A05 — Use-After-Free: The Problem of Accessing Freed Memory Key insight: Continuing to use a freed memory block is like continuing to build a house on land you’ve already sold — sooner or later someone will come to tear it down. What is Use-After-Free Use-After-Free (UAF) refers to accessing memory that has already been freed... » read more

Long Article 104: Memory Management – Virtual Part I: In-Depth Page Table Operations and Virtual Memory Areas (VMA) Analysis “Virtual memory is the cornerstone of modern operating systems, and VMA is the ‘map’ of the process address space. This article dives deep into x86 page table structures and VMA design principles, comparing Linux implementation details... » read more

A01 — The Internals of malloc: How brk and mmap Work Together Key Insight: Every block of memory you allocate with malloc is backed by the system making allocation decisions on your behalf. malloc is Not a System Call malloc is a glibc (ptmalloc) library function, not a system call. Two paths for malloc: 1.... » read more

# Long Article 106: Memory Management — Advanced: Deep Dive into Copy-on-Write, Swapping, and NUMA Optimization “When physical memory is insufficient, how does the OS handle it gracefully? This article covers CoW, Swapping, and NUMA optimization.” Introduction Three advanced features for memory pressure: CoW: Share pages on fork, copy only on write Swapping: Move inactive... » read more

Writing an OS Kernel from Scratch | VFS — The Virtual File System: How Linux’s “Everything is a File” Works You use cat /proc/cpuinfo, ls /dev/null, echo "hello" > /tmp/a.txt — three different operations, all using the same open/read/write system calls. Why? The answer is VFS (Virtual File System Switch) — an abstraction layer that... » read more

K10 — NUMA Systems: Memory Nodes and Local Allocation Key Insight: On multi-socket servers, “local memory” and “remote memory” access latency can differ by up to 3x — NUMA is the source of this difference. The Concept of NUMA NUMA (Non-Uniform Memory Access) means each CPU core has local memory. Local access is fast, remote... » read more

B03 — The Complete Boot Flow: From Pressing Power to Handing Control to the Kernel Key Insight: Every boot is a precision relay race. Every handoff must be flawless. Overview of the Complete Boot Flow After pressing the power button, the computer goes through a series of stages before finally handing control to the OS... » read more

K09 — Memory Leaks: Why malloc Without free Causes Unrecoverable Memory Key Insight: After a program ends, the system reclaims its memory — but while running, leaked memory is truly leaked. What Is a Memory Leak A memory leak occurs when a program dynamically allocates memory but fails to release it, making that memory permanently... » read more

A10 — Memory Analysis Tools: malloc_stats, Valgrind Massif, pmap Key Insight: The first step to optimizing memory is knowing where it is being used. malloc_stats: glibc Allocation Statistics malloc_stats() 输出所有 arena 的统计信息： #include <malloc.h> malloc_stats(); 输出示例： Arena 0: system bytes = 1048576 memory bytes = 1048576 96 malloc-chunks in use (12345 bytes) Arena 1: system... » read more

从零开始写一个操作系统kernel-Part 1: 不只是”Hello World” 🌱 从零开始写一个操作系统kernel-Part 1: 不只是”Hello World”! 你是否曾好奇: ✅ Windows, Linux, macOS 这些操作系统是怎么”从无到有”启动的? ✅ kernel到底长什么样? 能不能自己写一个? ✅ 为什么kernel代码不能用 printf , 却能直接显示文字? 🛠️ 第一步: 准备开发环境 我们要构建一个 32位 x86 kernel , 通过 GRUB 引导 , 并在 QEMU 中运行 — 这样既安全又快捷! 你需要安装: ⚠️ 为了规范编译, 推荐使用 交叉编译器 i686-elf-gcc (避免宿主系统库干扰) . 教程可Reference: OSDev Wiki – GCC Cross-Compiler 🚀... » read more

Writing an OS Kernel from Scratch | Windows MBR+BIOS Boot: What Happens Before BOOTMGR and How to Fix It Have you noticed a phenomenon: You assemble a computer, install Windows 10, the System Reserved partition takes up 100MB, and the C: drive takes everything else. This 100MB partition is usually invisible in File Explorer. Only... » read more

Writing an OS Kernel from Scratch | Interrupt and Exception Handling — How the CPU Gets “Interrupted” by Peripherals Your program is running, and suddenly you press a key on the keyboard — how does the operating system know about it? How does the CPU instantly switch from executing code to handling keyboard input? The... » read more

B04 — From Real Mode to Protected Mode: GDT and CR0 Setup Key Insight: Protected mode doesn’t “protect” memory. It allows the CPU to manage more complex memory access rules. Limitations of Real Mode After reset, the CPU defaults to Real Mode, the operating mode from the 8086 era. Real Mode has two severe limitations:... » read more

Writing an OS Kernel from Scratch | Audio Subsystem — How ALSA Plays Sound Have you ever wondered about this process: When playing a song, how does the CPU turn digital signals into vibrations from the speaker? From WAV/MP3 files to music in your headphones, there’s sampling rate, bit depth, alsa-lib, the ALSA driver, HDA... » read more

B08 — Memory Layout of Kernel Space and User Space: vmalloc vs kmalloc Key Insight: The division of virtual address space is one of the most important OS design decisions. x86-64 Virtual Address Space Layout Modern Linux uses a 48-bit virtual address space. User space and kernel space each have separate regions: x86-64 虚拟地址空间布局： 0x0000000000000000... » read more

title: [Writing an OS Kernel from Scratch] 337 – DRAM Training: From Principles to Debugging category: os tag: [dram, ddr, embedded, signal-integrity] source: https://github.com/golang12306/os-kernel-from-scratch [Writing an OS Kernel from Scratch] 337 – DRAM Training: From Principles to Debugging 1. What Is DRAM Training? DRAM Training is the process where the DDR controller automatically adjusts signal... » read more

Writing an OS Kernel from Scratch | Virtual Memory — The Complete Journey of Paging and Linear Addresses You write int *p = (int*)0x00401000; *p = 42; — is this address a real physical address? How does the operating system ensure every process feels it has 4GB of memory when there’s actually only 8GB of... » read more

H01 — How Memory Modules Plug Into the Motherboard: DIMM Structure and Socket Design Key Insight: Behind every visible interface lie countless electrical conventions. DIMM Full Name and Basic Concepts DIMM = Dual Inline Memory Module. DIMM vs SIMM： SIMM（Single Inline Memory Module）： - 单面引脚（只能接触一侧的触点） - 72-pin 或 30-pin（早期） - 只能提供 32-bit 或 16-bit 数据宽度... » read more

Writing an OS Kernel from Scratch | I2C Bus — The Blood Vessels of Embedded Systems Have you ever wondered: How does a gyroscope chip or touchscreen communicate with the main controller? They are not as complex as USB, nor do they need the massive bandwidth of PCIe — they use I2C. I2C (Inter-Integrated Circuit)... » read more

K12 — Memory Fragmentation and Compaction: Why Large Memory Allocations Fail Key Insight: Fragmentation is the chronic disease of memory — it doesn’t hurt normally, but when it flares up, it can be fatal. What Is Memory Fragmentation Memory fragmentation refers to the presence of many “small holes” in memory that make it impossible to... » read more