8086 Disassembler 4 5: A Simple and Efficient Way to Analyze, Debug, Reverse Engineer or Modify Executable Files
8086 Disassembler Download 4 5
If you are interested in learning more about the inner workings of executable files, you may want to use a disassembler. A disassembler is a tool that converts machine code into human-readable assembly code. In this article, we will introduce you to one of the best disassemblers for original Intel 8086/8088 instructions: 8086 disassembler 4 5. We will explain what a disassembler is, what 8086 is, how to download and use 8086 disassembler 4 5, and what are its benefits and limitations.
8086 disassembler download 4 5
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What is a disassembler and why do you need one?
A disassembler is a tool that converts machine code into human-readable assembly code
Machine code is the lowest level of programming language that can be executed by a computer. It consists of binary digits (0s and 1s) that represent instructions for the processor. Machine code is usually stored in executable files, such as .exe or .com files.
Assembly code is a higher level of programming language that uses mnemonics (abbreviations) to represent instructions for the processor. Assembly code is easier to read and understand than machine code, but still requires knowledge of the processor architecture and instruction set.
A disassembler is a tool that converts machine code into assembly code. It analyzes the binary digits in an executable file and translates them into corresponding mnemonics. A disassembler can also show other information about the executable file, such as its sections, strings, symbols, raw hex and machine level instructions.
A disassembler can help you analyze, debug, reverse engineer or modify executable files
A disassembler can be useful for various purposes, such as:
Analyzing: You can use a disassembler to examine the structure and logic of an executable file. You can see how it interacts with the operating system, the memory, the hardware devices and other programs. You can also learn how it implements certain algorithms or functions.
Debugging: You can use a disassembler to find and fix errors or bugs in an executable file. You can trace the execution flow of the program and identify where it crashes or behaves unexpectedly. You can also modify the assembly code to correct the errors or bugs.
Reverse engineering: You can use a disassembler to understand how an executable file works without having access to its source code. You can recover the original design or logic of the program and recreate its functionality or behavior. You can also discover any hidden features or secrets in the program.
Modifying: You can use a disassembler to change or enhance an executable file according to your needs or preferences. You can add new features or functions to the program or remove unwanted ones. You can also alter the appearance or performance of the program.
What is 8086 and what are its features?
8086 is a 16-bit microprocessor developed by Intel in 1978
The Intel 8086 was one of the first microprocessors designed for personal computers. It was released in June 1978 as an extension of the previous Intel 8080 processor. It was also compatible with the Intel 8085 processor.
The Intel 8086 was based on a new architecture called x86, which became one of the most popular and widely used architectures in computing history. The x86 architecture has evolved over time with new generations of processors, such as x86-32 (also known as IA-32 or i386) and x86-64 (also known as AMD64 or x64).
8086 has a segmented memory model, a 20-bit address bus and a 16-bit data bus
The Intel 8086 had a segmented memory model, which means that it divided the memory into segments of up to 64KB each. The segments could be accessed by using segment registers (CS for code segment, DS for data segment, SS for stack segment and ES for extra segment) and offset registers (IP for instruction pointer, SP for stack pointer, BP for base pointer, SI for source index and DI for destination index).
The Intel 8086 had a 20-bit address bus, which means that it could address up to 2^20 = 1MB of memory. However, since each segment could be up to 64KB, there was some overlap between segments. The actual address of a memory location was calculated by adding the segment register value multiplied by 16 (or shifted left by 4 bits) to the offset register value.
The Intel 8086 had a 16-bit data bus, which means that it could transfer 16 bits (or 2 bytes) of data at a time between the processor and the memory or I/O devices.
8086 supports 256 instructions, including arithmetic, logic, control, string and I/O operations
The Intel mov ax,bx ; move bx into ax add ax,cx ; add cx to ax sub ax,dx ; subtract dx from ax mul bx ; multiply ax by bx div cx ; divide ax by cx and ax,bx ; perform bitwise AND between ax and bx or ax,cx ; perform bitwise OR between ax and cx xor ax,dx ; perform bitwise XOR between ax and dx not ax ; perform bitwise NOT on ax shl ax,n ; shift ax left by n bits shr ax,n ; shift ax right by n bits jmp label ; jump unconditionally to label jz label ; jump to label if zero flag is set jnz label ; jump to label if zero flag is not set je label ; jump to label if equal flag is set jne label ; jump to label if equal flag is not set jl label ; jump to label if less flag is set jg label ; jump to label if greater flag is set jle label ; jump to label if less or equal flag is set jge label ; jump to label if greater or equal flag is set call proc ; call procedure proc ret ; return from procedure push ax ; push ax onto stack pop bx ; pop bx from stack int n ; generate software interrupt n in al,port ; input byte from port into al ; output byte from al to port movsb ; move byte from [si] to [di] cmpsb ; compare byte at [si] and [di] scasb ; scan byte at [di] against al stosb ; store byte from al to [di] lodsb ; load byte from [si] to al rep ; repeat instruction while cx is not zero
These are some examples of the instructions that the Intel 8086 supports. You can find the complete list and description of the instructions in the official Intel 8086 Programmer's Reference Manual.
How to download and use 8086 disassembler 4 5?
8086 disassembler 4 5 is a free and open source tool that can disassemble raw 16-bit x86 machine code
One of the best disassemblers for original Intel 8086/8088 instructions is 8086 disassembler 4 5. It is a free and open source tool that can disassemble raw 16-bit x86 machine code, such as .com or .bin files. It was written by Gintaras Zilius as an optional exercise during the Computer Architecture course in Vilnius University.
You can download it from GitHub or use an online service like disassembler.io
You can download 8086 disassembler 4 5 from its GitHub repository: https://github.com/gzili/8086-disassembler. You will find the source code (disasm.asm and opcodes.inc) and the executable file (disasm.exe) in the repository. You can also compile the source code yourself using Turbo Assembler (TASM) and Turbo Link (TLINK).
If you don't want to download or compile anything, you can also use an online service like disassembler.io: https://onlinedisassembler.com/. This is a lightweight, online service that can disassemble various types of executable files, including raw binary files. You just need to upload your file and choose the appropriate options for the architecture and the syntax.
You can run it with two positional arguments: input file name and output file name
To use 8086 disassembler 4 5, you need to run it with two positional arguments: input file name and output file name. For example, if you want to disassemble an executable file test.com and output the result into test.asm, you need to run:
disasm test.com test.asm
The input file name should be a valid raw binary file that contains 16-bit x86 machine code. The output file name should be a valid assembly file that will contain the disassembled code.
You can specify different options for the architecture and the syntax
You can also specify different options for the architecture and the syntax of the disassembled code. For example, you can use:
objdump -D -Mintel,i8086 -b binary -m i386 test.com
This will use objdump, another popular disassembler tool, to disassemble test.com using Intel syntax (-Mintel) and i8086 architecture (-Mi8086). You also need to specify that the input file is a binary file (-b binary) and that the machine is i386 (-m i386).
You can find more options and details in the documentation of each tool.
What are the benefits and limitations of 8086 disassembler 4 5?
It supports every instruction from the original Intel 8086/8088 instruction set
One of the benefits of 8086 disassembler 4 5 is that it supports every instruction from the original Intel 8086/8088 instruction set. This means that it can handle any valid machine code that was written for these processors. It can also handle some extensions or variations of these instructions, such as prefixes or operands.
It has a small executable file size (less than 6KB) and fully-buffered file I/O
Another benefit of 8086 disassembler 4 5 is that it has a small executable file size (less than 6KB). This means that it does not take much space or memory to run. It also has fully-buffered file I/O, which means that it reads and writes files in large chunks rather than byte by byte. This improves its performance and efficiency.
It prints helpful error messages for various different I/O errors
A third benefit of 8086 disassembler 4 5 is that it prints helpful error messages for various different I/O errors. For example, if you try to run it without any arguments or with invalid arguments, it will print:
Nepateiktas įvesties failo pavadinimas Nepateiktas išvesties failo pavadinimas Netinkamas įvesties failo pavadinimas Netinkamas išvesties failo pavadinimas Nepavyko atidaryti įvesties failo Nepavyko atidaryti išvesties failo Nepavyko perskaityti įvesties failo Nepavyko įrašyti į išvesties failo
These messages mean:
No input file name given No output file name given Invalid input file name Invalid output file name Failed to open input file Failed to open output file Failed to read input file Failed to write output file
It does not output the results in a more-readable DOS Debug format
One of the limitations of 8086 disassembler 4 5 is that it does not output the results in a more-readable DOS Debug format. DOS Debug is a built-in debugger program in MS-DOS that can also disassemble executable files. It uses a format that shows the offset, hex bytes and assembly code in columns, such as:
-u100 l10 0B9A:0100 B409 MOV AH,09 0B9A:0102 BA0E01 MOV DX,010E 0B9A:0105 CD21 INT 21 0B9A:0107 B8004C MOV AX,4C00 0B9A:010A CD21 INT 21
This format is easier to read and compare than the format used by 8086 disassembler 4 5, which shows only the assembly code in lines, such as:
mov ah,09h mov dx,010eh int 21h mov ax,4c00h int 21h
It does not translate error messages from Lithuanian language (original) to English
Another limitation of 8086 disassembler 4 5 is that it does not translate error messages from Lithuanian language (original) to English. As we saw before, the error messages are printed in Lithuanian language, which may not be understandable for some users. It would be better if there was an option to choose the language of the error messages or if they were translated automatically.
It does not print a usage message when command-line arguments are supplied incorrectly
A third limitation of 8086 disassembler 4 5 is that it does not print a usage message when command-line arguments are supplied incorrectly. A usage message is a message that shows how to use a program correctly by giving examples of valid arguments and options. For example, a usage message for objdump could be:
Usage: objdump [-a-d-D-r-s-g-e-f-i-l-t-x] [-M ] [-b ] [-m ]
A usage message for 8086 disassembler could be:
Usage: disasm
Conclusion and FAQs
8086/8088 instructions. We have also seen that this tool has some features that make it useful and efficient, such as supporting every instruction, having a small file size and printing error messages. However, we have also seen that this tool has some drawbacks that make it less user-friendly, such as not outputting in DOS Debug format, not translating error messages and not printing a usage message.
If you want to learn more about 8086 disassembler 4 5 or try it yourself, you can visit its GitHub repository or use an online service like disassembler.io. You can also check out other disassembler tools, such as objdump or ndisasm, and compare their results and features.
Here are some frequently asked questions about 8086 disassembler 4 5:
Q: What is the difference between a disassembler and a decompiler?
A: A disassembler converts machine code into assembly code, while a decompiler converts machine code into a higher-level programming language, such as C or Java. A decompiler is more advanced and complex than a disassembler, but it may not be able to recover the exact source code of the original program.
Q: What is the difference between a .com and a .exe file?
A: A .com file is a simple executable file format that contains raw binary code for 16-bit processors. A .exe file is a more complex executable file format that contains header information and relocation tables for 16-bit or 32-bit processors. A .com file can be up to 64KB in size, while a .exe file can be larger.
Q: How can I run a .com file on a modern computer?
A: You can use an emulator or a virtual machine that simulates an old computer with a 16-bit processor and an MS-DOS operating system. For example, you can use DOSBox or VirtualBox to run a .com file on your modern computer.
Q: How can I create a .com file from an assembly file?
A: You can use an assembler and a linker that can generate .com files from assembly files. For example, you can use Turbo Assembler (TASM) and Turbo Link (TLINK) to create a .com file from an assembly file.
Q: How can I modify a .com file after disassembling it?
A: You can edit the assembly code in the output file of the disassembler using a text editor or an IDE. Then you can reassemble and relink the modified assembly code using an assembler and a linker. Alternatively, you can use a hex editor to directly edit the binary code in the input file of the disassembler.