Fixed stack unwind bugs (works!)

kernel/src/lib.rs

@@ -36,6 +36,7 @@ use crate::{
 use arch::x86_64::memory::mapping;
 use core::arch::asm;
 use limine::BaseRevision;
+use std::unwind::UNWINDER;
 use x86_64::VirtAddr;
 
 pub mod arch;
@@ -144,5 +145,7 @@ pub fn boot() -> Result<(), &'static str> {
     x86_64::instructions::interrupts::enable();
     debugln!("[Success]");
 
+    UNWINDER.lock(); // Initialises the Unwinder once and only once :fingers_crossed:.
+
     Ok(())
 }

kernel/src/std/unwind/mod.rs

@@ -1,3 +1,23 @@
+use core::arch::asm;
+
+use eh_info::ELF;
+use spin::{Lazy, Mutex};
+use unwinder::{RegisterSet, Unwinder};
+
 pub mod eh_info;
 pub mod panic;
 pub mod unwinder;
+
+/// We should initialise on program start.
+pub static UNWINDER: Lazy<Mutex<Unwinder>> = Lazy::new(|| {
+    // Setup stack traces and proper panic handler. TODO: Handle panics
+    // differently if not initialised.
+    let eh_frame_ptr = ELF
+        .get_section_addr(".eh_frame_hdr")
+        .expect("Could not get `.eh_frame_hdr` address.");
+
+    let eh_info = unsafe { eh_info::EhInfo::from_hdr_ptr(eh_frame_ptr) };
+    let mut registers = RegisterSet::default();
+
+    Mutex::new(Unwinder::new(eh_info, registers))
+});

kernel/src/std/unwind/panic.rs

@@ -10,7 +10,7 @@ use super::unwinder::Unwinder;
 use crate::{
     hcf,
     prelude::*,
-    std::unwind::{eh_info::ELF, unwinder::RegisterSet},
+    std::unwind::{UNWINDER, eh_info::ELF, unwinder::RegisterSet},
 };
 
 #[panic_handler]
@@ -19,27 +19,18 @@ pub fn panic_handler(info: &PanicInfo<'_>) -> ! {
     println!("Kernel panic: {}", info);
     serial_println!("Kernel panic: {}", info);
 
-    // Setup stack traces and proper panic handler. TODO: Handle panics
-    // differently if not initialised.
-    let eh_frame_ptr = ELF
-        .get_section_addr(".eh_frame_hdr")
-        .expect("Could not get `.eh_frame_hdr` address.");
-
-    let eh_info = unsafe { super::eh_info::EhInfo::from_hdr_ptr(eh_frame_ptr) };
-    let mut registers = RegisterSet::default();
-
     let mut rip: u64;
     let mut rsp: u64;
-
     unsafe {
         asm!("lea {0}, [rip]", 
         "mov {1}, rsp",
         out(reg) rip, out(reg) rsp);
     }
-    registers.set_pc(rip);
-    registers.set_stack_ptr(rsp);
 
-    let mut unwinder = Unwinder::new(eh_info, registers);
+    let mut unwinder = UNWINDER.lock();
+    unwinder.regs.set_pc(rip);
+    unwinder.regs.set_stack_ptr(rsp);
+
     while let Some(call_frame) = unwinder.next().unwrap_or_else(|err| {
         // If an unwind error occurred.
         eprintln!("{:?}", err);

kernel/src/std/unwind/unwinder.rs

@@ -27,7 +27,7 @@ pub struct Unwinder {
     unwind_ctx: UnwindContext<usize, StoreOnHeap>,
     /// The current values of ABI/architecture independent registers. There are
     /// used by DWARF.
-    regs: RegisterSet,
+    pub regs: RegisterSet,
     /// The current CFA address.
     cfa: u64,
     /// Is this the first iteration?
@@ -112,7 +112,10 @@ impl FallibleIterator for Unwinder {
         };
 
         // REVIEWME: Must be a nicer way of doing this.
-        let pc = pc - 1;
+        let Some(pc) = pc.checked_sub(1) else {
+            // REVIEWME: This should handle underflow now.
+            return Ok(None);
+        };
 
         self.regs.set_pc(pc);