//! Writing an [OS] in Rust: [Double Faults]
//!
//! [os]: https://os.phil-opp.com
//! [double faults]: https://os.phil-opp.com/double-fault-exceptions/
#![no_std]
#![no_main]
#![feature(custom_test_frameworks)]
#![test_runner(rustos::test_runner)]
#![reexport_test_harness_main = "test_main"]
#![feature(abi_x86_interrupt)]
extern crate rustos;
use core::panic::PanicInfo;
use rustos::println;

#[no_mangle]
pub extern "C" fn _start() -> ! {
    println!("Welcome to the real world!");
    init();
    #[cfg(not(test))]
    stack_overflow();
    #[cfg(test)]
    test_main();
    println!("It did not crash!!!");
    loop {}
}

#[cfg(not(test))]
#[allow(unconditional_recursion)]
fn stack_overflow() {
    stack_overflow();
}

#[cfg(not(test))]
#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
    println!("{}", info);
    loop {}
}

#[cfg(test)]
#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
    rustos::test_panic_handler(info)
}

extern crate lazy_static;
extern crate x86_64;
use lazy_static::lazy_static;
#[allow(unused_imports)]
use x86_64::{
    structures::{
        gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector},
        idt::{InterruptDescriptorTable, InterruptStackFrame},
        tss::TaskStateSegment,
    },
    VirtAddr,
};

pub fn init() {
    use x86_64::instructions::segmentation::set_cs;
    use x86_64::instructions::tables::load_tss;
    GDT.0.load();
    unsafe {
        set_cs(GDT.1.code_selector);
        load_tss(GDT.1.tss_selector);
    }
    IDT.load();
}

lazy_static! {
    static ref GDT: (GlobalDescriptorTable, Selectors) = {
        let mut gdt = GlobalDescriptorTable::new();
        let code_selector = gdt.add_entry(Descriptor::kernel_code_segment());
        let tss_selector = gdt.add_entry(Descriptor::tss_segment(&TSS));
        (
            gdt,
            Selectors {
                code_selector,
                tss_selector,
            },
        )
    };
}

struct Selectors {
    code_selector: SegmentSelector,
    tss_selector: SegmentSelector,
}

const DOUBLE_FAULT_IST_INDEX: u16 = 0;

lazy_static! {
    static ref TSS: TaskStateSegment = {
        let mut tss = TaskStateSegment::new();
        tss.interrupt_stack_table[DOUBLE_FAULT_IST_INDEX as usize] = {
            const STACK_SIZE: usize = 4096;
            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
            let stack_start = VirtAddr::from_ptr(unsafe { &STACK });
            stack_start + STACK_SIZE
        };
        tss
    };
}

lazy_static! {
    static ref IDT: InterruptDescriptorTable = {
        let mut idt = InterruptDescriptorTable::new();
        unsafe {
            idt.double_fault
                .set_handler_fn(double_fault_handler)
                .set_stack_index(DOUBLE_FAULT_IST_INDEX);
        }
        idt
    };
}

extern "x86-interrupt" fn double_fault_handler(
    stack_frame: &mut InterruptStackFrame,
    _error_code: u64,
) -> ! {
    panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
}