Low-Level Programming

Learning Objectives Differentiate between user-space and kernel-space execution. Explain the purpose and mechanism of a system call. Manage memory manually on the stack and the heap. Implement basic file I/O operations using low-level system calls. Describe the difference between a process and a thread. Identify potential memory management errors like leaks and dangling pointers. Ever wonder how your computer runs multiple programs at once without them crashing into each other? 🤔 Let's pull back the curtain and see how the operating system manages everything! This chapter explores Systems Programming, the art of writing software that interacts directly with the computer's hardware and operating system. You will learn how programs request services from the OS, man...

TermDefinitionExample System CallA programmatic way in which a computer program requests a service from the kernel of the operating system it is executed on. It's the bridge between an application (user-space) and the OS (kernel-space).When your C++ program uses `std::ofstream` to write to a file, the library eventually makes a system call like `write()` to ask the operating system to perform the actual disk write operation. Kernel Space vs. User SpaceA memory protection mechanism. User space is where normal applications run with restricted permissions. Kernel space is where the core of the OS runs with full, privileged access to all hardware.Your web browser runs in user space. When it needs to access the network, it makes a system call, which transitions the CPU into kernel mode to...

The System Call Pattern 1. Prepare arguments in registers/stack. 2. Trigger a software interrupt (e.g., `int 0x80` or `syscall`). 3. CPU switches to kernel mode. 4. Kernel executes the requested service. 5. Kernel places return value in a register. 6. CPU switches back to user mode. This is the fundamental sequence for any user-space application to request a privileged operation from the operating system kernel, such as file I/O, process creation, or network communication. Manual Memory Management (Heap) For every `malloc()` or `new`, there must be a corresponding `free()` or `delete`. For every `new[]`, there must be a corresponding `delete[]`. This rule ensures that dynamically allocated memory on the heap is returned to the system when it's no longer needed. Failing...