src/librustc_mir/interpret/machine.rs

   1 //! This module contains everything needed to instantiate an interpreter.
   2 //! This separation exists to ensure that no fancy miri features like
   3 //! interpreting common C functions leak into CTFE.
   4
   5 use std::borrow::{Borrow, Cow};
   6 use std::hash::Hash;
   7
   8 use rustc::hir::def_id::DefId;
   9 use rustc::mir;
  10 use rustc::ty::{self, Ty, TyCtxt};
  11 use syntax_pos::Span;
  12
  13 use super::{
  14     Allocation, AllocId, InterpResult, Scalar, AllocationExtra, AssertMessage,
  15     InterpCx, PlaceTy, OpTy, ImmTy, MemoryKind, Pointer, Memory,
  16     Frame, Operand,
  17 };
  18
  19 /// Data returned by Machine::stack_pop,
  20 /// to provide further control over the popping of the stack frame
  21 #[derive(Eq, PartialEq, Debug, Copy, Clone)]
  22 pub enum StackPopInfo {
  23     /// Indicates that no special handling should be
  24     /// done - we'll either return normally or unwind
  25     /// based on the terminator for the function
  26     /// we're leaving.
  27     Normal,
  28
  29     /// Indicates that we should stop unwinding,
  30     /// as we've reached a catch frame
  31     StopUnwinding
  32 }
  33
  34 /// Whether this kind of memory is allowed to leak
  35 pub trait MayLeak: Copy {
  36     fn may_leak(self) -> bool;
  37 }
  38
  39 /// The functionality needed by memory to manage its allocations
  40 pub trait AllocMap<K: Hash + Eq, V> {
  41     /// Tests if the map contains the given key.
  42     /// Deliberately takes `&mut` because that is sufficient, and some implementations
  43     /// can be more efficient then (using `RefCell::get_mut`).
  44     fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
  45         where K: Borrow<Q>;
  46
  47     /// Inserts a new entry into the map.
  48     fn insert(&mut self, k: K, v: V) -> Option<V>;
  49
  50     /// Removes an entry from the map.
  51     fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
  52         where K: Borrow<Q>;
  53
  54     /// Returns data based the keys and values in the map.
  55     fn filter_map_collect<T>(&self, f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T>;
  56
  57     /// Returns a reference to entry `k`. If no such entry exists, call
  58     /// `vacant` and either forward its error, or add its result to the map
  59     /// and return a reference to *that*.
  60     fn get_or<E>(
  61         &self,
  62         k: K,
  63         vacant: impl FnOnce() -> Result<V, E>
  64     ) -> Result<&V, E>;
  65
  66     /// Returns a mutable reference to entry `k`. If no such entry exists, call
  67     /// `vacant` and either forward its error, or add its result to the map
  68     /// and return a reference to *that*.
  69     fn get_mut_or<E>(
  70         &mut self,
  71         k: K,
  72         vacant: impl FnOnce() -> Result<V, E>
  73     ) -> Result<&mut V, E>;
  74
  75     /// Read-only lookup.
  76     fn get(&self, k: K) -> Option<&V> {
  77         self.get_or(k, || Err(())).ok()
  78     }
  79
  80     /// Mutable lookup.
  81     fn get_mut(&mut self, k: K) -> Option<&mut V> {
  82         self.get_mut_or(k, || Err(())).ok()
  83     }
  84 }
  85
  86 /// Methods of this trait signifies a point where CTFE evaluation would fail
  87 /// and some use case dependent behaviour can instead be applied.
  88 pub trait Machine<'mir, 'tcx>: Sized {
  89     /// Additional memory kinds a machine wishes to distinguish from the builtin ones
  90     type MemoryKinds: ::std::fmt::Debug + MayLeak + Eq + 'static;
  91
  92     /// Tag tracked alongside every pointer. This is used to implement "Stacked Borrows"
  93     /// <https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html>.
  94     /// The `default()` is used for pointers to consts, statics, vtables and functions.
  95     type PointerTag: ::std::fmt::Debug + Copy + Eq + Hash + 'static;
  96
  97     /// Machines can define extra (non-instance) things that represent values of function pointers.
  98     /// For example, Miri uses this to return a function pointer from `dlsym`
  99     /// that can later be called to execute the right thing.
 100     type ExtraFnVal: ::std::fmt::Debug + Copy;
 101
 102     /// Extra data stored in every call frame.
 103     type FrameExtra;
 104
 105     /// Extra data stored in memory. A reference to this is available when `AllocExtra`
 106     /// gets initialized, so you can e.g., have an `Rc` here if there is global state you
 107     /// need access to in the `AllocExtra` hooks.
 108     type MemoryExtra;
 109
 110     /// Extra data stored in every allocation.
 111     type AllocExtra: AllocationExtra<Self::PointerTag> + 'static;
 112
 113     /// Memory's allocation map
 114     type MemoryMap:
 115         AllocMap<
 116             AllocId,
 117             (MemoryKind<Self::MemoryKinds>, Allocation<Self::PointerTag, Self::AllocExtra>)
 118         > +
 119         Default +
 120         Clone;
 121
 122     /// The memory kind to use for copied statics -- or None if statics should not be mutated
 123     /// and thus any such attempt will cause a `ModifiedStatic` error to be raised.
 124     /// Statics are copied under two circumstances: When they are mutated, and when
 125     /// `tag_allocation` or `find_foreign_static` (see below) returns an owned allocation
 126     /// that is added to the memory so that the work is not done twice.
 127     const STATIC_KIND: Option<Self::MemoryKinds>;
 128
 129     /// Whether memory accesses should be alignment-checked.
 130     const CHECK_ALIGN: bool;
 131
 132     /// Whether to enforce the validity invariant
 133     fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>) -> bool;
 134
 135     /// Called before a basic block terminator is executed.
 136     /// You can use this to detect endlessly running programs.
 137     fn before_terminator(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx>;
 138
 139     /// Entry point to all function calls.
 140     ///
 141     /// Returns either the mir to use for the call, or `None` if execution should
 142     /// just proceed (which usually means this hook did all the work that the
 143     /// called function should usually have done). In the latter case, it is
 144     /// this hook's responsibility to advance the instruction pointer!
 145     /// (This is to support functions like `__rust_maybe_catch_panic` that neither find a MIR
 146     /// nor just jump to `ret`, but instead push their own stack frame.)
 147     /// Passing `dest`and `ret` in the same `Option` proved very annoying when only one of them
 148     /// was used.
 149     fn find_mir_or_eval_fn(
 150         ecx: &mut InterpCx<'mir, 'tcx, Self>,
 151         instance: ty::Instance<'tcx>,
 152         args: &[OpTy<'tcx, Self::PointerTag>],
 153         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
 154         unwind: Option<mir::BasicBlock>,
 155     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>>;
 156
 157     /// Execute `fn_val`.  It is the hook's responsibility to advance the instruction
 158     /// pointer as appropriate.
 159     fn call_extra_fn(
 160         ecx: &mut InterpCx<'mir, 'tcx, Self>,
 161         fn_val: Self::ExtraFnVal,
 162         args: &[OpTy<'tcx, Self::PointerTag>],
 163         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
 164         unwind: Option<mir::BasicBlock>,
 165     ) -> InterpResult<'tcx>;
 166
 167     /// Directly process an intrinsic without pushing a stack frame. It is the hook's
 168     /// responsibility to advance the instruction pointer as appropriate.
 169     fn call_intrinsic(
 170         ecx: &mut InterpCx<'mir, 'tcx, Self>,
 171         span: Span,
 172         instance: ty::Instance<'tcx>,
 173         args: &[OpTy<'tcx, Self::PointerTag>],
 174         ret: Option<(PlaceTy<'tcx, Self::PointerTag>, mir::BasicBlock)>,
 175         unwind: Option<mir::BasicBlock>,
 176     ) -> InterpResult<'tcx>;
 177
 178     /// Called to evaluate `Assert` MIR terminators that trigger a panic.
 179     fn assert_panic(
 180         ecx: &mut InterpCx<'mir, 'tcx, Self>,
 181         span: Span,
 182         msg: &AssertMessage<'tcx>,
 183         unwind: Option<mir::BasicBlock>,
 184     ) -> InterpResult<'tcx>;
 185
 186     /// Called for read access to a foreign static item.
 187     ///
 188     /// This will only be called once per static and machine; the result is cached in
 189     /// the machine memory. (This relies on `AllocMap::get_or` being able to add the
 190     /// owned allocation to the map even when the map is shared.)
 191     ///
 192     /// This allocation will then be fed to `tag_allocation` to initialize the "extra" state.
 193     fn find_foreign_static(
 194         tcx: TyCtxt<'tcx>,
 195         def_id: DefId,
 196     ) -> InterpResult<'tcx, Cow<'tcx, Allocation>>;
 197
 198     /// Called for all binary operations where the LHS has pointer type.
 199     ///
 200     /// Returns a (value, overflowed) pair if the operation succeeded
 201     fn binary_ptr_op(
 202         ecx: &InterpCx<'mir, 'tcx, Self>,
 203         bin_op: mir::BinOp,
 204         left: ImmTy<'tcx, Self::PointerTag>,
 205         right: ImmTy<'tcx, Self::PointerTag>,
 206     ) -> InterpResult<'tcx, (Scalar<Self::PointerTag>, bool, Ty<'tcx>)>;
 207
 208     /// Heap allocations via the `box` keyword.
 209     fn box_alloc(
 210         ecx: &mut InterpCx<'mir, 'tcx, Self>,
 211         dest: PlaceTy<'tcx, Self::PointerTag>,
 212     ) -> InterpResult<'tcx>;
 213
 214     /// Called to read the specified `local` from the `frame`.
 215     fn access_local(
 216         _ecx: &InterpCx<'mir, 'tcx, Self>,
 217         frame: &Frame<'mir, 'tcx, Self::PointerTag, Self::FrameExtra>,
 218         local: mir::Local,
 219     ) -> InterpResult<'tcx, Operand<Self::PointerTag>> {
 220         frame.locals[local].access()
 221     }
 222
 223     /// Called before a `StaticKind::Static` value is accessed.
 224     fn before_access_static(
 225         _allocation: &Allocation,
 226     ) -> InterpResult<'tcx> {
 227         Ok(())
 228     }
 229
 230     /// Called to initialize the "extra" state of an allocation and make the pointers
 231     /// it contains (in relocations) tagged.  The way we construct allocations is
 232     /// to always first construct it without extra and then add the extra.
 233     /// This keeps uniform code paths for handling both allocations created by CTFE
 234     /// for statics, and allocations ceated by Miri during evaluation.
 235     ///
 236     /// `kind` is the kind of the allocation being tagged; it can be `None` when
 237     /// it's a static and `STATIC_KIND` is `None`.
 238     ///
 239     /// This should avoid copying if no work has to be done! If this returns an owned
 240     /// allocation (because a copy had to be done to add tags or metadata), machine memory will
 241     /// cache the result. (This relies on `AllocMap::get_or` being able to add the
 242     /// owned allocation to the map even when the map is shared.)
 243     ///
 244     /// Also return the "base" tag to use for this allocation: the one that is used for direct
 245     /// accesses to this allocation. If `kind == STATIC_KIND`, this tag must be consistent
 246     /// with `tag_static_base_pointer`.
 247     fn init_allocation_extra<'b>(
 248         memory_extra: &Self::MemoryExtra,
 249         id: AllocId,
 250         alloc: Cow<'b, Allocation>,
 251         kind: Option<MemoryKind<Self::MemoryKinds>>,
 252     ) -> (Cow<'b, Allocation<Self::PointerTag, Self::AllocExtra>>, Self::PointerTag);
 253
 254     /// Return the "base" tag for the given *static* allocation: the one that is used for direct
 255     /// accesses to this static/const/fn allocation. If `id` is not a static allocation,
 256     /// this will return an unusable tag (i.e., accesses will be UB)!
 257     fn tag_static_base_pointer(
 258         memory_extra: &Self::MemoryExtra,
 259         id: AllocId,
 260     ) -> Self::PointerTag;
 261
 262     /// Executes a retagging operation
 263     #[inline]
 264     fn retag(
 265         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
 266         _kind: mir::RetagKind,
 267         _place: PlaceTy<'tcx, Self::PointerTag>,
 268     ) -> InterpResult<'tcx> {
 269         Ok(())
 270     }
 271
 272     /// Called immediately before a new stack frame got pushed
 273     fn stack_push(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx, Self::FrameExtra>;
 274
 275     /// Called immediately after a stack frame gets popped
 276     fn stack_pop(
 277         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
 278         _extra: Self::FrameExtra,
 279         _unwinding: bool
 280     ) -> InterpResult<'tcx, StackPopInfo> {
 281         // By default, we do not support unwinding from panics
 282         Ok(StackPopInfo::Normal)
 283     }
 284
 285     fn int_to_ptr(
 286         _mem: &Memory<'mir, 'tcx, Self>,
 287         int: u64,
 288     ) -> InterpResult<'tcx, Pointer<Self::PointerTag>> {
 289         Err((if int == 0 {
 290             err_unsup!(InvalidNullPointerUsage)
 291         } else {
 292             err_unsup!(ReadBytesAsPointer)
 293         }).into())
 294     }
 295
 296     fn ptr_to_int(
 297         _mem: &Memory<'mir, 'tcx, Self>,
 298         _ptr: Pointer<Self::PointerTag>,
 299     ) -> InterpResult<'tcx, u64>;
 300 }