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Rollup merge of #121179 - RalfJung:zst-mutable-refs, r=oli-obk

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allow mutable references in const values when they point to no memory

Fixes https://github.com/rust-lang/rust/issues/120450

The second commit is just some drive-by test suite cleanup.

r? `@oli-obk`
This commit is contained in:
Guillaume Gomez 2024-02-16 17:08:13 +01:00 • committed by GitHub
commit 0c92146034
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21 changed files with 209 additions and 387 deletions
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85
compiler/rustc_const_eval/src/interpret/validity.rs
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@ -445,22 +445,22 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
// Determine whether this pointer expects to be pointing to something mutable.
let ptr_expected_mutbl = match ptr_kind {
PointerKind::Box => Mutability::Mut,
PointerKind::Ref => {
let tam = value.layout.ty.builtin_deref(false).unwrap();
// ZST never require mutability. We do not take into account interior mutability
// here since we cannot know if there really is an `UnsafeCell` inside
// `Option<UnsafeCell>` -- so we check that in the recursive descent behind this
// reference.
if size == Size::ZERO { Mutability::Not } else { tam.mutbl }
PointerKind::Ref(mutbl) => {
// We do not take into account interior mutability here since we cannot know if
// there really is an `UnsafeCell` inside `Option<UnsafeCell>` -- so we check
// that in the recursive descent behind this reference (controlled by
// `allow_immutable_unsafe_cell`).
mutbl
}
};
// Proceed recursively even for ZST, no reason to skip them!
// `!` is a ZST and we want to validate it.
if let Ok((alloc_id, _offset, _prov)) = self.ecx.ptr_try_get_alloc_id(place.ptr()) {
let mut skip_recursive_check = false;
// Let's see what kind of memory this points to.
// `unwrap` since dangling pointers have already been handled.
let alloc_kind = self.ecx.tcx.try_get_global_alloc(alloc_id).unwrap();
match alloc_kind {
let alloc_actual_mutbl = match alloc_kind {
GlobalAlloc::Static(did) => {
// Special handling for pointers to statics (irrespective of their type).
assert!(!self.ecx.tcx.is_thread_local_static(did));
@ -474,12 +474,6 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
.no_bound_vars()
.expect("statics should not have generic parameters")
.is_freeze(*self.ecx.tcx, ty::ParamEnv::reveal_all());
// Mutability check.
if ptr_expected_mutbl == Mutability::Mut {
if !is_mut {
throw_validation_failure!(self.path, MutableRefToImmutable);
}
}
// Mode-specific checks
match self.ctfe_mode {
Some(
@ -494,15 +488,9 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
// trigger cycle errors if we try to compute the value of the other static
// and that static refers back to us (potentially through a promoted).
// This could miss some UB, but that's fine.
return Ok(());
skip_recursive_check = true;
}
Some(CtfeValidationMode::Const { .. }) => {
// For consts on the other hand we have to recursively check;
// pattern matching assumes a valid value. However we better make
// sure this is not mutable.
if is_mut {
throw_validation_failure!(self.path, ConstRefToMutable);
}
// We can't recursively validate `extern static`, so we better reject them.
if self.ecx.tcx.is_foreign_item(did) {
throw_validation_failure!(self.path, ConstRefToExtern);
@ -510,25 +498,38 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
}
None => {}
}
// Return alloc mutability
if is_mut { Mutability::Mut } else { Mutability::Not }
}
GlobalAlloc::Memory(alloc) => {
if alloc.inner().mutability == Mutability::Mut
&& matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { .. }))
{
throw_validation_failure!(self.path, ConstRefToMutable);
}
if ptr_expected_mutbl == Mutability::Mut
&& alloc.inner().mutability == Mutability::Not
{
throw_validation_failure!(self.path, MutableRefToImmutable);
}
}
GlobalAlloc::Memory(alloc) => alloc.inner().mutability,
GlobalAlloc::Function(..) | GlobalAlloc::VTable(..) => {
// These are immutable, we better don't allow mutable pointers here.
if ptr_expected_mutbl == Mutability::Mut {
throw_validation_failure!(self.path, MutableRefToImmutable);
}
Mutability::Not
}
};
// Mutability check.
// If this allocation has size zero, there is no actual mutability here.
let (size, _align, _alloc_kind) = self.ecx.get_alloc_info(alloc_id);
if size != Size::ZERO {
if ptr_expected_mutbl == Mutability::Mut
&& alloc_actual_mutbl == Mutability::Not
{
throw_validation_failure!(self.path, MutableRefToImmutable);
}
if ptr_expected_mutbl == Mutability::Mut
&& self.ctfe_mode.is_some_and(|c| !c.may_contain_mutable_ref())
{
throw_validation_failure!(self.path, MutableRefInConstOrStatic);
}
if alloc_actual_mutbl == Mutability::Mut
&& matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { .. }))
{
throw_validation_failure!(self.path, ConstRefToMutable);
}
}
// Potentially skip recursive check.
if skip_recursive_check {
return Ok(());
}
}
let path = &self.path;
@ -598,16 +599,8 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
}
Ok(true)
}
ty::Ref(_, ty, mutbl) => {
if self.ctfe_mode.is_some_and(|c| !c.may_contain_mutable_ref())
&& *mutbl == Mutability::Mut
{
let layout = self.ecx.layout_of(*ty)?;
if !layout.is_zst() {
throw_validation_failure!(self.path, MutableRefInConst);
}
}
self.check_safe_pointer(value, PointerKind::Ref)?;
ty::Ref(_, _ty, mutbl) => {
self.check_safe_pointer(value, PointerKind::Ref(*mutbl))?;
Ok(true)
}
ty::FnPtr(_sig) => {