From 130fc3e075cea4b36ba6b8123774d4fcf52e04ca Mon Sep 17 00:00:00 2001
From: Philipp Oppermann <dev@phil-opp.com>
Date: Tue, 10 Dec 2019 17:02:17 +0100
Subject: [PATCH] Make double fault handler diverging

---
 .../second-edition/posts/06-double-faults/index.md        | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/blog/content/second-edition/posts/06-double-faults/index.md b/blog/content/second-edition/posts/06-double-faults/index.md
index a0f587d9..ce2a8f91 100644
--- a/blog/content/second-edition/posts/06-double-faults/index.md
+++ b/blog/content/second-edition/posts/06-double-faults/index.md
@@ -79,13 +79,15 @@ lazy_static! {
 
 // new
 extern "x86-interrupt" fn double_fault_handler(
-    stack_frame: &mut InterruptStackFrame, _error_code: u64)
+    stack_frame: &mut InterruptStackFrame, _error_code: u64) -> !
 {
     panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
 }
 ```
 
-Our handler prints a short error message and dumps the exception stack frame. The error code of the double fault handler is always zero, so there's no reason to print it.
+Our handler prints a short error message and dumps the exception stack frame. The error code of the double fault handler is always zero, so there's no reason to print it. One difference to the breakpoint handler is that the double fault handler is [_diverging_]. The reason is that the `x86_64` architecture does not permit returning from a double fault exception.
+
+[_diverging_]: https://doc.rust-lang.org/stable/rust-by-example/fn/diverging.html
 
 When we start our kernel now, we should see that the double fault handler is invoked:
 
@@ -517,7 +519,7 @@ use x86_64::structures::idt::InterruptStackFrame;
 extern "x86-interrupt" fn test_double_fault_handler(
     _stack_frame: &mut InterruptStackFrame,
     _error_code: u64,
-) {
+) -> ! {
     serial_println!("[ok]");
     exit_qemu(QemuExitCode::Success);
     loop {}