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, GlobalId, ImmTy, Immediate, InterpCx,
19 InterpResult, LocalValue, Machine, MemoryKind, OpTy, Operand, Pointer, PointerArithmetic,
20 RawConst, Scalar, ScalarMaybeUndef,
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 Unsized(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_unsized(self) -> Scalar<Tag, Id> {
40 Self::Unsized(s) => s,
41 Self::None | Self::Poison => {
42 bug!("expected wide pointer extra data (e.g. slice length or trait object vtable)")
46 fn is_unsized(self) -> bool {
48 Self::Unsized(_) => true,
49 Self::None | Self::Poison => false,
54 impl<Tag> MemPlaceMeta<Tag> {
55 pub fn erase_tag(self) -> MemPlaceMeta<()> {
57 Self::Unsized(s) => MemPlaceMeta::Unsized(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::Unsized(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_unsized().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_unsized(),
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::Unsized(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.is_unsized());
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::Unsized(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.is_unsized());
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 use rustc::mir::StaticKind;
630 Ok(match place_static.kind {
631 StaticKind::Promoted(promoted, promoted_substs) => {
632 let substs = self.subst_from_frame_and_normalize_erasing_regions(promoted_substs);
633 let instance = ty::Instance::new(place_static.def_id, substs);
635 // Even after getting `substs` from the frame, this instance may still be
636 // polymorphic because `ConstProp` will try to promote polymorphic MIR.
637 if instance.needs_subst() {
638 throw_inval!(TooGeneric);
641 self.const_eval_raw(GlobalId { instance, promoted: Some(promoted) })?
644 StaticKind::Static => {
645 let ty = place_static.ty;
646 assert!(!ty.needs_subst());
647 let layout = self.layout_of(ty)?;
648 // Just create a lazy reference, so we can support recursive statics.
649 // tcx takes care of assigning every static one and only one unique AllocId.
650 // When the data here is ever actually used, memory will notice,
651 // and it knows how to deal with alloc_id that are present in the
652 // global table but not in its local memory: It calls back into tcx through
653 // a query, triggering the CTFE machinery to actually turn this lazy reference
654 // into a bunch of bytes. IOW, statics are evaluated with CTFE even when
655 // this InterpCx uses another Machine (e.g., in miri). This is what we
656 // want! This way, computing statics works consistently between codegen
657 // and miri: They use the same query to eventually obtain a `ty::Const`
658 // and use that for further computation.
660 // Notice that statics have *two* AllocIds: the lazy one, and the resolved
661 // one. Here we make sure that the interpreted program never sees the
662 // resolved ID. Also see the doc comment of `Memory::get_static_alloc`.
663 let alloc_id = self.tcx.alloc_map.lock().create_static_alloc(place_static.def_id);
664 let ptr = self.tag_static_base_pointer(Pointer::from(alloc_id));
665 MPlaceTy::from_aligned_ptr(ptr, layout)
670 /// Computes a place. You should only use this if you intend to write into this
671 /// place; for reading, a more efficient alternative is `eval_place_for_read`.
674 place: &mir::Place<'tcx>,
675 ) -> InterpResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
676 use rustc::mir::PlaceBase;
678 let mut place_ty = match &place.base {
679 PlaceBase::Local(mir::RETURN_PLACE) => {
680 // `return_place` has the *caller* layout, but we want to use our
681 // `layout to verify our assumption. The caller will validate
682 // their layout on return.
684 place: match self.frame().return_place {
686 // Even if we don't have a return place, we sometimes need to
687 // create this place, but any attempt to read from / write to it
688 // (even a ZST read/write) needs to error, so let us make this
691 // FIXME: Ideally we'd make sure that the place projections also
693 None => Place::null(&*self),
695 layout: self.layout_of(self.subst_from_frame_and_normalize_erasing_regions(
696 self.frame().body.return_ty(),
700 PlaceBase::Local(local) => PlaceTy {
701 // This works even for dead/uninitialized locals; we check further when writing
702 place: Place::Local { frame: self.cur_frame(), local: *local },
703 layout: self.layout_of_local(self.frame(), *local, None)?,
705 PlaceBase::Static(place_static) => self.eval_static_to_mplace(&place_static)?.into(),
708 for elem in place.projection.iter() {
709 place_ty = self.place_projection(place_ty, elem)?
712 self.dump_place(place_ty.place);
716 /// Write a scalar to a place
720 val: impl Into<ScalarMaybeUndef<M::PointerTag>>,
721 dest: PlaceTy<'tcx, M::PointerTag>,
722 ) -> InterpResult<'tcx> {
723 self.write_immediate(Immediate::Scalar(val.into()), dest)
726 /// Write an immediate to a place
728 pub fn write_immediate(
730 src: Immediate<M::PointerTag>,
731 dest: PlaceTy<'tcx, M::PointerTag>,
732 ) -> InterpResult<'tcx> {
733 self.write_immediate_no_validate(src, dest)?;
735 if M::enforce_validity(self) {
736 // Data got changed, better make sure it matches the type!
737 self.validate_operand(self.place_to_op(dest)?, vec![], None)?;
743 /// Write an `Immediate` to memory.
745 pub fn write_immediate_to_mplace(
747 src: Immediate<M::PointerTag>,
748 dest: MPlaceTy<'tcx, M::PointerTag>,
749 ) -> InterpResult<'tcx> {
750 self.write_immediate_to_mplace_no_validate(src, dest)?;
752 if M::enforce_validity(self) {
753 // Data got changed, better make sure it matches the type!
754 self.validate_operand(dest.into(), vec![], None)?;
760 /// Write an immediate to a place.
761 /// If you use this you are responsible for validating that things got copied at the
763 fn write_immediate_no_validate(
765 src: Immediate<M::PointerTag>,
766 dest: PlaceTy<'tcx, M::PointerTag>,
767 ) -> InterpResult<'tcx> {
768 if cfg!(debug_assertions) {
769 // This is a very common path, avoid some checks in release mode
770 assert!(!dest.layout.is_unsized(), "Cannot write unsized data");
772 Immediate::Scalar(ScalarMaybeUndef::Scalar(Scalar::Ptr(_))) => assert_eq!(
775 "Size mismatch when writing pointer"
777 Immediate::Scalar(ScalarMaybeUndef::Scalar(Scalar::Raw { size, .. })) => {
779 Size::from_bytes(size.into()),
781 "Size mismatch when writing bits"
784 Immediate::Scalar(ScalarMaybeUndef::Undef) => {} // undef can have any size
785 Immediate::ScalarPair(_, _) => {
786 // FIXME: Can we check anything here?
790 trace!("write_immediate: {:?} <- {:?}: {}", *dest, src, dest.layout.ty);
792 // See if we can avoid an allocation. This is the counterpart to `try_read_immediate`,
793 // but not factored as a separate function.
794 let mplace = match dest.place {
795 Place::Local { frame, local } => {
796 match self.stack[frame].locals[local].access_mut()? {
798 // Local can be updated in-place.
799 *local = LocalValue::Live(Operand::Immediate(src));
803 // The local is in memory, go on below.
808 Place::Ptr(mplace) => mplace, // already referring to memory
810 let dest = MPlaceTy { mplace, layout: dest.layout };
812 // This is already in memory, write there.
813 self.write_immediate_to_mplace_no_validate(src, dest)
816 /// Write an immediate to memory.
817 /// If you use this you are responsible for validating that things got copied at the
819 fn write_immediate_to_mplace_no_validate(
821 value: Immediate<M::PointerTag>,
822 dest: MPlaceTy<'tcx, M::PointerTag>,
823 ) -> InterpResult<'tcx> {
824 // Note that it is really important that the type here is the right one, and matches the
825 // type things are read at. In case `src_val` is a `ScalarPair`, we don't do any magic here
826 // to handle padding properly, which is only correct if we never look at this data with the
829 // Invalid places are a thing: the return place of a diverging function
830 let ptr = match self.check_mplace_access(dest, None)? {
832 None => return Ok(()), // zero-sized access
835 let tcx = &*self.tcx;
836 // FIXME: We should check that there are dest.layout.size many bytes available in
837 // memory. The code below is not sufficient, with enough padding it might not
838 // cover all the bytes!
840 Immediate::Scalar(scalar) => {
841 match dest.layout.abi {
842 layout::Abi::Scalar(_) => {} // fine
844 bug!("write_immediate_to_mplace: invalid Scalar layout: {:#?}", dest.layout)
847 self.memory.get_raw_mut(ptr.alloc_id)?.write_scalar(
854 Immediate::ScalarPair(a_val, b_val) => {
855 // We checked `ptr_align` above, so all fields will have the alignment they need.
856 // We would anyway check against `ptr_align.restrict_for_offset(b_offset)`,
857 // which `ptr.offset(b_offset)` cannot possibly fail to satisfy.
858 let (a, b) = match dest.layout.abi {
859 layout::Abi::ScalarPair(ref a, ref b) => (&a.value, &b.value),
861 "write_immediate_to_mplace: invalid ScalarPair layout: {:#?}",
865 let (a_size, b_size) = (a.size(self), b.size(self));
866 let b_offset = a_size.align_to(b.align(self).abi);
867 let b_ptr = ptr.offset(b_offset, self)?;
869 // It is tempting to verify `b_offset` against `layout.fields.offset(1)`,
870 // but that does not work: We could be a newtype around a pair, then the
871 // fields do not match the `ScalarPair` components.
873 self.memory.get_raw_mut(ptr.alloc_id)?.write_scalar(tcx, ptr, a_val, a_size)?;
874 self.memory.get_raw_mut(b_ptr.alloc_id)?.write_scalar(tcx, b_ptr, b_val, b_size)
879 /// Copies the data from an operand to a place. This does not support transmuting!
880 /// Use `copy_op_transmute` if the layouts could disagree.
884 src: OpTy<'tcx, M::PointerTag>,
885 dest: PlaceTy<'tcx, M::PointerTag>,
886 ) -> InterpResult<'tcx> {
887 self.copy_op_no_validate(src, dest)?;
889 if M::enforce_validity(self) {
890 // Data got changed, better make sure it matches the type!
891 self.validate_operand(self.place_to_op(dest)?, vec![], None)?;
897 /// Copies the data from an operand to a place. This does not support transmuting!
898 /// Use `copy_op_transmute` if the layouts could disagree.
899 /// Also, if you use this you are responsible for validating that things get copied at the
901 fn copy_op_no_validate(
903 src: OpTy<'tcx, M::PointerTag>,
904 dest: PlaceTy<'tcx, M::PointerTag>,
905 ) -> InterpResult<'tcx> {
906 // We do NOT compare the types for equality, because well-typed code can
907 // actually "transmute" `&mut T` to `&T` in an assignment without a cast.
909 src.layout.details == dest.layout.details,
910 "Layout mismatch when copying!\nsrc: {:#?}\ndest: {:#?}",
915 // Let us see if the layout is simple so we take a shortcut, avoid force_allocation.
916 let src = match self.try_read_immediate(src)? {
918 assert!(!src.layout.is_unsized(), "cannot have unsized immediates");
919 // Yay, we got a value that we can write directly.
920 // FIXME: Add a check to make sure that if `src` is indirect,
921 // it does not overlap with `dest`.
922 return self.write_immediate_no_validate(*src_val, dest);
924 Err(mplace) => mplace,
926 // Slow path, this does not fit into an immediate. Just memcpy.
927 trace!("copy_op: {:?} <- {:?}: {}", *dest, src, dest.layout.ty);
929 // This interprets `src.meta` with the `dest` local's layout, if an unsized local
930 // is being initialized!
931 let (dest, size) = self.force_allocation_maybe_sized(dest, src.meta)?;
932 let size = size.unwrap_or_else(|| {
934 !dest.layout.is_unsized(),
935 "Cannot copy into already initialized unsized place"
939 assert_eq!(src.meta, dest.meta, "Can only copy between equally-sized instances");
942 .check_mplace_access(src, Some(size))
943 .expect("places should be checked on creation");
945 .check_mplace_access(dest, Some(size))
946 .expect("places should be checked on creation");
947 let (src_ptr, dest_ptr) = match (src, dest) {
948 (Some(src_ptr), Some(dest_ptr)) => (src_ptr, dest_ptr),
949 (None, None) => return Ok(()), // zero-sized copy
950 _ => bug!("The pointers should both be Some or both None"),
953 self.memory.copy(src_ptr, dest_ptr, size, /*nonoverlapping*/ true)
956 /// Copies the data from an operand to a place. The layouts may disagree, but they must
957 /// have the same size.
958 pub fn copy_op_transmute(
960 src: OpTy<'tcx, M::PointerTag>,
961 dest: PlaceTy<'tcx, M::PointerTag>,
962 ) -> InterpResult<'tcx> {
963 if src.layout.details == dest.layout.details {
964 // Fast path: Just use normal `copy_op`
965 return self.copy_op(src, dest);
967 // We still require the sizes to match.
968 if src.layout.size != dest.layout.size {
969 // FIXME: This should be an assert instead of an error, but if we transmute within an
970 // array length computation, `typeck` may not have yet been run and errored out. In fact
971 // most likey we *are* running `typeck` right now. Investigate whether we can bail out
972 // on `typeck_tables().has_errors` at all const eval entry points.
973 debug!("Size mismatch when transmuting!\nsrc: {:#?}\ndest: {:#?}", src, dest);
974 throw_unsup!(TransmuteSizeDiff(src.layout.ty, dest.layout.ty));
976 // Unsized copies rely on interpreting `src.meta` with `dest.layout`, we want
977 // to avoid that here.
979 !src.layout.is_unsized() && !dest.layout.is_unsized(),
980 "Cannot transmute unsized data"
983 // The hard case is `ScalarPair`. `src` is already read from memory in this case,
984 // using `src.layout` to figure out which bytes to use for the 1st and 2nd field.
985 // We have to write them to `dest` at the offsets they were *read at*, which is
986 // not necessarily the same as the offsets in `dest.layout`!
987 // Hence we do the copy with the source layout on both sides. We also make sure to write
988 // into memory, because if `dest` is a local we would not even have a way to write
989 // at the `src` offsets; the fact that we came from a different layout would
991 let dest = self.force_allocation(dest)?;
992 self.copy_op_no_validate(
994 PlaceTy::from(MPlaceTy { mplace: *dest, layout: src.layout }),
997 if M::enforce_validity(self) {
998 // Data got changed, better make sure it matches the type!
999 self.validate_operand(dest.into(), vec![], None)?;
1005 /// Ensures that a place is in memory, and returns where it is.
1006 /// If the place currently refers to a local that doesn't yet have a matching allocation,
1007 /// create such an allocation.
1008 /// This is essentially `force_to_memplace`.
1010 /// This supports unsized types and returns the computed size to avoid some
1011 /// redundant computation when copying; use `force_allocation` for a simpler, sized-only
1013 pub fn force_allocation_maybe_sized(
1015 place: PlaceTy<'tcx, M::PointerTag>,
1016 meta: MemPlaceMeta<M::PointerTag>,
1017 ) -> InterpResult<'tcx, (MPlaceTy<'tcx, M::PointerTag>, Option<Size>)> {
1018 let (mplace, size) = match place.place {
1019 Place::Local { frame, local } => {
1020 match self.stack[frame].locals[local].access_mut()? {
1021 Ok(&mut local_val) => {
1022 // We need to make an allocation.
1024 // We need the layout of the local. We can NOT use the layout we got,
1025 // that might e.g., be an inner field of a struct with `Scalar` layout,
1026 // that has different alignment than the outer field.
1027 let local_layout = self.layout_of_local(&self.stack[frame], local, None)?;
1028 // We also need to support unsized types, and hence cannot use `allocate`.
1029 let (size, align) = self
1030 .size_and_align_of(meta, local_layout)?
1031 .expect("Cannot allocate for non-dyn-sized type");
1032 let ptr = self.memory.allocate(size, align, MemoryKind::Stack);
1033 let mplace = MemPlace { ptr: ptr.into(), align, meta };
1034 if let LocalValue::Live(Operand::Immediate(value)) = local_val {
1035 // Preserve old value.
1036 // We don't have to validate as we can assume the local
1037 // was already valid for its type.
1038 let mplace = MPlaceTy { mplace, layout: local_layout };
1039 self.write_immediate_to_mplace_no_validate(value, mplace)?;
1041 // Now we can call `access_mut` again, asserting it goes well,
1042 // and actually overwrite things.
1043 *self.stack[frame].locals[local].access_mut().unwrap().unwrap() =
1044 LocalValue::Live(Operand::Indirect(mplace));
1045 (mplace, Some(size))
1047 Err(mplace) => (mplace, None), // this already was an indirect local
1050 Place::Ptr(mplace) => (mplace, None),
1052 // Return with the original layout, so that the caller can go on
1053 Ok((MPlaceTy { mplace, layout: place.layout }, size))
1057 pub fn force_allocation(
1059 place: PlaceTy<'tcx, M::PointerTag>,
1060 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
1061 Ok(self.force_allocation_maybe_sized(place, MemPlaceMeta::None)?.0)
1066 layout: TyLayout<'tcx>,
1067 kind: MemoryKind<M::MemoryKinds>,
1068 ) -> MPlaceTy<'tcx, M::PointerTag> {
1069 let ptr = self.memory.allocate(layout.size, layout.align.abi, kind);
1070 MPlaceTy::from_aligned_ptr(ptr, layout)
1073 /// Returns a wide MPlace.
1074 pub fn allocate_str(
1077 kind: MemoryKind<M::MemoryKinds>,
1078 ) -> MPlaceTy<'tcx, M::PointerTag> {
1079 let ptr = self.memory.allocate_static_bytes(str.as_bytes(), kind);
1080 let meta = Scalar::from_uint(str.len() as u128, self.pointer_size());
1081 let mplace = MemPlace {
1083 align: Align::from_bytes(1).unwrap(),
1084 meta: MemPlaceMeta::Unsized(meta),
1087 let layout = self.layout_of(self.tcx.mk_static_str()).unwrap();
1088 MPlaceTy { mplace, layout }
1091 pub fn write_discriminant_index(
1093 variant_index: VariantIdx,
1094 dest: PlaceTy<'tcx, M::PointerTag>,
1095 ) -> InterpResult<'tcx> {
1096 // Layout computation excludes uninhabited variants from consideration
1097 // therefore there's no way to represent those variants in the given layout.
1098 if dest.layout.for_variant(self, variant_index).abi.is_uninhabited() {
1099 throw_ub!(Unreachable);
1102 match dest.layout.variants {
1103 layout::Variants::Single { index } => {
1104 assert_eq!(index, variant_index);
1106 layout::Variants::Multiple {
1107 discr_kind: layout::DiscriminantKind::Tag,
1108 discr: ref discr_layout,
1112 // No need to validate that the discriminant here because the
1113 // `TyLayout::for_variant()` call earlier already checks the variant is valid.
1116 dest.layout.ty.discriminant_for_variant(*self.tcx, variant_index).unwrap().val;
1118 // raw discriminants for enums are isize or bigger during
1119 // their computation, but the in-memory tag is the smallest possible
1121 let size = discr_layout.value.size(self);
1122 let discr_val = truncate(discr_val, size);
1124 let discr_dest = self.place_field(dest, discr_index as u64)?;
1125 self.write_scalar(Scalar::from_uint(discr_val, size), discr_dest)?;
1127 layout::Variants::Multiple {
1129 layout::DiscriminantKind::Niche { dataful_variant, ref niche_variants, niche_start },
1130 discr: ref discr_layout,
1134 // No need to validate that the discriminant here because the
1135 // `TyLayout::for_variant()` call earlier already checks the variant is valid.
1137 if variant_index != dataful_variant {
1138 let variants_start = niche_variants.start().as_u32();
1139 let variant_index_relative = variant_index
1141 .checked_sub(variants_start)
1142 .expect("overflow computing relative variant idx");
1143 // We need to use machine arithmetic when taking into account `niche_start`:
1144 // discr_val = variant_index_relative + niche_start_val
1145 let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
1146 let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
1147 let variant_index_relative_val =
1148 ImmTy::from_uint(variant_index_relative, discr_layout);
1149 let discr_val = self.binary_op(
1151 variant_index_relative_val,
1155 let niche_dest = self.place_field(dest, discr_index as u64)?;
1156 self.write_immediate(*discr_val, niche_dest)?;
1164 pub fn raw_const_to_mplace(
1166 raw: RawConst<'tcx>,
1167 ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
1168 // This must be an allocation in `tcx`
1169 assert!(self.tcx.alloc_map.lock().get(raw.alloc_id).is_some());
1170 let ptr = self.tag_static_base_pointer(Pointer::from(raw.alloc_id));
1171 let layout = self.layout_of(raw.ty)?;
1172 Ok(MPlaceTy::from_aligned_ptr(ptr, layout))
1175 /// Turn a place with a `dyn Trait` type into a place with the actual dynamic type.
1176 /// Also return some more information so drop doesn't have to run the same code twice.
1177 pub(super) fn unpack_dyn_trait(
1179 mplace: MPlaceTy<'tcx, M::PointerTag>,
1180 ) -> InterpResult<'tcx, (ty::Instance<'tcx>, MPlaceTy<'tcx, M::PointerTag>)> {
1181 let vtable = mplace.vtable(); // also sanity checks the type
1182 let (instance, ty) = self.read_drop_type_from_vtable(vtable)?;
1183 let layout = self.layout_of(ty)?;
1185 // More sanity checks
1186 if cfg!(debug_assertions) {
1187 let (size, align) = self.read_size_and_align_from_vtable(vtable)?;
1188 assert_eq!(size, layout.size);
1189 // only ABI alignment is preserved
1190 assert_eq!(align, layout.align.abi);
1193 let mplace = MPlaceTy { mplace: MemPlace { meta: MemPlaceMeta::None, ..*mplace }, layout };
1194 Ok((instance, mplace))