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adjust union access unsafety check logic to take into account Deref and the actual type of the assignment

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This commit is contained in:
Ralf Jung 2020-10-24 21:12:32 +02:00
parent 3ac1df8b99
commit 64856e29c1
3 changed files with 108 additions and 58 deletions
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35
compiler/rustc_mir/src/transform/check_unsafety.rs
View file

@ -190,7 +190,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
}
}
for (i, elem) in place.projection.iter().enumerate() {
for (i, _elem) in place.projection.iter().enumerate() {
let proj_base = &place.projection[..i];
if context.is_borrow() {
if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
@ -236,23 +236,28 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
UnsafetyViolationDetails::DerefOfRawPointer,
),
ty::Adt(adt, _) if adt.is_union() => {
if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
let assign_to_field = context
== PlaceContext::MutatingUse(MutatingUseContext::Store)
|| context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
|| context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
{
let elem_ty = match elem {
ProjectionElem::Field(_, ty) => ty,
_ => span_bug!(
self.source_info.span,
"non-field projection {:?} from union?",
place
),
};
let manually_drop = elem_ty
|| context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput);
// If there is a `Deref` further along the projection chain, this is *not* an
// assignment to a union field. In that case the union field is just read to
// obtain the pointer/reference.
let assign_to_field = assign_to_field
&& !place.projection[i..]
.iter()
.any(|elem| matches!(elem, ProjectionElem::Deref));
// If this is just an assignment, determine if the assigned type needs dropping.
if assign_to_field {
// We have to check the actual type of the assignment, as that determines if the
// old value is being dropped.
let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
// To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
let manually_drop = assigned_ty
.ty_adt_def()
.map_or(false, |adt_def| adt_def.is_manually_drop());
let nodrop = manually_drop
|| elem_ty.is_copy_modulo_regions(
|| assigned_ty.is_copy_modulo_regions(
self.tcx.at(self.source_info.span),
self.param_env,
);
@ -260,7 +265,7 @@ impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
self.require_unsafe(
UnsafetyViolationKind::GeneralAndConstFn,
UnsafetyViolationDetails::AssignToDroppingUnionField,
)
);
} else {
// write to non-drop union field, safe
}

21
src/test/ui/union/union-unsafe.rs
View file

@ -1,4 +1,6 @@
#![feature(untagged_unions)]
use std::mem::ManuallyDrop;
use std::cell::RefCell;
union U1 {
a: u8
@ -16,6 +18,25 @@ union U4<T: Copy> {
a: T
}
union URef {
p: &'static mut i32,
}
union URefCell { // field that does not drop but is not `Copy`, either
a: (RefCell<i32>, i32),
}
fn deref_union_field(mut u: URef) {
// Not an assignment but an access to the union field!
*(u.p) = 13; //~ ERROR access to union field is unsafe
}
fn assign_noncopy_union_field(mut u: URefCell) {
u.a = (RefCell::new(0), 1); //~ ERROR assignment to union field that needs dropping
u.a.0 = RefCell::new(0); //~ ERROR assignment to union field that needs dropping
u.a.1 = 1; // OK
}
fn generic_noncopy<T: Default>() {
let mut u3 = U3 { a: ManuallyDrop::new(T::default()) };
u3.a = ManuallyDrop::new(T::default()); // OK (assignment does not drop)

110
src/test/ui/union/union-unsafe.stderr
View file

@ -1,67 +1,91 @@
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:22:6
--> $DIR/union-unsafe.rs:31:5
|
LL | *(u.p) = 13;
| ^^^^^^^^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: assignment to union field that needs dropping is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:35:5
|
LL | u.a = (RefCell::new(0), 1);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to union field that needs dropping
|
= note: the previous content of the field will be dropped, which causes undefined behavior if the field was not properly initialized
error[E0133]: assignment to union field that needs dropping is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:36:5
|
LL | u.a.0 = RefCell::new(0);
| ^^^^^^^^^^^^^^^^^^^^^^^ assignment to union field that needs dropping
|
= note: the previous content of the field will be dropped, which causes undefined behavior if the field was not properly initialized
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:43:6
|
LL | *u3.a = T::default();
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:28:6
|
LL | *u3.a = T::default();
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:36:13
|
LL | let a = u1.a;
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:39:14
|
LL | let U1 { a } = u1;
| ^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:40:20
|
LL | if let U1 { a: 12 } = u1 {}
| ^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:45:6
|
LL | *u2.a = String::from("new");
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:49:6
|
LL | *u3.a = T::default();
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:57:13
|
LL | let a = u1.a;
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:60:14
|
LL | let U1 { a } = u1;
| ^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:61:20
|
LL | if let U1 { a: 12 } = u1 {}
| ^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:66:6
|
LL | *u2.a = String::from("new");
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:70:6
|
LL | *u3.a = 1;
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error[E0133]: access to union field is unsafe and requires unsafe function or block
--> $DIR/union-unsafe.rs:53:6
--> $DIR/union-unsafe.rs:74:6
|
LL | *u3.a = String::from("new");
| ^^^^ access to union field
|
= note: the field may not be properly initialized: using uninitialized data will cause undefined behavior
error: aborting due to 8 previous errors
error: aborting due to 11 previous errors
For more information about this error, try `rustc --explain E0133`.