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Showing posts from February, 2022

How do programs work on a computer? (Part 1/2)

Let's take a very simple program for understanding how this system works. The following example is a very basic C code that assigns 2 variables (x and y) and then adds them to generate a value 'z'.  Note: We do not output anything in this program void main() { int x = 3; int y = 4; int z = x + y; } But we have a pressing question. Computers inherently work on electronics and logic, so how does it understand and execute the program? The answer is not very simple and you have to bear with me through a tiny journey. Basic Logic Circuits Let's first begin with a very basic Circuit which implements AND logic and OR logic (skip if you are familiar)  As seen in the circuits above, for the left circuit, the LED lights up only when both switches are on. This is AND logic as "Switch 1 AND Switch 2 need to be on". In the circuit on the right, either of the switch will switch on the LED. Note that in the

Dynamically extending the Linux Kernel! An introduction to eBPF

A simple Google search of "eBPF" will tell you that it stands for "extended Berkeley Packet Filter". The words "packet filter" in the name makes me think this has something to do with Computer Networks. But, while it started as a packet filter system, it has extended much beyond that functionality since then. Facebook also had Whatsapp, Instagram, Oculus etc., under its belt, and hence the board decided to rename the company to Meta to symbolise this. In the same way, maybe eBPF should be renamed to represent what it is! So, what exactly is eBPF? To understand eBPF, let us first understand why it is required. A short video explaining eBPF can be found here . Pre-requisites In this journey, the first thing to learn is the difference between userspace and kernel space. This  sub-section of my previous post gives you an overview. As mentioned there, you don't want your user application to have access to any data of any other running application unless spe