| //! This file implements "place projections"; basically a symmetric API for 3 types: MPlaceTy, OpTy, PlaceTy. |
| //! |
| //! OpTy and PlaceTy generally work by "let's see if we are actually an MPlaceTy, and do something custom if not". |
| //! For PlaceTy, the custom thing is basically always to call `force_allocation` and then use the MPlaceTy logic anyway. |
| //! For OpTy, the custom thing on field pojections has to be pretty clever (since `Operand::Immediate` can have fields), |
| //! but for array/slice operations it only has to worry about `Operand::Uninit`. That makes the value part trivial, |
| //! but we still need to do bounds checking and adjust the layout. To not duplicate that with MPlaceTy, we actually |
| //! implement the logic on OpTy, and MPlaceTy calls that. |
| |
| use std::marker::PhantomData; |
| use std::ops::Range; |
| |
| use rustc_middle::mir; |
| use rustc_middle::ty; |
| use rustc_middle::ty::layout::{LayoutOf, TyAndLayout}; |
| use rustc_middle::ty::Ty; |
| use rustc_target::abi::Size; |
| use rustc_target::abi::{self, VariantIdx}; |
| |
| use super::{InterpCx, InterpResult, MPlaceTy, Machine, MemPlaceMeta, OpTy, Provenance, Scalar}; |
| |
| /// Describes the constraints placed on offset-projections. |
| #[derive(Copy, Clone, Debug)] |
| pub enum OffsetMode { |
| /// The offset has to be inbounds, like `ptr::offset`. |
| Inbounds, |
| /// No constraints, just wrap around the edge of the address space. |
| Wrapping, |
| } |
| |
| /// A thing that we can project into, and that has a layout. |
| pub trait Projectable<'tcx, Prov: Provenance>: Sized + std::fmt::Debug { |
| /// Get the layout. |
| fn layout(&self) -> TyAndLayout<'tcx>; |
| |
| /// Get the metadata of a wide value. |
| fn meta(&self) -> MemPlaceMeta<Prov>; |
| |
| /// Get the length of a slice/string/array stored here. |
| fn len<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>( |
| &self, |
| ecx: &InterpCx<'mir, 'tcx, M>, |
| ) -> InterpResult<'tcx, u64> { |
| let layout = self.layout(); |
| if layout.is_unsized() { |
| // We need to consult `meta` metadata |
| match layout.ty.kind() { |
| ty::Slice(..) | ty::Str => self.meta().unwrap_meta().to_target_usize(ecx), |
| _ => bug!("len not supported on unsized type {:?}", layout.ty), |
| } |
| } else { |
| // Go through the layout. There are lots of types that support a length, |
| // e.g., SIMD types. (But not all repr(simd) types even have FieldsShape::Array!) |
| match layout.fields { |
| abi::FieldsShape::Array { count, .. } => Ok(count), |
| _ => bug!("len not supported on sized type {:?}", layout.ty), |
| } |
| } |
| } |
| |
| /// Offset the value by the given amount, replacing the layout and metadata. |
| fn offset_with_meta<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>( |
| &self, |
| offset: Size, |
| mode: OffsetMode, |
| meta: MemPlaceMeta<Prov>, |
| layout: TyAndLayout<'tcx>, |
| ecx: &InterpCx<'mir, 'tcx, M>, |
| ) -> InterpResult<'tcx, Self>; |
| |
| fn offset<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>( |
| &self, |
| offset: Size, |
| layout: TyAndLayout<'tcx>, |
| ecx: &InterpCx<'mir, 'tcx, M>, |
| ) -> InterpResult<'tcx, Self> { |
| assert!(layout.is_sized()); |
| self.offset_with_meta(offset, OffsetMode::Inbounds, MemPlaceMeta::None, layout, ecx) |
| } |
| |
| fn transmute<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>( |
| &self, |
| layout: TyAndLayout<'tcx>, |
| ecx: &InterpCx<'mir, 'tcx, M>, |
| ) -> InterpResult<'tcx, Self> { |
| assert!(self.layout().is_sized() && layout.is_sized()); |
| assert_eq!(self.layout().size, layout.size); |
| self.offset_with_meta(Size::ZERO, OffsetMode::Wrapping, MemPlaceMeta::None, layout, ecx) |
| } |
| |
| /// Convert this to an `OpTy`. This might be an irreversible transformation, but is useful for |
| /// reading from this thing. |
| fn to_op<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>( |
| &self, |
| ecx: &InterpCx<'mir, 'tcx, M>, |
| ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>; |
| } |
| |
| /// A type representing iteration over the elements of an array. |
| pub struct ArrayIterator<'tcx, 'a, Prov: Provenance, P: Projectable<'tcx, Prov>> { |
| base: &'a P, |
| range: Range<u64>, |
| stride: Size, |
| field_layout: TyAndLayout<'tcx>, |
| _phantom: PhantomData<Prov>, // otherwise it says `Prov` is never used... |
| } |
| |
| impl<'tcx, 'a, Prov: Provenance, P: Projectable<'tcx, Prov>> ArrayIterator<'tcx, 'a, Prov, P> { |
| /// Should be the same `ecx` on each call, and match the one used to create the iterator. |
| pub fn next<'mir, M: Machine<'mir, 'tcx, Provenance = Prov>>( |
| &mut self, |
| ecx: &InterpCx<'mir, 'tcx, M>, |
| ) -> InterpResult<'tcx, Option<(u64, P)>> { |
| let Some(idx) = self.range.next() else { return Ok(None) }; |
| // We use `Wrapping` here since the offset has already been checked when the iterator was created. |
| Ok(Some(( |
| idx, |
| self.base.offset_with_meta( |
| self.stride * idx, |
| OffsetMode::Wrapping, |
| MemPlaceMeta::None, |
| self.field_layout, |
| ecx, |
| )?, |
| ))) |
| } |
| } |
| |
| // FIXME: Working around https://github.com/rust-lang/rust/issues/54385 |
| impl<'mir, 'tcx: 'mir, Prov, M> InterpCx<'mir, 'tcx, M> |
| where |
| Prov: Provenance, |
| M: Machine<'mir, 'tcx, Provenance = Prov>, |
| { |
| /// Offset a pointer to project to a field of a struct/union. Unlike `place_field`, this is |
| /// always possible without allocating, so it can take `&self`. Also return the field's layout. |
| /// This supports both struct and array fields, but not slices! |
| /// |
| /// This also works for arrays, but then the `usize` index type is restricting. |
| /// For indexing into arrays, use `mplace_index`. |
| pub fn project_field<P: Projectable<'tcx, M::Provenance>>( |
| &self, |
| base: &P, |
| field: usize, |
| ) -> InterpResult<'tcx, P> { |
| // Slices nominally have length 0, so they will panic somewhere in `fields.offset`. |
| debug_assert!( |
| !matches!(base.layout().ty.kind(), ty::Slice(..)), |
| "`field` projection called on a slice -- call `index` projection instead" |
| ); |
| let offset = base.layout().fields.offset(field); |
| // Computing the layout does normalization, so we get a normalized type out of this |
| // even if the field type is non-normalized (possible e.g. via associated types). |
| let field_layout = base.layout().field(self, field); |
| |
| // Offset may need adjustment for unsized fields. |
| let (meta, offset) = if field_layout.is_unsized() { |
| assert!(!base.layout().is_sized()); |
| let base_meta = base.meta(); |
| // Re-use parent metadata to determine dynamic field layout. |
| // With custom DSTS, this *will* execute user-defined code, but the same |
| // happens at run-time so that's okay. |
| match self.size_and_align_of(&base_meta, &field_layout)? { |
| Some((_, align)) => { |
| // For packed types, we need to cap alignment. |
| let align = if let ty::Adt(def, _) = base.layout().ty.kind() |
| && let Some(packed) = def.repr().pack |
| { |
| align.min(packed) |
| } else { |
| align |
| }; |
| (base_meta, offset.align_to(align)) |
| } |
| None if offset == Size::ZERO => { |
| // If the offset is 0, then rounding it up to alignment wouldn't change anything, |
| // so we can do this even for types where we cannot determine the alignment. |
| (base_meta, offset) |
| } |
| None => { |
| // We don't know the alignment of this field, so we cannot adjust. |
| throw_unsup_format!("`extern type` does not have a known offset") |
| } |
| } |
| } else { |
| // base_meta could be present; we might be accessing a sized field of an unsized |
| // struct. |
| (MemPlaceMeta::None, offset) |
| }; |
| |
| base.offset_with_meta(offset, OffsetMode::Inbounds, meta, field_layout, self) |
| } |
| |
| /// Downcasting to an enum variant. |
| pub fn project_downcast<P: Projectable<'tcx, M::Provenance>>( |
| &self, |
| base: &P, |
| variant: VariantIdx, |
| ) -> InterpResult<'tcx, P> { |
| assert!(!base.meta().has_meta()); |
| // Downcasts only change the layout. |
| // (In particular, no check about whether this is even the active variant -- that's by design, |
| // see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.) |
| // So we just "offset" by 0. |
| let layout = base.layout().for_variant(self, variant); |
| // This variant may in fact be uninhabited. |
| // See <https://github.com/rust-lang/rust/issues/120337>. |
| |
| // This cannot be `transmute` as variants *can* have a smaller size than the entire enum. |
| base.offset(Size::ZERO, layout, self) |
| } |
| |
| /// Compute the offset and field layout for accessing the given index. |
| pub fn project_index<P: Projectable<'tcx, M::Provenance>>( |
| &self, |
| base: &P, |
| index: u64, |
| ) -> InterpResult<'tcx, P> { |
| // Not using the layout method because we want to compute on u64 |
| let (offset, field_layout) = match base.layout().fields { |
| abi::FieldsShape::Array { stride, count: _ } => { |
| // `count` is nonsense for slices, use the dynamic length instead. |
| let len = base.len(self)?; |
| if index >= len { |
| // This can only be reached in ConstProp and non-rustc-MIR. |
| throw_ub!(BoundsCheckFailed { len, index }); |
| } |
| let offset = stride * index; // `Size` multiplication |
| // All fields have the same layout. |
| let field_layout = base.layout().field(self, 0); |
| (offset, field_layout) |
| } |
| _ => span_bug!( |
| self.cur_span(), |
| "`mplace_index` called on non-array type {:?}", |
| base.layout().ty |
| ), |
| }; |
| |
| base.offset(offset, field_layout, self) |
| } |
| |
| fn project_constant_index<P: Projectable<'tcx, M::Provenance>>( |
| &self, |
| base: &P, |
| offset: u64, |
| min_length: u64, |
| from_end: bool, |
| ) -> InterpResult<'tcx, P> { |
| let n = base.len(self)?; |
| if n < min_length { |
| // This can only be reached in ConstProp and non-rustc-MIR. |
| throw_ub!(BoundsCheckFailed { len: min_length, index: n }); |
| } |
| |
| let index = if from_end { |
| assert!(0 < offset && offset <= min_length); |
| n.checked_sub(offset).unwrap() |
| } else { |
| assert!(offset < min_length); |
| offset |
| }; |
| |
| self.project_index(base, index) |
| } |
| |
| /// Iterates over all fields of an array. Much more efficient than doing the |
| /// same by repeatedly calling `project_index`. |
| pub fn project_array_fields<'a, P: Projectable<'tcx, M::Provenance>>( |
| &self, |
| base: &'a P, |
| ) -> InterpResult<'tcx, ArrayIterator<'tcx, 'a, M::Provenance, P>> { |
| let abi::FieldsShape::Array { stride, .. } = base.layout().fields else { |
| span_bug!(self.cur_span(), "project_array_fields: expected an array layout"); |
| }; |
| let len = base.len(self)?; |
| let field_layout = base.layout().field(self, 0); |
| // Ensure that all the offsets are in-bounds once, up-front. |
| debug!("project_array_fields: {base:?} {len}"); |
| base.offset(len * stride, self.layout_of(self.tcx.types.unit).unwrap(), self)?; |
| // Create the iterator. |
| Ok(ArrayIterator { base, range: 0..len, stride, field_layout, _phantom: PhantomData }) |
| } |
| |
| /// Subslicing |
| fn project_subslice<P: Projectable<'tcx, M::Provenance>>( |
| &self, |
| base: &P, |
| from: u64, |
| to: u64, |
| from_end: bool, |
| ) -> InterpResult<'tcx, P> { |
| let len = base.len(self)?; // also asserts that we have a type where this makes sense |
| let actual_to = if from_end { |
| if from.checked_add(to).map_or(true, |to| to > len) { |
| // This can only be reached in ConstProp and non-rustc-MIR. |
| throw_ub!(BoundsCheckFailed { len: len, index: from.saturating_add(to) }); |
| } |
| len.checked_sub(to).unwrap() |
| } else { |
| to |
| }; |
| |
| // Not using layout method because that works with usize, and does not work with slices |
| // (that have count 0 in their layout). |
| let from_offset = match base.layout().fields { |
| abi::FieldsShape::Array { stride, .. } => stride * from, // `Size` multiplication is checked |
| _ => { |
| span_bug!( |
| self.cur_span(), |
| "unexpected layout of index access: {:#?}", |
| base.layout() |
| ) |
| } |
| }; |
| |
| // Compute meta and new layout |
| let inner_len = actual_to.checked_sub(from).unwrap(); |
| let (meta, ty) = match base.layout().ty.kind() { |
| // It is not nice to match on the type, but that seems to be the only way to |
| // implement this. |
| ty::Array(inner, _) => { |
| (MemPlaceMeta::None, Ty::new_array(self.tcx.tcx, *inner, inner_len)) |
| } |
| ty::Slice(..) => { |
| let len = Scalar::from_target_usize(inner_len, self); |
| (MemPlaceMeta::Meta(len), base.layout().ty) |
| } |
| _ => { |
| span_bug!( |
| self.cur_span(), |
| "cannot subslice non-array type: `{:?}`", |
| base.layout().ty |
| ) |
| } |
| }; |
| let layout = self.layout_of(ty)?; |
| |
| base.offset_with_meta(from_offset, OffsetMode::Inbounds, meta, layout, self) |
| } |
| |
| /// Applying a general projection |
| #[instrument(skip(self), level = "trace")] |
| pub fn project<P>(&self, base: &P, proj_elem: mir::PlaceElem<'tcx>) -> InterpResult<'tcx, P> |
| where |
| P: Projectable<'tcx, M::Provenance> + From<MPlaceTy<'tcx, M::Provenance>> + std::fmt::Debug, |
| { |
| use rustc_middle::mir::ProjectionElem::*; |
| Ok(match proj_elem { |
| OpaqueCast(ty) => { |
| span_bug!(self.cur_span(), "OpaqueCast({ty}) encountered after borrowck") |
| } |
| // We don't want anything happening here, this is here as a dummy. |
| Subtype(_) => base.transmute(base.layout(), self)?, |
| Field(field, _) => self.project_field(base, field.index())?, |
| Downcast(_, variant) => self.project_downcast(base, variant)?, |
| Deref => self.deref_pointer(&base.to_op(self)?)?.into(), |
| Index(local) => { |
| let layout = self.layout_of(self.tcx.types.usize)?; |
| let n = self.local_to_op(local, Some(layout))?; |
| let n = self.read_target_usize(&n)?; |
| self.project_index(base, n)? |
| } |
| ConstantIndex { offset, min_length, from_end } => { |
| self.project_constant_index(base, offset, min_length, from_end)? |
| } |
| Subslice { from, to, from_end } => self.project_subslice(base, from, to, from_end)?, |
| }) |
| } |
| } |
