From d8df82cdadeef422bee3850adec0bd3160d3d24b Mon Sep 17 00:00:00 2001
From: Yash Karandikar <nerdstep710@gmail.com>
Date: Thu, 16 Sep 2021 11:20:56 -0500
Subject: [PATCH] Handle more double faults

---
 src/gdt.rs        | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 src/interrupts.rs |  6 +++++-
 src/main.rs       |  8 ++++++--
 3 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 src/gdt.rs

diff --git a/src/gdt.rs b/src/gdt.rs
new file mode 100644
index 0000000..fe2d203
--- /dev/null
+++ b/src/gdt.rs
@@ -0,0 +1,46 @@
+use x86_64::VirtAddr;
+use x86_64::structures::tss::TaskStateSegment;
+use x86_64::structures::gdt::{GlobalDescriptorTable, Descriptor, SegmentSelector};
+use lazy_static::lazy_static;
+
+pub const DOUBLE_FAULT_IST_INDEX: u16 = 0;
+
+struct Selectors {
+    code_selector: SegmentSelector,
+    tss_selector: SegmentSelector
+}
+
+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(unsafe { &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 })
+    };
+}
+
+pub fn init_gdt() {
+    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);
+    }
+}
diff --git a/src/interrupts.rs b/src/interrupts.rs
index e032946..381a526 100644
--- a/src/interrupts.rs
+++ b/src/interrupts.rs
@@ -1,12 +1,16 @@
 use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
 use crate::println;
 use lazy_static::lazy_static;
+use crate::gdt;
 
 lazy_static! {
     static ref IDT: InterruptDescriptorTable = {
         let mut idt = InterruptDescriptorTable::new();
         idt.breakpoint.set_handler_fn(breakpoint_handler);
-        idt.double_fault.set_handler_fn(double_fault_handler);
+        unsafe {
+            idt.double_fault.set_handler_fn(double_fault_handler)
+                .set_stack_index(gdt::DOUBLE_FAULT_IST_INDEX);
+        }
         idt
     };
 }
diff --git a/src/main.rs b/src/main.rs
index 17e0d42..bee18c3 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -9,6 +9,7 @@
 
 mod vga_buffer;
 mod interrupts;
+mod gdt;
 use core::panic::PanicInfo;
 
 
@@ -19,6 +20,7 @@ fn panic(info: &PanicInfo) -> ! {
 }
 
 fn init() {
+    gdt::init_gdt();
     interrupts::init_idt();
 }
 
@@ -30,10 +32,12 @@ pub extern "C" fn _start() {
 
     x86_64::instructions::interrupts::int3();
 
-    unsafe {
-        *(0xdeadbeef as *mut u64) = 42;
+    fn stack_overflow() {
+        stack_overflow();
     }
 
+    stack_overflow();
+
     #[cfg(test)]
     test_main();