Add additional helpers to bitmask data structure

This commit addresses the case where a struct containing a bitfield
is wrapped in a struct such as UnsafeCell which allows interior
mutability.

Previously, bitfield accessors only allowed a receiver. This becomes
problematic in the case of interior mutability as raw pointer access may
be required so as not to violate the aliasing rules in Rust.

Author: jbaublitz

bindgen/codegen/bitfield_unit.rs

@@ -16,12 +16,7 @@ where
     Storage: AsRef<[u8]> + AsMut<[u8]>,
 {
     #[inline]
-    pub fn get_bit(&self, index: usize) -> bool {
-        debug_assert!(index / 8 < self.storage.as_ref().len());
-
-        let byte_index = index / 8;
-        let byte = self.storage.as_ref()[byte_index];
-
+    fn extract_bit(byte: u8, index: usize) -> bool {
         let bit_index = if cfg!(target_endian = "big") {
             7 - (index % 8)
         } else {
@@ -34,12 +29,28 @@ where
     }
 
     #[inline]
-    pub fn set_bit(&mut self, index: usize, val: bool) {
+    pub fn get_bit(&self, index: usize) -> bool {
         debug_assert!(index / 8 < self.storage.as_ref().len());
 
         let byte_index = index / 8;
-        let byte = &mut self.storage.as_mut()[byte_index];
+        let byte = self.storage.as_ref()[byte_index];
+
+        Self::extract_bit(byte, index)
+    }
+
+    #[inline]
+    pub unsafe fn raw_get_bit(this: *const Self, index: usize) -> bool {
+        debug_assert!(index / 8 < std::mem::size_of::<Storage>());
+
+        let byte_index = index / 8;
+        let byte = *(std::ptr::addr_of!((*this).storage) as *const u8)
+            .offset(byte_index as isize);
+
+        Self::extract_bit(byte, index)
+    }
 
+    #[inline]
+    fn change_bit(byte: u8, index: usize, val: bool) -> u8 {
         let bit_index = if cfg!(target_endian = "big") {
             7 - (index % 8)
         } else {
@@ -48,12 +59,33 @@ where
 
         let mask = 1 << bit_index;
         if val {
-            *byte |= mask;
+            byte | mask
         } else {
-            *byte &= !mask;
+            byte & !mask
         }
     }
 
+    #[inline]
+    pub fn set_bit(&mut self, index: usize, val: bool) {
+        debug_assert!(index / 8 < self.storage.as_ref().len());
+
+        let byte_index = index / 8;
+        let byte = &mut self.storage.as_mut()[byte_index];
+
+        *byte = Self::change_bit(*byte, index, val);
+    }
+
+    #[inline]
+    pub unsafe fn raw_set_bit(this: *mut Self, index: usize, val: bool) {
+        debug_assert!(index / 8 < std::mem::size_of::<Storage>());
+
+        let byte_index = index / 8;
+        let byte = (std::ptr::addr_of_mut!((*this).storage) as *mut u8)
+            .offset(byte_index as isize);
+
+        *byte = Self::change_bit(*byte, index, val);
+    }
+
     #[inline]
     pub fn get(&self, bit_offset: usize, bit_width: u8) -> u64 {
         debug_assert!(bit_width <= 64);
@@ -79,6 +111,35 @@ where
         val
     }
 
+    #[inline]
+    pub unsafe fn raw_get(
+        this: *const Self,
+        bit_offset: usize,
+        bit_width: u8,
+    ) -> u64 {
+        debug_assert!(bit_width <= 64);
+        debug_assert!(bit_offset / 8 < std::mem::size_of::<Storage>());
+        debug_assert!(
+            (bit_offset + (bit_width as usize)) / 8 <=
+                std::mem::size_of::<Storage>()
+        );
+
+        let mut val = 0;
+
+        for i in 0..(bit_width as usize) {
+            if Self::raw_get_bit(this, i + bit_offset) {
+                let index = if cfg!(target_endian = "big") {
+                    bit_width as usize - 1 - i
+                } else {
+                    i
+                };
+                val |= 1 << index;
+            }
+        }
+
+        val
+    }
+
     #[inline]
     pub fn set(&mut self, bit_offset: usize, bit_width: u8, val: u64) {
         debug_assert!(bit_width <= 64);
@@ -99,4 +160,30 @@ where
             self.set_bit(index + bit_offset, val_bit_is_set);
         }
     }
+
+    #[inline]
+    pub unsafe fn raw_set(
+        this: *mut Self,
+        bit_offset: usize,
+        bit_width: u8,
+        val: u64,
+    ) {
+        debug_assert!(bit_width <= 64);
+        debug_assert!(bit_offset / 8 < std::mem::size_of::<Storage>());
+        debug_assert!(
+            (bit_offset + (bit_width as usize)) / 8 <=
+                std::mem::size_of::<Storage>()
+        );
+
+        for i in 0..(bit_width as usize) {
+            let mask = 1 << i;
+            let val_bit_is_set = val & mask == mask;
+            let index = if cfg!(target_endian = "big") {
+                bit_width as usize - 1 - i
+            } else {
+                i
+            };
+            Self::raw_set_bit(this, index + bit_offset, val_bit_is_set);
+        }
+    }
 }

bindgen/codegen/mod.rs

@@ -1849,6 +1849,15 @@ fn bitfield_getter_name(
     quote! { #name }
 }
 
+fn bitfield_raw_getter_name(
+    ctx: &BindgenContext,
+    bitfield: &Bitfield,
+) -> proc_macro2::TokenStream {
+    let name = bitfield.getter_name();
+    let name = ctx.rust_ident_raw(format!("raw_{name}"));
+    quote! { #name }
+}
+
 fn bitfield_setter_name(
     ctx: &BindgenContext,
     bitfield: &Bitfield,
@@ -1858,6 +1867,15 @@ fn bitfield_setter_name(
     quote! { #setter }
 }
 
+fn bitfield_raw_setter_name(
+    ctx: &BindgenContext,
+    bitfield: &Bitfield,
+) -> proc_macro2::TokenStream {
+    let setter = bitfield.setter_name();
+    let setter = ctx.rust_ident_raw(format!("raw_{setter}"));
+    quote! { #setter }
+}
+
 impl<'a> FieldCodegen<'a> for Bitfield {
     type Extra = (&'a str, &'a mut bool, &'a mut FieldVisibilityKind);
 
@@ -1885,6 +1903,8 @@ impl<'a> FieldCodegen<'a> for Bitfield {
         let prefix = ctx.trait_prefix();
         let getter_name = bitfield_getter_name(ctx, self);
         let setter_name = bitfield_setter_name(ctx, self);
+        let raw_getter_name = bitfield_raw_getter_name(ctx, self);
+        let raw_setter_name = bitfield_raw_setter_name(ctx, self);
         let unit_field_ident = Ident::new(unit_field_name, Span::call_site());
 
         let bitfield_ty_item = ctx.resolve_item(self.ty());
@@ -1951,6 +1971,25 @@ impl<'a> FieldCodegen<'a> for Bitfield {
                         )
                     }
                 }
+
+                #[inline]
+                #access_spec unsafe fn #raw_getter_name(this: *const Self) -> #bitfield_ty {
+                    unsafe {
+                        ::std::mem::transmute(__BindgenBitfieldUnit::raw_get(
+                            addr_of!((*this).#unit_field_ident),
+                            #offset,
+                            #width,
+                        ) as #bitfield_int_ty)
+                    }
+                }
+
+                #[inline]
+                #access_spec unsafe fn #raw_setter_name(this: *mut Self, val: #bitfield_ty) {
+                    unsafe {
+                        let val: #bitfield_int_ty = ::std::mem::transmute(val);
+                        __BindgenBitfieldUnit::raw_set(addr_of!((*this)._bitfield_1), #offset, #width, val as u64)
+                    }
+                }
             }));
         } else {
             methods.extend(Some(quote! {