src/librustc_mir/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, LayoutOf as _, Primitive, Size};
  18
  19 use super::{CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy};
  20
  21 mod caller_location;
  22 mod type_name;
  23
  24 fn numeric_intrinsic<'tcx, Tag>(
  25     name: Symbol,
  26     bits: u128,
  27     kind: Primitive,
  28 ) -> InterpResult<'tcx, Scalar<Tag>> {
  29     let size = match kind {
  30         Primitive::Int(integer, _) => integer.size(),
  31         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  32     };
  33     let extra = 128 - u128::from(size.bits());
  34     let bits_out = match name {
  35         sym::ctpop => u128::from(bits.count_ones()),
  36         sym::ctlz => u128::from(bits.leading_zeros()) - extra,
  37         sym::cttz => u128::from((bits << extra).trailing_zeros()) - extra,
  38         sym::bswap => (bits << extra).swap_bytes(),
  39         sym::bitreverse => (bits << extra).reverse_bits(),
  40         _ => bug!("not a numeric intrinsic: {}", name),
  41     };
  42     Ok(Scalar::from_uint(bits_out, size))
  43 }
  44
  45 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  46 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  47 crate fn eval_nullary_intrinsic<'tcx>(
  48     tcx: TyCtxt<'tcx>,
  49     param_env: ty::ParamEnv<'tcx>,
  50     def_id: DefId,
  51     substs: SubstsRef<'tcx>,
  52 ) -> InterpResult<'tcx, ConstValue<'tcx>> {
  53     let tp_ty = substs.type_at(0);
  54     let name = tcx.item_name(def_id);
  55     Ok(match name {
  56         sym::type_name => {
  57             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  58             ConstValue::Slice { data: alloc, start: 0, end: alloc.len() }
  59         }
  60         sym::needs_drop => ConstValue::from_bool(tp_ty.needs_drop(tcx, param_env)),
  61         sym::size_of | sym::min_align_of | sym::pref_align_of => {
  62             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  63             let n = match name {
  64                 sym::pref_align_of => layout.align.pref.bytes(),
  65                 sym::min_align_of => layout.align.abi.bytes(),
  66                 sym::size_of => layout.size.bytes(),
  67                 _ => bug!(),
  68             };
  69             ConstValue::from_machine_usize(n, &tcx)
  70         }
  71         sym::type_id => ConstValue::from_u64(tcx.type_id_hash(tp_ty)),
  72         other => bug!("`{}` is not a zero arg intrinsic", other),
  73     })
  74 }
  75
  76 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  77     /// Returns `true` if emulation happened.
  78     pub fn emulate_intrinsic(
  79         &mut self,
  80         instance: ty::Instance<'tcx>,
  81         args: &[OpTy<'tcx, M::PointerTag>],
  82         ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
  83     ) -> InterpResult<'tcx, bool> {
  84         let substs = instance.substs;
  85         let intrinsic_name = self.tcx.item_name(instance.def_id());
  86
  87         // First handle intrinsics without return place.
  88         let (dest, ret) = match ret {
  89             None => match intrinsic_name {
  90                 sym::transmute => throw_ub_format!("transmuting to uninhabited type"),
  91                 sym::abort => M::abort(self)?,
  92                 // Unsupported diverging intrinsic.
  93                 _ => return Ok(false),
  94             },
  95             Some(p) => p,
  96         };
  97
  98         // Keep the patterns in this match ordered the same as the list in
  99         // `src/librustc_middle/ty/constness.rs`
 100         match intrinsic_name {
 101             sym::caller_location => {
 102                 let span = self.find_closest_untracked_caller_location();
 103                 let location = self.alloc_caller_location_for_span(span);
 104                 self.write_scalar(location.ptr, dest)?;
 105             }
 106
 107             sym::min_align_of
 108             | sym::pref_align_of
 109             | sym::needs_drop
 110             | sym::size_of
 111             | sym::type_id
 112             | sym::type_name => {
 113                 let gid = GlobalId { instance, promoted: None };
 114                 let ty = match intrinsic_name {
 115                     sym::min_align_of | sym::pref_align_of | sym::size_of => self.tcx.types.usize,
 116                     sym::needs_drop => self.tcx.types.bool,
 117                     sym::type_id => self.tcx.types.u64,
 118                     sym::type_name => self.tcx.mk_static_str(),
 119                     _ => bug!("already checked for nullary intrinsics"),
 120                 };
 121                 let val = self.const_eval(gid, ty)?;
 122                 self.copy_op(val, dest)?;
 123             }
 124
 125             sym::ctpop
 126             | sym::cttz
 127             | sym::cttz_nonzero
 128             | sym::ctlz
 129             | sym::ctlz_nonzero
 130             | sym::bswap
 131             | sym::bitreverse => {
 132                 let ty = substs.type_at(0);
 133                 let layout_of = self.layout_of(ty)?;
 134                 let val = self.read_scalar(args[0])?.not_undef()?;
 135                 let bits = self.force_bits(val, layout_of.size)?;
 136                 let kind = match layout_of.abi {
 137                     Abi::Scalar(ref scalar) => scalar.value,
 138                     _ => bug!("{} called on invalid type {:?}", intrinsic_name, ty),
 139                 };
 140                 let (nonzero, intrinsic_name) = match intrinsic_name {
 141                     sym::cttz_nonzero => (true, sym::cttz),
 142                     sym::ctlz_nonzero => (true, sym::ctlz),
 143                     other => (false, other),
 144                 };
 145                 if nonzero && bits == 0 {
 146                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 147                 }
 148                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
 149                 self.write_scalar(out_val, dest)?;
 150             }
 151             sym::wrapping_add
 152             | sym::wrapping_sub
 153             | sym::wrapping_mul
 154             | sym::add_with_overflow
 155             | sym::sub_with_overflow
 156             | sym::mul_with_overflow => {
 157                 let lhs = self.read_immediate(args[0])?;
 158                 let rhs = self.read_immediate(args[1])?;
 159                 let (bin_op, ignore_overflow) = match intrinsic_name {
 160                     sym::wrapping_add => (BinOp::Add, true),
 161                     sym::wrapping_sub => (BinOp::Sub, true),
 162                     sym::wrapping_mul => (BinOp::Mul, true),
 163                     sym::add_with_overflow => (BinOp::Add, false),
 164                     sym::sub_with_overflow => (BinOp::Sub, false),
 165                     sym::mul_with_overflow => (BinOp::Mul, false),
 166                     _ => bug!("Already checked for int ops"),
 167                 };
 168                 if ignore_overflow {
 169                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 170                 } else {
 171                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 172                 }
 173             }
 174             sym::saturating_add | sym::saturating_sub => {
 175                 let l = self.read_immediate(args[0])?;
 176                 let r = self.read_immediate(args[1])?;
 177                 let is_add = intrinsic_name == sym::saturating_add;
 178                 let (val, overflowed, _ty) =
 179                     self.overflowing_binary_op(if is_add { BinOp::Add } else { BinOp::Sub }, l, r)?;
 180                 let val = if overflowed {
 181                     let num_bits = l.layout.size.bits();
 182                     if l.layout.abi.is_signed() {
 183                         // For signed ints the saturated value depends on the sign of the first
 184                         // term since the sign of the second term can be inferred from this and
 185                         // the fact that the operation has overflowed (if either is 0 no
 186                         // overflow can occur)
 187                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 188                         let first_term_positive = first_term & (1 << (num_bits - 1)) == 0;
 189                         if first_term_positive {
 190                             // Negative overflow not possible since the positive first term
 191                             // can only increase an (in range) negative term for addition
 192                             // or corresponding negated positive term for subtraction
 193                             Scalar::from_uint(
 194                                 (1u128 << (num_bits - 1)) - 1, // max positive
 195                                 Size::from_bits(num_bits),
 196                             )
 197                         } else {
 198                             // Positive overflow not possible for similar reason
 199                             // max negative
 200                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 201                         }
 202                     } else {
 203                         // unsigned
 204                         if is_add {
 205                             // max unsigned
 206                             Scalar::from_uint(
 207                                 u128::MAX >> (128 - num_bits),
 208                                 Size::from_bits(num_bits),
 209                             )
 210                         } else {
 211                             // underflow to 0
 212                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 213                         }
 214                     }
 215                 } else {
 216                     val
 217                 };
 218                 self.write_scalar(val, dest)?;
 219             }
 220             sym::discriminant_value => {
 221                 let place = self.deref_operand(args[0])?;
 222                 let discr_val = self.read_discriminant(place.into())?.0;
 223                 self.write_scalar(discr_val, dest)?;
 224             }
 225             sym::unchecked_shl
 226             | sym::unchecked_shr
 227             | sym::unchecked_add
 228             | sym::unchecked_sub
 229             | sym::unchecked_mul
 230             | sym::unchecked_div
 231             | sym::unchecked_rem => {
 232                 let l = self.read_immediate(args[0])?;
 233                 let r = self.read_immediate(args[1])?;
 234                 let bin_op = match intrinsic_name {
 235                     sym::unchecked_shl => BinOp::Shl,
 236                     sym::unchecked_shr => BinOp::Shr,
 237                     sym::unchecked_add => BinOp::Add,
 238                     sym::unchecked_sub => BinOp::Sub,
 239                     sym::unchecked_mul => BinOp::Mul,
 240                     sym::unchecked_div => BinOp::Div,
 241                     sym::unchecked_rem => BinOp::Rem,
 242                     _ => bug!("Already checked for int ops"),
 243                 };
 244                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 245                 if overflowed {
 246                     let layout = self.layout_of(substs.type_at(0))?;
 247                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 248                     if let sym::unchecked_shl | sym::unchecked_shr = intrinsic_name {
 249                         throw_ub_format!("overflowing shift by {} in `{}`", r_val, intrinsic_name);
 250                     } else {
 251                         throw_ub_format!("overflow executing `{}`", intrinsic_name);
 252                     }
 253                 }
 254                 self.write_scalar(val, dest)?;
 255             }
 256             sym::rotate_left | sym::rotate_right => {
 257                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 258                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 259                 let layout = self.layout_of(substs.type_at(0))?;
 260                 let val = self.read_scalar(args[0])?.not_undef()?;
 261                 let val_bits = self.force_bits(val, layout.size)?;
 262                 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
 263                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 264                 let width_bits = u128::from(layout.size.bits());
 265                 let shift_bits = raw_shift_bits % width_bits;
 266                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 267                 let result_bits = if intrinsic_name == sym::rotate_left {
 268                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 269                 } else {
 270                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 271                 };
 272                 let truncated_bits = self.truncate(result_bits, layout);
 273                 let result = Scalar::from_uint(truncated_bits, layout.size);
 274                 self.write_scalar(result, dest)?;
 275             }
 276             sym::offset => {
 277                 let ptr = self.read_scalar(args[0])?.not_undef()?;
 278                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;
 279                 let pointee_ty = substs.type_at(0);
 280
 281                 let offset_ptr = self.ptr_offset_inbounds(ptr, pointee_ty, offset_count)?;
 282                 self.write_scalar(offset_ptr, dest)?;
 283             }
 284             sym::arith_offset => {
 285                 let ptr = self.read_scalar(args[0])?.not_undef()?;
 286                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;
 287                 let pointee_ty = substs.type_at(0);
 288
 289                 let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 290                 let offset_bytes = offset_count.wrapping_mul(pointee_size);
 291                 let offset_ptr = ptr.ptr_wrapping_signed_offset(offset_bytes, self);
 292                 self.write_scalar(offset_ptr, dest)?;
 293             }
 294             sym::ptr_offset_from => {
 295                 let a = self.read_immediate(args[0])?.to_scalar()?;
 296                 let b = self.read_immediate(args[1])?.to_scalar()?;
 297
 298                 // Special case: if both scalars are *equal integers*
 299                 // and not NULL, we pretend there is an allocation of size 0 right there,
 300                 // and their offset is 0. (There's never a valid object at NULL, making it an
 301                 // exception from the exception.)
 302                 // This is the dual to the special exception for offset-by-0
 303                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 304                 //
 305                 // Control flow is weird because we cannot early-return (to reach the
 306                 // `go_to_block` at the end).
 307                 let done = if a.is_bits() && b.is_bits() {
 308                     let a = a.to_machine_usize(self)?;
 309                     let b = b.to_machine_usize(self)?;
 310                     if a == b && a != 0 {
 311                         self.write_scalar(Scalar::from_machine_isize(0, self), dest)?;
 312                         true
 313                     } else {
 314                         false
 315                     }
 316                 } else {
 317                     false
 318                 };
 319
 320                 if !done {
 321                     // General case: we need two pointers.
 322                     let a = self.force_ptr(a)?;
 323                     let b = self.force_ptr(b)?;
 324                     if a.alloc_id != b.alloc_id {
 325                         throw_ub_format!(
 326                             "ptr_offset_from cannot compute offset of pointers into different \
 327                             allocations.",
 328                         );
 329                     }
 330                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 331                     let isize_layout = self.layout_of(self.tcx.types.isize)?;
 332                     let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 333                     let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 334                     let (val, _overflowed, _ty) =
 335                         self.overflowing_binary_op(BinOp::Sub, a_offset, b_offset)?;
 336                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 337                     let val = ImmTy::from_scalar(val, isize_layout);
 338                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 339                     self.exact_div(val, size, dest)?;
 340                 }
 341             }
 342
 343             sym::transmute => {
 344                 self.copy_op_transmute(args[0], dest)?;
 345             }
 346             sym::simd_insert => {
 347                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 348                 let elem = args[2];
 349                 let input = args[0];
 350                 let (len, e_ty) = input.layout.ty.simd_size_and_type(*self.tcx);
 351                 assert!(
 352                     index < len,
 353                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 354                     index,
 355                     e_ty,
 356                     len
 357                 );
 358                 assert_eq!(
 359                     input.layout, dest.layout,
 360                     "Return type `{}` must match vector type `{}`",
 361                     dest.layout.ty, input.layout.ty
 362                 );
 363                 assert_eq!(
 364                     elem.layout.ty, e_ty,
 365                     "Scalar element type `{}` must match vector element type `{}`",
 366                     elem.layout.ty, e_ty
 367                 );
 368
 369                 for i in 0..len {
 370                     let place = self.place_index(dest, i)?;
 371                     let value = if i == index { elem } else { self.operand_index(input, i)? };
 372                     self.copy_op(value, place)?;
 373                 }
 374             }
 375             sym::simd_extract => {
 376                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 377                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(*self.tcx);
 378                 assert!(
 379                     index < len,
 380                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 381                     index,
 382                     e_ty,
 383                     len
 384                 );
 385                 assert_eq!(
 386                     e_ty, dest.layout.ty,
 387                     "Return type `{}` must match vector element type `{}`",
 388                     dest.layout.ty, e_ty
 389                 );
 390                 self.copy_op(self.operand_index(args[0], index)?, dest)?;
 391             }
 392             // FIXME(#73156): Handle source code coverage in const eval
 393             sym::count_code_region => (),
 394             _ => return Ok(false),
 395         }
 396
 397         self.dump_place(*dest);
 398         self.go_to_block(ret);
 399         Ok(true)
 400     }
 401
 402     pub fn exact_div(
 403         &mut self,
 404         a: ImmTy<'tcx, M::PointerTag>,
 405         b: ImmTy<'tcx, M::PointerTag>,
 406         dest: PlaceTy<'tcx, M::PointerTag>,
 407     ) -> InterpResult<'tcx> {
 408         // Performs an exact division, resulting in undefined behavior where
 409         // `x % y != 0` or `y == 0` or `x == T::MIN && y == -1`.
 410         // First, check x % y != 0 (or if that computation overflows).
 411         let (res, overflow, _ty) = self.overflowing_binary_op(BinOp::Rem, a, b)?;
 412         if overflow || res.assert_bits(a.layout.size) != 0 {
 413             // Then, check if `b` is -1, which is the "MIN / -1" case.
 414             let minus1 = Scalar::from_int(-1, dest.layout.size);
 415             let b_scalar = b.to_scalar().unwrap();
 416             if b_scalar == minus1 {
 417                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 418             } else {
 419                 throw_ub_format!("exact_div: {} cannot be divided by {} without remainder", a, b,)
 420             }
 421         }
 422         // `Rem` says this is all right, so we can let `Div` do its job.
 423         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 424     }
 425
 426     /// Offsets a pointer by some multiple of its type, returning an error if the pointer leaves its
 427     /// allocation. For integer pointers, we consider each of them their own tiny allocation of size
 428     /// 0, so offset-by-0 (and only 0) is okay -- except that NULL cannot be offset by _any_ value.
 429     pub fn ptr_offset_inbounds(
 430         &self,
 431         ptr: Scalar<M::PointerTag>,
 432         pointee_ty: Ty<'tcx>,
 433         offset_count: i64,
 434     ) -> InterpResult<'tcx, Scalar<M::PointerTag>> {
 435         // We cannot overflow i64 as a type's size must be <= isize::MAX.
 436         let pointee_size = i64::try_from(self.layout_of(pointee_ty)?.size.bytes()).unwrap();
 437         // The computed offset, in bytes, cannot overflow an isize.
 438         let offset_bytes =
 439             offset_count.checked_mul(pointee_size).ok_or(err_ub!(PointerArithOverflow))?;
 440         // The offset being in bounds cannot rely on "wrapping around" the address space.
 441         // So, first rule out overflows in the pointer arithmetic.
 442         let offset_ptr = ptr.ptr_signed_offset(offset_bytes, self)?;
 443         // ptr and offset_ptr must be in bounds of the same allocated object. This means all of the
 444         // memory between these pointers must be accessible. Note that we do not require the
 445         // pointers to be properly aligned (unlike a read/write operation).
 446         let min_ptr = if offset_bytes >= 0 { ptr } else { offset_ptr };
 447         let size: u64 = uabs(offset_bytes);
 448         // This call handles checking for integer/NULL pointers.
 449         self.memory.check_ptr_access_align(
 450             min_ptr,
 451             Size::from_bytes(size),
 452             None,
 453             CheckInAllocMsg::InboundsTest,
 454         )?;
 455         Ok(offset_ptr)
 456     }
 457 }