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