From 63edda1d28e08584bcacaaa21d149e5ee0d7439b Mon Sep 17 00:00:00 2001
From: August <shibedrill1@gmail.com>
Date: Thu, 8 Oct 2026 18:33:18 +0000
Subject: [PATCH] Fix badly loaded TSS descriptor

---
 src/kernel/arch/x86_64/gdt.rs        | 18 ++++++++++--------
 src/kernel/arch/x86_64/interrupts.rs |  6 +++++-
 src/kernel/arch/x86_64/startup.rs    |  9 +++++++--
 src/kernel/main.rs                   |  6 +++++-
 4 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/src/kernel/arch/x86_64/gdt.rs b/src/kernel/arch/x86_64/gdt.rs
index 57cfd5b..74b9218 100644
--- a/src/kernel/arch/x86_64/gdt.rs
+++ b/src/kernel/arch/x86_64/gdt.rs
@@ -79,16 +79,18 @@ lazy_static! {
         let sel_tss = gdt.append(
             {
                 let tss_addr = addr_of!(TSS) as u128;
-                let tss_size = size_of_val(&TSS) as u128;
+                log_trace!("TSS address: 0x{:032x}", tss_addr);
+                let tss_size = size_of::<TaskStateSegment>() as u128 - 1;
+                log_trace!("TSS size: 0x{:x}", tss_size);
                 let mut tss_descriptor: u128 = 0;
-                tss_descriptor.set_bits(0..=15, tss_size.bits(0..=15)); // Limit bits 0..=15
+                tss_descriptor.set_bits(56..=95, tss_addr.bits(24..=63)); // Base bits 24..=63
+                tss_descriptor.set_bits(52..=55, 0b0000); // Flags: 1-byte granularity
                 tss_descriptor.set_bits(48..=51, tss_size.bits(16..=19)); // Limit bits 16..=19
-                tss_descriptor.set_bits(16..=39, tss_addr.bits(0..=24)); // Base bits 0..=24
-                tss_descriptor.set_bits(56..=95, tss_addr.bits(25..=63)); // Base bits 25..=63
-                tss_descriptor.set_bits(40..=47, 0b10110001);
-                tss_descriptor.set_bits(52..=55, 0b1010);
-                log_info!("TSS descriptor (calculated manually): 0x{:032x}", tss_descriptor);
-                Descriptor::SystemSegment(tss_descriptor.bits(64..=127) as u64, tss_descriptor.bits(0..=63) as u64)
+                tss_descriptor.set_bits(40..=47, 0b10001001); // Access: Present, ring 0, system segment
+                tss_descriptor.set_bits(16..=39, tss_addr.bits(0..=23)); // Base bits 0..=23
+                tss_descriptor.set_bits(0..=15, tss_size.bits(0..=15)); // Limit bits 0..=15
+                // MAKE SURE that the lower half is the first byte! This is loaded little-endian into the GDT!
+                Descriptor::SystemSegment(tss_descriptor.bits(0..=63) as u64, tss_descriptor.bits(64..=127) as u64)
             }
         );
         Selectors {
diff --git a/src/kernel/arch/x86_64/interrupts.rs b/src/kernel/arch/x86_64/interrupts.rs
index e270c29..cf966c8 100644
--- a/src/kernel/arch/x86_64/interrupts.rs
+++ b/src/kernel/arch/x86_64/interrupts.rs
@@ -51,7 +51,11 @@ lazy_static! {
 }
 
 extern "x86-interrupt" fn div_zero(info: InterruptStackFrame) {
-    log_error!("Divide by zero error: 0x{:x}, {:?}", info.instruction_pointer, info.code_segment.rpl());
+    log_error!(
+        "Divide by zero error: 0x{:x}, {:?}",
+        info.instruction_pointer,
+        info.code_segment.rpl()
+    );
     unsafe { info.iretq() }
 }
 
diff --git a/src/kernel/arch/x86_64/startup.rs b/src/kernel/arch/x86_64/startup.rs
index e951a08..a39d7b4 100644
--- a/src/kernel/arch/x86_64/startup.rs
+++ b/src/kernel/arch/x86_64/startup.rs
@@ -1,4 +1,8 @@
-use x86_64::{VirtAddr, registers::{rflags::RFlags, segmentation::Segment}, structures::idt::InterruptStackFrameValue};
+use x86_64::{
+    VirtAddr,
+    registers::{rflags::RFlags, segmentation::Segment},
+    structures::idt::InterruptStackFrameValue,
+};
 
 use crate::{
     arch::{
@@ -28,8 +32,9 @@ pub fn init() -> Result<(), ()> {
         x86_64::registers::segmentation::CS::set_reg(SELECTORS.sel_kernel_code);
         x86_64::registers::segmentation::SS::set_reg(SELECTORS.sel_kernel_stack);
     }
-    //ltr(SELECTORS.sel_tss.index()) // THIS WILL CAUSE A GPF, YOU STUPID WHORE
+    log_info!("Segment registers loaded!");
     ltr(SELECTORS.sel_tss.0);
+    log_info!("Task register loaded!");
     Ok(())
 }
 
diff --git a/src/kernel/main.rs b/src/kernel/main.rs
index e7c8b42..f58a715 100644
--- a/src/kernel/main.rs
+++ b/src/kernel/main.rs
@@ -97,7 +97,11 @@ unsafe extern "C" fn main() -> ! {
     memory::log_memory();
     memory::log_address();
 
-    log_info!("TSS descriptor: 0x{:08x} {:08x}", SELECTORS.gdt.entries()[SELECTORS.sel_tss.index() as usize + 1].raw(), SELECTORS.gdt.entries()[SELECTORS.sel_tss.index() as usize].raw());
+    log_info!(
+        "TSS descriptor: 0x{:08x} {:08x}",
+        SELECTORS.gdt.entries()[SELECTORS.sel_tss.index() as usize + 1].raw(),
+        SELECTORS.gdt.entries()[SELECTORS.sel_tss.index() as usize].raw()
+    );
     if let Some(modules_list) = *MODULE_RESPONSE
         && modules_list.modules()[0].path().ends_with("/userboot.bin")
     {