Debug: Disallow extra bits in Dr7Flags

Replace Dr7Value::flags_mut with explicit *_flags methods.

Author: mkroening

src/registers/debug.rs

@@ -4,7 +4,6 @@
 
 use core::arch::asm;
 use core::convert::TryFrom;
-use core::mem;
 use core::ops::Range;
 
 use crate::VirtAddr;
@@ -149,7 +148,6 @@ impl Dr6Flags {
 
 bitflags! {
     /// Debug control flags of the [`Dr7`] register.
-    // SAFETY: We choose to allow extra bits in `Dr7Flags` to be used for fields in `Dr7Value`.
     #[repr(transparent)]
     pub struct Dr7Flags: u64 {
         /// Breakpoint 0 is enabled for the current task.
@@ -370,18 +368,35 @@ impl Dr7Value {
     /// Returns the [`Dr7Flags`] in this value.
     #[inline]
     pub const fn flags(self) -> Dr7Flags {
-        // SAFETY: The extra bits used in fields are valid in our representation of `Dr7Flags`.
-        unsafe { Dr7Flags::from_bits_unchecked(self.bits) }
+        Dr7Flags::from_bits_truncate(self.bits)
     }
 
-    /// Returns a mutable reference to the [`Dr7Flags`] in this value.
-    ///
-    /// This can be used to modify the flags of this value in-place.
+    /// Inserts the specified [`Dr7Flags`] in-place.
+    #[inline]
+    pub fn insert_flags(&mut self, flags: Dr7Flags) {
+        self.bits |= flags.bits();
+    }
+
+    /// Removes the specified [`Dr7Flags`] in-place.
+    #[inline]
+    pub fn remove_flags(&mut self, flags: Dr7Flags) {
+        self.bits &= !flags.bits();
+    }
+
+    /// Toggles the specified [`Dr7Flags`] in-place.
+    #[inline]
+    pub fn toggle_flags(&mut self, flags: Dr7Flags) {
+        self.bits ^= flags.bits();
+    }
+
+    /// Inserts or removes the specified [`Dr7Flags`] depending on the passed value.
     #[inline]
-    pub fn flags_mut(&mut self) -> &mut Dr7Flags {
-        // SAFETY: The extra bits used in fields are valid in our representation of `Dr7Flags`.
-        // SAFETY: `Dr7Flags` has the same representation as `Dr7Value`.
-        unsafe { mem::transmute(self) }
+    pub fn set_flags(&mut self, flags: Dr7Flags, value: bool) {
+        if value {
+            self.insert_flags(flags);
+        } else {
+            self.remove_flags(flags);
+        }
     }
 
     /// Returns the condition field of a debug address register.