From fe04effa3d093f0db38533136de99ffb3bafaa4d Mon Sep 17 00:00:00 2001
From: ami-chuu <amichuu73@proton.me>
Date: Mon, 30 Mar 2026 16:17:25 +0300
Subject: [PATCH] Added Double Fault Handler

---
 src/gdt.rs        | 52 +++++++++++++++++++++++++++++++++++++++++++++++
 src/interrupts.rs | 14 +++++++++++++
 src/lib.rs        |  2 ++
 src/main.rs       |  2 --
 4 files changed, 68 insertions(+), 2 deletions(-)
 create mode 100644 src/gdt.rs

diff --git a/src/gdt.rs b/src/gdt.rs
new file mode 100644
index 0000000..05b074d
--- /dev/null
+++ b/src/gdt.rs
@@ -0,0 +1,52 @@
+use lazy_static::lazy_static;
+use x86_64::structures::gdt::{Descriptor, GlobalDescriptorTable, SegmentSelector};
+use x86_64::structures::tss::TaskStateSegment;
+use x86_64::VirtAddr;
+
+pub 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 * 5;
+            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
+
+            let stack_start = VirtAddr::from_ptr(&raw const STACK);
+            let stack_end = stack_start + STACK_SIZE;
+            stack_end
+        };
+        tss
+    };
+}
+
+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,
+}
+
+pub fn init() {
+    use x86_64::instructions::segmentation::{Segment, CS};
+    use x86_64::instructions::tables::load_tss;
+
+    GDT.0.load();
+    unsafe {
+        CS::set_reg(GDT.1.code_selector);
+        load_tss(GDT.1.tss_selector);
+    }
+}
diff --git a/src/interrupts.rs b/src/interrupts.rs
index 405c1e9..6f660c7 100644
--- a/src/interrupts.rs
+++ b/src/interrupts.rs
@@ -1,3 +1,4 @@
+use crate::gdt;
 use crate::println;
 use lazy_static::lazy_static;
 use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
@@ -6,6 +7,12 @@ lazy_static! {
     static ref IDT: InterruptDescriptorTable = {
         let mut idt = InterruptDescriptorTable::new();
         idt.breakpoint.set_handler_fn(breakpoint_handler);
+        unsafe {
+            idt.double_fault
+                .set_handler_fn(double_fault_handler)
+                .set_stack_index(gdt::DOUBLE_FAULT_IST_INDEX);
+        }
+
         idt
     };
 }
@@ -18,6 +25,13 @@ extern "x86-interrupt" fn breakpoint_handler(stack_frame: InterruptStackFrame) {
     println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
 }
 
+extern "x86-interrupt" fn double_fault_handler(
+    stack_frame: InterruptStackFrame,
+    _error_code: u64,
+) -> ! {
+    panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
+}
+
 #[test_case]
 fn test_breakpoint_exception() {
     // invoke a breakpoint exception
diff --git a/src/lib.rs b/src/lib.rs
index ae4e3a3..6f6f9c1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@
 
 use core::panic::PanicInfo;
 
+pub mod gdt;
 pub mod interrupts;
 pub mod serial;
 pub mod vga_buffer;
@@ -73,5 +74,6 @@ pub fn exit_qemu(exit_code: QemuExitCode) {
 }
 
 pub fn init() {
+    gdt::init();
     interrupts::init_idt();
 }
diff --git a/src/main.rs b/src/main.rs
index f153785..0b41888 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,8 +13,6 @@ pub extern "C" fn _start() -> ! {
 
     amix::init();
 
-    x86_64::instructions::interrupts::int3();
-
     #[cfg(test)]
     test_main();