compiler/rustc_mir/src/interpret/machine.rs - third_party/rust - Git at Google

 //! This module contains everything needed to instantiate an interpreter.
 //! This separation exists to ensure that no fancy miri features like
 //! interpreting common C functions leak into CTFE.

 use std::borrow::{Borrow, Cow};
 use std::fmt::Debug;
 use std::hash::Hash;

 use rustc_middle::mir;
 use rustc_middle::ty::{self, Ty};
 use rustc_span::def_id::DefId;

 use super::{
     AllocId, Allocation, AllocationExtra, CheckInAllocMsg, Frame, ImmTy, InterpCx, InterpResult,
     LocalValue, MemPlace, Memory, MemoryKind, OpTy, Operand, PlaceTy, Pointer, Scalar,
 };

 /// Data returned by Machine::stack_pop,
 /// to provide further control over the popping of the stack frame
 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
 pub enum StackPopJump {
     /// Indicates that no special handling should be
     /// done - we'll either return normally or unwind
     /// based on the terminator for the function
     /// we're leaving.
     Normal,

     /// Indicates that we should *not* jump to the return/unwind address, as the callback already
     /// took care of everything.
     NoJump,
 }

 /// Whether this kind of memory is allowed to leak
 pub trait MayLeak: Copy {
     fn may_leak(self) -> bool;
 }

 /// The functionality needed by memory to manage its allocations
 pub trait AllocMap<K: Hash + Eq, V> {
     /// Tests if the map contains the given key.
     /// Deliberately takes `&mut` because that is sufficient, and some implementations
     /// can be more efficient then (using `RefCell::get_mut`).
     fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
     where
         K: Borrow<Q>;

     /// Inserts a new entry into the map.
     fn insert(&mut self, k: K, v: V) -> Option<V>;

     /// Removes an entry from the map.
     fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
     where
         K: Borrow<Q>;

     /// Returns data based on the keys and values in the map.
     fn filter_map_collect<T>(&self, f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T>;

     /// Returns a reference to entry `k`. If no such entry exists, call
     /// `vacant` and either forward its error, or add its result to the map
     /// and return a reference to *that*.
     fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E>;

     /// Returns a mutable reference to entry `k`. If no such entry exists, call
     /// `vacant` and either forward its error, or add its result to the map
     /// and return a reference to *that*.
     fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E>;

     /// Read-only lookup.
     fn get(&self, k: K) -> Option<&V> {
         self.get_or(k, || Err(())).ok()
     }

     /// Mutable lookup.
     fn get_mut(&mut self, k: K) -> Option<&mut V> {
         self.get_mut_or(k, || Err(())).ok()
     }
 }

 /// Methods of this trait signifies a point where CTFE evaluation would fail
 /// and some use case dependent behaviour can instead be applied.
 pub trait Machine<'mir, 'tcx>: Sized {
     /// Additional memory kinds a machine wishes to distinguish from the builtin ones
     type MemoryKind: Debug + std::fmt::Display + MayLeak + Eq + 'static;

     /// Tag tracked alongside every pointer. This is used to implement "Stacked Borrows"
     /// <https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html>.
     /// The `default()` is used for pointers to consts, statics, vtables and functions.
     /// The `Debug` formatting is used for displaying pointers; we cannot use `Display`
     /// as `()` does not implement that, but it should be "nice" output.
     type PointerTag: Debug + Copy + Eq + Hash + 'static;

     /// Machines can define extra (non-instance) things that represent values of function pointers.
     /// For example, Miri uses this to return a function pointer from `dlsym`
     /// that can later be called to execute the right thing.
     type ExtraFnVal: Debug + Copy;

     /// Extra data stored in every call frame.
     type FrameExtra;

     /// Extra data stored in memory. A reference to this is available when `AllocExtra`
     /// gets initialized, so you can e.g., have an `Rc` here if there is global state you
     /// need access to in the `AllocExtra` hooks.
     type MemoryExtra;

     /// Extra data stored in every allocation.
     type AllocExtra: AllocationExtra<Self::PointerTag> + 'static;

     /// Memory's allocation map
     type MemoryMap: AllocMap<
             AllocId,
             (MemoryKind<Self::MemoryKind>, Allocation<Self::PointerTag, Self::AllocExtra>),
         > + Default
         + Clone;

     /// The memory kind to use for copied global memory (held in `tcx`) --
     /// or None if such memory should not be mutated and thus any such attempt will cause
     /// a `ModifiedStatic` error to be raised.
     /// Statics are copied under two circumstances: When they are mutated, and when
     /// `tag_allocation` (see below) returns an owned allocation
     /// that is added to the memory so that the work is not done twice.
     const GLOBAL_KIND: Option<Self::MemoryKind>;

     /// Whether memory accesses should be alignment-checked.
     fn enforce_alignment(memory_extra: &Self::MemoryExtra) -> bool;

     /// Whether, when checking alignment, we should `force_int` and thus support
     /// custom alignment logic based on whatever the integer address happens to be.
     fn force_int_for_alignment_check(memory_extra: &Self::MemoryExtra) -> bool;

     /// Whether to enforce the validity invariant
     fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;

     /// Entry point to all function calls.
     ///
     /// Returns either the mir to use for the call, or `None` if execution should
     /// just proceed (which usually means this hook did all the work that the
     /// called function should usually have done). In the latter case, it is
     /// this hook's responsibility to advance the instruction pointer!
     /// (This is to support functions like `__rust_maybe_catch_panic` that neither find a MIR
     /// nor just jump to `ret`, but instead push their own stack frame.)
     /// Passing `dest`and `ret` in the same `Option` proved very annoying when only one of them
     /// was used.
     fn find_mir_or_eval_fn(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, Self::PointerTag>],
         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
         unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>>;

     /// Execute `fn_val`.  It is the hook's responsibility to advance the instruction
     /// pointer as appropriate.
     fn call_extra_fn(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         fn_val: Self::ExtraFnVal,
         args: &[OpTy<'tcx, Self::PointerTag>],
         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
         unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx>;

     /// Directly process an intrinsic without pushing a stack frame. It is the hook's
     /// responsibility to advance the instruction pointer as appropriate.
     fn call_intrinsic(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         instance: ty::Instance<'tcx>,
         args: &[OpTy<'tcx, Self::PointerTag>],
         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
         unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx>;

     /// Called to evaluate `Assert` MIR terminators that trigger a panic.
     fn assert_panic(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         msg: &mir::AssertMessage<'tcx>,
         unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<'tcx>;

     /// Called to evaluate `Abort` MIR terminator.
     fn abort(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx, !> {
         throw_unsup_format!("aborting execution is not supported")
     }

     /// Called for all binary operations where the LHS has pointer type.
     ///
     /// Returns a (value, overflowed) pair if the operation succeeded
     fn binary_ptr_op(
         ecx: &InterpCx<'mir, 'tcx, Self>,
         bin_op: mir::BinOp,
         left: ImmTy<'tcx, Self::PointerTag>,
         right: ImmTy<'tcx, Self::PointerTag>,
     ) -> InterpResult<'tcx, (Scalar<Self::PointerTag>, bool, Ty<'tcx>)>;

     /// Heap allocations via the `box` keyword.
     fn box_alloc(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         dest: PlaceTy<'tcx, Self::PointerTag>,
     ) -> InterpResult<'tcx>;

     /// Called to read the specified `local` from the `frame`.
     /// Since reading a ZST is not actually accessing memory or locals, this is never invoked
     /// for ZST reads.
     #[inline]
     fn access_local(
         _ecx: &InterpCx<'mir, 'tcx, Self>,
         frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
         local: mir::Local,
     ) -> InterpResult<'tcx, Operand<Self::PointerTag>> {
         frame.locals[local].access()
     }

     /// Called to write the specified `local` from the `frame`.
     /// Since writing a ZST is not actually accessing memory or locals, this is never invoked
     /// for ZST reads.
     #[inline]
     fn access_local_mut<'a>(
         ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
         frame: usize,
         local: mir::Local,
     ) -> InterpResult<'tcx, Result<&'a mut LocalValue<Self::PointerTag>, MemPlace<Self::PointerTag>>>
     where
         'tcx: 'mir,
     {
         ecx.stack_mut()[frame].locals[local].access_mut()
     }

     /// Called before a basic block terminator is executed.
     /// You can use this to detect endlessly running programs.
     #[inline]
     fn before_terminator(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
         Ok(())
     }

     /// Called before a global allocation is accessed.
     /// `def_id` is `Some` if this is the "lazy" allocation of a static.
     #[inline]
     fn before_access_global(
         _memory_extra: &Self::MemoryExtra,
         _alloc_id: AllocId,
         _allocation: &Allocation,
         _static_def_id: Option<DefId>,
         _is_write: bool,
     ) -> InterpResult<'tcx> {
         Ok(())
     }

     /// Return the `AllocId` for the given thread-local static in the current thread.
     fn thread_local_static_alloc_id(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         def_id: DefId,
     ) -> InterpResult<'tcx, AllocId> {
         throw_unsup!(ThreadLocalStatic(def_id))
     }

     /// Return the `AllocId` backing the given `extern static`.
     fn extern_static_alloc_id(
         mem: &Memory<'mir, 'tcx, Self>,
         def_id: DefId,
     ) -> InterpResult<'tcx, AllocId> {
         // Use the `AllocId` associated with the `DefId`. Any actual *access* will fail.
         Ok(mem.tcx.create_static_alloc(def_id))
     }

     /// Return the "base" tag for the given *global* allocation: the one that is used for direct
     /// accesses to this static/const/fn allocation. If `id` is not a global allocation,
     /// this will return an unusable tag (i.e., accesses will be UB)!
     ///
     /// Called on the id returned by `thread_local_static_alloc_id` and `extern_static_alloc_id`, if needed.
     fn tag_global_base_pointer(memory_extra: &Self::MemoryExtra, id: AllocId) -> Self::PointerTag;

     /// Called to initialize the "extra" state of an allocation and make the pointers
     /// it contains (in relocations) tagged.  The way we construct allocations is
     /// to always first construct it without extra and then add the extra.
     /// This keeps uniform code paths for handling both allocations created by CTFE
     /// for globals, and allocations created by Miri during evaluation.
     ///
     /// `kind` is the kind of the allocation being tagged; it can be `None` when
     /// it's a global and `GLOBAL_KIND` is `None`.
     ///
     /// This should avoid copying if no work has to be done! If this returns an owned
     /// allocation (because a copy had to be done to add tags or metadata), machine memory will
     /// cache the result. (This relies on `AllocMap::get_or` being able to add the
     /// owned allocation to the map even when the map is shared.)
     ///
     /// Also return the "base" tag to use for this allocation: the one that is used for direct
     /// accesses to this allocation. If `kind == STATIC_KIND`, this tag must be consistent
     /// with `tag_global_base_pointer`.
     fn init_allocation_extra<'b>(
         memory_extra: &Self::MemoryExtra,
         id: AllocId,
         alloc: Cow<'b, Allocation>,
         kind: Option<MemoryKind<Self::MemoryKind>>,
     ) -> (Cow<'b, Allocation<Self::PointerTag, Self::AllocExtra>>, Self::PointerTag);

     /// Called to notify the machine before a deallocation occurs.
     fn before_deallocation(
         _memory_extra: &mut Self::MemoryExtra,
         _id: AllocId,
     ) -> InterpResult<'tcx> {
         Ok(())
     }

     /// Executes a retagging operation
     #[inline]
     fn retag(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         _kind: mir::RetagKind,
         _place: PlaceTy<'tcx, Self::PointerTag>,
     ) -> InterpResult<'tcx> {
         Ok(())
     }

     /// Called immediately before a new stack frame gets pushed.
     fn init_frame_extra(
         ecx: &mut InterpCx<'mir, 'tcx, Self>,
         frame: Frame<'mir, 'tcx, Self::PointerTag>,
     ) -> InterpResult<'tcx, Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>>;

     /// Borrow the current thread's stack.
     fn stack(
         ecx: &'a InterpCx<'mir, 'tcx, Self>,
     ) -> &'a [Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>];

     /// Mutably borrow the current thread's stack.
     fn stack_mut(
         ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
     ) -> &'a mut Vec<Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>>;

     /// Called immediately after a stack frame got pushed and its locals got initialized.
     fn after_stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
         Ok(())
     }

     /// Called immediately after a stack frame got popped, but before jumping back to the caller.
     fn after_stack_pop(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         _frame: Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
         _unwinding: bool,
     ) -> InterpResult<'tcx, StackPopJump> {
         // By default, we do not support unwinding from panics
         Ok(StackPopJump::Normal)
     }

     fn int_to_ptr(
         _mem: &Memory<'mir, 'tcx, Self>,
         int: u64,
     ) -> InterpResult<'tcx, Pointer<Self::PointerTag>> {
         Err((if int == 0 {
             // This is UB, seriously.
             err_ub!(DanglingIntPointer(0, CheckInAllocMsg::InboundsTest))
         } else {
             // This is just something we cannot support during const-eval.
             err_unsup!(ReadBytesAsPointer)
         })
         .into())
     }

     fn ptr_to_int(
         _mem: &Memory<'mir, 'tcx, Self>,
         _ptr: Pointer<Self::PointerTag>,
     ) -> InterpResult<'tcx, u64>;
 }

 // A lot of the flexibility above is just needed for `Miri`, but all "compile-time" machines
 // (CTFE and ConstProp) use the same instance.  Here, we share that code.
 pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
     type PointerTag = ();
     type ExtraFnVal = !;

     type MemoryKind = !;
     type MemoryMap = rustc_data_structures::fx::FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
     const GLOBAL_KIND: Option<!> = None; // no copying of globals from `tcx` to machine memory

     type AllocExtra = ();
     type FrameExtra = ();

     #[inline(always)]
     fn enforce_alignment(_memory_extra: &Self::MemoryExtra) -> bool {
         // We do not check for alignment to avoid having to carry an `Align`
         // in `ConstValue::ByRef`.
         false
     }

     #[inline(always)]
     fn force_int_for_alignment_check(_memory_extra: &Self::MemoryExtra) -> bool {
         // We do not support `force_int`.
         false
     }

     #[inline(always)]
     fn enforce_validity(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
         false // for now, we don't enforce validity
     }

     #[inline(always)]
     fn call_extra_fn(
         _ecx: &mut InterpCx<$mir, $tcx, Self>,
         fn_val: !,
         _args: &[OpTy<$tcx>],
         _ret: Option<(PlaceTy<$tcx>, mir::BasicBlock)>,
         _unwind: Option<mir::BasicBlock>,
     ) -> InterpResult<$tcx> {
         match fn_val {}
     }

     #[inline(always)]
     fn init_allocation_extra<'b>(
         _memory_extra: &Self::MemoryExtra,
         _id: AllocId,
         alloc: Cow<'b, Allocation>,
         _kind: Option<MemoryKind<!>>,
     ) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
         // We do not use a tag so we can just cheaply forward the allocation
         (alloc, ())
     }

     #[inline(always)]
     fn tag_global_base_pointer(
         _memory_extra: &Self::MemoryExtra,
         _id: AllocId,
     ) -> Self::PointerTag {
         ()
     }
 }
	//! This module contains everything needed to instantiate an interpreter.
	//! This separation exists to ensure that no fancy miri features like
	//! interpreting common C functions leak into CTFE.

	use std::borrow::{Borrow, Cow};
	use std::fmt::Debug;
	use std::hash::Hash;

	use rustc_middle::mir;
	use rustc_middle::ty::{self, Ty};
	use rustc_span::def_id::DefId;

	use super::{
	AllocId, Allocation, AllocationExtra, CheckInAllocMsg, Frame, ImmTy, InterpCx, InterpResult,
	LocalValue, MemPlace, Memory, MemoryKind, OpTy, Operand, PlaceTy, Pointer, Scalar,
	};

	/// Data returned by Machine::stack_pop,
	/// to provide further control over the popping of the stack frame
	#[derive(Eq, PartialEq, Debug, Copy, Clone)]
	pub enum StackPopJump {
	/// Indicates that no special handling should be
	/// done - we'll either return normally or unwind
	/// based on the terminator for the function
	/// we're leaving.
	Normal,

	/// Indicates that we should not jump to the return/unwind address, as the callback already
	/// took care of everything.
	NoJump,
	}

	/// Whether this kind of memory is allowed to leak
	pub trait MayLeak: Copy {
	fn may_leak(self) -> bool;
	}

	/// The functionality needed by memory to manage its allocations
	pub trait AllocMap<K: Hash + Eq, V> {
	/// Tests if the map contains the given key.
	/// Deliberately takes `&mut` because that is sufficient, and some implementations
	/// can be more efficient then (using `RefCell::get_mut`).
	fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
	where
	K: Borrow<Q>;

	/// Inserts a new entry into the map.
	fn insert(&mut self, k: K, v: V) -> Option<V>;

	/// Removes an entry from the map.
	fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
	where
	K: Borrow<Q>;

	/// Returns data based on the keys and values in the map.
	fn filter_map_collect<T>(&self, f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T>;

	/// Returns a reference to entry `k`. If no such entry exists, call
	/// `vacant` and either forward its error, or add its result to the map
	/// and return a reference to that.
	fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E>;

	/// Returns a mutable reference to entry `k`. If no such entry exists, call
	/// `vacant` and either forward its error, or add its result to the map
	/// and return a reference to that.
	fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E>;

	/// Read-only lookup.
	fn get(&self, k: K) -> Option<&V> {
	self.get_or(k, \|\| Err(())).ok()
	}

	/// Mutable lookup.
	fn get_mut(&mut self, k: K) -> Option<&mut V> {
	self.get_mut_or(k, \|\| Err(())).ok()
	}
	}

	/// Methods of this trait signifies a point where CTFE evaluation would fail
	/// and some use case dependent behaviour can instead be applied.
	pub trait Machine<'mir, 'tcx>: Sized {
	/// Additional memory kinds a machine wishes to distinguish from the builtin ones
	type MemoryKind: Debug + std::fmt::Display + MayLeak + Eq + 'static;

	/// Tag tracked alongside every pointer. This is used to implement "Stacked Borrows"
	/// <https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html>.
	/// The `default()` is used for pointers to consts, statics, vtables and functions.
	/// The `Debug` formatting is used for displaying pointers; we cannot use `Display`
	/// as `()` does not implement that, but it should be "nice" output.
	type PointerTag: Debug + Copy + Eq + Hash + 'static;

	/// Machines can define extra (non-instance) things that represent values of function pointers.
	/// For example, Miri uses this to return a function pointer from `dlsym`
	/// that can later be called to execute the right thing.
	type ExtraFnVal: Debug + Copy;

	/// Extra data stored in every call frame.
	type FrameExtra;

	/// Extra data stored in memory. A reference to this is available when `AllocExtra`
	/// gets initialized, so you can e.g., have an `Rc` here if there is global state you
	/// need access to in the `AllocExtra` hooks.
	type MemoryExtra;

	/// Extra data stored in every allocation.
	type AllocExtra: AllocationExtra<Self::PointerTag> + 'static;

	/// Memory's allocation map
	type MemoryMap: AllocMap<
	AllocId,
	(MemoryKind<Self::MemoryKind>, Allocation<Self::PointerTag, Self::AllocExtra>),
	> + Default
	+ Clone;

	/// The memory kind to use for copied global memory (held in `tcx`) --
	/// or None if such memory should not be mutated and thus any such attempt will cause
	/// a `ModifiedStatic` error to be raised.
	/// Statics are copied under two circumstances: When they are mutated, and when
	/// `tag_allocation` (see below) returns an owned allocation
	/// that is added to the memory so that the work is not done twice.
	const GLOBAL_KIND: Option<Self::MemoryKind>;

	/// Whether memory accesses should be alignment-checked.
	fn enforce_alignment(memory_extra: &Self::MemoryExtra) -> bool;

	/// Whether, when checking alignment, we should `force_int` and thus support
	/// custom alignment logic based on whatever the integer address happens to be.
	fn force_int_for_alignment_check(memory_extra: &Self::MemoryExtra) -> bool;

	/// Whether to enforce the validity invariant
	fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;

	/// Entry point to all function calls.
	///
	/// Returns either the mir to use for the call, or `None` if execution should
	/// just proceed (which usually means this hook did all the work that the
	/// called function should usually have done). In the latter case, it is
	/// this hook's responsibility to advance the instruction pointer!
	/// (This is to support functions like `__rust_maybe_catch_panic` that neither find a MIR
	/// nor just jump to `ret`, but instead push their own stack frame.)
	/// Passing `dest`and `ret` in the same `Option` proved very annoying when only one of them
	/// was used.
	fn find_mir_or_eval_fn(
	ecx: &mut InterpCx<'mir, 'tcx, Self>,
	instance: ty::Instance<'tcx>,
	args: &[OpTy<'tcx, Self::PointerTag>],
	ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
	unwind: Option<mir::BasicBlock>,
	) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>>;

	/// Execute `fn_val`. It is the hook's responsibility to advance the instruction
	/// pointer as appropriate.
	fn call_extra_fn(
	ecx: &mut InterpCx<'mir, 'tcx, Self>,
	fn_val: Self::ExtraFnVal,
	args: &[OpTy<'tcx, Self::PointerTag>],
	ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
	unwind: Option<mir::BasicBlock>,
	) -> InterpResult<'tcx>;

	/// Directly process an intrinsic without pushing a stack frame. It is the hook's
	/// responsibility to advance the instruction pointer as appropriate.
	fn call_intrinsic(
	ecx: &mut InterpCx<'mir, 'tcx, Self>,
	instance: ty::Instance<'tcx>,
	args: &[OpTy<'tcx, Self::PointerTag>],
	ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
	unwind: Option<mir::BasicBlock>,
	) -> InterpResult<'tcx>;

	/// Called to evaluate `Assert` MIR terminators that trigger a panic.
	fn assert_panic(
	ecx: &mut InterpCx<'mir, 'tcx, Self>,
	msg: &mir::AssertMessage<'tcx>,
	unwind: Option<mir::BasicBlock>,
	) -> InterpResult<'tcx>;

	/// Called to evaluate `Abort` MIR terminator.
	fn abort(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx, !> {
	throw_unsup_format!("aborting execution is not supported")
	}

	/// Called for all binary operations where the LHS has pointer type.
	///
	/// Returns a (value, overflowed) pair if the operation succeeded
	fn binary_ptr_op(
	ecx: &InterpCx<'mir, 'tcx, Self>,
	bin_op: mir::BinOp,
	left: ImmTy<'tcx, Self::PointerTag>,
	right: ImmTy<'tcx, Self::PointerTag>,
	) -> InterpResult<'tcx, (Scalar<Self::PointerTag>, bool, Ty<'tcx>)>;

	/// Heap allocations via the `box` keyword.
	fn box_alloc(
	ecx: &mut InterpCx<'mir, 'tcx, Self>,
	dest: PlaceTy<'tcx, Self::PointerTag>,
	) -> InterpResult<'tcx>;

	/// Called to read the specified `local` from the `frame`.
	/// Since reading a ZST is not actually accessing memory or locals, this is never invoked
	/// for ZST reads.
	#[inline]
	fn access_local(
	_ecx: &InterpCx<'mir, 'tcx, Self>,
	frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
	local: mir::Local,
	) -> InterpResult<'tcx, Operand<Self::PointerTag>> {
	frame.locals[local].access()
	}

	/// Called to write the specified `local` from the `frame`.
	/// Since writing a ZST is not actually accessing memory or locals, this is never invoked
	/// for ZST reads.
	#[inline]
	fn access_local_mut<'a>(
	ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
	frame: usize,
	local: mir::Local,
	) -> InterpResult<'tcx, Result<&'a mut LocalValue<Self::PointerTag>, MemPlace<Self::PointerTag>>>
	where
	'tcx: 'mir,
	{
	ecx.stack_mut()[frame].locals[local].access_mut()
	}

	/// Called before a basic block terminator is executed.
	/// You can use this to detect endlessly running programs.
	#[inline]
	fn before_terminator(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
	Ok(())
	}

	/// Called before a global allocation is accessed.
	/// `def_id` is `Some` if this is the "lazy" allocation of a static.
	#[inline]
	fn before_access_global(
	_memory_extra: &Self::MemoryExtra,
	_alloc_id: AllocId,
	_allocation: &Allocation,
	_static_def_id: Option<DefId>,
	_is_write: bool,
	) -> InterpResult<'tcx> {
	Ok(())
	}

	/// Return the `AllocId` for the given thread-local static in the current thread.
	fn thread_local_static_alloc_id(
	_ecx: &mut InterpCx<'mir, 'tcx, Self>,
	def_id: DefId,
	) -> InterpResult<'tcx, AllocId> {
	throw_unsup!(ThreadLocalStatic(def_id))
	}

	/// Return the `AllocId` backing the given `extern static`.
	fn extern_static_alloc_id(
	mem: &Memory<'mir, 'tcx, Self>,
	def_id: DefId,
	) -> InterpResult<'tcx, AllocId> {
	// Use the `AllocId` associated with the `DefId`. Any actual access will fail.
	Ok(mem.tcx.create_static_alloc(def_id))
	}

	/// Return the "base" tag for the given global allocation: the one that is used for direct
	/// accesses to this static/const/fn allocation. If `id` is not a global allocation,
	/// this will return an unusable tag (i.e., accesses will be UB)!
	///
	/// Called on the id returned by `thread_local_static_alloc_id` and `extern_static_alloc_id`, if needed.
	fn tag_global_base_pointer(memory_extra: &Self::MemoryExtra, id: AllocId) -> Self::PointerTag;

	/// Called to initialize the "extra" state of an allocation and make the pointers
	/// it contains (in relocations) tagged. The way we construct allocations is
	/// to always first construct it without extra and then add the extra.
	/// This keeps uniform code paths for handling both allocations created by CTFE
	/// for globals, and allocations created by Miri during evaluation.
	///
	/// `kind` is the kind of the allocation being tagged; it can be `None` when
	/// it's a global and `GLOBAL_KIND` is `None`.
	///
	/// This should avoid copying if no work has to be done! If this returns an owned
	/// allocation (because a copy had to be done to add tags or metadata), machine memory will
	/// cache the result. (This relies on `AllocMap::get_or` being able to add the
	/// owned allocation to the map even when the map is shared.)
	///
	/// Also return the "base" tag to use for this allocation: the one that is used for direct
	/// accesses to this allocation. If `kind == STATIC_KIND`, this tag must be consistent
	/// with `tag_global_base_pointer`.
	fn init_allocation_extra<'b>(
	memory_extra: &Self::MemoryExtra,
	id: AllocId,
	alloc: Cow<'b, Allocation>,
	kind: Option<MemoryKind<Self::MemoryKind>>,
	) -> (Cow<'b, Allocation<Self::PointerTag, Self::AllocExtra>>, Self::PointerTag);

	/// Called to notify the machine before a deallocation occurs.
	fn before_deallocation(
	_memory_extra: &mut Self::MemoryExtra,
	_id: AllocId,
	) -> InterpResult<'tcx> {
	Ok(())
	}

	/// Executes a retagging operation
	#[inline]
	fn retag(
	_ecx: &mut InterpCx<'mir, 'tcx, Self>,
	_kind: mir::RetagKind,
	_place: PlaceTy<'tcx, Self::PointerTag>,
	) -> InterpResult<'tcx> {
	Ok(())
	}

	/// Called immediately before a new stack frame gets pushed.
	fn init_frame_extra(
	ecx: &mut InterpCx<'mir, 'tcx, Self>,
	frame: Frame<'mir, 'tcx, Self::PointerTag>,
	) -> InterpResult<'tcx, Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>>;

	/// Borrow the current thread's stack.
	fn stack(
	ecx: &'a InterpCx<'mir, 'tcx, Self>,
	) -> &'a [Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>];

	/// Mutably borrow the current thread's stack.
	fn stack_mut(
	ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
	) -> &'a mut Vec<Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>>;

	/// Called immediately after a stack frame got pushed and its locals got initialized.
	fn after_stack_push(_ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
	Ok(())
	}

	/// Called immediately after a stack frame got popped, but before jumping back to the caller.
	fn after_stack_pop(
	_ecx: &mut InterpCx<'mir, 'tcx, Self>,
	_frame: Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
	_unwinding: bool,
	) -> InterpResult<'tcx, StackPopJump> {
	// By default, we do not support unwinding from panics
	Ok(StackPopJump::Normal)
	}

	fn int_to_ptr(
	_mem: &Memory<'mir, 'tcx, Self>,
	int: u64,
	) -> InterpResult<'tcx, Pointer<Self::PointerTag>> {
	Err((if int == 0 {
	// This is UB, seriously.
	err_ub!(DanglingIntPointer(0, CheckInAllocMsg::InboundsTest))
	} else {
	// This is just something we cannot support during const-eval.
	err_unsup!(ReadBytesAsPointer)
	})
	.into())
	}

	fn ptr_to_int(
	_mem: &Memory<'mir, 'tcx, Self>,
	_ptr: Pointer<Self::PointerTag>,
	) -> InterpResult<'tcx, u64>;
	}

	// A lot of the flexibility above is just needed for `Miri`, but all "compile-time" machines
	// (CTFE and ConstProp) use the same instance. Here, we share that code.
	pub macro compile_time_machine(<$mir: lifetime, $tcx: lifetime>) {
	type PointerTag = ();
	type ExtraFnVal = !;

	type MemoryKind = !;
	type MemoryMap = rustc_data_structures::fx::FxHashMap<AllocId, (MemoryKind<!>, Allocation)>;
	const GLOBAL_KIND: Option<!> = None; // no copying of globals from `tcx` to machine memory

	type AllocExtra = ();
	type FrameExtra = ();

	#[inline(always)]
	fn enforce_alignment(_memory_extra: &Self::MemoryExtra) -> bool {
	// We do not check for alignment to avoid having to carry an `Align`
	// in `ConstValue::ByRef`.
	false
	}

	#[inline(always)]
	fn force_int_for_alignment_check(_memory_extra: &Self::MemoryExtra) -> bool {
	// We do not support `force_int`.
	false
	}

	#[inline(always)]
	fn enforce_validity(_ecx: &InterpCx<$mir, $tcx, Self>) -> bool {
	false // for now, we don't enforce validity
	}

	#[inline(always)]
	fn call_extra_fn(
	_ecx: &mut InterpCx<$mir, $tcx, Self>,
	fn_val: !,
	_args: &[OpTy<$tcx>],
	_ret: Option<(PlaceTy<$tcx>, mir::BasicBlock)>,
	_unwind: Option<mir::BasicBlock>,
	) -> InterpResult<$tcx> {
	match fn_val {}
	}

	#[inline(always)]
	fn init_allocation_extra<'b>(
	_memory_extra: &Self::MemoryExtra,
	_id: AllocId,
	alloc: Cow<'b, Allocation>,
	_kind: Option<MemoryKind<!>>,
	) -> (Cow<'b, Allocation<Self::PointerTag>>, Self::PointerTag) {
	// We do not use a tag so we can just cheaply forward the allocation
	(alloc, ())
	}

	#[inline(always)]
	fn tag_global_base_pointer(
	_memory_extra: &Self::MemoryExtra,
	_id: AllocId,
	) -> Self::PointerTag {
	()
	}
	}