openharmony/third_party_rust_memoffset
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share more code in raw_field

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Ralf Jung
2020-06-22 09:55:08 +02:00
parent 525c81e24f
commit fcbad2f16e
1 changed files with 24 additions and 34 deletions
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src/raw_field.rs
+24 -34
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@@ -18,17 +18,24 @@
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.
/// Deref-coercion protection macro.
/// `raw_const!`, or just ref-then-cast when that is not available.
#[cfg(feature = "unstable_raw")]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check {
($type:path, $field:tt) => {
// Make sure the field actually exists. This line ensures that a
// compile-time error is generated if $field is accessed through a
// Deref impl.
#[cfg_attr(allow_clippy, allow(clippy::unneeded_field_pattern))]
let $type { $field: _, .. };
};
macro_rules! _memoffset__raw_const {
($path:expr) => {{
$crate::ptr::raw_const!($path)
}};
}
#[cfg(not(feature = "unstable_raw"))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__raw_const {
($path:expr) => {{
// This is UB because we create an intermediate reference to uninitialized memory.
// Nothing we can do about that without `raw_const!` though.
&$path as *const _
}};
}
/// Computes a const raw pointer to the given field of the given base pointer
@@ -36,38 +43,21 @@ macro_rules! _memoffset__field_check {
///
/// The `base` pointer *must not* be dangling, but it *may* point to
/// uninitialized memory.
#[cfg(not(feature = "unstable_raw"))] // Incorrect (UB) variant that creates an intermediate reference.
#[macro_export(local_inner_macros)]
macro_rules! raw_field {
($base:expr, $parent:path, $field:tt) => {{
_memoffset__field_check!($parent, $field);
let base_ptr: *const $parent = $base;
// Make sure the field actually exists. This line ensures that a
// compile-time error is generated if $field is accessed through a
// Deref impl.
#[cfg_attr(allow_clippy, allow(clippy::unneeded_field_pattern))]
let $parent { $field: _, .. };
// Get the field address. This is UB because we are creating a reference to
// the uninitialized field. Will be updated to use `&raw` before rustc
// starts exploiting such UB.
// Get the field address.
// Crucially, we know that this will not trigger a deref coercion because
// of the `field_check!` we did above.
// of the field check we did above.
#[allow(unused_unsafe)] // for when the macro is used in an unsafe block
unsafe {
&(*base_ptr).$field as *const _
}
}};
}
#[cfg(feature = "unstable_raw")] // Correct variant that uses `raw_const!`.
#[macro_export(local_inner_macros)]
macro_rules! raw_field {
($base:expr, $parent:path, $field:tt) => {{
_memoffset__field_check!($parent, $field);
let base_ptr: *const $parent = $base;
// Get the field address without creating a reference.
// Crucially, we know that this will not trigger a deref coercion because
// of the `field_check!` we did above.
#[allow(unused_unsafe)] // for when the macro is used in an unsafe block
unsafe {
$crate::ptr::raw_const!((*base_ptr).$field)
_memoffset__raw_const!((*($base as *const $parent)).$field)
}
}};
}