1 //! Functions concerning immediate values and operands, and reading from operands.
2 //! All high-level functions to read from memory work on operands as sources.
4 use std::convert::TryInto;
7 use rustc::ty::layout::{self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt, VariantIdx};
9 use rustc::mir::interpret::{
10 GlobalId, AllocId, InboundsCheck,
11 ConstValue, Pointer, Scalar,
12 EvalResult, EvalErrorKind,
13 sign_extend, truncate,
17 MemPlace, MPlaceTy, PlaceTy, Place, MemoryKind,
19 pub use rustc::mir::interpret::ScalarMaybeUndef;
21 /// A `Value` represents a single immediate self-contained Rust value.
23 /// For optimization of a few very common cases, there is also a representation for a pair of
24 /// primitive values (`ScalarPair`). It allows Miri to avoid making allocations for checked binary
25 /// operations and fat pointers. This idea was taken from rustc's codegen.
26 /// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely
27 /// defined on `Immediate`, and do not have to work with a `Place`.
28 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
29 pub enum Immediate<Tag=(), Id=AllocId> {
30 Scalar(ScalarMaybeUndef<Tag, Id>),
31 ScalarPair(ScalarMaybeUndef<Tag, Id>, ScalarMaybeUndef<Tag, Id>),
36 pub fn with_default_tag<Tag>(self) -> Immediate<Tag>
40 Immediate::Scalar(x) => Immediate::Scalar(x.with_default_tag()),
41 Immediate::ScalarPair(x, y) =>
42 Immediate::ScalarPair(x.with_default_tag(), y.with_default_tag()),
47 impl<'tcx, Tag> Immediate<Tag> {
49 pub fn from_scalar(val: Scalar<Tag>) -> Self {
50 Immediate::Scalar(ScalarMaybeUndef::Scalar(val))
54 pub fn erase_tag(self) -> Immediate
57 Immediate::Scalar(x) => Immediate::Scalar(x.erase_tag()),
58 Immediate::ScalarPair(x, y) =>
59 Immediate::ScalarPair(x.erase_tag(), y.erase_tag()),
66 cx: &impl HasDataLayout
68 Immediate::ScalarPair(
70 Scalar::from_uint(len, cx.data_layout().pointer_size).into(),
74 pub fn new_dyn_trait(val: Scalar<Tag>, vtable: Pointer<Tag>) -> Self {
75 Immediate::ScalarPair(val.into(), Scalar::Ptr(vtable).into())
79 pub fn to_scalar_or_undef(self) -> ScalarMaybeUndef<Tag> {
81 Immediate::Scalar(val) => val,
82 Immediate::ScalarPair(..) => bug!("Got a fat pointer where a scalar was expected"),
87 pub fn to_scalar(self) -> EvalResult<'tcx, Scalar<Tag>> {
88 self.to_scalar_or_undef().not_undef()
92 pub fn to_scalar_pair(self) -> EvalResult<'tcx, (Scalar<Tag>, Scalar<Tag>)> {
94 Immediate::Scalar(..) => bug!("Got a thin pointer where a scalar pair was expected"),
95 Immediate::ScalarPair(a, b) => Ok((a.not_undef()?, b.not_undef()?))
99 /// Converts the immediate into a pointer (or a pointer-sized integer).
100 /// Throws away the second half of a ScalarPair!
102 pub fn to_scalar_ptr(self) -> EvalResult<'tcx, Scalar<Tag>> {
104 Immediate::Scalar(ptr) |
105 Immediate::ScalarPair(ptr, _) => ptr.not_undef(),
109 /// Converts the value into its metadata.
110 /// Throws away the first half of a ScalarPair!
112 pub fn to_meta(self) -> EvalResult<'tcx, Option<Scalar<Tag>>> {
114 Immediate::Scalar(_) => None,
115 Immediate::ScalarPair(_, meta) => Some(meta.not_undef()?),
120 // ScalarPair needs a type to interpret, so we often have an immediate and a type together
121 // as input for binary and cast operations.
122 #[derive(Copy, Clone, Debug)]
123 pub struct ImmTy<'tcx, Tag=()> {
124 pub imm: Immediate<Tag>,
125 pub layout: TyLayout<'tcx>,
128 impl<'tcx, Tag> ::std::ops::Deref for ImmTy<'tcx, Tag> {
129 type Target = Immediate<Tag>;
131 fn deref(&self) -> &Immediate<Tag> {
136 /// An `Operand` is the result of computing a `mir::Operand`. It can be immediate,
137 /// or still in memory. The latter is an optimization, to delay reading that chunk of
138 /// memory and to avoid having to store arbitrary-sized data here.
139 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
140 pub enum Operand<Tag=(), Id=AllocId> {
141 Immediate(Immediate<Tag, Id>),
142 Indirect(MemPlace<Tag, Id>),
147 pub fn with_default_tag<Tag>(self) -> Operand<Tag>
151 Operand::Immediate(x) => Operand::Immediate(x.with_default_tag()),
152 Operand::Indirect(x) => Operand::Indirect(x.with_default_tag()),
157 impl<Tag> Operand<Tag> {
159 pub fn erase_tag(self) -> Operand
162 Operand::Immediate(x) => Operand::Immediate(x.erase_tag()),
163 Operand::Indirect(x) => Operand::Indirect(x.erase_tag()),
168 pub fn to_mem_place(self) -> MemPlace<Tag>
169 where Tag: ::std::fmt::Debug
172 Operand::Indirect(mplace) => mplace,
173 _ => bug!("to_mem_place: expected Operand::Indirect, got {:?}", self),
179 pub fn to_immediate(self) -> Immediate<Tag>
180 where Tag: ::std::fmt::Debug
183 Operand::Immediate(imm) => imm,
184 _ => bug!("to_immediate: expected Operand::Immediate, got {:?}", self),
190 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
191 pub struct OpTy<'tcx, Tag=()> {
193 pub layout: TyLayout<'tcx>,
196 impl<'tcx, Tag> ::std::ops::Deref for OpTy<'tcx, Tag> {
197 type Target = Operand<Tag>;
199 fn deref(&self) -> &Operand<Tag> {
204 impl<'tcx, Tag: Copy> From<MPlaceTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
206 fn from(mplace: MPlaceTy<'tcx, Tag>) -> Self {
208 op: Operand::Indirect(*mplace),
209 layout: mplace.layout
214 impl<'tcx, Tag> From<ImmTy<'tcx, Tag>> for OpTy<'tcx, Tag> {
216 fn from(val: ImmTy<'tcx, Tag>) -> Self {
218 op: Operand::Immediate(val.imm),
224 impl<'tcx, Tag: Copy> ImmTy<'tcx, Tag>
227 pub fn from_scalar(val: Scalar<Tag>, layout: TyLayout<'tcx>) -> Self {
228 ImmTy { imm: Immediate::from_scalar(val), layout }
232 pub fn to_bits(self) -> EvalResult<'tcx, u128> {
233 self.to_scalar()?.to_bits(self.layout.size)
237 impl<'tcx, Tag> OpTy<'tcx, Tag>
240 pub fn erase_tag(self) -> OpTy<'tcx>
243 op: self.op.erase_tag(),
249 // Use the existing layout if given (but sanity check in debug mode),
250 // or compute the layout.
252 pub(super) fn from_known_layout<'tcx>(
253 layout: Option<TyLayout<'tcx>>,
254 compute: impl FnOnce() -> EvalResult<'tcx, TyLayout<'tcx>>
255 ) -> EvalResult<'tcx, TyLayout<'tcx>> {
259 if cfg!(debug_assertions) {
260 let layout2 = compute()?;
261 assert_eq!(layout.details, layout2.details,
262 "Mismatch in layout of supposedly equal-layout types {:?} and {:?}",
263 layout.ty, layout2.ty);
270 impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
271 /// Try reading an immediate in memory; this is interesting particularly for ScalarPair.
272 /// Returns `None` if the layout does not permit loading this as a value.
273 fn try_read_immediate_from_mplace(
275 mplace: MPlaceTy<'tcx, M::PointerTag>,
276 ) -> EvalResult<'tcx, Option<Immediate<M::PointerTag>>> {
277 if mplace.layout.is_unsized() {
278 // Don't touch unsized
281 let (ptr, ptr_align) = mplace.to_scalar_ptr_align();
283 if mplace.layout.is_zst() {
284 // Not all ZSTs have a layout we would handle below, so just short-circuit them
286 self.memory.check_align(ptr, ptr_align)?;
287 return Ok(Some(Immediate::Scalar(Scalar::zst().into())));
290 // check for integer pointers before alignment to report better errors
291 let ptr = ptr.to_ptr()?;
292 self.memory.check_align(ptr.into(), ptr_align)?;
293 match mplace.layout.abi {
294 layout::Abi::Scalar(..) => {
295 let scalar = self.memory
297 .read_scalar(self, ptr, mplace.layout.size)?;
298 Ok(Some(Immediate::Scalar(scalar)))
300 layout::Abi::ScalarPair(ref a, ref b) => {
301 let (a, b) = (&a.value, &b.value);
302 let (a_size, b_size) = (a.size(self), b.size(self));
304 let b_offset = a_size.align_to(b.align(self).abi);
305 assert!(b_offset.bytes() > 0); // we later use the offset to test which field to use
306 let b_ptr = ptr.offset(b_offset, self)?;
307 let a_val = self.memory
309 .read_scalar(self, a_ptr, a_size)?;
310 let b_align = ptr_align.restrict_for_offset(b_offset);
311 self.memory.check_align(b_ptr.into(), b_align)?;
312 let b_val = self.memory
314 .read_scalar(self, b_ptr, b_size)?;
315 Ok(Some(Immediate::ScalarPair(a_val, b_val)))
321 /// Try returning an immediate for the operand.
322 /// If the layout does not permit loading this as an immediate, return where in memory
323 /// we can find the data.
324 /// Note that for a given layout, this operation will either always fail or always
325 /// succeed! Whether it succeeds depends on whether the layout can be represented
326 /// in a `Immediate`, not on which data is stored there currently.
327 pub(super) fn try_read_immediate(
329 src: OpTy<'tcx, M::PointerTag>,
330 ) -> EvalResult<'tcx, Result<Immediate<M::PointerTag>, MemPlace<M::PointerTag>>> {
331 Ok(match src.try_as_mplace() {
333 if let Some(val) = self.try_read_immediate_from_mplace(mplace)? {
343 /// Read an immediate from a place, asserting that that is possible with the given layout.
345 pub fn read_immediate(
347 op: OpTy<'tcx, M::PointerTag>
348 ) -> EvalResult<'tcx, ImmTy<'tcx, M::PointerTag>> {
349 if let Ok(imm) = self.try_read_immediate(op)? {
350 Ok(ImmTy { imm, layout: op.layout })
352 bug!("primitive read failed for type: {:?}", op.layout.ty);
356 /// Read a scalar from a place
359 op: OpTy<'tcx, M::PointerTag>
360 ) -> EvalResult<'tcx, ScalarMaybeUndef<M::PointerTag>> {
361 Ok(self.read_immediate(op)?.to_scalar_or_undef())
364 // Turn the MPlace into a string (must already be dereferenced!)
367 mplace: MPlaceTy<'tcx, M::PointerTag>,
368 ) -> EvalResult<'tcx, &str> {
369 let len = mplace.len(self)?;
370 let bytes = self.memory.read_bytes(mplace.ptr, Size::from_bytes(len as u64))?;
371 let str = ::std::str::from_utf8(bytes)
372 .map_err(|err| EvalErrorKind::ValidationFailure(err.to_string()))?;
376 pub fn uninit_operand(
378 layout: TyLayout<'tcx>
379 ) -> EvalResult<'tcx, Operand<M::PointerTag>> {
380 // This decides which types we will use the Immediate optimization for, and hence should
381 // match what `try_read_immediate` and `eval_place_to_op` support.
383 return Ok(Operand::Immediate(Immediate::Scalar(Scalar::zst().into())));
386 Ok(match layout.abi {
387 layout::Abi::Scalar(..) =>
388 Operand::Immediate(Immediate::Scalar(ScalarMaybeUndef::Undef)),
389 layout::Abi::ScalarPair(..) =>
390 Operand::Immediate(Immediate::ScalarPair(
391 ScalarMaybeUndef::Undef,
392 ScalarMaybeUndef::Undef,
395 trace!("Forcing allocation for local of type {:?}", layout.ty);
397 *self.allocate(layout, MemoryKind::Stack)
403 /// Projection functions
404 pub fn operand_field(
406 op: OpTy<'tcx, M::PointerTag>,
408 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
409 let base = match op.try_as_mplace() {
412 let field = self.mplace_field(mplace, field)?;
413 return Ok(field.into());
418 let field = field.try_into().unwrap();
419 let field_layout = op.layout.field(self, field)?;
420 if field_layout.is_zst() {
421 let immediate = Immediate::Scalar(Scalar::zst().into());
422 return Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout });
424 let offset = op.layout.fields.offset(field);
425 let immediate = match base {
426 // the field covers the entire type
427 _ if offset.bytes() == 0 && field_layout.size == op.layout.size => base,
428 // extract fields from types with `ScalarPair` ABI
429 Immediate::ScalarPair(a, b) => {
430 let val = if offset.bytes() == 0 { a } else { b };
431 Immediate::Scalar(val)
433 Immediate::Scalar(val) =>
434 bug!("field access on non aggregate {:#?}, {:#?}", val, op.layout),
436 Ok(OpTy { op: Operand::Immediate(immediate), layout: field_layout })
439 pub fn operand_downcast(
441 op: OpTy<'tcx, M::PointerTag>,
443 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
444 // Downcasts only change the layout
445 Ok(match op.try_as_mplace() {
447 self.mplace_downcast(mplace, variant)?.into()
450 let layout = op.layout.for_variant(self, variant);
451 OpTy { layout, ..op }
456 pub fn operand_projection(
458 base: OpTy<'tcx, M::PointerTag>,
459 proj_elem: &mir::PlaceElem<'tcx>,
460 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
461 use rustc::mir::ProjectionElem::*;
462 Ok(match *proj_elem {
463 Field(field, _) => self.operand_field(base, field.index() as u64)?,
464 Downcast(_, variant) => self.operand_downcast(base, variant)?,
465 Deref => self.deref_operand(base)?.into(),
466 Subslice { .. } | ConstantIndex { .. } | Index(_) => if base.layout.is_zst() {
468 op: Operand::Immediate(Immediate::Scalar(Scalar::zst().into())),
469 // the actual index doesn't matter, so we just pick a convenient one like 0
470 layout: base.layout.field(self, 0)?,
473 // The rest should only occur as mplace, we do not use Immediates for types
474 // allowing such operations. This matches place_projection forcing an allocation.
475 let mplace = base.to_mem_place();
476 self.mplace_projection(mplace, proj_elem)?.into()
481 /// This is used by [priroda](https://github.com/oli-obk/priroda) to get an OpTy from a local
484 frame: &super::Frame<'mir, 'tcx, M::PointerTag, M::FrameExtra>,
486 layout: Option<TyLayout<'tcx>>,
487 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
488 assert_ne!(local, mir::RETURN_PLACE);
489 let op = *frame.locals[local].access()?;
490 let layout = self.layout_of_local(frame, local, layout)?;
491 Ok(OpTy { op, layout })
494 /// Every place can be read from, so we can turm them into an operand
498 place: PlaceTy<'tcx, M::PointerTag>
499 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
500 let op = match *place {
501 Place::Ptr(mplace) => {
502 Operand::Indirect(mplace)
504 Place::Local { frame, local } =>
505 *self.stack[frame].locals[local].access()?
507 Ok(OpTy { op, layout: place.layout })
510 // Evaluate a place with the goal of reading from it. This lets us sometimes
511 // avoid allocations.
512 pub(super) fn eval_place_to_op(
514 mir_place: &mir::Place<'tcx>,
515 layout: Option<TyLayout<'tcx>>,
516 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
517 use rustc::mir::Place::*;
518 use rustc::mir::PlaceBase;
519 let op = match *mir_place {
520 Base(PlaceBase::Local(mir::RETURN_PLACE)) => return err!(ReadFromReturnPointer),
521 Base(PlaceBase::Local(local)) => self.access_local(self.frame(), local, layout)?,
523 Projection(ref proj) => {
524 let op = self.eval_place_to_op(&proj.base, None)?;
525 self.operand_projection(op, &proj.elem)?
528 _ => self.eval_place_to_mplace(mir_place)?.into(),
531 trace!("eval_place_to_op: got {:?}", *op);
535 /// Evaluate the operand, returning a place where you can then find the data.
536 /// if you already know the layout, you can save two some table lookups
537 /// by passing it in here.
540 mir_op: &mir::Operand<'tcx>,
541 layout: Option<TyLayout<'tcx>>,
542 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
543 use rustc::mir::Operand::*;
544 let op = match *mir_op {
545 // FIXME: do some more logic on `move` to invalidate the old location
548 self.eval_place_to_op(place, layout)?,
550 Constant(ref constant) => self.eval_lazy_const_to_op(*constant.literal, layout)?,
552 trace!("{:?}: {:?}", mir_op, *op);
556 /// Evaluate a bunch of operands at once
557 pub(super) fn eval_operands(
559 ops: &[mir::Operand<'tcx>],
560 ) -> EvalResult<'tcx, Vec<OpTy<'tcx, M::PointerTag>>> {
562 .map(|op| self.eval_operand(op, None))
566 // Used when Miri runs into a constant, and by const propagation.
567 crate fn eval_lazy_const_to_op(
569 val: ty::LazyConst<'tcx>,
570 layout: Option<TyLayout<'tcx>>,
571 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
572 trace!("const_to_op: {:?}", val);
574 ty::LazyConst::Unevaluated(def_id, substs) => {
575 let instance = self.resolve(def_id, substs)?;
576 return Ok(OpTy::from(self.const_eval_raw(GlobalId {
581 ty::LazyConst::Evaluated(c) => self.const_to_op(c, layout),
585 // Used when the miri-engine runs into a constant and for extracting information from constants
586 // in patterns via the `const_eval` module
587 crate fn const_to_op(
589 val: ty::Const<'tcx>,
590 layout: Option<TyLayout<'tcx>>,
591 ) -> EvalResult<'tcx, OpTy<'tcx, M::PointerTag>> {
592 let layout = from_known_layout(layout, || {
593 let ty = self.monomorphize(val.ty)?;
596 let op = match val.val {
597 ConstValue::ByRef(ptr, alloc) => {
598 // We rely on mutability being set correctly in that allocation to prevent writes
599 // where none should happen -- and for `static mut`, we copy on demand anyway.
601 MemPlace::from_ptr(ptr, alloc.align)
604 ConstValue::Slice(a, b) =>
605 Operand::Immediate(Immediate::ScalarPair(
607 Scalar::from_uint(b, self.tcx.data_layout.pointer_size).into(),
608 )).with_default_tag(),
609 ConstValue::Scalar(x) =>
610 Operand::Immediate(Immediate::Scalar(x.into())).with_default_tag(),
618 /// Read discriminant, return the runtime value as well as the variant index.
619 pub fn read_discriminant(
621 rval: OpTy<'tcx, M::PointerTag>,
622 ) -> EvalResult<'tcx, (u128, VariantIdx)> {
623 trace!("read_discriminant_value {:#?}", rval.layout);
625 match rval.layout.variants {
626 layout::Variants::Single { index } => {
627 let discr_val = rval.layout.ty.ty_adt_def().map_or(
628 index.as_u32() as u128,
629 |def| def.discriminant_for_variant(*self.tcx, index).val);
630 return Ok((discr_val, index));
632 layout::Variants::Tagged { .. } |
633 layout::Variants::NicheFilling { .. } => {},
635 // read raw discriminant value
636 let discr_op = self.operand_field(rval, 0)?;
637 let discr_val = self.read_immediate(discr_op)?;
638 let raw_discr = discr_val.to_scalar_or_undef();
639 trace!("discr value: {:?}", raw_discr);
641 Ok(match rval.layout.variants {
642 layout::Variants::Single { .. } => bug!(),
643 layout::Variants::Tagged { .. } => {
644 let bits_discr = match raw_discr.to_bits(discr_val.layout.size) {
645 Ok(raw_discr) => raw_discr,
646 Err(_) => return err!(InvalidDiscriminant(raw_discr.erase_tag())),
648 let real_discr = if discr_val.layout.ty.is_signed() {
649 // going from layout tag type to typeck discriminant type
650 // requires first sign extending with the layout discriminant
651 let sexted = sign_extend(bits_discr, discr_val.layout.size) as i128;
652 // and then zeroing with the typeck discriminant type
653 let discr_ty = rval.layout.ty
654 .ty_adt_def().expect("tagged layout corresponds to adt")
657 let size = layout::Integer::from_attr(self, discr_ty).size();
658 let truncatee = sexted as u128;
659 truncate(truncatee, size)
663 // Make sure we catch invalid discriminants
664 let index = rval.layout.ty
666 .expect("tagged layout for non adt")
667 .discriminants(self.tcx.tcx)
668 .find(|(_, var)| var.val == real_discr)
669 .ok_or_else(|| EvalErrorKind::InvalidDiscriminant(raw_discr.erase_tag()))?;
670 (real_discr, index.0)
672 layout::Variants::NicheFilling {
678 let variants_start = niche_variants.start().as_u32() as u128;
679 let variants_end = niche_variants.end().as_u32() as u128;
681 ScalarMaybeUndef::Scalar(Scalar::Ptr(ptr)) => {
682 // The niche must be just 0 (which an inbounds pointer value never is)
683 let ptr_valid = niche_start == 0 && variants_start == variants_end &&
684 self.memory.check_bounds_ptr(ptr, InboundsCheck::MaybeDead).is_ok();
686 return err!(InvalidDiscriminant(raw_discr.erase_tag()));
688 (dataful_variant.as_u32() as u128, dataful_variant)
690 ScalarMaybeUndef::Scalar(Scalar::Bits { bits: raw_discr, size }) => {
691 assert_eq!(size as u64, discr_val.layout.size.bytes());
692 let adjusted_discr = raw_discr.wrapping_sub(niche_start)
693 .wrapping_add(variants_start);
694 if variants_start <= adjusted_discr && adjusted_discr <= variants_end {
695 let index = adjusted_discr as usize;
696 assert_eq!(index as u128, adjusted_discr);
697 assert!(index < rval.layout.ty
699 .expect("tagged layout for non adt")
701 (adjusted_discr, VariantIdx::from_usize(index))
703 (dataful_variant.as_u32() as u128, dataful_variant)
706 ScalarMaybeUndef::Undef =>
707 return err!(InvalidDiscriminant(ScalarMaybeUndef::Undef)),