mayant15 / bottleos

A bare bones OS kernel made for educational purposes

Hi there 👋

🎓 Masters' student @UBC-SPL.

🔭 Interested in Program Analysis, Compilers and Graphics.

⚡ Dabbling in Zig

📫 Sometimes I write about stuff on my website.

bottleos's Issues

General protection fault while serving exceptions

Problem:
The iret instruction in isr_handler_stub generates a general protection fault after returning from the fault_handler.

To Reproduce:

• Remove the abort() call from fault_handler() and run the kernel, general protection faults will flood the screen.

Expected Result:

• Ideally, the kernel should hang because of the infinite loop in boot.s and not because of the abort()

Proposed Solution:

• Look into interrupts vs. traps. There are subtle differences in the way iret restores state after each of these
• Use different fault handlers for different exceptions

References:

• https://stackoverflow.com/questions/25540913/x86-interrupt-service-routine-causes-general-protection-fault
• https://stackoverflow.com/questions/10581224/why-does-iret-from-a-page-fault-handler-generate-interrupt-13-general-protectio

Handle hardware interrupts

Problem:

• The kernel doesn't handle hardware interrupts
• Some IRQs are mapped by default to positions in the IDT that are already taken, which calls wrong ISRs.

Proposed Solution:

• Hardware interrupts are handled through calls made in response to IRQs. These should be implemented just like existing ISRs for exceptions.
• Tell the PIC to remap IRQs based on the current IDT structure.

References:

• Botched interrupts causing triple faults
• Bran's Kernel Dev Tutorial
• OSDev Interrupts Tutorial

Use CMake for build setup

Proposal:
I am much more comfortable writing a CMakeLists.txt than a Makefile. The build system carried over from the Meaty Skeleton tutorial should be replaced by CMake.

Tasks:

• Configure CMake to use the cross-compiler
• Setup subprojects for kernel and libc
• Use the existing scripts for detecting target architecture (?)
• Profit! :D

References:

• Specify GCC path for CMake
• Mixing C and ASM
• OSDev CMake
• OSDev Hard Build System

Add QEMU to GitHub Actions setup

Problem:
Tests require QEMU to function

To Reproduce:

• Run cargo test without QEMU installed

Expected Result:

• Tests should pass

Proposed Solution:

• apt install qemu? or have a docker container for build and test?

Port the project to Rust

Rust is a modern systems programming language that I've been interested in for a while. It seems like there are already a large number of OSes written in Rust. Since the project is still very small, I can migrate it to Rust pretty easily. Some benefits are:

• Much simpler toolchain and build setup
• Unit testing, documentation tools etc. can be run through cargo
• Default Rust conventions are safer to use that C
• Catch more bugs at compile time