Copy GDT Segments from xv6 x86_64. Split IRQ mod.

src/interrupts/gdt.rs

@@ -1,3 +1,5 @@
+use core::fmt;
+use core::fmt::Debug;
 use x86_64::structures::tss::TaskStateSegment;
 use x86_64::structures::gdt::SegmentSelector;
 use x86_64::PrivilegeLevel;
@@ -85,11 +87,27 @@ impl Descriptor {
 }
 
 bitflags! {
+    /// Reference: https://wiki.osdev.org/GDT
     flags DescriptorFlags: u64 {
+        const ACCESSED          = 1 << 40,
+        const DATA_WRITABLE     = 1 << 41,
+        const CODE_READABLE     = 1 << 41,
         const CONFORMING        = 1 << 42,
         const EXECUTABLE        = 1 << 43,
         const USER_SEGMENT      = 1 << 44,
+        const USER_MODE         = 1 << 45 | 1 << 46,
         const PRESENT           = 1 << 47,
         const LONG_MODE         = 1 << 53,
     }
 }
+
+impl Debug for Descriptor {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        match self {
+            Descriptor::UserSegment(flags) => 
+                write!(f, "UserSegment( {:?} )", DescriptorFlags{bits: *flags}),
+            Descriptor::SystemSegment(low, high) =>
+                write!(f, "SystemSegment{:?}", (low, high)),
+        }
+    }
+}

src/interrupts/irq.rs

@@ -0,0 +1,21 @@
+use x86_64::structures::idt::*;
+
+pub extern "x86-interrupt" fn breakpoint_handler(
+    stack_frame: &mut ExceptionStackFrame)
+{
+    println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
+}
+
+pub extern "x86-interrupt" fn double_fault_handler(
+    stack_frame: &mut ExceptionStackFrame, _error_code: u64)
+{
+    println!("\nEXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
+    loop {}
+}
+
+pub extern "x86-interrupt" fn page_fault_handler(
+    stack_frame: &mut ExceptionStackFrame, error_code: PageFaultErrorCode)
+{
+    println!("\nEXCEPTION: PAGE FAULT\n{:#?}\n{:#?}", stack_frame, error_code);
+    loop {}
+}

src/interrupts/mod.rs

@@ -1,13 +1,15 @@
 use x86_64::VirtualAddress;
-use x86_64::structures::idt::*;
+use x86_64::structures::idt::Idt;
 use x86_64::structures::tss::TaskStateSegment;
 use memory::MemoryController;
 use spin::Once;
 
 mod gdt;
+mod irq;
 
 lazy_static! {
     static ref IDT: Idt = {
+        use self::irq::*;
         let mut idt = Idt::new();
         idt.breakpoint.set_handler_fn(breakpoint_handler);
         idt.page_fault.set_handler_fn(page_fault_handler);        
@@ -19,12 +21,22 @@ lazy_static! {
     };
 }
 
+// Copied from xv6 x86_64
+const GNULL: gdt::Descriptor = gdt::Descriptor::UserSegment(0);
+const KCODE: gdt::Descriptor = gdt::Descriptor::UserSegment(0x0020980000000000);  // EXECUTABLE | USER_SEGMENT | PRESENT | LONG_MODE
+const UCODE: gdt::Descriptor = gdt::Descriptor::UserSegment(0x0020F80000000000);  // EXECUTABLE | USER_SEGMENT | USER_MODE | PRESENT | LONG_MODE
+const KDATA: gdt::Descriptor = gdt::Descriptor::UserSegment(0x0000920000000000);  // DATA_WRITABLE | USER_SEGMENT | PRESENT
+const UDATA: gdt::Descriptor = gdt::Descriptor::UserSegment(0x0000F20000000000);  // DATA_WRITABLE | USER_SEGMENT | USER_MODE | PRESENT
+
 static TSS: Once<TaskStateSegment> = Once::new();
 static GDT: Once<gdt::Gdt> = Once::new();
 
 const DOUBLE_FAULT_IST_INDEX: usize = 0;
 
 pub fn init(memory_controller: &mut MemoryController) {
+
+    test::print_flags();
+
     use x86_64::structures::gdt::SegmentSelector;
     use x86_64::instructions::segmentation::set_cs;
     use x86_64::instructions::tables::load_tss;
@@ -43,7 +55,12 @@ pub fn init(memory_controller: &mut MemoryController) {
     let mut tss_selector = SegmentSelector(0);
     let gdt = GDT.call_once(|| {
         let mut gdt = gdt::Gdt::new();
-        code_selector = gdt.add_entry(gdt::Descriptor::kernel_code_segment());
+        gdt.add_entry(GNULL);
+        kcode_selector = 
+        gdt.add_entry(KCODE);
+        gdt.add_entry(UCODE);
+        gdt.add_entry(KDATA);
+        gdt.add_entry(UDATA);
         tss_selector = gdt.add_entry(gdt::Descriptor::tss_segment(&tss));
         gdt
     });
@@ -59,22 +76,21 @@ pub fn init(memory_controller: &mut MemoryController) {
     IDT.load();
 }
 
-extern "x86-interrupt" fn breakpoint_handler(
+pub mod test
-    stack_frame: &mut ExceptionStackFrame)
 {
-    println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
+    pub fn print_flags() {
+        use super::gdt::*;
+        // The following 4 GDT entries were copied from xv6 x86_64
+        let list: [(&str, Descriptor); 4] = [
+            ("KCODE", super::KCODE), // Code, DPL=0, R/X
+            ("UCODE", super::UCODE), // Code, DPL=3, R/X
+            ("KDATA", super::KDATA), // Data, DPL=0, W
+            ("UDATA", super::UDATA), // Data, DPL=3, W
+        ];
+        // Let's see what that means
+        println!("GDT Segments from xv6 x86_64:");
+        for (name, desc) in list.iter() {
+            println!("  {}: {:?}", name, desc);
         }
-
-extern "x86-interrupt" fn double_fault_handler(
-    stack_frame: &mut ExceptionStackFrame, _error_code: u64)
-{
-    println!("\nEXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
-    loop {}
     }
-
-extern "x86-interrupt" fn page_fault_handler(
-    stack_frame: &mut ExceptionStackFrame, error_code: PageFaultErrorCode)
-{
-    println!("\nEXCEPTION: PAGE FAULT\n{:#?}\n{:#?}", stack_frame, error_code);
-    loop {}
 }