#objdump

How to reduce the size of an executable file written in C++

𝒐𝒃𝒋𝒅𝒖𝒎𝒑 is a command-line program that is part of the GNU Binutils suite of tools. It’s used primarily for displaying various information from object files, which are typically produced as intermediate files during the compilation of a program.objdump can show information from a wide range of object file formats, including ELF (Executable and Linkable Format), which is the standard format for…

http://stupefydeveloper.blogspot.com/2008/08/cc-embed-binary-data-into-elf.html

I was trying to figure out how a specific Linux utility worked. I will call this utility "util". I don't want to name anything specific, just in case ;). The company that made this utility have an SDK, but for the life of me, I couldn't see a mention in their documentation about how I could use an API to mimic util's functionality. 

I didn't have access to the source or project files, so I couldn't look using the regular means. After much thinking, I thought that maybe I could work through it backwards using objdump and strace.

As I had mentioned in one of my earlier posts, strace is a Linux tool that can show us the system calls that are used by an executable. I wondered if the functionality of util that I was interested in was being implemented using ioctl calls. It turns out that it wasn't, but the beginning of the strace output gave me an interesting lead. I noticed that util was using a specific shared object that was not part of gcc or anything usually Linux related. I decided to look at the symbols listing of this mysterious shared object, using objdump: "objdump -dR libmystery.so". I noticed that there were symbols being exported with very interesting names - names that related to the functionality that I was trying to figure out.

I googled the name of the shared object library that util was using. I saw a changelog talking about my mystery library, and the changelog description mentioned the functionality that I was interested in. I was getting closer! Now I needed to figure out how I could use this shared object library. It turns out, after much (like a lot of) digging in google, I found out that the company who made the utility had just recently released the API for what I needed. I was in luck! I found the header file for the API, and tested it out using a small program that linked with the mystery library (the same one that util was using) - it worked.