From 92533cb5d20fc1ab975f3bd2caccb43c1f3034d2 Mon Sep 17 00:00:00 2001
From: Greg Shuflin <greg.shuflin@protonmail.com>
Date: Thu, 9 Nov 2023 17:32:46 -0800
Subject: [PATCH] Some code?

---
 src/gdt.rs  | 33 +++++++++++++++++++++++++++++++++
 src/main.rs |  5 ++---
 2 files changed, 35 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..1df968d
--- /dev/null
+++ b/src/gdt.rs
@@ -0,0 +1,33 @@
+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(unsafe { &STACK });
+            let stack_end = stack_start + STACK_SIZE;
+            stack_end
+        };
+        tss
+    };
+}
+
+lazy_static! {
+    static ref GDT: GlobalDescriptorTable = {
+        let mut gdt = GlobalDescriptorTable::new();
+        gdt.add_entry(Descriptor::kernel_code_segment());
+        gdt.add_entry(Descriptor::tss_segment(&TSS));
+        gdt
+    };
+}
+
+pub fn init() {
+    GDT.load();
+}
diff --git a/src/main.rs b/src/main.rs
index 87c4092..b04071f 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -9,6 +9,7 @@
 mod vga_buffer;
 #[macro_use]
 mod serial;
+mod gdt;
 mod interrupts;
 mod test_utils;
 
@@ -31,9 +32,6 @@ pub extern "C" fn _start() -> ! {
     x86_64::instructions::interrupts::int3();
 
     println!("We're here now");
-    unsafe {
-        *(0xff00ff00 as *mut u64) = 44;
-    }
     loop {}
 }
 
@@ -48,5 +46,6 @@ fn basic_test2() {
 }
 
 pub fn init() {
+    gdt::init();
     interrupts::init_idt();
 }