x86 Basic Interrupt Handling Kind of Working

August 24, 2020

My hobby OS adventure has led to the need to handle interrupts. In x86, you set up a data structure called an “Interrupt Descriptor Table” (IDT) which tells the hardware which function to call in response to different interrupts. My setup kind of works; I can trigger an interrupt with the int instruction, or cause a page fault in kernel mode by accessing unmapped memory, and see that my interrupt handler is invoked. For some reason immediately after switching to user mode a page fault is generated (unsurprising as nothing is mapped user-accessible yet), but my handler is not invoked. No idea why this could be!