1 //! Computations on places -- field projections, going from mir::Place, and writing
3 //! All high-level functions to write to memory work on places as destinations.
5 use std::convert::TryFrom;
9 use rustc::mir::interpret::truncate;
10 use rustc::ty::layout::{
11 self, Align, HasDataLayout, LayoutOf, PrimitiveExt, Size, TyLayout, VariantIdx,
13 use rustc::ty::TypeFoldable;
14 use rustc::ty::{self, Ty};
15 use rustc_macros::HashStable;
18 AllocId, AllocMap, Allocation, AllocationExtra, ImmTy, Immediate, InterpCx, InterpResult,
19 LocalValue, Machine, MemoryKind, OpTy, Operand, Pointer, PointerArithmetic, RawConst, Scalar,
23 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, HashStable)]
24 /// Information required for the sound usage of a `MemPlace`.
25 pub enum MemPlaceMeta<Tag = (), Id = AllocId> {
26 /// The unsized payload (e.g. length for slices or vtable pointer for trait objects).
27 Meta(Scalar<Tag, Id>),
28 /// `Sized` types or unsized `extern type`
30 /// The address of this place may not be taken. This protects the `MemPlace` from coming from
31 /// a ZST Operand with a backing allocation and being converted to an integer address. This
32 /// should be impossible, because you can't take the address of an operand, but this is a second
33 /// protection layer ensuring that we don't mess up.
37 impl<Tag, Id> MemPlaceMeta<Tag, Id> {
38 pub fn unwrap_meta(self) -> Scalar<Tag, Id> {
41 Self::None | Self::Poison => {
42 bug!("expected wide pointer extra data (e.g. slice length or trait object vtable)")
46 fn has_meta(self) -> bool {
48 Self::Meta(_) => true,
49 Self::None | Self::Poison => false,
54 impl<Tag> MemPlaceMeta<Tag> {
55 pub fn erase_tag(self) -> MemPlaceMeta<()> {
57 Self::Meta(s) => MemPlaceMeta::Meta(s.erase_tag()),
58 Self::None => MemPlaceMeta::None,
59 Self::Poison => MemPlaceMeta::Poison,
64 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, HashStable)]
65 pub struct MemPlace<Tag = (), Id = AllocId> {
66 /// A place may have an integral pointer for ZSTs, and since it might
67 /// be turned back into a reference before ever being dereferenced.
68 /// However, it may never be undef.
69 pub ptr: Scalar<Tag, Id>,
71 /// Metadata for unsized places. Interpretation is up to the type.
72 /// Must not be present for sized types, but can be missing for unsized types
73 /// (e.g., `extern type`).
74 pub meta: MemPlaceMeta<Tag, Id>,
77 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, HashStable)]
78 pub enum Place<Tag = (), Id = AllocId> {
79 /// A place referring to a value allocated in the `Memory` system.
80 Ptr(MemPlace<Tag, Id>),
82 /// To support alloc-free locals, we are able to write directly to a local.
83 /// (Without that optimization, we'd just always be a `MemPlace`.)
84 Local { frame: usize, local: mir::Local },
87 #[derive(Copy, Clone, Debug)]
88 pub struct PlaceTy<'tcx, Tag = ()> {
89 place: Place<Tag>, // Keep this private; it helps enforce invariants.
90 pub layout: TyLayout<'tcx>,
93 impl<'tcx, Tag> ::std::ops::Deref for PlaceTy<'tcx, Tag> {
94 type Target = Place<Tag>;
96 fn deref(&self) -> &Place<Tag> {
101 /// A MemPlace with its layout. Constructing it is only possible in this module.
102 #[derive(Copy, Clone, Debug, Hash, Eq, PartialEq)]
103 pub struct MPlaceTy<'tcx, Tag = ()> {
104 mplace: MemPlace<Tag>,
105 pub layout: TyLayout<'tcx>,
108 impl<'tcx, Tag> ::std::ops::Deref for MPlaceTy<'tcx, Tag> {
109 type Target = MemPlace<Tag>;
111 fn deref(&self) -> &MemPlace<Tag> {
116 impl<'tcx, Tag> From<MPlaceTy<'tcx, Tag>> for PlaceTy<'tcx, Tag> {
118 fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
119 PlaceTy { place: Place::Ptr(mplace.mplace), layout: mplace.layout }
123 impl<Tag> MemPlace<Tag> {
124 /// Replace ptr tag, maintain vtable tag (if any)
126 pub fn replace_tag(self, new_tag: Tag) -> Self {
127 MemPlace { ptr: self.ptr.erase_tag().with_tag(new_tag), align: self.align, meta: self.meta }
131 pub fn erase_tag(self) -> MemPlace {
132 MemPlace { ptr: self.ptr.erase_tag(), align: self.align, meta: self.meta.erase_tag() }
136 fn from_scalar_ptr(ptr: Scalar<Tag>, align: Align) -> Self {
137 MemPlace { ptr, align, meta: MemPlaceMeta::None }
140 /// Produces a Place that will error if attempted to be read from or written to
142 fn null(cx: &impl HasDataLayout) -> Self {
143 Self::from_scalar_ptr(Scalar::ptr_null(cx), Align::from_bytes(1).unwrap())
147 pub fn from_ptr(ptr: Pointer<Tag>, align: Align) -> Self {
148 Self::from_scalar_ptr(ptr.into(), align)
151 /// Turn a mplace into a (thin or wide) pointer, as a reference, pointing to the same space.
152 /// This is the inverse of `ref_to_mplace`.
154 pub fn to_ref(self) -> Immediate<Tag> {
156 MemPlaceMeta::None => Immediate::Scalar(self.ptr.into()),
157 MemPlaceMeta::Meta(meta) => Immediate::ScalarPair(self.ptr.into(), meta.into()),
158 MemPlaceMeta::Poison => bug!(
159 "MPlaceTy::dangling may never be used to produce a \
160 place that will have the address of its pointee taken"
168 meta: MemPlaceMeta<Tag>,
169 cx: &impl HasDataLayout,
170 ) -> InterpResult<'tcx, Self> {
172 ptr: self.ptr.ptr_offset(offset, cx)?,
173 align: self.align.restrict_for_offset(offset),
179 impl<'tcx, Tag> MPlaceTy<'tcx, Tag> {
180 /// Produces a MemPlace that works for ZST but nothing else
182 pub fn dangling(layout: TyLayout<'tcx>, cx: &impl HasDataLayout) -> Self {
183 let align = layout.align.abi;
184 let ptr = Scalar::from_uint(align.bytes(), cx.pointer_size());
185 // `Poison` this to make sure that the pointer value `ptr` is never observable by the program.
186 MPlaceTy { mplace: MemPlace { ptr, align, meta: MemPlaceMeta::Poison }, layout }
189 /// Replace ptr tag, maintain vtable tag (if any)
191 pub fn replace_tag(self, new_tag: Tag) -> Self {
192 MPlaceTy { mplace: self.mplace.replace_tag(new_tag), layout: self.layout }
199 meta: MemPlaceMeta<Tag>,
200 layout: TyLayout<'tcx>,
201 cx: &impl HasDataLayout,
202 ) -> InterpResult<'tcx, Self> {
203 Ok(MPlaceTy { mplace: self.mplace.offset(offset, meta, cx)?, layout })
207 fn from_aligned_ptr(ptr: Pointer<Tag>, layout: TyLayout<'tcx>) -> Self {
208 MPlaceTy { mplace: MemPlace::from_ptr(ptr, layout.align.abi), layout }
212 pub(super) fn len(self, cx: &impl HasDataLayout) -> InterpResult<'tcx, u64> {
213 if self.layout.is_unsized() {
214 // We need to consult `meta` metadata
215 match self.layout.ty.kind {
216 ty::Slice(..) | ty::Str => {
217 return self.mplace.meta.unwrap_meta().to_machine_usize(cx);
219 _ => bug!("len not supported on unsized type {:?}", self.layout.ty),
222 // Go through the layout. There are lots of types that support a length,
224 match self.layout.fields {
225 layout::FieldPlacement::Array { count, .. } => Ok(count),
226 _ => bug!("len not supported on sized type {:?}", self.layout.ty),
232 pub(super) fn vtable(self) -> Scalar<Tag> {
233 match self.layout.ty.kind {
234 ty::Dynamic(..) => self.mplace.meta.unwrap_meta(),
235 _ => bug!("vtable not supported on type {:?}", self.layout.ty),
240 // These are defined here because they produce a place.
241 impl<'tcx, Tag: ::std::fmt::Debug + Copy> OpTy<'tcx, Tag> {
243 /// Note: do not call `as_ref` on the resulting place. This function should only be used to
244 /// read from the resulting mplace, not to get its address back.
245 pub fn try_as_mplace(
247 cx: &impl HasDataLayout,
248 ) -> Result<MPlaceTy<'tcx, Tag>, ImmTy<'tcx, Tag>> {
250 Operand::Indirect(mplace) => Ok(MPlaceTy { mplace, layout: self.layout }),
251 Operand::Immediate(_) if self.layout.is_zst() => {
252 Ok(MPlaceTy::dangling(self.layout, cx))
254 Operand::Immediate(imm) => Err(ImmTy { imm, layout: self.layout }),
259 /// Note: do not call `as_ref` on the resulting place. This function should only be used to
260 /// read from the resulting mplace, not to get its address back.
261 pub fn assert_mem_place(self, cx: &impl HasDataLayout) -> MPlaceTy<'tcx, Tag> {
262 self.try_as_mplace(cx).unwrap()
266 impl<Tag: ::std::fmt::Debug> Place<Tag> {
267 /// Produces a Place that will error if attempted to be read from or written to
269 fn null(cx: &impl HasDataLayout) -> Self {
270 Place::Ptr(MemPlace::null(cx))
274 pub fn assert_mem_place(self) -> MemPlace<Tag> {
276 Place::Ptr(mplace) => mplace,
277 _ => bug!("assert_mem_place: expected Place::Ptr, got {:?}", self),
282 impl<'tcx, Tag: ::std::fmt::Debug> PlaceTy<'tcx, Tag> {
284 pub fn assert_mem_place(self) -> MPlaceTy<'tcx, Tag> {
285 MPlaceTy { mplace: self.place.assert_mem_place(), layout: self.layout }
289 // separating the pointer tag for `impl Trait`, see https://github.com/rust-lang/rust/issues/54385
290 impl<'mir, 'tcx, Tag, M> InterpCx<'mir, 'tcx, M>
292 // FIXME: Working around https://github.com/rust-lang/rust/issues/54385
293 Tag: ::std::fmt::Debug + Copy + Eq + Hash + 'static,
294 M: Machine<'mir, 'tcx, PointerTag = Tag>,
295 // FIXME: Working around https://github.com/rust-lang/rust/issues/24159
296 M::MemoryMap: AllocMap<AllocId, (MemoryKind<M::MemoryKinds>, Allocation<Tag, M::AllocExtra>)>,
297 M::AllocExtra: AllocationExtra<Tag>,
299 /// Take a value, which represents a (thin or wide) reference, and make it a place.
300 /// Alignment is just based on the type. This is the inverse of `MemPlace::to_ref()`.
302 /// Only call this if you are sure the place is "valid" (aligned and inbounds), or do not
303 /// want to ever use the place for memory access!
304 /// Generally prefer `deref_operand`.
305 pub fn ref_to_mplace(
307 val: ImmTy<'tcx, M::PointerTag>,
308 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
310 val.layout.ty.builtin_deref(true).expect("`ref_to_mplace` called on non-ptr type").ty;
311 let layout = self.layout_of(pointee_type)?;
312 let (ptr, meta) = match *val {
313 Immediate::Scalar(ptr) => (ptr.not_undef()?, MemPlaceMeta::None),
314 Immediate::ScalarPair(ptr, meta) => {
315 (ptr.not_undef()?, MemPlaceMeta::Meta(meta.not_undef()?))
319 let mplace = MemPlace {
321 // We could use the run-time alignment here. For now, we do not, because
322 // the point of tracking the alignment here is to make sure that the *static*
323 // alignment information emitted with the loads is correct. The run-time
324 // alignment can only be more restrictive.
325 align: layout.align.abi,
328 Ok(MPlaceTy { mplace, layout })
331 /// Take an operand, representing a pointer, and dereference it to a place -- that
332 /// will always be a MemPlace. Lives in `place.rs` because it creates a place.
333 pub fn deref_operand(
335 src: OpTy<'tcx, M::PointerTag>,
336 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
337 let val = self.read_immediate(src)?;
338 trace!("deref to {} on {:?}", val.layout.ty, *val);
339 let place = self.ref_to_mplace(val)?;
340 self.mplace_access_checked(place)
343 /// Check if the given place is good for memory access with the given
344 /// size, falling back to the layout's size if `None` (in the latter case,
345 /// this must be a statically sized type).
347 /// On success, returns `None` for zero-sized accesses (where nothing else is
348 /// left to do) and a `Pointer` to use for the actual access otherwise.
350 pub(super) fn check_mplace_access(
352 place: MPlaceTy<'tcx, M::PointerTag>,
354 ) -> InterpResult<'tcx, Option<Pointer<M::PointerTag>>> {
355 let size = size.unwrap_or_else(|| {
356 assert!(!place.layout.is_unsized());
357 assert!(!place.meta.has_meta());
360 self.memory.check_ptr_access(place.ptr, size, place.align)
363 /// Return the "access-checked" version of this `MPlace`, where for non-ZST
364 /// this is definitely a `Pointer`.
365 pub fn mplace_access_checked(
367 mut place: MPlaceTy<'tcx, M::PointerTag>,
368 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
369 let (size, align) = self
370 .size_and_align_of_mplace(place)?
371 .unwrap_or((place.layout.size, place.layout.align.abi));
372 assert!(place.mplace.align <= align, "dynamic alignment less strict than static one?");
373 place.mplace.align = align; // maximally strict checking
374 // When dereferencing a pointer, it must be non-NULL, aligned, and live.
375 if let Some(ptr) = self.check_mplace_access(place, Some(size))? {
376 place.mplace.ptr = ptr.into();
381 /// Force `place.ptr` to a `Pointer`.
382 /// Can be helpful to avoid lots of `force_ptr` calls later, if this place is used a lot.
383 pub(super) fn force_mplace_ptr(
385 mut place: MPlaceTy<'tcx, M::PointerTag>,
386 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
387 place.mplace.ptr = self.force_ptr(place.mplace.ptr)?.into();
391 /// Offset a pointer to project to a field. Unlike `place_field`, this is always
392 /// possible without allocating, so it can take `&self`. Also return the field's layout.
393 /// This supports both struct and array fields.
397 base: MPlaceTy<'tcx, M::PointerTag>,
399 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
400 // Not using the layout method because we want to compute on u64
401 let offset = match base.layout.fields {
402 layout::FieldPlacement::Arbitrary { ref offsets, .. } => {
403 offsets[usize::try_from(field).unwrap()]
405 layout::FieldPlacement::Array { stride, .. } => {
406 let len = base.len(self)?;
408 // This can only be reached in ConstProp and non-rustc-MIR.
409 throw_ub!(BoundsCheckFailed { len, index: field });
413 layout::FieldPlacement::Union(count) => {
415 field < count as u64,
416 "Tried to access field {} of union {:#?} with {} fields",
421 // Offset is always 0
425 // the only way conversion can fail if is this is an array (otherwise we already panicked
426 // above). In that case, all fields are equal.
427 let field_layout = base.layout.field(self, usize::try_from(field).unwrap_or(0))?;
429 // Offset may need adjustment for unsized fields.
430 let (meta, offset) = if field_layout.is_unsized() {
431 // Re-use parent metadata to determine dynamic field layout.
432 // With custom DSTS, this *will* execute user-defined code, but the same
433 // happens at run-time so that's okay.
434 let align = match self.size_and_align_of(base.meta, field_layout)? {
435 Some((_, align)) => align,
436 None if offset == Size::ZERO =>
437 // An extern type at offset 0, we fall back to its static alignment.
438 // FIXME: Once we have made decisions for how to handle size and alignment
439 // of `extern type`, this should be adapted. It is just a temporary hack
440 // to get some code to work that probably ought to work.
442 field_layout.align.abi
444 None => bug!("Cannot compute offset for extern type field at non-0 offset"),
446 (base.meta, offset.align_to(align))
448 // base.meta could be present; we might be accessing a sized field of an unsized
450 (MemPlaceMeta::None, offset)
453 // We do not look at `base.layout.align` nor `field_layout.align`, unlike
454 // codegen -- mostly to see if we can get away with that
455 base.offset(offset, meta, field_layout, self)
458 // Iterates over all fields of an array. Much more efficient than doing the
459 // same by repeatedly calling `mplace_array`.
460 pub(super) fn mplace_array_fields(
462 base: MPlaceTy<'tcx, Tag>,
463 ) -> InterpResult<'tcx, impl Iterator<Item = InterpResult<'tcx, MPlaceTy<'tcx, Tag>>> + 'tcx>
465 let len = base.len(self)?; // also asserts that we have a type where this makes sense
466 let stride = match base.layout.fields {
467 layout::FieldPlacement::Array { stride, .. } => stride,
468 _ => bug!("mplace_array_fields: expected an array layout"),
470 let layout = base.layout.field(self, 0)?;
471 let dl = &self.tcx.data_layout;
472 Ok((0..len).map(move |i| base.offset(i * stride, MemPlaceMeta::None, layout, dl)))
477 base: MPlaceTy<'tcx, M::PointerTag>,
481 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
482 let len = base.len(self)?; // also asserts that we have a type where this makes sense
483 let actual_to = if from_end {
485 // This can only be reached in ConstProp and non-rustc-MIR.
486 throw_ub!(BoundsCheckFailed { len: len as u64, index: from as u64 + to as u64 });
493 // Not using layout method because that works with usize, and does not work with slices
494 // (that have count 0 in their layout).
495 let from_offset = match base.layout.fields {
496 layout::FieldPlacement::Array { stride, .. } => stride * from,
497 _ => bug!("Unexpected layout of index access: {:#?}", base.layout),
500 // Compute meta and new layout
501 let inner_len = actual_to - from;
502 let (meta, ty) = match base.layout.ty.kind {
503 // It is not nice to match on the type, but that seems to be the only way to
505 ty::Array(inner, _) => (MemPlaceMeta::None, self.tcx.mk_array(inner, inner_len)),
507 let len = Scalar::from_uint(inner_len, self.pointer_size());
508 (MemPlaceMeta::Meta(len), base.layout.ty)
510 _ => bug!("cannot subslice non-array type: `{:?}`", base.layout.ty),
512 let layout = self.layout_of(ty)?;
513 base.offset(from_offset, meta, layout, self)
516 pub(super) fn mplace_downcast(
518 base: MPlaceTy<'tcx, M::PointerTag>,
520 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
521 // Downcasts only change the layout
522 assert!(!base.meta.has_meta());
523 Ok(MPlaceTy { layout: base.layout.for_variant(self, variant), ..base })
526 /// Project into an mplace
527 pub(super) fn mplace_projection(
529 base: MPlaceTy<'tcx, M::PointerTag>,
530 proj_elem: &mir::PlaceElem<'tcx>,
531 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
532 use rustc::mir::ProjectionElem::*;
533 Ok(match *proj_elem {
534 Field(field, _) => self.mplace_field(base, field.index() as u64)?,
535 Downcast(_, variant) => self.mplace_downcast(base, variant)?,
536 Deref => self.deref_operand(base.into())?,
539 let layout = self.layout_of(self.tcx.types.usize)?;
540 let n = self.access_local(self.frame(), local, Some(layout))?;
541 let n = self.read_scalar(n)?;
542 let n = self.force_bits(n.not_undef()?, self.tcx.data_layout.pointer_size)?;
543 self.mplace_field(base, u64::try_from(n).unwrap())?
546 ConstantIndex { offset, min_length, from_end } => {
547 let n = base.len(self)?;
548 if n < min_length as u64 {
549 // This can only be reached in ConstProp and non-rustc-MIR.
550 throw_ub!(BoundsCheckFailed { len: min_length as u64, index: n as u64 });
553 let index = if from_end {
554 assert!(0 < offset && offset - 1 < min_length);
555 n - u64::from(offset)
557 assert!(offset < min_length);
561 self.mplace_field(base, index)?
564 Subslice { from, to, from_end } => {
565 self.mplace_subslice(base, u64::from(from), u64::from(to), from_end)?
570 /// Gets the place of a field inside the place, and also the field's type.
571 /// Just a convenience function, but used quite a bit.
572 /// This is the only projection that might have a side-effect: We cannot project
573 /// into the field of a local `ScalarPair`, we have to first allocate it.
576 base: PlaceTy<'tcx, M::PointerTag>,
578 ) -> InterpResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
579 // FIXME: We could try to be smarter and avoid allocation for fields that span the
581 let mplace = self.force_allocation(base)?;
582 Ok(self.mplace_field(mplace, field)?.into())
585 pub fn place_downcast(
587 base: PlaceTy<'tcx, M::PointerTag>,
589 ) -> InterpResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
590 // Downcast just changes the layout
591 Ok(match base.place {
592 Place::Ptr(mplace) => {
593 self.mplace_downcast(MPlaceTy { mplace, layout: base.layout }, variant)?.into()
595 Place::Local { .. } => {
596 let layout = base.layout.for_variant(self, variant);
597 PlaceTy { layout, ..base }
602 /// Projects into a place.
603 pub fn place_projection(
605 base: PlaceTy<'tcx, M::PointerTag>,
606 proj_elem: &mir::ProjectionElem<mir::Local, Ty<'tcx>>,
607 ) -> InterpResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
608 use rustc::mir::ProjectionElem::*;
609 Ok(match *proj_elem {
610 Field(field, _) => self.place_field(base, field.index() as u64)?,
611 Downcast(_, variant) => self.place_downcast(base, variant)?,
612 Deref => self.deref_operand(self.place_to_op(base)?)?.into(),
613 // For the other variants, we have to force an allocation.
614 // This matches `operand_projection`.
615 Subslice { .. } | ConstantIndex { .. } | Index(_) => {
616 let mplace = self.force_allocation(base)?;
617 self.mplace_projection(mplace, proj_elem)?.into()
622 /// Evaluate statics and promoteds to an `MPlace`. Used to share some code between
623 /// `eval_place` and `eval_place_to_op`.
624 pub(super) fn eval_static_to_mplace(
626 place_static: &mir::Static<'tcx>,
627 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
628 let ty = place_static.ty;
629 assert!(!ty.needs_subst());
630 let layout = self.layout_of(ty)?;
631 // Just create a lazy reference, so we can support recursive statics.
632 // tcx takes care of assigning every static one and only one unique AllocId.
633 // When the data here is ever actually used, memory will notice,
634 // and it knows how to deal with alloc_id that are present in the
635 // global table but not in its local memory: It calls back into tcx through
636 // a query, triggering the CTFE machinery to actually turn this lazy reference
637 // into a bunch of bytes. IOW, statics are evaluated with CTFE even when
638 // this InterpCx uses another Machine (e.g., in miri). This is what we
639 // want! This way, computing statics works consistently between codegen
640 // and miri: They use the same query to eventually obtain a `ty::Const`
641 // and use that for further computation.
643 // Notice that statics have *two* AllocIds: the lazy one, and the resolved
644 // one. Here we make sure that the interpreted program never sees the
645 // resolved ID. Also see the doc comment of `Memory::get_static_alloc`.
646 let alloc_id = self.tcx.alloc_map.lock().create_static_alloc(place_static.def_id);
647 let ptr = self.tag_static_base_pointer(Pointer::from(alloc_id));
648 Ok(MPlaceTy::from_aligned_ptr(ptr, layout))
651 /// Computes a place. You should only use this if you intend to write into this
652 /// place; for reading, a more efficient alternative is `eval_place_for_read`.
655 place: &mir::Place<'tcx>,
656 ) -> InterpResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
657 use rustc::mir::PlaceBase;
659 let mut place_ty = match &place.base {
660 PlaceBase::Local(mir::RETURN_PLACE) => {
661 // `return_place` has the *caller* layout, but we want to use our
662 // `layout to verify our assumption. The caller will validate
663 // their layout on return.
665 place: match self.frame().return_place {
667 // Even if we don't have a return place, we sometimes need to
668 // create this place, but any attempt to read from / write to it
669 // (even a ZST read/write) needs to error, so let us make this
672 // FIXME: Ideally we'd make sure that the place projections also
674 None => Place::null(&*self),
676 layout: self.layout_of(self.subst_from_frame_and_normalize_erasing_regions(
677 self.frame().body.return_ty(),
681 PlaceBase::Local(local) => PlaceTy {
682 // This works even for dead/uninitialized locals; we check further when writing
683 place: Place::Local { frame: self.cur_frame(), local: *local },
684 layout: self.layout_of_local(self.frame(), *local, None)?,
686 PlaceBase::Static(place_static) => self.eval_static_to_mplace(&place_static)?.into(),
689 for elem in place.projection.iter() {
690 place_ty = self.place_projection(place_ty, elem)?
693 self.dump_place(place_ty.place);
697 /// Write a scalar to a place
701 val: impl Into<ScalarMaybeUndef<M::PointerTag>>,
702 dest: PlaceTy<'tcx, M::PointerTag>,
703 ) -> InterpResult<'tcx> {
704 self.write_immediate(Immediate::Scalar(val.into()), dest)
707 /// Write an immediate to a place
709 pub fn write_immediate(
711 src: Immediate<M::PointerTag>,
712 dest: PlaceTy<'tcx, M::PointerTag>,
713 ) -> InterpResult<'tcx> {
714 self.write_immediate_no_validate(src, dest)?;
716 if M::enforce_validity(self) {
717 // Data got changed, better make sure it matches the type!
718 self.validate_operand(self.place_to_op(dest)?, vec![], None)?;
724 /// Write an `Immediate` to memory.
726 pub fn write_immediate_to_mplace(
728 src: Immediate<M::PointerTag>,
729 dest: MPlaceTy<'tcx, M::PointerTag>,
730 ) -> InterpResult<'tcx> {
731 self.write_immediate_to_mplace_no_validate(src, dest)?;
733 if M::enforce_validity(self) {
734 // Data got changed, better make sure it matches the type!
735 self.validate_operand(dest.into(), vec![], None)?;
741 /// Write an immediate to a place.
742 /// If you use this you are responsible for validating that things got copied at the
744 fn write_immediate_no_validate(
746 src: Immediate<M::PointerTag>,
747 dest: PlaceTy<'tcx, M::PointerTag>,
748 ) -> InterpResult<'tcx> {
749 if cfg!(debug_assertions) {
750 // This is a very common path, avoid some checks in release mode
751 assert!(!dest.layout.is_unsized(), "Cannot write unsized data");
753 Immediate::Scalar(ScalarMaybeUndef::Scalar(Scalar::Ptr(_))) => assert_eq!(
756 "Size mismatch when writing pointer"
758 Immediate::Scalar(ScalarMaybeUndef::Scalar(Scalar::Raw { size, .. })) => {
760 Size::from_bytes(size.into()),
762 "Size mismatch when writing bits"
765 Immediate::Scalar(ScalarMaybeUndef::Undef) => {} // undef can have any size
766 Immediate::ScalarPair(_, _) => {
767 // FIXME: Can we check anything here?
771 trace!("write_immediate: {:?} <- {:?}: {}", *dest, src, dest.layout.ty);
773 // See if we can avoid an allocation. This is the counterpart to `try_read_immediate`,
774 // but not factored as a separate function.
775 let mplace = match dest.place {
776 Place::Local { frame, local } => {
777 match self.stack[frame].locals[local].access_mut()? {
779 // Local can be updated in-place.
780 *local = LocalValue::Live(Operand::Immediate(src));
784 // The local is in memory, go on below.
789 Place::Ptr(mplace) => mplace, // already referring to memory
791 let dest = MPlaceTy { mplace, layout: dest.layout };
793 // This is already in memory, write there.
794 self.write_immediate_to_mplace_no_validate(src, dest)
797 /// Write an immediate to memory.
798 /// If you use this you are responsible for validating that things got copied at the
800 fn write_immediate_to_mplace_no_validate(
802 value: Immediate<M::PointerTag>,
803 dest: MPlaceTy<'tcx, M::PointerTag>,
804 ) -> InterpResult<'tcx> {
805 // Note that it is really important that the type here is the right one, and matches the
806 // type things are read at. In case `src_val` is a `ScalarPair`, we don't do any magic here
807 // to handle padding properly, which is only correct if we never look at this data with the
810 // Invalid places are a thing: the return place of a diverging function
811 let ptr = match self.check_mplace_access(dest, None)? {
813 None => return Ok(()), // zero-sized access
816 let tcx = &*self.tcx;
817 // FIXME: We should check that there are dest.layout.size many bytes available in
818 // memory. The code below is not sufficient, with enough padding it might not
819 // cover all the bytes!
821 Immediate::Scalar(scalar) => {
822 match dest.layout.abi {
823 layout::Abi::Scalar(_) => {} // fine
825 bug!("write_immediate_to_mplace: invalid Scalar layout: {:#?}", dest.layout)
828 self.memory.get_raw_mut(ptr.alloc_id)?.write_scalar(
835 Immediate::ScalarPair(a_val, b_val) => {
836 // We checked `ptr_align` above, so all fields will have the alignment they need.
837 // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
838 // which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
839 let (a, b) = match dest.layout.abi {
840 layout::Abi::ScalarPair(ref a, ref b) => (&a.value, &b.value),
842 "write_immediate_to_mplace: invalid ScalarPair layout: {:#?}",
846 let (a_size, b_size) = (a.size(self), b.size(self));
847 let b_offset = a_size.align_to(b.align(self).abi);
848 let b_ptr = ptr.offset(b_offset, self)?;
850 // It is tempting to verify `b_offset` against `layout.fields.offset(1)`,
851 // but that does not work: We could be a newtype around a pair, then the
852 // fields do not match the `ScalarPair` components.
854 self.memory.get_raw_mut(ptr.alloc_id)?.write_scalar(tcx, ptr, a_val, a_size)?;
855 self.memory.get_raw_mut(b_ptr.alloc_id)?.write_scalar(tcx, b_ptr, b_val, b_size)
860 /// Copies the data from an operand to a place. This does not support transmuting!
861 /// Use `copy_op_transmute` if the layouts could disagree.
865 src: OpTy<'tcx, M::PointerTag>,
866 dest: PlaceTy<'tcx, M::PointerTag>,
867 ) -> InterpResult<'tcx> {
868 self.copy_op_no_validate(src, dest)?;
870 if M::enforce_validity(self) {
871 // Data got changed, better make sure it matches the type!
872 self.validate_operand(self.place_to_op(dest)?, vec![], None)?;
878 /// Copies the data from an operand to a place. This does not support transmuting!
879 /// Use `copy_op_transmute` if the layouts could disagree.
880 /// Also, if you use this you are responsible for validating that things get copied at the
882 fn copy_op_no_validate(
884 src: OpTy<'tcx, M::PointerTag>,
885 dest: PlaceTy<'tcx, M::PointerTag>,
886 ) -> InterpResult<'tcx> {
887 // We do NOT compare the types for equality, because well-typed code can
888 // actually "transmute" `&mut T` to `&T` in an assignment without a cast.
890 src.layout.details == dest.layout.details,
891 "Layout mismatch when copying!\nsrc: {:#?}\ndest: {:#?}",
896 // Let us see if the layout is simple so we take a shortcut, avoid force_allocation.
897 let src = match self.try_read_immediate(src)? {
899 assert!(!src.layout.is_unsized(), "cannot have unsized immediates");
900 // Yay, we got a value that we can write directly.
901 // FIXME: Add a check to make sure that if `src` is indirect,
902 // it does not overlap with `dest`.
903 return self.write_immediate_no_validate(*src_val, dest);
905 Err(mplace) => mplace,
907 // Slow path, this does not fit into an immediate. Just memcpy.
908 trace!("copy_op: {:?} <- {:?}: {}", *dest, src, dest.layout.ty);
910 // This interprets `src.meta` with the `dest` local's layout, if an unsized local
911 // is being initialized!
912 let (dest, size) = self.force_allocation_maybe_sized(dest, src.meta)?;
913 let size = size.unwrap_or_else(|| {
915 !dest.layout.is_unsized(),
916 "Cannot copy into already initialized unsized place"
920 assert_eq!(src.meta, dest.meta, "Can only copy between equally-sized instances");
923 .check_mplace_access(src, Some(size))
924 .expect("places should be checked on creation");
926 .check_mplace_access(dest, Some(size))
927 .expect("places should be checked on creation");
928 let (src_ptr, dest_ptr) = match (src, dest) {
929 (Some(src_ptr), Some(dest_ptr)) => (src_ptr, dest_ptr),
930 (None, None) => return Ok(()), // zero-sized copy
931 _ => bug!("The pointers should both be Some or both None"),
934 self.memory.copy(src_ptr, dest_ptr, size, /*nonoverlapping*/ true)
937 /// Copies the data from an operand to a place. The layouts may disagree, but they must
938 /// have the same size.
939 pub fn copy_op_transmute(
941 src: OpTy<'tcx, M::PointerTag>,
942 dest: PlaceTy<'tcx, M::PointerTag>,
943 ) -> InterpResult<'tcx> {
944 if src.layout.details == dest.layout.details {
945 // Fast path: Just use normal `copy_op`
946 return self.copy_op(src, dest);
948 // We still require the sizes to match.
949 if src.layout.size != dest.layout.size {
950 // FIXME: This should be an assert instead of an error, but if we transmute within an
951 // array length computation, `typeck` may not have yet been run and errored out. In fact
952 // most likey we *are* running `typeck` right now. Investigate whether we can bail out
953 // on `typeck_tables().has_errors` at all const eval entry points.
954 debug!("Size mismatch when transmuting!\nsrc: {:#?}\ndest: {:#?}", src, dest);
955 throw_unsup!(TransmuteSizeDiff(src.layout.ty, dest.layout.ty));
957 // Unsized copies rely on interpreting `src.meta` with `dest.layout`, we want
958 // to avoid that here.
960 !src.layout.is_unsized() && !dest.layout.is_unsized(),
961 "Cannot transmute unsized data"
964 // The hard case is `ScalarPair`. `src` is already read from memory in this case,
965 // using `src.layout` to figure out which bytes to use for the 1st and 2nd field.
966 // We have to write them to `dest` at the offsets they were *read at*, which is
967 // not necessarily the same as the offsets in `dest.layout`!
968 // Hence we do the copy with the source layout on both sides. We also make sure to write
969 // into memory, because if `dest` is a local we would not even have a way to write
970 // at the `src` offsets; the fact that we came from a different layout would
972 let dest = self.force_allocation(dest)?;
973 self.copy_op_no_validate(
975 PlaceTy::from(MPlaceTy { mplace: *dest, layout: src.layout }),
978 if M::enforce_validity(self) {
979 // Data got changed, better make sure it matches the type!
980 self.validate_operand(dest.into(), vec![], None)?;
986 /// Ensures that a place is in memory, and returns where it is.
987 /// If the place currently refers to a local that doesn't yet have a matching allocation,
988 /// create such an allocation.
989 /// This is essentially `force_to_memplace`.
991 /// This supports unsized types and returns the computed size to avoid some
992 /// redundant computation when copying; use `force_allocation` for a simpler, sized-only
994 pub fn force_allocation_maybe_sized(
996 place: PlaceTy<'tcx, M::PointerTag>,
997 meta: MemPlaceMeta<M::PointerTag>,
998 ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::PointerTag>, Option<Size>)> {
999 let (mplace, size) = match place.place {
1000 Place::Local { frame, local } => {
1001 match self.stack[frame].locals[local].access_mut()? {
1002 Ok(&mut local_val) => {
1003 // We need to make an allocation.
1005 // We need the layout of the local. We can NOT use the layout we got,
1006 // that might e.g., be an inner field of a struct with `Scalar` layout,
1007 // that has different alignment than the outer field.
1008 let local_layout = self.layout_of_local(&self.stack[frame], local, None)?;
1009 // We also need to support unsized types, and hence cannot use `allocate`.
1010 let (size, align) = self
1011 .size_and_align_of(meta, local_layout)?
1012 .expect("Cannot allocate for non-dyn-sized type");
1013 let ptr = self.memory.allocate(size, align, MemoryKind::Stack);
1014 let mplace = MemPlace { ptr: ptr.into(), align, meta };
1015 if let LocalValue::Live(Operand::Immediate(value)) = local_val {
1016 // Preserve old value.
1017 // We don't have to validate as we can assume the local
1018 // was already valid for its type.
1019 let mplace = MPlaceTy { mplace, layout: local_layout };
1020 self.write_immediate_to_mplace_no_validate(value, mplace)?;
1022 // Now we can call `access_mut` again, asserting it goes well,
1023 // and actually overwrite things.
1024 *self.stack[frame].locals[local].access_mut().unwrap().unwrap() =
1025 LocalValue::Live(Operand::Indirect(mplace));
1026 (mplace, Some(size))
1028 Err(mplace) => (mplace, None), // this already was an indirect local
1031 Place::Ptr(mplace) => (mplace, None),
1033 // Return with the original layout, so that the caller can go on
1034 Ok((MPlaceTy { mplace, layout: place.layout }, size))
1038 pub fn force_allocation(
1040 place: PlaceTy<'tcx, M::PointerTag>,
1041 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
1042 Ok(self.force_allocation_maybe_sized(place, MemPlaceMeta::None)?.0)
1047 layout: TyLayout<'tcx>,
1048 kind: MemoryKind<M::MemoryKinds>,
1049 ) -> MPlaceTy<'tcx, M::PointerTag> {
1050 let ptr = self.memory.allocate(layout.size, layout.align.abi, kind);
1051 MPlaceTy::from_aligned_ptr(ptr, layout)
1054 /// Returns a wide MPlace.
1055 pub fn allocate_str(
1058 kind: MemoryKind<M::MemoryKinds>,
1059 ) -> MPlaceTy<'tcx, M::PointerTag> {
1060 let ptr = self.memory.allocate_static_bytes(str.as_bytes(), kind);
1061 let meta = Scalar::from_uint(str.len() as u128, self.pointer_size());
1062 let mplace = MemPlace {
1064 align: Align::from_bytes(1).unwrap(),
1065 meta: MemPlaceMeta::Meta(meta),
1068 let layout = self.layout_of(self.tcx.mk_static_str()).unwrap();
1069 MPlaceTy { mplace, layout }
1072 pub fn write_discriminant_index(
1074 variant_index: VariantIdx,
1075 dest: PlaceTy<'tcx, M::PointerTag>,
1076 ) -> InterpResult<'tcx> {
1077 // Layout computation excludes uninhabited variants from consideration
1078 // therefore there's no way to represent those variants in the given layout.
1079 if dest.layout.for_variant(self, variant_index).abi.is_uninhabited() {
1080 throw_ub!(Unreachable);
1083 match dest.layout.variants {
1084 layout::Variants::Single { index } => {
1085 assert_eq!(index, variant_index);
1087 layout::Variants::Multiple {
1088 discr_kind: layout::DiscriminantKind::Tag,
1089 discr: ref discr_layout,
1093 // No need to validate that the discriminant here because the
1094 // `TyLayout::for_variant()` call earlier already checks the variant is valid.
1097 dest.layout.ty.discriminant_for_variant(*self.tcx, variant_index).unwrap().val;
1099 // raw discriminants for enums are isize or bigger during
1100 // their computation, but the in-memory tag is the smallest possible
1102 let size = discr_layout.value.size(self);
1103 let discr_val = truncate(discr_val, size);
1105 let discr_dest = self.place_field(dest, discr_index as u64)?;
1106 self.write_scalar(Scalar::from_uint(discr_val, size), discr_dest)?;
1108 layout::Variants::Multiple {
1110 layout::DiscriminantKind::Niche { dataful_variant, ref niche_variants, niche_start },
1111 discr: ref discr_layout,
1115 // No need to validate that the discriminant here because the
1116 // `TyLayout::for_variant()` call earlier already checks the variant is valid.
1118 if variant_index != dataful_variant {
1119 let variants_start = niche_variants.start().as_u32();
1120 let variant_index_relative = variant_index
1122 .checked_sub(variants_start)
1123 .expect("overflow computing relative variant idx");
1124 // We need to use machine arithmetic when taking into account `niche_start`:
1125 // discr_val = variant_index_relative + niche_start_val
1126 let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
1127 let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
1128 let variant_index_relative_val =
1129 ImmTy::from_uint(variant_index_relative, discr_layout);
1130 let discr_val = self.binary_op(
1132 variant_index_relative_val,
1136 let niche_dest = self.place_field(dest, discr_index as u64)?;
1137 self.write_immediate(*discr_val, niche_dest)?;
1145 pub fn raw_const_to_mplace(
1147 raw: RawConst<'tcx>,
1148 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
1149 // This must be an allocation in `tcx`
1150 assert!(self.tcx.alloc_map.lock().get(raw.alloc_id).is_some());
1151 let ptr = self.tag_static_base_pointer(Pointer::from(raw.alloc_id));
1152 let layout = self.layout_of(raw.ty)?;
1153 Ok(MPlaceTy::from_aligned_ptr(ptr, layout))
1156 /// Turn a place with a `dyn Trait` type into a place with the actual dynamic type.
1157 /// Also return some more information so drop doesn't have to run the same code twice.
1158 pub(super) fn unpack_dyn_trait(
1160 mplace: MPlaceTy<'tcx, M::PointerTag>,
1161 ) -> InterpResult<'tcx, (ty::Instance<'tcx>, MPlaceTy<'tcx, M::PointerTag>)> {
1162 let vtable = mplace.vtable(); // also sanity checks the type
1163 let (instance, ty) = self.read_drop_type_from_vtable(vtable)?;
1164 let layout = self.layout_of(ty)?;
1166 // More sanity checks
1167 if cfg!(debug_assertions) {
1168 let (size, align) = self.read_size_and_align_from_vtable(vtable)?;
1169 assert_eq!(size, layout.size);
1170 // only ABI alignment is preserved
1171 assert_eq!(align, layout.align.abi);
1174 let mplace = MPlaceTy { mplace: MemPlace { meta: MemPlaceMeta::None, ..*mplace }, layout };
1175 Ok((instance, mplace))