Always save proccess registers

Not sure if this is going to be required, and I'm not sure if this will
hurt performance, y'know, *always* doing this.

src/arch/x86_64/interrupt/exception.rs

@@ -18,8 +18,6 @@ interrupt_stack!(divide_by_zero, stack, {
 interrupt_stack!(debug, stack, {
     let mut handled = false;
 
-    let guard = ptrace::set_process_regs(stack);
-
     // Disable singlestep before there is a breakpoint, since the breakpoint
     // handler might end up setting it again but unless it does we want the
     // default to be false.
@@ -33,8 +31,6 @@ interrupt_stack!(debug, stack, {
         stack.set_singlestep(had_singlestep);
     }
 
-    drop(guard);
-
     if !handled {
         println!("Debug trap");
         stack.dump();
@@ -61,11 +57,7 @@ interrupt_stack!(breakpoint, stack, {
     // int3 instruction. After all, it's the sanest thing to do.
     stack.iret.rip -= 1;
 
-    let guard = ptrace::set_process_regs(stack);
-
     if ptrace::breakpoint_callback(PTRACE_STOP_BREAKPOINT, None).is_none() {
-        drop(guard);
-
         println!("Breakpoint trap");
         stack.dump();
         ksignal(SIGTRAP);

src/arch/x86_64/interrupt/irq.rs

@@ -189,7 +189,6 @@ interrupt_stack!(pit, stack, {
     timeout::trigger();
 
     if PIT_TICKS.fetch_add(1, Ordering::SeqCst) >= 10 {
-        let _guard = ptrace::set_process_regs(stack);
         let _ = context::switch();
     }
 });

src/arch/x86_64/macros.rs

@@ -335,6 +335,7 @@ macro_rules! interrupt_stack {
         pub unsafe extern fn $name () {
             #[inline(never)]
             unsafe fn inner($stack: &mut $crate::arch::x86_64::macros::InterruptStack) {
+                let _guard = ptrace::set_process_regs($stack);
                 $func
             }