Chapter 9 — Cooperative Multitasking and Kernel Threads

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This entry is part 9 of 27 in the series Writing A Linux Style Operating System From Scratch

We now have enough foundation to start multitasking: This chapter adds the first scheduler. Not a preemptive scheduler yet. A cooperative scheduler. That means each kernel thread keeps running until it voluntarily calls: “` cthread_yield(); textkernel thread objectper-thread kernel stackready queuex86 context switch assemblythread_create()thread_yield()thread_exit()round-robin cooperative schedulingtwo-thread test textcreate two kernel threadsswitch between them cooperativelyprove both

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Chapter 8 – Moving the Heap onto Virtual Memory

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Chapter 8 – Moving the Heap onto Virtual Memory
This entry is part 8 of 27 in the series Writing A Linux Style Operating System From Scratch

In Chapter 6, the kernel heap still depended on low identity-mapped physical pages. That worked as a bootstrap step, but it tied the heap to the first 16 MiB of RAM. In Chapter 7, we added a real VMM and proved that the kernel can map and unmap pages anywhere the page tables allow. That

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Chapter 7 — A Real Virtual Memory Mapping Layer

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Chapter 7 — A Real Virtual Memory Mapping Layer
This entry is part 7 of 27 in the series Writing A Linux Style Operating System From Scratch

In Chapter 5 we enabled paging, but only with a fixed identity map: In Chapter 6 we built a heap, but it still had an important weakness: because only the first 16 MiB were identity-mapped. Now we fix the architectural problem. This chapter adds a small virtual memory manager, or VMM: This lets the kernel

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Chapter 6 — Building the First Kernel Heap

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Chapter 6 — Building the First Kernel Heap
This entry is part 6 of 27 in the series Writing A Linux Style Operating System From Scratch

In Chapter 5, we enabled paging with a simple identity map: That gave us a working paged kernel, but not yet a comfortable way to allocate variable-sized objects. The physical memory manager gives us whole pages: But kernel code usually needs smaller objects: So this chapter builds the first kernel heap. We will keep it

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Chapter 5 — Turning On Paging

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Chapter 5 — Turning On Paging
This entry is part 5 of 27 in the series Writing A Linux Style Operating System From Scratch

In Chapter 4, we built the first memory-management layer: Now we add the next layer: paging. Paging lets the CPU translate a virtual address into a physical address through page tables. In 32-bit x86 paging without PAE, a virtual address is split into a page-directory index, page-table index, and page offset; page directories and page

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Chapter 4 — Reading the Memory Map and Building a Physical Page Allocator

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Chapter 4 — Reading the Memory Map and Building a Physical Page Allocator
This entry is part 4 of 27 in the series Writing A Linux Style Operating System From Scratch

Before we add paging, a heap, processes, filesystems, or user programs, the kernel must answer a basic question: Which physical 4 KiB pages of RAM are safe for me to use? Right now, our kernel can boot, print text, catch CPU exceptions, and receive timer/keyboard interrupts. But it still cannot safely allocate memory. This chapter

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Chapter 3 — Hardware Interrupts: PIC, PIT Timer, and Keyboard Input

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Chapter 3 — Hardware Interrupts: PIC, PIT Timer, and Keyboard Input
This entry is part 3 of 27 in the series Writing A Linux Style Operating System From Scratch

In Chapter 2 we taught the CPU how to call our code when something goes wrong: Now we will teach the machine how to call our code when hardware wants attention: This is the first step toward a living kernel. A timer interrupt eventually gives us scheduling. Keyboard input eventually gives us a kernel monitor

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Chapter 2 — GDT, IDT, and Surviving Your First Kernel Crash

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Chapter 2 — GDT, IDT, and Surviving Your First Kernel Crash
This entry is part 2 of 27 in the series Writing A Linux Style Operating System From Scratch

In Chapter 1, we got control of the machine: Now we need something more important than printing text: we need the CPU to call our code when something goes wrong. Right now, if the kernel executes an invalid instruction, divides by zero, touches unmapped memory later, or faults during setup, the machine may reset, hang,

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Writing a Linux-style Operating System From Scratch

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Writing a Linux-style Operating System From Scratch
This entry is part 1 of 27 in the series Writing A Linux Style Operating System From Scratch

Today, we are beginning a new article series: “Writing a Linux-Style Operating System From Scratch.” In this series, we will walk step by step through the process of creating our own operating system from the ground up. Many operating system tutorials stop shortly after the system boots and prints a simple message on the screen.

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Building the i686-elf-gcc Cross-Compiler

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Together, these tools allow us to assemble, compile, link, inspect, and transform kernel binaries without using the host operating system’s normal compiler target.

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