[interrupt-handlers] added IDT

- added IdtEntry structure (w/ some tmp hardcoded values in its new impl for now),
- created IDT static mut array, and
- made fxns to init_idt and set_idt_entry.

Signed-off-by: danbugs <[email protected]>

Author: danbugs

src/hyperlight_guest/src/idt.rs

@@ -0,0 +1,94 @@
+/*
+Copyright 2024 The Hyperlight Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+use crate::interrupt_entry::{
+    _do_excp0, _do_excp1, _do_excp2, _do_excp3, _do_excp4, _do_excp5, _do_excp6, _do_excp7,
+    _do_excp8, _do_excp9, _do_excp10, _do_excp11, _do_excp12, _do_excp13, _do_excp14, _do_excp15,
+    _do_excp16, _do_excp17, _do_excp18, _do_excp19, _do_excp20, _do_excp30,
+};
+
+// For reference, see: https://wiki.osdev.org/Interrupt_Descriptor_Table#Structure_on_x86-64
+#[repr(C)]
+pub(crate) struct IdtEntry {
+    offset_low: u16,  // Lower 16 bits of handler address
+    selector: u16,    // code segment selector in GDT
+    ist: u8,          // Interrupt Stack Table offset
+    type_attr: u8,    // Gate type and flags (0x8E)
+    offset_mid: u16,  // Middle 16 bits of handler address
+    offset_high: u32, // High 32 bits of handler address
+    zero: u32,        // Reserved (always 0)
+}
+
+impl IdtEntry {
+    fn new(handler: u64) -> Self {
+        Self {
+            offset_low: handler as u16,
+            selector: 0x08,
+            // ^ this selector equates to the GDT's kernel code segment,
+            // we set this manually because, currently, Hyperlight
+            // guests only run in kernel mode.
+            ist: 0,
+            // ^ for now, we don't use the IST feature.
+            // This means that the interrupt handler will use the
+            // stack that was in use when the interrupt was triggered.
+            // For some exceptions (like double faults), this can be
+            // a problem, but we'll address that later.
+            // TODO: set up IST for exceptions that need it
+            type_attr: 0x8E,
+            // ^ 0x8E is the type_attr for an interrupt gate
+            offset_mid: (handler >> 16) as u16,
+            offset_high: (handler >> 32) as u32,
+            zero: 0,
+        }
+    }
+}
+
+// The IDT is an array of 256 IDT entries
+// (as per https://wiki.osdev.org/Interrupt_Descriptor_Table#Structure_on_x86-64)
+pub(crate) static mut IDT: [IdtEntry; 256] = unsafe { core::mem::zeroed() };
+
+pub(crate) fn init_idt() {
+    set_idt_entry(0, _do_excp0);
+    set_idt_entry(1, _do_excp1);
+    set_idt_entry(2, _do_excp2);
+    set_idt_entry(3, _do_excp3);
+    set_idt_entry(4, _do_excp4);
+    set_idt_entry(5, _do_excp5);
+    set_idt_entry(6, _do_excp6);
+    set_idt_entry(7, _do_excp7);
+    set_idt_entry(8, _do_excp8);
+    set_idt_entry(9, _do_excp9);
+    set_idt_entry(10, _do_excp10);
+    set_idt_entry(11, _do_excp11);
+    set_idt_entry(12, _do_excp12);
+    set_idt_entry(13, _do_excp13);
+    set_idt_entry(14, _do_excp14);
+    set_idt_entry(15, _do_excp15);
+    set_idt_entry(16, _do_excp16);
+    set_idt_entry(17, _do_excp17);
+    set_idt_entry(18, _do_excp18);
+    set_idt_entry(19, _do_excp19);
+    set_idt_entry(20, _do_excp20);
+    set_idt_entry(30, _do_excp30);
+
+    // TODO: set hardware interrupt handlers
+    // (i.e., after we have the PIC set up)
+}
+
+fn set_idt_entry(index: usize, handler: unsafe extern "sysv64" fn()) {
+    let handler_addr = handler as u64;
+    unsafe { IDT[index] = IdtEntry::new(handler_addr); }
+}

src/hyperlight_guest/src/lib.rs

@@ -53,6 +53,7 @@ pub mod error;
 pub mod logging;
 pub mod interrupt_entry;
 pub mod interrupt_handlers;
+pub mod idt;
 
 // Unresolved symbols
 ///cbindgen:ignore