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Validate the special layout restriction on DynMetadata

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This commit is contained in:
Scott McMurray
2024-05-23 23:17:58 -07:00
parent 5baee04b63
commit d83f3ca8ca
2 changed files with 28 additions and 8 deletions
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27
library/core/src/ptr/metadata.rs
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@@ -178,8 +178,8 @@ impl<T: ?Sized> Clone for PtrComponents<T> {
/// compare equal (since identical vtables can be deduplicated within a codegen unit).
#[lang = "dyn_metadata"]
pub struct DynMetadata<Dyn: ?Sized> {
vtable_ptr: &'static VTable,
phantom: crate::marker::PhantomData<Dyn>,
_vtable_ptr: &'static VTable,
_phantom: crate::marker::PhantomData<Dyn>,
}
extern "C" {
@@ -191,6 +191,17 @@ extern "C" {
}
impl<Dyn: ?Sized> DynMetadata<Dyn> {
/// One of the things that rustc_middle does with this being a lang item is
/// give it `FieldsShape::Primitive`, which means that as far as codegen can
/// tell, it *is* a reference, and thus doesn't have any fields.
/// That means we can't use field access, and have to transmute it instead.
#[inline]
fn vtable_ptr(self) -> *const VTable {
// SAFETY: this layout assumption is hard-coded into the compiler.
// If it's somehow not a size match, the transmute will error.
unsafe { crate::mem::transmute::<Self, &'static VTable>(self) }
}
/// Returns the size of the type associated with this vtable.
#[inline]
pub fn size_of(self) -> usize {
@@ -199,7 +210,7 @@ impl<Dyn: ?Sized> DynMetadata<Dyn> {
// `Send` part!
// SAFETY: DynMetadata always contains a valid vtable pointer
return unsafe {
crate::intrinsics::vtable_size(self.vtable_ptr as *const VTable as *const ())
crate::intrinsics::vtable_size(self.vtable_ptr() as *const ())
};
}
@@ -208,7 +219,7 @@ impl<Dyn: ?Sized> DynMetadata<Dyn> {
pub fn align_of(self) -> usize {
// SAFETY: DynMetadata always contains a valid vtable pointer
return unsafe {
crate::intrinsics::vtable_align(self.vtable_ptr as *const VTable as *const ())
crate::intrinsics::vtable_align(self.vtable_ptr() as *const ())
};
}
@@ -226,7 +237,7 @@ unsafe impl<Dyn: ?Sized> Sync for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> fmt::Debug for DynMetadata<Dyn> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_tuple("DynMetadata").field(&(self.vtable_ptr as *const VTable)).finish()
f.debug_tuple("DynMetadata").field(&self.vtable_ptr()).finish()
}
}
@@ -248,7 +259,7 @@ impl<Dyn: ?Sized> Eq for DynMetadata<Dyn> {}
impl<Dyn: ?Sized> PartialEq for DynMetadata<Dyn> {
#[inline]
fn eq(&self, other: &Self) -> bool {
crate::ptr::eq::<VTable>(self.vtable_ptr, other.vtable_ptr)
crate::ptr::eq::<VTable>(self.vtable_ptr(), other.vtable_ptr())
}
}
@@ -256,7 +267,7 @@ impl<Dyn: ?Sized> Ord for DynMetadata<Dyn> {
#[inline]
#[allow(ambiguous_wide_pointer_comparisons)]
fn cmp(&self, other: &Self) -> crate::cmp::Ordering {
(self.vtable_ptr as *const VTable).cmp(&(other.vtable_ptr as *const VTable))
<*const VTable>::cmp(&self.vtable_ptr(), &other.vtable_ptr())
}
}
@@ -270,6 +281,6 @@ impl<Dyn: ?Sized> PartialOrd for DynMetadata<Dyn> {
impl<Dyn: ?Sized> Hash for DynMetadata<Dyn> {
#[inline]
fn hash<H: Hasher>(&self, hasher: &mut H) {
crate::ptr::hash::<VTable, _>(self.vtable_ptr, hasher)
crate::ptr::hash::<VTable, _>(self.vtable_ptr(), hasher)
}
}