Understanding and Viewing UNIX Binaries: From Hex Dumps to Disassembly
When it comes to examining the inner workings of a UNIX binary file, there are several tools and techniques available to provide a detailed view of the 1's and 0's that make up the executable. In this article, we will explore how to use these tools effectively, focusing on the od, objdump, and hexdump utilities.
Introduction to UNIX Binaries
UNIX binaries are compiled executable files that contain machine code and other data required for the program to run on a UNIX-based system. These files are typically in the ELF (Executable and Linkable Format) format, though older ones might be in the a.out format. To understand the contents of these files, it is helpful to view them in a binary or hexadecimal format.
Using od for Hexadecimal Dumping
The od command, or octal dump, is a versatile tool for displaying files in various formats. By default, od uses octal numbers, but with the appropriate options, it can be used to display data in hexadecimal format. Here’s how you can use od to view your UNIX binary:
Open your terminal. Type man od to view the manual page for od. To perform a hexadecimal dump, use the following command:od -t x1 -an -N 100 /path/to/binary
This command will display the first 100 bytes of the binary file in hexadecimal format. The -t x1 option specifies hexadecimal format with one byte per output line, -an suppresses output of block numbers, and -N 100 specifies the number of bytes to read.
Using objdump for Disassembly
objdump is a powerful tool that provides detailed disassembly of the code within a binary file. It is especially useful when you want to understand the machine instructions contained in the binary. Here’s how you can use objdump to disassemble a UNIX binary:
Open your terminal. Type the following command to disassemble the binary:objdump -d /path/to/binary
This command will disassemble the machine code into human-readable assembly instructions. You can then analyze these instructions to gain a deeper understanding of the program's logic.
Additional Tools for Hex Dumping
There are other tools available for hex dumping in UNIX, such as hd and hexdump. These tools can provide similar functionality to od and objdump but may have slightly different options and outputs. Here are a few examples:
hd:hd /path/to/binary
The hd command displays the binary file in a hexadecimal format, similar to od.
hexdump:hexdump -C /path/to/binary
The hexdump -C command shows a readable view of the file, with both the hexadecimal and ASCII representations side by side, making it easier to understand.
Viewing Binaries on Mac OS
For Mac users, many of these tools are available through the Xcode Command Line Tools or installers like Homebrew. Here’s how to install Homebrew and get objdump and hexdump:
Install Homebrew via the terminal: Install objdump and hexdump using Homebrew:curl -fsSL
brew install binutils
This command installs the binutils package, which includes objdump and other tools.
Conclusion
Viewing the contents of a UNIX binary can provide insights into its internal structure and functionality. Whether you choose to use od for hex dumping, objdump for disassembly, or other tools like hd and hexdump, these utilities are invaluable for examining the low-level details of your binaries. By understanding these tools, you can gain a deeper understanding of how UNIX binaries work and can troubleshoot issues more effectively.