src/librustc_mir/interpret/validity.rs

   1 //! Check the validity invariant of a given value, and tell the user
   2 //! where in the value it got violated.
   3 //! In const context, this goes even further and tries to approximate const safety.
   4 //! That's useful because it means other passes (e.g. promotion) can rely on `const`s
   5 //! to be const-safe.
   6
   7 use std::fmt::Write;
   8 use std::ops::RangeInclusive;
   9
  10 use rustc::hir;
  11 use rustc::ty;
  12 use rustc::ty::layout::{self, LayoutOf, TyLayout, VariantIdx};
  13 use rustc_data_structures::fx::FxHashSet;
  14 use syntax_pos::symbol::{sym, Symbol};
  15
  16 use std::hash::Hash;
  17
  18 use super::{
  19     CheckInAllocMsg, GlobalAlloc, InterpCx, InterpResult, MPlaceTy, Machine, OpTy, Scalar,
  20     ValueVisitor,
  21 };
  22
  23 macro_rules! throw_validation_failure {
  24     ($what:expr, $where:expr, $details:expr) => {{
  25         let mut msg = format!("encountered {}", $what);
  26         let where_ = &$where;
  27         if !where_.is_empty() {
  28             msg.push_str(" at ");
  29             write_path(&mut msg, where_);
  30         }
  31         write!(&mut msg, ", but expected {}", $details).unwrap();
  32         throw_unsup!(ValidationFailure(msg))
  33     }};
  34     ($what:expr, $where:expr) => {{
  35         let mut msg = format!("encountered {}", $what);
  36         let where_ = &$where;
  37         if !where_.is_empty() {
  38             msg.push_str(" at ");
  39             write_path(&mut msg, where_);
  40         }
  41         throw_unsup!(ValidationFailure(msg))
  42     }};
  43 }
  44
  45 macro_rules! try_validation {
  46     ($e:expr, $what:expr, $where:expr, $details:expr) => {{
  47         match $e {
  48             Ok(x) => x,
  49             Err(_) => throw_validation_failure!($what, $where, $details),
  50         }
  51     }};
  52
  53     ($e:expr, $what:expr, $where:expr) => {{
  54         match $e {
  55             Ok(x) => x,
  56             Err(_) => throw_validation_failure!($what, $where),
  57         }
  58     }};
  59 }
  60
  61 /// We want to show a nice path to the invalid field for diagnostics,
  62 /// but avoid string operations in the happy case where no error happens.
  63 /// So we track a `Vec<PathElem>` where `PathElem` contains all the data we
  64 /// need to later print something for the user.
  65 #[derive(Copy, Clone, Debug)]
  66 pub enum PathElem {
  67     Field(Symbol),
  68     Variant(Symbol),
  69     GeneratorState(VariantIdx),
  70     ClosureVar(Symbol),
  71     ArrayElem(usize),
  72     TupleElem(usize),
  73     Deref,
  74     Tag,
  75     DynDowncast,
  76 }
  77
  78 /// State for tracking recursive validation of references
  79 pub struct RefTracking<T, PATH = ()> {
  80     pub seen: FxHashSet<T>,
  81     pub todo: Vec<(T, PATH)>,
  82 }
  83
  84 impl<T: Copy + Eq + Hash + std::fmt::Debug, PATH: Default> RefTracking<T, PATH> {
  85     pub fn empty() -> Self {
  86         RefTracking { seen: FxHashSet::default(), todo: vec![] }
  87     }
  88     pub fn new(op: T) -> Self {
  89         let mut ref_tracking_for_consts =
  90             RefTracking { seen: FxHashSet::default(), todo: vec![(op, PATH::default())] };
  91         ref_tracking_for_consts.seen.insert(op);
  92         ref_tracking_for_consts
  93     }
  94
  95     pub fn track(&mut self, op: T, path: impl FnOnce() -> PATH) {
  96         if self.seen.insert(op) {
  97             trace!("Recursing below ptr {:#?}", op);
  98             let path = path();
  99             // Remember to come back to this later.
 100             self.todo.push((op, path));
 101         }
 102     }
 103 }
 104
 105 /// Format a path
 106 fn write_path(out: &mut String, path: &Vec<PathElem>) {
 107     use self::PathElem::*;
 108
 109     for elem in path.iter() {
 110         match elem {
 111             Field(name) => write!(out, ".{}", name),
 112             Variant(name) => write!(out, ".<downcast-variant({})>", name),
 113             GeneratorState(idx) => write!(out, ".<generator-state({})>", idx.index()),
 114             ClosureVar(name) => write!(out, ".<closure-var({})>", name),
 115             TupleElem(idx) => write!(out, ".{}", idx),
 116             ArrayElem(idx) => write!(out, "[{}]", idx),
 117             Deref =>
 118             // This does not match Rust syntax, but it is more readable for long paths -- and
 119             // some of the other items here also are not Rust syntax.  Actually we can't
 120             // even use the usual syntax because we are just showing the projections,
 121             // not the root.
 122             {
 123                 write!(out, ".<deref>")
 124             }
 125             Tag => write!(out, ".<enum-tag>"),
 126             DynDowncast => write!(out, ".<dyn-downcast>"),
 127         }
 128         .unwrap()
 129     }
 130 }
 131
 132 // Test if a range that wraps at overflow contains `test`
 133 fn wrapping_range_contains(r: &RangeInclusive<u128>, test: u128) -> bool {
 134     let (lo, hi) = r.clone().into_inner();
 135     if lo > hi {
 136         // Wrapped
 137         (..=hi).contains(&test) || (lo..).contains(&test)
 138     } else {
 139         // Normal
 140         r.contains(&test)
 141     }
 142 }
 143
 144 // Formats such that a sentence like "expected something {}" to mean
 145 // "expected something <in the given range>" makes sense.
 146 fn wrapping_range_format(r: &RangeInclusive<u128>, max_hi: u128) -> String {
 147     let (lo, hi) = r.clone().into_inner();
 148     debug_assert!(hi <= max_hi);
 149     if lo > hi {
 150         format!("less or equal to {}, or greater or equal to {}", hi, lo)
 151     } else if lo == hi {
 152         format!("equal to {}", lo)
 153     } else if lo == 0 {
 154         debug_assert!(hi < max_hi, "should not be printing if the range covers everything");
 155         format!("less or equal to {}", hi)
 156     } else if hi == max_hi {
 157         debug_assert!(lo > 0, "should not be printing if the range covers everything");
 158         format!("greater or equal to {}", lo)
 159     } else {
 160         format!("in the range {:?}", r)
 161     }
 162 }
 163
 164 struct ValidityVisitor<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> {
 165     /// The `path` may be pushed to, but the part that is present when a function
 166     /// starts must not be changed!  `visit_fields` and `visit_array` rely on
 167     /// this stack discipline.
 168     path: Vec<PathElem>,
 169     ref_tracking_for_consts:
 170         Option<&'rt mut RefTracking<MPlaceTy<'tcx, M::PointerTag>, Vec<PathElem>>>,
 171     ecx: &'rt InterpCx<'mir, 'tcx, M>,
 172 }
 173
 174 impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, 'tcx, M> {
 175     fn aggregate_field_path_elem(&mut self, layout: TyLayout<'tcx>, field: usize) -> PathElem {
 176         match layout.ty.kind {
 177             // generators and closures.
 178             ty::Closure(def_id, _) | ty::Generator(def_id, _, _) => {
 179                 let mut name = None;
 180                 if def_id.is_local() {
 181                     let tables = self.ecx.tcx.typeck_tables_of(def_id);
 182                     if let Some(upvars) = tables.upvar_list.get(&def_id) {
 183                         // Sometimes the index is beyond the number of upvars (seen
 184                         // for a generator).
 185                         if let Some((&var_hir_id, _)) = upvars.get_index(field) {
 186                             let node = self.ecx.tcx.hir().get(var_hir_id);
 187                             if let hir::Node::Binding(pat) = node {
 188                                 if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
 189                                     name = Some(ident.name);
 190                                 }
 191                             }
 192                         }
 193                     }
 194                 }
 195
 196                 PathElem::ClosureVar(name.unwrap_or_else(|| {
 197                     // Fall back to showing the field index.
 198                     sym::integer(field)
 199                 }))
 200             }
 201
 202             // tuples
 203             ty::Tuple(_) => PathElem::TupleElem(field),
 204
 205             // enums
 206             ty::Adt(def, ..) if def.is_enum() => {
 207                 // we might be projecting *to* a variant, or to a field *in*a variant.
 208                 match layout.variants {
 209                     layout::Variants::Single { index } =>
 210                     // Inside a variant
 211                     {
 212                         PathElem::Field(def.variants[index].fields[field].ident.name)
 213                     }
 214                     _ => bug!(),
 215                 }
 216             }
 217
 218             // other ADTs
 219             ty::Adt(def, _) => PathElem::Field(def.non_enum_variant().fields[field].ident.name),
 220
 221             // arrays/slices
 222             ty::Array(..) | ty::Slice(..) => PathElem::ArrayElem(field),
 223
 224             // dyn traits
 225             ty::Dynamic(..) => PathElem::DynDowncast,
 226
 227             // nothing else has an aggregate layout
 228             _ => bug!("aggregate_field_path_elem: got non-aggregate type {:?}", layout.ty),
 229         }
 230     }
 231
 232     fn visit_elem(
 233         &mut self,
 234         new_op: OpTy<'tcx, M::PointerTag>,
 235         elem: PathElem,
 236     ) -> InterpResult<'tcx> {
 237         // Remember the old state
 238         let path_len = self.path.len();
 239         // Perform operation
 240         self.path.push(elem);
 241         self.visit_value(new_op)?;
 242         // Undo changes
 243         self.path.truncate(path_len);
 244         Ok(())
 245     }
 246
 247     fn check_wide_ptr_meta(
 248         &mut self,
 249         meta: Option<Scalar<M::PointerTag>>,
 250         pointee: TyLayout<'tcx>,
 251     ) -> InterpResult<'tcx> {
 252         let tail = self.ecx.tcx.struct_tail_erasing_lifetimes(pointee.ty, self.ecx.param_env);
 253         match tail.kind {
 254             ty::Dynamic(..) => {
 255                 let vtable = meta.unwrap();
 256                 try_validation!(
 257                     self.ecx.memory.check_ptr_access(
 258                         vtable,
 259                         3 * self.ecx.tcx.data_layout.pointer_size, // drop, size, align
 260                         self.ecx.tcx.data_layout.pointer_align.abi,
 261                     ),
 262                     "dangling or unaligned vtable pointer in wide pointer or too small vtable",
 263                     self.path
 264                 );
 265                 try_validation!(
 266                     self.ecx.read_drop_type_from_vtable(vtable),
 267                     "invalid drop fn in vtable",
 268                     self.path
 269                 );
 270                 try_validation!(
 271                     self.ecx.read_size_and_align_from_vtable(vtable),
 272                     "invalid size or align in vtable",
 273                     self.path
 274                 );
 275                 // FIXME: More checks for the vtable.
 276             }
 277             ty::Slice(..) | ty::Str => {
 278                 let _len = try_validation!(
 279                     meta.unwrap().to_machine_usize(self.ecx),
 280                     "non-integer slice length in wide pointer",
 281                     self.path
 282                 );
 283                 // We do not check that `len * elem_size <= isize::MAX`:
 284                 // that is only required for references, and there it falls out of the
 285                 // "dereferenceable" check performed by Stacked Borrows.
 286             }
 287             ty::Foreign(..) => {
 288                 // Unsized, but not wide.
 289             }
 290             _ => bug!("Unexpected unsized type tail: {:?}", tail),
 291         }
 292
 293         Ok(())
 294     }
 295 }
 296
 297 impl<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
 298     for ValidityVisitor<'rt, 'mir, 'tcx, M>
 299 {
 300     type V = OpTy<'tcx, M::PointerTag>;
 301
 302     #[inline(always)]
 303     fn ecx(&self) -> &InterpCx<'mir, 'tcx, M> {
 304         &self.ecx
 305     }
 306
 307     #[inline]
 308     fn visit_field(
 309         &mut self,
 310         old_op: OpTy<'tcx, M::PointerTag>,
 311         field: usize,
 312         new_op: OpTy<'tcx, M::PointerTag>,
 313     ) -> InterpResult<'tcx> {
 314         let elem = self.aggregate_field_path_elem(old_op.layout, field);
 315         self.visit_elem(new_op, elem)
 316     }
 317
 318     #[inline]
 319     fn visit_variant(
 320         &mut self,
 321         old_op: OpTy<'tcx, M::PointerTag>,
 322         variant_id: VariantIdx,
 323         new_op: OpTy<'tcx, M::PointerTag>,
 324     ) -> InterpResult<'tcx> {
 325         let name = match old_op.layout.ty.kind {
 326             ty::Adt(adt, _) => PathElem::Variant(adt.variants[variant_id].ident.name),
 327             // Generators also have variants
 328             ty::Generator(..) => PathElem::GeneratorState(variant_id),
 329             _ => bug!("Unexpected type with variant: {:?}", old_op.layout.ty),
 330         };
 331         self.visit_elem(new_op, name)
 332     }
 333
 334     #[inline]
 335     fn visit_value(&mut self, op: OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx> {
 336         trace!("visit_value: {:?}, {:?}", *op, op.layout);
 337         // Translate some possible errors to something nicer.
 338         match self.walk_value(op) {
 339             Ok(()) => Ok(()),
 340             Err(err) => match err.kind {
 341                 err_ub!(InvalidDiscriminant(val)) => {
 342                     throw_validation_failure!(val, self.path, "a valid enum discriminant")
 343                 }
 344                 err_unsup!(ReadPointerAsBytes) => {
 345                     throw_validation_failure!("a pointer", self.path, "plain (non-pointer) bytes")
 346                 }
 347                 _ => Err(err),
 348             },
 349         }
 350     }
 351
 352     fn visit_primitive(&mut self, value: OpTy<'tcx, M::PointerTag>) -> InterpResult<'tcx> {
 353         let value = self.ecx.read_immediate(value)?;
 354         // Go over all the primitive types
 355         let ty = value.layout.ty;
 356         match ty.kind {
 357             ty::Bool => {
 358                 let value = value.to_scalar_or_undef();
 359                 try_validation!(value.to_bool(), value, self.path, "a boolean");
 360             }
 361             ty::Char => {
 362                 let value = value.to_scalar_or_undef();
 363                 try_validation!(value.to_char(), value, self.path, "a valid unicode codepoint");
 364             }
 365             ty::Float(_) | ty::Int(_) | ty::Uint(_) => {
 366                 // NOTE: Keep this in sync with the array optimization for int/float
 367                 // types below!
 368                 let size = value.layout.size;
 369                 let value = value.to_scalar_or_undef();
 370                 if self.ref_tracking_for_consts.is_some() {
 371                     // Integers/floats in CTFE: Must be scalar bits, pointers are dangerous
 372                     try_validation!(
 373                         value.to_bits(size),
 374                         value,
 375                         self.path,
 376                         "initialized plain (non-pointer) bytes"
 377                     );
 378                 } else {
 379                     // At run-time, for now, we accept *anything* for these types, including
 380                     // undef. We should fix that, but let's start low.
 381                 }
 382             }
 383             ty::RawPtr(..) => {
 384                 // We are conservative with undef for integers, but try to
 385                 // actually enforce our current rules for raw pointers.
 386                 let place =
 387                     try_validation!(self.ecx.ref_to_mplace(value), "undefined pointer", self.path);
 388                 if place.layout.is_unsized() {
 389                     self.check_wide_ptr_meta(place.meta, place.layout)?;
 390                 }
 391             }
 392             _ if ty.is_box() || ty.is_region_ptr() => {
 393                 // Handle wide pointers.
 394                 // Check metadata early, for better diagnostics
 395                 let place =
 396                     try_validation!(self.ecx.ref_to_mplace(value), "undefined pointer", self.path);
 397                 if place.layout.is_unsized() {
 398                     self.check_wide_ptr_meta(place.meta, place.layout)?;
 399                 }
 400                 // Make sure this is dereferenceable and all.
 401                 let (size, align) = self
 402                     .ecx
 403                     .size_and_align_of(place.meta, place.layout)?
 404                     // for the purpose of validity, consider foreign types to have
 405                     // alignment and size determined by the layout (size will be 0,
 406                     // alignment should take attributes into account).
 407                     .unwrap_or_else(|| (place.layout.size, place.layout.align.abi));
 408                 let ptr: Option<_> = match self.ecx.memory.check_ptr_access_align(
 409                     place.ptr,
 410                     size,
 411                     Some(align),
 412                     CheckInAllocMsg::InboundsTest,
 413                 ) {
 414                     Ok(ptr) => ptr,
 415                     Err(err) => {
 416                         info!(
 417                             "{:?} did not pass access check for size {:?}, align {:?}",
 418                             place.ptr, size, align
 419                         );
 420                         match err.kind {
 421                             err_unsup!(InvalidNullPointerUsage) => {
 422                                 throw_validation_failure!("NULL reference", self.path)
 423                             }
 424                             err_unsup!(AlignmentCheckFailed { required, has }) => {
 425                                 throw_validation_failure!(
 426                                     format_args!(
 427                                         "unaligned reference \
 428                                     (required {} byte alignment but found {})",
 429                                         required.bytes(),
 430                                         has.bytes()
 431                                     ),
 432                                     self.path
 433                                 )
 434                             }
 435                             err_unsup!(ReadBytesAsPointer) => throw_validation_failure!(
 436                                 "dangling reference (created from integer)",
 437                                 self.path
 438                             ),
 439                             _ => throw_validation_failure!(
 440                                 "dangling reference (not entirely in bounds)",
 441                                 self.path
 442                             ),
 443                         }
 444                     }
 445                 };
 446                 // Recursive checking
 447                 if let Some(ref mut ref_tracking) = self.ref_tracking_for_consts {
 448                     if let Some(ptr) = ptr {
 449                         // not a ZST
 450                         // Skip validation entirely for some external statics
 451                         let alloc_kind = self.ecx.tcx.alloc_map.lock().get(ptr.alloc_id);
 452                         if let Some(GlobalAlloc::Static(did)) = alloc_kind {
 453                             // `extern static` cannot be validated as they have no body.
 454                             // FIXME: Statics from other crates are also skipped.
 455                             // They might be checked at a different type, but for now we
 456                             // want to avoid recursing too deeply.  This is not sound!
 457                             if !did.is_local() || self.ecx.tcx.is_foreign_item(did) {
 458                                 return Ok(());
 459                             }
 460                         }
 461                     }
 462                     // Proceed recursively even for ZST, no reason to skip them!
 463                     // `!` is a ZST and we want to validate it.
 464                     // Normalize before handing `place` to tracking because that will
 465                     // check for duplicates.
 466                     let place = if size.bytes() > 0 {
 467                         self.ecx.force_mplace_ptr(place).expect("we already bounds-checked")
 468                     } else {
 469                         place
 470                     };
 471                     let path = &self.path;
 472                     ref_tracking.track(place, || {
 473                         // We need to clone the path anyway, make sure it gets created
 474                         // with enough space for the additional `Deref`.
 475                         let mut new_path = Vec::with_capacity(path.len() + 1);
 476                         new_path.clone_from(path);
 477                         new_path.push(PathElem::Deref);
 478                         new_path
 479                     });
 480                 }
 481             }
 482             ty::FnPtr(_sig) => {
 483                 let value = value.to_scalar_or_undef();
 484                 let _fn = try_validation!(
 485                     value.not_undef().and_then(|ptr| self.ecx.memory.get_fn(ptr)),
 486                     value,
 487                     self.path,
 488                     "a function pointer"
 489                 );
 490                 // FIXME: Check if the signature matches
 491             }
 492             // This should be all the primitive types
 493             _ => bug!("Unexpected primitive type {}", value.layout.ty),
 494         }
 495         Ok(())
 496     }
 497
 498     fn visit_uninhabited(&mut self) -> InterpResult<'tcx> {
 499         throw_validation_failure!("a value of an uninhabited type", self.path)
 500     }
 501
 502     fn visit_scalar(
 503         &mut self,
 504         op: OpTy<'tcx, M::PointerTag>,
 505         layout: &layout::Scalar,
 506     ) -> InterpResult<'tcx> {
 507         let value = self.ecx.read_scalar(op)?;
 508         // Determine the allowed range
 509         let (lo, hi) = layout.valid_range.clone().into_inner();
 510         // `max_hi` is as big as the size fits
 511         let max_hi = u128::max_value() >> (128 - op.layout.size.bits());
 512         assert!(hi <= max_hi);
 513         // We could also write `(hi + 1) % (max_hi + 1) == lo` but `max_hi + 1` overflows for `u128`
 514         if (lo == 0 && hi == max_hi) || (hi + 1 == lo) {
 515             // Nothing to check
 516             return Ok(());
 517         }
 518         // At least one value is excluded. Get the bits.
 519         let value = try_validation!(
 520             value.not_undef(),
 521             value,
 522             self.path,
 523             format_args!("something {}", wrapping_range_format(&layout.valid_range, max_hi),)
 524         );
 525         let bits = match value.to_bits_or_ptr(op.layout.size, self.ecx) {
 526             Err(ptr) => {
 527                 if lo == 1 && hi == max_hi {
 528                     // Only NULL is the niche.  So make sure the ptr is NOT NULL.
 529                     if self.ecx.memory.ptr_may_be_null(ptr) {
 530                         throw_validation_failure!(
 531                             "a potentially NULL pointer",
 532                             self.path,
 533                             format_args!(
 534                                 "something that cannot possibly fail to be {}",
 535                                 wrapping_range_format(&layout.valid_range, max_hi)
 536                             )
 537                         )
 538                     }
 539                     return Ok(());
 540                 } else {
 541                     // Conservatively, we reject, because the pointer *could* have a bad
 542                     // value.
 543                     throw_validation_failure!(
 544                         "a pointer",
 545                         self.path,
 546                         format_args!(
 547                             "something that cannot possibly fail to be {}",
 548                             wrapping_range_format(&layout.valid_range, max_hi)
 549                         )
 550                     )
 551                 }
 552             }
 553             Ok(data) => data,
 554         };
 555         // Now compare. This is slightly subtle because this is a special "wrap-around" range.
 556         if wrapping_range_contains(&layout.valid_range, bits) {
 557             Ok(())
 558         } else {
 559             throw_validation_failure!(
 560                 bits,
 561                 self.path,
 562                 format_args!("something {}", wrapping_range_format(&layout.valid_range, max_hi))
 563             )
 564         }
 565     }
 566
 567     fn visit_aggregate(
 568         &mut self,
 569         op: OpTy<'tcx, M::PointerTag>,
 570         fields: impl Iterator<Item = InterpResult<'tcx, Self::V>>,
 571     ) -> InterpResult<'tcx> {
 572         match op.layout.ty.kind {
 573             ty::Str => {
 574                 let mplace = op.assert_mem_place(); // strings are never immediate
 575                 try_validation!(
 576                     self.ecx.read_str(mplace),
 577                     "uninitialized or non-UTF-8 data in str",
 578                     self.path
 579                 );
 580             }
 581             ty::Array(tys, ..) | ty::Slice(tys)
 582                 if {
 583                     // This optimization applies for types that can hold arbitrary bytes (such as
 584                     // integer and floating point types) or for structs or tuples with no fields.
 585                     // FIXME(wesleywiser) This logic could be extended further to arbitrary structs
 586                     // or tuples made up of integer/floating point types or inhabited ZSTs with no
 587                     // padding.
 588                     match tys.kind {
 589                         ty::Int(..) | ty::Uint(..) | ty::Float(..) => true,
 590                         ty::Tuple(tys) if tys.len() == 0 => true,
 591                         ty::Adt(adt_def, _)
 592                             if adt_def.is_struct() && adt_def.all_fields().next().is_none() =>
 593                         {
 594                             true
 595                         }
 596                         _ => false,
 597                     }
 598                 } =>
 599             {
 600                 // Optimized handling for arrays of integer/float type.
 601
 602                 // bailing out for zsts is ok, since the array element type can only be int/float
 603                 if op.layout.is_zst() {
 604                     return Ok(());
 605                 }
 606                 // non-ZST array cannot be immediate, slices are never immediate
 607                 let mplace = op.assert_mem_place();
 608                 // This is the length of the array/slice.
 609                 let len = mplace.len(self.ecx)?;
 610                 // zero length slices have nothing to be checked
 611                 if len == 0 {
 612                     return Ok(());
 613                 }
 614                 // This is the element type size.
 615                 let ty_size = self.ecx.layout_of(tys)?.size;
 616                 // This is the size in bytes of the whole array.
 617                 let size = ty_size * len;
 618                 // Size is not 0, get a pointer.
 619                 let ptr = self.ecx.force_ptr(mplace.ptr)?;
 620
 621                 // Optimization: we just check the entire range at once.
 622                 // NOTE: Keep this in sync with the handling of integer and float
 623                 // types above, in `visit_primitive`.
 624                 // In run-time mode, we accept pointers in here.  This is actually more
 625                 // permissive than a per-element check would be, e.g., we accept
 626                 // an &[u8] that contains a pointer even though bytewise checking would
 627                 // reject it.  However, that's good: We don't inherently want
 628                 // to reject those pointers, we just do not have the machinery to
 629                 // talk about parts of a pointer.
 630                 // We also accept undef, for consistency with the slow path.
 631                 match self.ecx.memory.get_raw(ptr.alloc_id)?.check_bytes(
 632                     self.ecx,
 633                     ptr,
 634                     size,
 635                     /*allow_ptr_and_undef*/ self.ref_tracking_for_consts.is_none(),
 636                 ) {
 637                     // In the happy case, we needn't check anything else.
 638                     Ok(()) => {}
 639                     // Some error happened, try to provide a more detailed description.
 640                     Err(err) => {
 641                         // For some errors we might be able to provide extra information
 642                         match err.kind {
 643                             err_unsup!(ReadUndefBytes(offset)) => {
 644                                 // Some byte was undefined, determine which
 645                                 // element that byte belongs to so we can
 646                                 // provide an index.
 647                                 let i = (offset.bytes() / ty_size.bytes()) as usize;
 648                                 self.path.push(PathElem::ArrayElem(i));
 649
 650                                 throw_validation_failure!("undefined bytes", self.path)
 651                             }
 652                             // Other errors shouldn't be possible
 653                             _ => return Err(err),
 654                         }
 655                     }
 656                 }
 657             }
 658             _ => {
 659                 self.walk_aggregate(op, fields)? // default handler
 660             }
 661         }
 662         Ok(())
 663     }
 664 }
 665
 666 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 667     /// This function checks the data at `op`. `op` is assumed to cover valid memory if it
 668     /// is an indirect operand.
 669     /// It will error if the bits at the destination do not match the ones described by the layout.
 670     ///
 671     /// `ref_tracking_for_consts` can be `None` to avoid recursive checking below references.
 672     /// This also toggles between "run-time" (no recursion) and "compile-time" (with recursion)
 673     /// validation (e.g., pointer values are fine in integers at runtime) and various other const
 674     /// specific validation checks.
 675     pub fn validate_operand(
 676         &self,
 677         op: OpTy<'tcx, M::PointerTag>,
 678         path: Vec<PathElem>,
 679         ref_tracking_for_consts: Option<
 680             &mut RefTracking<MPlaceTy<'tcx, M::PointerTag>, Vec<PathElem>>,
 681         >,
 682     ) -> InterpResult<'tcx> {
 683         trace!("validate_operand: {:?}, {:?}", *op, op.layout.ty);
 684
 685         // Construct a visitor
 686         let mut visitor = ValidityVisitor { path, ref_tracking_for_consts, ecx: self };
 687
 688         // Try to cast to ptr *once* instead of all the time.
 689         let op = self.force_op_ptr(op).unwrap_or(op);
 690
 691         // Run it
 692         visitor.visit_value(op)
 693     }
 694 }