compiler/rustc_mir/src/interpret/intrinsics.rs

   1 //! Intrinsics and other functions that the miri engine executes without
   2 //! looking at their MIR. Intrinsics/functions supported here are shared by CTFE
   3 //! and miri.
   4
   5 use std::convert::TryFrom;
   6
   7 use rustc_hir::def_id::DefId;
   8 use rustc_middle::mir::{
   9     self,
  10     interpret::{uabs, ConstValue, GlobalId, InterpResult, Scalar},
  11     BinOp,
  12 };
  13 use rustc_middle::ty;
  14 use rustc_middle::ty::subst::SubstsRef;
  15 use rustc_middle::ty::{Ty, TyCtxt};
  16 use rustc_span::symbol::{sym, Symbol};
  17 use rustc_target::abi::{Abi, Align, LayoutOf as _, Primitive, Size};
  18
  19 use super::{
  20     util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, MemoryKind, OpTy,
  21     PlaceTy,
  22 };
  23
  24 mod caller_location;
  25 mod type_name;
  26
  27 fn numeric_intrinsic<'tcx, Tag>(
  28     name: Symbol,
  29     bits: u128,
  30     kind: Primitive,
  31 ) -> InterpResult<'tcx, Scalar<Tag>> {
  32     let size = match kind {
  33         Primitive::Int(integer, _) => integer.size(),
  34         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  35     };
  36     let extra = 128 - u128::from(size.bits());
  37     let bits_out = match name {
  38         sym::ctpop => u128::from(bits.count_ones()),
  39         sym::ctlz => u128::from(bits.leading_zeros()) - extra,
  40         sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
  41         sym::bswap => (bits << extra).swap_bytes(),
  42         sym::bitreverse => (bits << extra).reverse_bits(),
  43         _ => bug!("not a numeric intrinsic: {}", name),
  44     };
  45     Ok(Scalar::from_uint(bits_out, size))
  46 }
  47
  48 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  49 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  50 crate fn eval_nullary_intrinsic<'tcx>(
  51     tcx: TyCtxt<'tcx>,
  52     param_env: ty::ParamEnv<'tcx>,
  53     def_id: DefId,
  54     substs: SubstsRef<'tcx>,
  55 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
  56     let tp_ty = substs.type_at(0);
  57     let name = tcx.item_name(def_id);
  58     Ok(match name {
  59         sym::type_name => {
  60             ensure_monomorphic_enough(tcx, tp_ty)?;
  61             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  62             ConstValue::Slice { data: alloc, start: 0, end: alloc.len() }
  63         }
  64         sym::needs_drop => ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env)),
  65         sym::size_of | sym::min_align_of | sym::pref_align_of => {
  66             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  67             let n = match name {
  68                 sym::pref_align_of => layout.align.pref.bytes(),
  69                 sym::min_align_of => layout.align.abi.bytes(),
  70                 sym::size_of => layout.size.bytes(),
  71                 _ => bug!(),
  72             };
  73             ConstValue::from_machine_usize(n, &tcx)
  74         }
  75         sym::type_id => {
  76             ensure_monomorphic_enough(tcx, tp_ty)?;
  77             ConstValue::from_u64(tcx.type_id_hash(tp_ty))
  78         }
  79         sym::variant_count => match tp_ty.kind() {
  80             ty::Adt(ref adt, _) => ConstValue::from_machine_usize(adt.variants.len() as u64, &tcx),
  81             ty::Projection(_)
  82             | ty::Opaque(_, _)
  83             | ty::Param(_)
  84             | ty::Bound(_, _)
  85             | ty::Placeholder(_)
  86             | ty::Infer(_) => throw_inval!(TooGeneric),
  87             ty::Bool
  88             | ty::Char
  89             | ty::Int(_)
  90             | ty::Uint(_)
  91             | ty::Float(_)
  92             | ty::Foreign(_)
  93             | ty::Str
  94             | ty::Array(_, _)
  95             | ty::Slice(_)
  96             | ty::RawPtr(_)
  97             | ty::Ref(_, _, _)
  98             | ty::FnDef(_, _)
  99             | ty::FnPtr(_)
 100             | ty::Dynamic(_, _)
 101             | ty::Closure(_, _)
 102             | ty::Generator(_, _, _)
 103             | ty::GeneratorWitness(_)
 104             | ty::Never
 105             | ty::Tuple(_)
 106             | ty::Error(_) => ConstValue::from_machine_usize(0u64, &tcx),
 107         },
 108         other => bug!("`{}` is not a zero arg intrinsic", other),
 109     })
 110 }
 111
 112 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
 113     /// Returns `true` if emulation happened.
 114     /// Here we implement the intrinsics that are common to all Miri instances; individual machines can add their own
 115     /// intrinsic handling.
 116     pub fn emulate_intrinsic(
 117         &mut self,
 118         instance: ty::Instance<'tcx>,
 119         args: &[OpTy<'tcx, M::PointerTag>],
 120         ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
 121     ) -> InterpResult<'tcx, bool> {
 122         let substs = instance.substs;
 123         let intrinsic_name = self.tcx.item_name(instance.def_id());
 124
 125         // First handle intrinsics without return place.
 126         let (dest, ret) = match ret {
 127             None => match intrinsic_name {
 128                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
 129                 sym::unreachable => throw_ub!(Unreachable),
 130                 sym::abort => M::abort(self)?,
 131                 // Unsupported diverging intrinsic.
 132                 _ => return Ok(false),
 133             },
 134             Some(p) => p,
 135         };
 136
 137         // Keep the patterns in this match ordered the same as the list in
 138         // `src/librustc_middle/ty/constness.rs`
 139         match intrinsic_name {
 140             sym::caller_location => {
 141                 let span = self.find_closest_untracked_caller_location();
 142                 let location = self.alloc_caller_location_for_span(span);
 143                 self.write_scalar(location.ptr, dest)?;
 144             }
 145
 146             sym::min_align_of_val | sym::size_of_val => {
 147                 let place = self.deref_operand(args[0])?;
 148                 let (size, align) = self
 149                     .size_and_align_of(place.meta, place.layout)?
 150                     .ok_or_else(|| err_unsup_format!("`extern type` does not have known layout"))?;
 151
 152                 let result = match intrinsic_name {
 153                     sym::min_align_of_val => align.bytes(),
 154                     sym::size_of_val => size.bytes(),
 155                     _ => bug!(),
 156                 };
 157
 158                 self.write_scalar(Scalar::from_machine_usize(result, self), dest)?;
 159             }
 160
 161             sym::min_align_of
 162             | sym::pref_align_of
 163             | sym::needs_drop
 164             | sym::size_of
 165             | sym::type_id
 166             | sym::type_name
 167             | sym::variant_count => {
 168                 let gid = GlobalId { instance, promoted: None };
 169                 let ty = match intrinsic_name {
 170                     sym::min_align_of | sym::pref_align_of | sym::size_of | sym::variant_count => {
 171                         self.tcx.types.usize
 172                     }
 173                     sym::needs_drop => self.tcx.types.bool,
 174                     sym::type_id => self.tcx.types.u64,
 175                     sym::type_name => self.tcx.mk_static_str(),
 176                     _ => bug!("already checked for nullary intrinsics"),
 177                 };
 178                 let val =
 179                     self.tcx.const_eval_global_id(self.param_env, gid, Some(self.tcx.span))?;
 180                 let const_ = ty::Const { val: ty::ConstKind::Value(val), ty };
 181                 let val = self.const_to_op(&const_, None)?;
 182                 self.copy_op(val, dest)?;
 183             }
 184
 185             sym::ctpop
 186             | sym::cttz
 187             | sym::cttz_nonzero
 188             | sym::ctlz
 189             | sym::ctlz_nonzero
 190             | sym::bswap
 191             | sym::bitreverse => {
 192                 let ty = substs.type_at(0);
 193                 let layout_of = self.layout_of(ty)?;
 194                 let val = self.read_scalar(args[0])?.check_init()?;
 195                 let bits = self.force_bits(val, layout_of.size)?;
 196                 let kind = match layout_of.abi {
 197                     Abi::Scalar(ref scalar) => scalar.value,
 198                     _ => span_bug!(
 199                         self.cur_span(),
 200                         "{} called on invalid type {:?}",
 201                         intrinsic_name,
 202                         ty
 203                     ),
 204                 };
 205                 let (nonzero, intrinsic_name) = match intrinsic_name {
 206                     sym::cttz_nonzero => (true, sym::cttz),
 207                     sym::ctlz_nonzero => (true, sym::ctlz),
 208                     other => (false, other),
 209                 };
 210                 if nonzero && bits == 0 {
 211                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 212                 }
 213                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
 214                 self.write_scalar(out_val, dest)?;
 215             }
 216             sym::wrapping_add
 217             | sym::wrapping_sub
 218             | sym::wrapping_mul
 219             | sym::add_with_overflow
 220             | sym::sub_with_overflow
 221             | sym::mul_with_overflow => {
 222                 let lhs = self.read_immediate(args[0])?;
 223                 let rhs = self.read_immediate(args[1])?;
 224                 let (bin_op, ignore_overflow) = match intrinsic_name {
 225                     sym::wrapping_add => (BinOp::Add, true),
 226                     sym::wrapping_sub => (BinOp::Sub, true),
 227                     sym::wrapping_mul => (BinOp::Mul, true),
 228                     sym::add_with_overflow => (BinOp::Add, false),
 229                     sym::sub_with_overflow => (BinOp::Sub, false),
 230                     sym::mul_with_overflow => (BinOp::Mul, false),
 231                     _ => bug!("Already checked for int ops"),
 232                 };
 233                 if ignore_overflow {
 234                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 235                 } else {
 236                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 237                 }
 238             }
 239             sym::saturating_add | sym::saturating_sub => {
 240                 let l = self.read_immediate(args[0])?;
 241                 let r = self.read_immediate(args[1])?;
 242                 let is_add = intrinsic_name == sym::saturating_add;
 243                 let (val, overflowed, _ty) =
 244                     self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?;
 245                 let val = if overflowed {
 246                     let num_bits = l.layout.size.bits();
 247                     if l.layout.abi.is_signed() {
 248                         // For signed ints the saturated value depends on the sign of the first
 249                         // term since the sign of the second term can be inferred from this and
 250                         // the fact that the operation has overflowed (if either is 0 no
 251                         // overflow can occur)
 252                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 253                         let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 254                         if first_term_positive {
 255                             // Negative overflow not possible since the positive first term
 256                             // can only increase an (in range) negative term for addition
 257                             // or corresponding negated positive term for subtraction
 258                             Scalar::from_uint(
 259                                 (1u128 << (num_bits - 1)) - 1, // max positive
 260                                 Size::from_bits(num_bits),
 261                             )
 262                         } else {
 263                             // Positive overflow not possible for similar reason
 264                             // max negative
 265                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 266                         }
 267                     } else {
 268                         // unsigned
 269                         if is_add {
 270                             // max unsigned
 271                             Scalar::from_uint(
 272                                 u128::MAX >> (128 - num_bits),
 273                                 Size::from_bits(num_bits),
 274                             )
 275                         } else {
 276                             // underflow to 0
 277                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 278                         }
 279                     }
 280                 } else {
 281                     val
 282                 };
 283                 self.write_scalar(val, dest)?;
 284             }
 285             sym::discriminant_value => {
 286                 let place = self.deref_operand(args[0])?;
 287                 let discr_val = self.read_discriminant(place.into())?.0;
 288                 self.write_scalar(discr_val, dest)?;
 289             }
 290             sym::unchecked_shl
 291             | sym::unchecked_shr
 292             | sym::unchecked_add
 293             | sym::unchecked_sub
 294             | sym::unchecked_mul
 295             | sym::unchecked_div
 296             | sym::unchecked_rem => {
 297                 let l = self.read_immediate(args[0])?;
 298                 let r = self.read_immediate(args[1])?;
 299                 let bin_op = match intrinsic_name {
 300                     sym::unchecked_shl => BinOp::Shl,
 301                     sym::unchecked_shr => BinOp::Shr,
 302                     sym::unchecked_add => BinOp::Add,
 303                     sym::unchecked_sub => BinOp::Sub,
 304                     sym::unchecked_mul => BinOp::Mul,
 305                     sym::unchecked_div => BinOp::Div,
 306                     sym::unchecked_rem => BinOp::Rem,
 307                     _ => bug!("Already checked for int ops"),
 308                 };
 309                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 310                 if overflowed {
 311                     let layout = self.layout_of(substs.type_at(0))?;
 312                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 313                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 314                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 315                     } else {
 316                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 317                     }
 318                 }
 319                 self.write_scalar(val, dest)?;
 320             }
 321             sym::rotate_left | sym::rotate_right => {
 322                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 323                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 324                 let layout = self.layout_of(substs.type_at(0))?;
 325                 let val = self.read_scalar(args[0])?.check_init()?;
 326                 let val_bits = self.force_bits(val, layout.size)?;
 327                 let raw_shift = self.read_scalar(args[1])?.check_init()?;
 328                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 329                 let width_bits = u128::from(layout.size.bits());
 330                 let shift_bits = raw_shift_bits % width_bits;
 331                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 332                 let result_bits = if intrinsic_name == sym::rotate_left {
 333                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 334                 } else {
 335                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 336                 };
 337                 let truncated_bits = self.truncate(result_bits, layout);
 338                 let result = Scalar::from_uint(truncated_bits, layout.size);
 339                 self.write_scalar(result, dest)?;
 340             }
 341             sym::const_allocate => {
 342                 let size = self.read_scalar(args[0])?.to_machine_usize(self)?;
 343                 let align = self.read_scalar(args[1])?.to_machine_usize(self)?;
 344
 345                 let align = match Align::from_bytes(align) {
 346                     Ok(a) => a,
 347                     Err(err) => throw_ub_format!("align has to be a power of 2, {}", err),
 348                 };
 349
 350                 let ptr =
 351                     self.memory.allocate(Size::from_bytes(size as u64), align, MemoryKind::Heap);
 352                 self.write_scalar(Scalar::Ptr(ptr), dest)?;
 353             }
 354             sym::offset => {
 355                 let ptr = self.read_scalar(args[0])?.check_init()?;
 356                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;
 357                 let pointee_ty = substs.type_at(0);
 358
 359                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 360                 self.write_scalar(offset_ptr, dest)?;
 361             }
 362             sym::arith_offset => {
 363                 let ptr = self.read_scalar(args[0])?.check_init()?;
 364                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;
 365                 let pointee_ty = substs.type_at(0);
 366
 367                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 368                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 369                 let offset_ptr = ptr.ptr_wrapping_signed_offset(offset_bytes, self);
 370                 self.write_scalar(offset_ptr, dest)?;
 371             }
 372             sym::ptr_offset_from => {
 373                 let a = self.read_immediate(args[0])?.to_scalar()?;
 374                 let b = self.read_immediate(args[1])?.to_scalar()?;
 375
 376                 // Special case: if both scalars are *equal integers*
 377                 // and not NULL, we pretend there is an allocation of size 0 right there,
 378                 // and their offset is 0. (There's never a valid object at NULL, making it an
 379                 // exception from the exception.)
 380                 // This is the dual to the special exception for offset-by-0
 381                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 382                 //
 383                 // Control flow is weird because we cannot early-return (to reach the
 384                 // `go_to_block` at the end).
 385                 let done = if a.is_bits() && b.is_bits() {
 386                     let a = a.to_machine_usize(self)?;
 387                     let b = b.to_machine_usize(self)?;
 388                     if a == b && a != 0 {
 389                         self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
 390                         true
 391                     } else {
 392                         false
 393                     }
 394                 } else {
 395                     false
 396                 };
 397
 398                 if !done {
 399                     // General case: we need two pointers.
 400                     let a = self.force_ptr(a)?;
 401                     let b = self.force_ptr(b)?;
 402                     if a.alloc_id != b.alloc_id {
 403                         throw_ub_format!(
 404                             "ptr_offset_from cannot compute offset of pointers into different \
 405                             allocations.",
 406                         );
 407                     }
 408                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 409                     let isize_layout = self.layout_of(self.tcx.types.isize)?;
 410                     let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 411                     let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 412                     let (val, _overflowed, _ty) =
 413                         self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?;
 414                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 415                     let val = ImmTy::from_scalar(val, isize_layout);
 416                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 417                     self.exact_div(val, size, dest)?;
 418                 }
 419             }
 420
 421             sym::transmute => {
 422                 self.copy_op_transmute(args[0], dest)?;
 423             }
 424             sym::simd_insert => {
 425                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 426                 let elem = args[2];
 427                 let input = args[0];
 428                 let (len, e_ty) = input.layout.ty.simd_size_and_type(*self.tcx);
 429                 assert!(
 430                     index < len,
 431                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 432                     index,
 433                     e_ty,
 434                     len
 435                 );
 436                 assert_eq!(
 437                     input.layout, dest.layout,
 438                     "Return type `{}` must match vector type `{}`",
 439                     dest.layout.ty, input.layout.ty
 440                 );
 441                 assert_eq!(
 442                     elem.layout.ty, e_ty,
 443                     "Scalar element type `{}` must match vector element type `{}`",
 444                     elem.layout.ty, e_ty
 445                 );
 446
 447                 for i in 0..len {
 448                     let place = self.place_index(dest, i)?;
 449                     let value = if i == index { elem } else { self.operand_index(input, i)? };
 450                     self.copy_op(value, place)?;
 451                 }
 452             }
 453             sym::simd_extract => {
 454                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 455                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(*self.tcx);
 456                 assert!(
 457                     index < len,
 458                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 459                     index,
 460                     e_ty,
 461                     len
 462                 );
 463                 assert_eq!(
 464                     e_ty, dest.layout.ty,
 465                     "Return type `{}` must match vector element type `{}`",
 466                     dest.layout.ty, e_ty
 467                 );
 468                 self.copy_op(self.operand_index(args[0], index)?, dest)?;
 469             }
 470             sym::likely | sym::unlikely => {
 471                 // These just return their argument
 472                 self.copy_op(args[0], dest)?;
 473             }
 474             sym::assume => {
 475                 let cond = self.read_scalar(args[0])?.check_init()?.to_bool()?;
 476                 if !cond {
 477                     throw_ub_format!("`assume` intrinsic called with `false`");
 478                 }
 479             }
 480             _ => return Ok(false),
 481         }
 482
 483         trace!("{:?}", self.dump_place(*dest));
 484         self.go_to_block(ret);
 485         Ok(true)
 486     }
 487
 488     pub fn exact_div(
 489         &mut self,
 490         a: ImmTy<'tcx, M::PointerTag>,
 491         b: ImmTy<'tcx, M::PointerTag>,
 492         dest: PlaceTy<'tcx, M::PointerTag>,
 493     ) -> InterpResult<'tcx> {
 494         // Performs an exact division, resulting in undefined behavior where
 495         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 496         // First, check x % y != 0 (or if that computation overflows).
 497         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?;
 498         if overflow || res.assert_bits(a.layout.size) != 0 {
 499             // Then, check if `b` is -1, which is the "MIN / -1" case.
 500             let minus1 = Scalar::from_int(-1, dest.layout.size);
 501             let b_scalar = b.to_scalar().unwrap();
 502             if b_scalar == minus1 {
 503                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 504             } else {
 505                 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
 506             }
 507         }
 508         // `Rem` says this is all right, so we can let `Div` do its job.
 509         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 510     }
 511
 512     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 513     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 514     /// 0, so offset-by-0 (and only 0) is okay -- except that NULL cannot be offset by _any_ value.
 515     pub fn ptr_offset_inbounds(
 516         &self,
 517         ptr: Scalar<M::PointerTag>,
 518         pointee_ty: Ty<'tcx>,
 519         offset_count: i64,
 520     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 521         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 522         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 523         // The computed offset, in bytes, cannot overflow an isize.
 524         let offset_bytes =
 525             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 526         // The offset being in bounds cannot rely on "wrapping around" the address space.
 527         // So, first rule out overflows in the pointer arithmetic.
 528         let offset_ptr = ptr.ptr_signed_offset(offset_bytes, self)?;
 529         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 530         // memory between these pointers must be accessible. Note that we do not require the
 531         // pointers to be properly aligned (unlike a read/write operation).
 532         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 533         let size: u64 = uabs(offset_bytes);
 534         // This call handles checking for integer/NULL pointers.
 535         self.memory.check_ptr_access_align(
 536             min_ptr,
 537             Size::from_bytes(size),
 538             None,
 539             CheckInAllocMsg::InboundsTest,
 540         )?;
 541         Ok(offset_ptr)
 542     }
 543 }