Interrupts and exceptions

This is implemented in interrupts.

This is where interrupts are managed. We have 2 types of interrupts.

Exceptions: These are errors that occur in the CPU, like division by zero, invalid opcode, etc, and these are defined in specific places in the IDT.
Interrupts: These are events that are triggered by devices, like the keyboard, timer, etc, these do not have specific placement in the IDT, and are instead handled mostly in the user_interrupts range of the IDT, which is from 32 to 255.

The last 16 entries of the user interrupts are used specially by the kernel as such:

SPECIAL_SCHEDULER_INTERRUPT=0xFF: Used by scheduler to switch between contexts.
SPECIAL_SYSCALL_INTERRUPT=0xFE: Used by the syscall instruction to switch to kernel mode, this is defined in kernel user link.

Generally we use functions like allocate_user_interrupt, which will allocate an interrupt entry, and puts our function there (see Interrupts Handlers later for types of interrupts), then it will give us where it was allocated, so we can use it later, for example with APIC.

The InterruptDescriptorTableEntry gives us some extra functionalities that are not provided by default. Such as:

set_stack_index which sets the stack index to use when handling the interrupt.
set_privilege_level which sets the privilege level of the interrupt.
set_disable_interrupts which sets if the interrupts flag should disabled when handling this interrupt.
override_code_segment which sets the code segment to use when handling the interrupt.

Interrupts handlers

There are 2 types of interrupts handlers based on what arguments they take:

The minimal, which takes InterruptStackFrame64, i.e. the data provided by the CPU automatically.

#![allow(unused)]
fn main() {
pub struct InterruptStackFrame64 {
    pub rip: u64,
    pub cs: u8,
    pub rflags: u64,
    pub rsp: u64,
    pub ss: u8,
}
}

The full, which takes all registers (except fxsave), this is used when we expect to switch between processes or need those extra registers.

#![allow(unused)]
fn main() {
pub struct InterruptAllSavedState {
    pub rest: RestSavedRegisters,   // contain all the rest of the registers
    pub number: u64,
    pub error: u64,
    pub frame: InterruptStackFrame64,
}
}

Generally, APIC is the only user of allocate_user_interrupt, as it uses it to allocate interrupts for hardware devices. Look at the APIC for more details on what interrupts we have now.

Emerald

Interrupts and exceptions

Interrupts handlers