrote (at this time, CS:IP points to the memory unit where our instructions are located). After executing the T command, the CPU executes the instructions pointed to by CS:IP, Then the instruction b8 01 00 (mov ax, 0001) at 1000:0 is executed. After the instruction is executed, Debug displays the status of the register in the output CPU

Note: After the instruction is executed, the content in AX is rewritten to 1, IP is changed to IP+3 (because the instruction length of mov ax,0001 is 3 bytes), CS:IP points to the next instruction

Continue to use the T command to execute the following instructions

Use the T command to continue to execute the following instructions, pay attention to the changes in the contents of the CPU related registers after each instruction is executed

#### A command

It is inconvenient to use the E command to write machine instructions. It is best to write the instructions directly in the form of assembly instructions. For this reason, Debug provides the A command, and the A command writes the machine instructions in the memory in the form of assembly instructions.

First use the A command to write a few instructions to the memory unit starting from 1000:0 in assembly language, and then use the D command to view the execution result of the A command

It can be seen that when using the A command to write instructions, we input assembly instructions. Debug translates these assembly instructions into corresponding machine instructions and writes their machine code to memory.

When using the A command to write assembly instructions, directly press the Enter key after the given start address to indicate the end of the operation

If the A command is not followed by an address, input the command from the preset address

#### ? Command

Type? to see more commands

The results are as follows: