1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! Computations on places -- field projections, going from mir::Place, and writing
13 //! All high-level functions to write to memory work on places as destinations.
15 use std::convert::TryFrom;
20 use rustc::ty::{self, Ty};
21 use rustc::ty::layout::{self, Size, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx};
24 GlobalId, AllocId, Allocation, Scalar, EvalResult, Pointer, PointerArithmetic,
25 EvalContext, Machine, AllocMap, AllocationExtra,
26 RawConst, Immediate, ImmTy, ScalarMaybeUndef, Operand, OpTy, MemoryKind
29 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
30 pub struct MemPlace<Tag=(), Id=AllocId> {
31 /// A place may have an integral pointer for ZSTs, and since it might
32 /// be turned back into a reference before ever being dereferenced.
33 /// However, it may never be undef.
34 pub ptr: Scalar<Tag, Id>,
36 /// Metadata for unsized places. Interpretation is up to the type.
37 /// Must not be present for sized types, but can be missing for unsized types
38 /// (e.g. `extern type`).
39 pub meta: Option<Scalar<Tag, Id>>,
42 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
43 pub enum Place<Tag=(), Id=AllocId> {
44 /// A place referring to a value allocated in the `Memory` system.
45 Ptr(MemPlace<Tag, Id>),
47 /// To support alloc-free locals, we are able to write directly to a local.
48 /// (Without that optimization, we'd just always be a `MemPlace`.)
55 #[derive(Copy, Clone, Debug)]
56 pub struct PlaceTy<'tcx, Tag=()> {
58 pub layout: TyLayout<'tcx>,
61 impl<'tcx, Tag> ::std::ops::Deref for PlaceTy<'tcx, Tag> {
62 type Target = Place<Tag>;
64 fn deref(&self) -> &Place<Tag> {
69 /// A MemPlace with its layout. Constructing it is only possible in this module.
70 #[derive(Copy, Clone, Debug)]
71 pub struct MPlaceTy<'tcx, Tag=()> {
72 mplace: MemPlace<Tag>,
73 pub layout: TyLayout<'tcx>,
76 impl<'tcx, Tag> ::std::ops::Deref for MPlaceTy<'tcx, Tag> {
77 type Target = MemPlace<Tag>;
79 fn deref(&self) -> &MemPlace<Tag> {
84 impl<'tcx, Tag> From<MPlaceTy<'tcx, Tag>> for PlaceTy<'tcx, Tag> {
86 fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
88 place: Place::Ptr(mplace.mplace),
96 pub fn with_default_tag<Tag>(self) -> MemPlace<Tag>
100 ptr: self.ptr.with_default_tag(),
102 meta: self.meta.map(Scalar::with_default_tag),
107 impl<Tag> MemPlace<Tag> {
109 pub fn erase_tag(self) -> MemPlace
112 ptr: self.ptr.erase_tag(),
114 meta: self.meta.map(Scalar::erase_tag),
119 pub fn from_scalar_ptr(ptr: Scalar<Tag>, align: Align) -> Self {
127 /// Produces a Place that will error if attempted to be read from or written to
129 pub fn null(cx: &impl HasDataLayout) -> Self {
130 Self::from_scalar_ptr(Scalar::ptr_null(cx), Align::from_bytes(1, 1).unwrap())
134 pub fn from_ptr(ptr: Pointer<Tag>, align: Align) -> Self {
135 Self::from_scalar_ptr(ptr.into(), align)
139 pub fn to_scalar_ptr_align(self) -> (Scalar<Tag>, Align) {
140 assert!(self.meta.is_none());
141 (self.ptr, self.align)
144 /// metact the ptr part of the mplace
146 pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
147 // At this point, we forget about the alignment information --
148 // the place has been turned into a reference, and no matter where it came from,
149 // it now must be aligned.
150 self.to_scalar_ptr_align().0.to_ptr()
153 /// Turn a mplace into a (thin or fat) pointer, as a reference, pointing to the same space.
154 /// This is the inverse of `ref_to_mplace`.
156 pub fn to_ref(self) -> Immediate<Tag> {
158 None => Immediate::Scalar(self.ptr.into()),
159 Some(meta) => Immediate::ScalarPair(self.ptr.into(), meta.into()),
164 impl<'tcx, Tag> MPlaceTy<'tcx, Tag> {
165 /// Produces a MemPlace that works for ZST but nothing else
167 pub fn dangling(layout: TyLayout<'tcx>, cx: &impl HasDataLayout) -> Self {
169 mplace: MemPlace::from_scalar_ptr(
170 Scalar::from_uint(layout.align.abi(), cx.pointer_size()),
178 fn from_aligned_ptr(ptr: Pointer<Tag>, layout: TyLayout<'tcx>) -> Self {
179 MPlaceTy { mplace: MemPlace::from_ptr(ptr, layout.align), layout }
183 pub(super) fn len(self, cx: &impl HasDataLayout) -> EvalResult<'tcx, u64> {
184 if self.layout.is_unsized() {
185 // We need to consult `meta` metadata
186 match self.layout.ty.sty {
187 ty::Slice(..) | ty::Str =>
188 return self.mplace.meta.unwrap().to_usize(cx),
189 _ => bug!("len not supported on unsized type {:?}", self.layout.ty),
192 // Go through the layout. There are lots of types that support a length,
194 match self.layout.fields {
195 layout::FieldPlacement::Array { count, .. } => Ok(count),
196 _ => bug!("len not supported on sized type {:?}", self.layout.ty),
202 pub(super) fn vtable(self) -> EvalResult<'tcx, Pointer<Tag>> {
203 match self.layout.ty.sty {
204 ty::Dynamic(..) => self.mplace.meta.unwrap().to_ptr(),
205 _ => bug!("vtable not supported on type {:?}", self.layout.ty),
210 impl<'tcx, Tag: ::std::fmt::Debug> OpTy<'tcx, Tag> {
212 pub fn try_as_mplace(self) -> Result<MPlaceTy<'tcx, Tag>, Immediate<Tag>> {
214 Operand::Indirect(mplace) => Ok(MPlaceTy { mplace, layout: self.layout }),
215 Operand::Immediate(imm) => Err(imm),
220 pub fn to_mem_place(self) -> MPlaceTy<'tcx, Tag> {
221 self.try_as_mplace().unwrap()
225 impl<'tcx, Tag: ::std::fmt::Debug> Place<Tag> {
226 /// Produces a Place that will error if attempted to be read from or written to
228 pub fn null(cx: &impl HasDataLayout) -> Self {
229 Place::Ptr(MemPlace::null(cx))
233 pub fn from_scalar_ptr(ptr: Scalar<Tag>, align: Align) -> Self {
234 Place::Ptr(MemPlace::from_scalar_ptr(ptr, align))
238 pub fn from_ptr(ptr: Pointer<Tag>, align: Align) -> Self {
239 Place::Ptr(MemPlace::from_ptr(ptr, align))
243 pub fn to_mem_place(self) -> MemPlace<Tag> {
245 Place::Ptr(mplace) => mplace,
246 _ => bug!("to_mem_place: expected Place::Ptr, got {:?}", self),
252 pub fn to_scalar_ptr_align(self) -> (Scalar<Tag>, Align) {
253 self.to_mem_place().to_scalar_ptr_align()
257 pub fn to_ptr(self) -> EvalResult<'tcx, Pointer<Tag>> {
258 self.to_mem_place().to_ptr()
262 impl<'tcx, Tag: ::std::fmt::Debug> PlaceTy<'tcx, Tag> {
264 pub fn to_mem_place(self) -> MPlaceTy<'tcx, Tag> {
265 MPlaceTy { mplace: self.place.to_mem_place(), layout: self.layout }
269 // separating the pointer tag for `impl Trait`, see https://github.com/rust-lang/rust/issues/54385
270 impl<'a, 'mir, 'tcx, Tag, M> EvalContext<'a, 'mir, 'tcx, M>
272 Tag: ::std::fmt::Debug+Default+Copy+Eq+Hash+'static,
273 M: Machine<'a, 'mir, 'tcx, PointerTag=Tag>,
274 M::MemoryMap: AllocMap<AllocId, (MemoryKind<M::MemoryKinds>, Allocation<Tag, M::AllocExtra>)>,
275 M::AllocExtra: AllocationExtra<Tag>,
277 /// Take a value, which represents a (thin or fat) reference, and make it a place.
278 /// Alignment is just based on the type. This is the inverse of `MemPlace::to_ref()`.
279 /// This does NOT call the "deref" machine hook, so it does NOT count as a
280 /// deref as far as Stacked Borrows is concerned. Use `deref_operand` for that!
281 pub fn ref_to_mplace(
283 val: ImmTy<'tcx, M::PointerTag>,
284 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
285 let pointee_type = val.layout.ty.builtin_deref(true).unwrap().ty;
286 let layout = self.layout_of(pointee_type)?;
288 let mplace = MemPlace {
289 ptr: val.to_scalar_ptr()?,
291 meta: val.to_meta()?,
293 Ok(MPlaceTy { mplace, layout })
296 // Take an operand, representing a pointer, and dereference it to a place -- that
297 // will always be a MemPlace. Lives in `place.rs` because it creates a place.
298 // This calls the "deref" machine hook, and counts as a deref as far as
299 // Stacked Borrows is concerned.
300 pub fn deref_operand(
302 src: OpTy<'tcx, M::PointerTag>,
303 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
304 let val = self.read_immediate(src)?;
305 trace!("deref to {} on {:?}", val.layout.ty, *val);
306 let mut place = self.ref_to_mplace(val)?;
307 // Pointer tag tracking might want to adjust the tag.
308 let mutbl = match val.layout.ty.sty {
309 // `builtin_deref` considers boxes immutable, that's useless for our purposes
310 ty::Ref(_, _, mutbl) => Some(mutbl),
311 ty::Adt(def, _) if def.is_box() => Some(hir::MutMutable),
312 ty::RawPtr(_) => None,
313 _ => bug!("Unexpected pointer type {}", val.layout.ty.sty),
315 place.mplace.ptr = M::tag_dereference(self, place, mutbl)?;
319 /// Offset a pointer to project to a field. Unlike place_field, this is always
320 /// possible without allocating, so it can take &self. Also return the field's layout.
321 /// This supports both struct and array fields.
325 base: MPlaceTy<'tcx, M::PointerTag>,
327 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
328 // Not using the layout method because we want to compute on u64
329 let offset = match base.layout.fields {
330 layout::FieldPlacement::Arbitrary { ref offsets, .. } =>
331 offsets[usize::try_from(field).unwrap()],
332 layout::FieldPlacement::Array { stride, .. } => {
333 let len = base.len(self)?;
334 assert!(field < len, "Tried to access element {} of array/slice with length {}",
338 layout::FieldPlacement::Union(count) => {
339 assert!(field < count as u64,
340 "Tried to access field {} of union with {} fields", field, count);
341 // Offset is always 0
345 // the only way conversion can fail if is this is an array (otherwise we already panicked
346 // above). In that case, all fields are equal.
347 let field_layout = base.layout.field(self, usize::try_from(field).unwrap_or(0))?;
349 // Offset may need adjustment for unsized fields
350 let (meta, offset) = if field_layout.is_unsized() {
351 // re-use parent metadata to determine dynamic field layout
352 let align = match self.size_and_align_of(base.meta, field_layout)? {
353 Some((_, align)) => align,
354 None if offset == Size::ZERO =>
355 // An extern type at offset 0, we fall back to its static alignment.
356 // FIXME: Once we have made decisions for how to handle size and alignment
357 // of `extern type`, this should be adapted. It is just a temporary hack
358 // to get some code to work that probably ought to work.
361 bug!("Cannot compute offset for extern type field at non-0 offset"),
363 (base.meta, offset.abi_align(align))
365 // base.meta could be present; we might be accessing a sized field of an unsized
370 let ptr = base.ptr.ptr_offset(offset, self)?;
371 let align = base.align
372 // We do not look at `base.layout.align` nor `field_layout.align`, unlike
373 // codegen -- mostly to see if we can get away with that
374 .restrict_for_offset(offset); // must be last thing that happens
376 Ok(MPlaceTy { mplace: MemPlace { ptr, align, meta }, layout: field_layout })
379 // Iterates over all fields of an array. Much more efficient than doing the
380 // same by repeatedly calling `mplace_array`.
381 pub fn mplace_array_fields(
383 base: MPlaceTy<'tcx, Tag>,
385 EvalResult<'tcx, impl Iterator<Item=EvalResult<'tcx, MPlaceTy<'tcx, Tag>>> + 'a>
387 let len = base.len(self)?; // also asserts that we have a type where this makes sense
388 let stride = match base.layout.fields {
389 layout::FieldPlacement::Array { stride, .. } => stride,
390 _ => bug!("mplace_array_fields: expected an array layout"),
392 let layout = base.layout.field(self, 0)?;
393 let dl = &self.tcx.data_layout;
394 Ok((0..len).map(move |i| {
395 let ptr = base.ptr.ptr_offset(i * stride, dl)?;
397 mplace: MemPlace { ptr, align: base.align, meta: None },
403 pub fn mplace_subslice(
405 base: MPlaceTy<'tcx, M::PointerTag>,
408 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
409 let len = base.len(self)?; // also asserts that we have a type where this makes sense
410 assert!(from <= len - to);
412 // Not using layout method because that works with usize, and does not work with slices
413 // (that have count 0 in their layout).
414 let from_offset = match base.layout.fields {
415 layout::FieldPlacement::Array { stride, .. } =>
417 _ => bug!("Unexpected layout of index access: {:#?}", base.layout),
419 let ptr = base.ptr.ptr_offset(from_offset, self)?;
421 // Compute meta and new layout
422 let inner_len = len - to - from;
423 let (meta, ty) = match base.layout.ty.sty {
424 // It is not nice to match on the type, but that seems to be the only way to
426 ty::Array(inner, _) =>
427 (None, self.tcx.mk_array(inner, inner_len)),
429 let len = Scalar::from_uint(inner_len, self.pointer_size());
430 (Some(len), base.layout.ty)
433 bug!("cannot subslice non-array type: `{:?}`", base.layout.ty),
435 let layout = self.layout_of(ty)?;
438 mplace: MemPlace { ptr, align: base.align, meta },
443 pub fn mplace_downcast(
445 base: MPlaceTy<'tcx, M::PointerTag>,
447 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
448 // Downcasts only change the layout
449 assert!(base.meta.is_none());
450 Ok(MPlaceTy { layout: base.layout.for_variant(self, variant), ..base })
453 /// Project into an mplace
454 pub fn mplace_projection(
456 base: MPlaceTy<'tcx, M::PointerTag>,
457 proj_elem: &mir::PlaceElem<'tcx>,
458 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
459 use rustc::mir::ProjectionElem::*;
460 Ok(match *proj_elem {
461 Field(field, _) => self.mplace_field(base, field.index() as u64)?,
462 Downcast(_, variant) => self.mplace_downcast(base, variant)?,
463 Deref => self.deref_operand(base.into())?,
466 let n = *self.frame().locals[local].access()?;
467 let n_layout = self.layout_of(self.tcx.types.usize)?;
468 let n = self.read_scalar(OpTy { op: n, layout: n_layout })?;
469 let n = n.to_bits(self.tcx.data_layout.pointer_size)?;
470 self.mplace_field(base, u64::try_from(n).unwrap())?
478 let n = base.len(self)?;
479 assert!(n >= min_length as u64);
481 let index = if from_end {
482 n - u64::from(offset)
487 self.mplace_field(base, index)?
490 Subslice { from, to } =>
491 self.mplace_subslice(base, u64::from(from), u64::from(to))?,
495 /// Get the place of a field inside the place, and also the field's type.
496 /// Just a convenience function, but used quite a bit.
497 /// This is the only projection that might have a side-effect: We cannot project
498 /// into the field of a local `ScalarPair`, we have to first allocate it.
501 base: PlaceTy<'tcx, M::PointerTag>,
503 ) -> EvalResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
504 // FIXME: We could try to be smarter and avoid allocation for fields that span the
506 let mplace = self.force_allocation(base)?;
507 Ok(self.mplace_field(mplace, field)?.into())
510 pub fn place_downcast(
512 base: PlaceTy<'tcx, M::PointerTag>,
514 ) -> EvalResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
515 // Downcast just changes the layout
516 Ok(match base.place {
517 Place::Ptr(mplace) =>
518 self.mplace_downcast(MPlaceTy { mplace, layout: base.layout }, variant)?.into(),
519 Place::Local { .. } => {
520 let layout = base.layout.for_variant(self, variant);
521 PlaceTy { layout, ..base }
526 /// Project into a place
527 pub fn place_projection(
529 base: PlaceTy<'tcx, M::PointerTag>,
530 proj_elem: &mir::ProjectionElem<'tcx, mir::Local, Ty<'tcx>>,
531 ) -> EvalResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
532 use rustc::mir::ProjectionElem::*;
533 Ok(match *proj_elem {
534 Field(field, _) => self.place_field(base, field.index() as u64)?,
535 Downcast(_, variant) => self.place_downcast(base, variant)?,
536 Deref => self.deref_operand(self.place_to_op(base)?)?.into(),
537 // For the other variants, we have to force an allocation.
538 // This matches `operand_projection`.
539 Subslice { .. } | ConstantIndex { .. } | Index(_) => {
540 let mplace = self.force_allocation(base)?;
541 self.mplace_projection(mplace, proj_elem)?.into()
546 /// Evaluate statics and promoteds to an `MPlace`. Used to share some code between
547 /// `eval_place` and `eval_place_to_op`.
548 pub(super) fn eval_place_to_mplace(
550 mir_place: &mir::Place<'tcx>
551 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
552 use rustc::mir::Place::*;
553 Ok(match *mir_place {
554 Promoted(ref promoted) => {
555 let instance = self.frame().instance;
556 let op = self.global_to_op(GlobalId {
558 promoted: Some(promoted.0),
560 let mplace = op.to_mem_place(); // these are always in memory
561 let ty = self.monomorphize(promoted.1, self.substs());
564 layout: self.layout_of(ty)?,
568 Static(ref static_) => {
569 let ty = self.monomorphize(static_.ty, self.substs());
570 let layout = self.layout_of(ty)?;
571 let instance = ty::Instance::mono(*self.tcx, static_.def_id);
576 // Just create a lazy reference, so we can support recursive statics.
577 // tcx takes are of assigning every static one and only one unique AllocId.
578 // When the data here is ever actually used, memory will notice,
579 // and it knows how to deal with alloc_id that are present in the
580 // global table but not in its local memory: It calls back into tcx through
581 // a query, triggering the CTFE machinery to actually turn this lazy reference
582 // into a bunch of bytes. IOW, statics are evaluated with CTFE even when
583 // this EvalContext uses another Machine (e.g., in miri). This is what we
584 // want! This way, computing statics works concistently between codegen
585 // and miri: They use the same query to eventually obtain a `ty::Const`
586 // and use that for further computation.
587 let alloc = self.tcx.alloc_map.lock().intern_static(cid.instance.def_id());
588 MPlaceTy::from_aligned_ptr(Pointer::from(alloc).with_default_tag(), layout)
591 _ => bug!("eval_place_to_mplace called on {:?}", mir_place),
595 /// Compute a place. You should only use this if you intend to write into this
596 /// place; for reading, a more efficient alternative is `eval_place_for_read`.
599 mir_place: &mir::Place<'tcx>
600 ) -> EvalResult<'tcx, PlaceTy<'tcx, M::PointerTag>> {
601 use rustc::mir::Place::*;
602 let place = match *mir_place {
603 Local(mir::RETURN_PLACE) => match self.frame().return_place {
604 Some(return_place) =>
605 // We use our layout to verify our assumption; caller will validate
606 // their layout on return.
608 place: *return_place,
609 layout: self.layout_of_local(self.frame(), mir::RETURN_PLACE)?,
611 None => return err!(InvalidNullPointerUsage),
613 Local(local) => PlaceTy {
614 place: Place::Local {
615 frame: self.cur_frame(),
618 layout: self.layout_of_local(self.frame(), local)?,
621 Projection(ref proj) => {
622 let place = self.eval_place(&proj.base)?;
623 self.place_projection(place, &proj.elem)?
626 _ => self.eval_place_to_mplace(mir_place)?.into(),
629 self.dump_place(place.place);
633 /// Write a scalar to a place
636 val: impl Into<ScalarMaybeUndef<M::PointerTag>>,
637 dest: PlaceTy<'tcx, M::PointerTag>,
638 ) -> EvalResult<'tcx> {
639 self.write_immediate(Immediate::Scalar(val.into()), dest)
642 /// Write an immediate to a place
644 pub fn write_immediate(
646 src: Immediate<M::PointerTag>,
647 dest: PlaceTy<'tcx, M::PointerTag>,
648 ) -> EvalResult<'tcx> {
649 self.write_immediate_no_validate(src, dest)?;
651 if M::enforce_validity(self) {
652 // Data got changed, better make sure it matches the type!
653 self.validate_operand(self.place_to_op(dest)?, vec![], None, /*const_mode*/false)?;
659 /// Write an immediate to a place.
660 /// If you use this you are responsible for validating that things got copied at the
662 fn write_immediate_no_validate(
664 src: Immediate<M::PointerTag>,
665 dest: PlaceTy<'tcx, M::PointerTag>,
666 ) -> EvalResult<'tcx> {
667 if cfg!(debug_assertions) {
668 // This is a very common path, avoid some checks in release mode
669 assert!(!dest.layout.is_unsized(), "Cannot write unsized data");
671 Immediate::Scalar(ScalarMaybeUndef::Scalar(Scalar::Ptr(_))) =>
672 assert_eq!(self.pointer_size(), dest.layout.size,
673 "Size mismatch when writing pointer"),
674 Immediate::Scalar(ScalarMaybeUndef::Scalar(Scalar::Bits { size, .. })) =>
675 assert_eq!(Size::from_bytes(size.into()), dest.layout.size,
676 "Size mismatch when writing bits"),
677 Immediate::Scalar(ScalarMaybeUndef::Undef) => {}, // undef can have any size
678 Immediate::ScalarPair(_, _) => {
679 // FIXME: Can we check anything here?
683 trace!("write_immediate: {:?} <- {:?}: {}", *dest, src, dest.layout.ty);
685 // See if we can avoid an allocation. This is the counterpart to `try_read_immediate`,
686 // but not factored as a separate function.
687 let mplace = match dest.place {
688 Place::Local { frame, local } => {
689 match *self.stack[frame].locals[local].access_mut()? {
690 Operand::Immediate(ref mut dest_val) => {
691 // Yay, we can just change the local directly.
695 Operand::Indirect(mplace) => mplace, // already in memory
698 Place::Ptr(mplace) => mplace, // already in memory
700 let dest = MPlaceTy { mplace, layout: dest.layout };
702 // This is already in memory, write there.
703 self.write_immediate_to_mplace_no_validate(src, dest)
706 /// Write an immediate to memory.
707 /// If you use this you are responsible for validating that things git copied at the
709 fn write_immediate_to_mplace_no_validate(
711 value: Immediate<M::PointerTag>,
712 dest: MPlaceTy<'tcx, M::PointerTag>,
713 ) -> EvalResult<'tcx> {
714 let (ptr, ptr_align) = dest.to_scalar_ptr_align();
715 // Note that it is really important that the type here is the right one, and matches the
716 // type things are read at. In case `src_val` is a `ScalarPair`, we don't do any magic here
717 // to handle padding properly, which is only correct if we never look at this data with the
720 // Nothing to do for ZSTs, other than checking alignment
721 if dest.layout.is_zst() {
722 self.memory.check_align(ptr, ptr_align)?;
726 let ptr = ptr.to_ptr()?;
727 // FIXME: We should check that there are dest.layout.size many bytes available in
728 // memory. The code below is not sufficient, with enough padding it might not
729 // cover all the bytes!
731 Immediate::Scalar(scalar) => {
732 match dest.layout.abi {
733 layout::Abi::Scalar(_) => {}, // fine
734 _ => bug!("write_immediate_to_mplace: invalid Scalar layout: {:#?}",
738 self.memory.write_scalar(
739 ptr, ptr_align.min(dest.layout.align), scalar, dest.layout.size
742 Immediate::ScalarPair(a_val, b_val) => {
743 let (a, b) = match dest.layout.abi {
744 layout::Abi::ScalarPair(ref a, ref b) => (&a.value, &b.value),
745 _ => bug!("write_immediate_to_mplace: invalid ScalarPair layout: {:#?}",
748 let (a_size, b_size) = (a.size(self), b.size(self));
749 let (a_align, b_align) = (a.align(self), b.align(self));
750 let b_offset = a_size.abi_align(b_align);
751 let b_ptr = ptr.offset(b_offset, self)?.into();
753 // It is tempting to verify `b_offset` against `layout.fields.offset(1)`,
754 // but that does not work: We could be a newtype around a pair, then the
755 // fields do not match the `ScalarPair` components.
757 self.memory.write_scalar(ptr, ptr_align.min(a_align), a_val, a_size)?;
758 self.memory.write_scalar(b_ptr, ptr_align.min(b_align), b_val, b_size)
763 /// Copy the data from an operand to a place. This does not support transmuting!
764 /// Use `copy_op_transmute` if the layouts could disagree.
768 src: OpTy<'tcx, M::PointerTag>,
769 dest: PlaceTy<'tcx, M::PointerTag>,
770 ) -> EvalResult<'tcx> {
771 self.copy_op_no_validate(src, dest)?;
773 if M::enforce_validity(self) {
774 // Data got changed, better make sure it matches the type!
775 self.validate_operand(self.place_to_op(dest)?, vec![], None, /*const_mode*/false)?;
781 /// Copy the data from an operand to a place. This does not support transmuting!
782 /// Use `copy_op_transmute` if the layouts could disagree.
783 /// Also, if you use this you are responsible for validating that things git copied at the
785 fn copy_op_no_validate(
787 src: OpTy<'tcx, M::PointerTag>,
788 dest: PlaceTy<'tcx, M::PointerTag>,
789 ) -> EvalResult<'tcx> {
790 debug_assert!(!src.layout.is_unsized() && !dest.layout.is_unsized(),
791 "Cannot copy unsized data");
792 // We do NOT compare the types for equality, because well-typed code can
793 // actually "transmute" `&mut T` to `&T` in an assignment without a cast.
794 assert!(src.layout.details == dest.layout.details,
795 "Layout mismatch when copying!\nsrc: {:#?}\ndest: {:#?}", src, dest);
797 // Let us see if the layout is simple so we take a shortcut, avoid force_allocation.
798 let src = match self.try_read_immediate(src)? {
800 // Yay, we got a value that we can write directly.
801 return self.write_immediate_no_validate(src_val, dest);
803 Err(mplace) => mplace,
805 // Slow path, this does not fit into an immediate. Just memcpy.
806 trace!("copy_op: {:?} <- {:?}: {}", *dest, src, dest.layout.ty);
808 let dest = self.force_allocation(dest)?;
809 let (src_ptr, src_align) = src.to_scalar_ptr_align();
810 let (dest_ptr, dest_align) = dest.to_scalar_ptr_align();
813 dest_ptr, dest_align,
814 dest.layout.size, false
820 /// Copy the data from an operand to a place. The layouts may disagree, but they must
821 /// have the same size.
822 pub fn copy_op_transmute(
824 src: OpTy<'tcx, M::PointerTag>,
825 dest: PlaceTy<'tcx, M::PointerTag>,
826 ) -> EvalResult<'tcx> {
827 if src.layout.details == dest.layout.details {
828 // Fast path: Just use normal `copy_op`
829 return self.copy_op(src, dest);
831 // We still require the sizes to match
832 debug_assert!(!src.layout.is_unsized() && !dest.layout.is_unsized(),
833 "Cannot copy unsized data");
834 assert!(src.layout.size == dest.layout.size,
835 "Size mismatch when transmuting!\nsrc: {:#?}\ndest: {:#?}", src, dest);
837 // The hard case is `ScalarPair`. `src` is already read from memory in this case,
838 // using `src.layout` to figure out which bytes to use for the 1st and 2nd field.
839 // We have to write them to `dest` at the offsets they were *read at*, which is
840 // not necessarily the same as the offsets in `dest.layout`!
841 // Hence we do the copy with the source layout on both sides. We also make sure to write
842 // into memory, because if `dest` is a local we would not even have a way to write
843 // at the `src` offsets; the fact that we came from a different layout would
845 let dest = self.force_allocation(dest)?;
846 self.copy_op_no_validate(
848 PlaceTy::from(MPlaceTy { mplace: *dest, layout: src.layout }),
851 if M::enforce_validity(self) {
852 // Data got changed, better make sure it matches the type!
853 self.validate_operand(dest.into(), vec![], None, /*const_mode*/false)?;
859 /// Make sure that a place is in memory, and return where it is.
860 /// If the place currently refers to a local that doesn't yet have a matching allocation,
861 /// create such an allocation.
862 /// This is essentially `force_to_memplace`.
863 pub fn force_allocation(
865 place: PlaceTy<'tcx, M::PointerTag>,
866 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
867 let mplace = match place.place {
868 Place::Local { frame, local } => {
869 match *self.stack[frame].locals[local].access()? {
870 Operand::Indirect(mplace) => mplace,
871 Operand::Immediate(value) => {
872 // We need to make an allocation.
873 // FIXME: Consider not doing anything for a ZST, and just returning
874 // a fake pointer? Are we even called for ZST?
876 // We need the layout of the local. We can NOT use the layout we got,
877 // that might e.g. be an inner field of a struct with `Scalar` layout,
878 // that has different alignment than the outer field.
879 let local_layout = self.layout_of_local(&self.stack[frame], local)?;
880 let ptr = self.allocate(local_layout, MemoryKind::Stack)?;
881 // We don't have to validate as we can assume the local
882 // was already valid for its type.
883 self.write_immediate_to_mplace_no_validate(value, ptr)?;
884 let mplace = ptr.mplace;
886 *self.stack[frame].locals[local].access_mut()? =
887 Operand::Indirect(mplace);
892 Place::Ptr(mplace) => mplace
894 // Return with the original layout, so that the caller can go on
895 Ok(MPlaceTy { mplace, layout: place.layout })
900 layout: TyLayout<'tcx>,
901 kind: MemoryKind<M::MemoryKinds>,
902 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
903 if layout.is_unsized() {
904 assert!(self.tcx.features().unsized_locals, "cannot alloc memory for unsized type");
905 // FIXME: What should we do here? We should definitely also tag!
906 Ok(MPlaceTy::dangling(layout, self))
908 let ptr = self.memory.allocate(layout.size, layout.align, kind)?;
909 let ptr = M::tag_new_allocation(self, ptr, kind)?;
910 Ok(MPlaceTy::from_aligned_ptr(ptr, layout))
914 pub fn write_discriminant_index(
916 variant_index: VariantIdx,
917 dest: PlaceTy<'tcx, M::PointerTag>,
918 ) -> EvalResult<'tcx> {
919 match dest.layout.variants {
920 layout::Variants::Single { index } => {
921 assert_eq!(index, variant_index);
923 layout::Variants::Tagged { ref tag, .. } => {
924 let adt_def = dest.layout.ty.ty_adt_def().unwrap();
925 assert!(variant_index.as_usize() < adt_def.variants.len());
926 let discr_val = adt_def
927 .discriminant_for_variant(*self.tcx, variant_index)
930 // raw discriminants for enums are isize or bigger during
931 // their computation, but the in-memory tag is the smallest possible
933 let size = tag.value.size(self);
934 let shift = 128 - size.bits();
935 let discr_val = (discr_val << shift) >> shift;
937 let discr_dest = self.place_field(dest, 0)?;
938 self.write_scalar(Scalar::from_uint(discr_val, size), discr_dest)?;
940 layout::Variants::NicheFilling {
947 variant_index.as_usize() < dest.layout.ty.ty_adt_def().unwrap().variants.len(),
949 if variant_index != dataful_variant {
951 self.place_field(dest, 0)?;
952 let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
953 let niche_value = (niche_value as u128)
954 .wrapping_add(niche_start);
956 Scalar::from_uint(niche_value, niche_dest.layout.size),
966 /// Every place can be read from, so we can turm them into an operand
970 place: PlaceTy<'tcx, M::PointerTag>
971 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
972 let op = match place.place {
973 Place::Ptr(mplace) => {
974 Operand::Indirect(mplace)
976 Place::Local { frame, local } =>
977 *self.stack[frame].locals[local].access()?
979 Ok(OpTy { op, layout: place.layout })
982 pub fn raw_const_to_mplace(
985 ) -> EvalResult<'tcx, MPlaceTy<'tcx, M::PointerTag>> {
986 // This must be an allocation in `tcx`
987 assert!(self.tcx.alloc_map.lock().get(raw.alloc_id).is_some());
988 let layout = self.layout_of(raw.ty)?;
989 Ok(MPlaceTy::from_aligned_ptr(
990 Pointer::new(raw.alloc_id, Size::ZERO).with_default_tag(),
995 /// Turn a place with a `dyn Trait` type into a place with the actual dynamic type.
996 /// Also return some more information so drop doesn't have to run the same code twice.
997 pub(super) fn unpack_dyn_trait(&self, mplace: MPlaceTy<'tcx, M::PointerTag>)
998 -> EvalResult<'tcx, (ty::Instance<'tcx>, MPlaceTy<'tcx, M::PointerTag>)> {
999 let vtable = mplace.vtable()?; // also sanity checks the type
1000 let (instance, ty) = self.read_drop_type_from_vtable(vtable)?;
1001 let layout = self.layout_of(ty)?;
1003 // More sanity checks
1004 if cfg!(debug_assertions) {
1005 let (size, align) = self.read_size_and_align_from_vtable(vtable)?;
1006 assert_eq!(size, layout.size);
1007 assert_eq!(align.abi(), layout.align.abi()); // only ABI alignment is preserved
1010 let mplace = MPlaceTy {
1011 mplace: MemPlace { meta: None, ..*mplace },
1014 Ok((instance, mplace))