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 syntax_pos::symbol::{sym, Symbol};
   6 use syntax_pos::Span;
   7 use rustc::ty;
   8 use rustc::ty::layout::{LayoutOf, Primitive, Size};
   9 use rustc::ty::subst::SubstsRef;
  10 use rustc::hir::def_id::DefId;
  11 use rustc::ty::TyCtxt;
  12 use rustc::mir::{
  13     self, BinOp,
  14     interpret::{InterpResult, Scalar, GlobalId, ConstValue}
  15 };
  16
  17 use super::{
  18     Machine, PlaceTy, OpTy, InterpCx, ImmTy,
  19 };
  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 - size.bits() as u128;
  34     let bits_out = match name {
  35         sym::ctpop => bits.count_ones() as u128,
  36         sym::ctlz => bits.leading_zeros() as u128 - extra,
  37         sym::cttz => (bits << extra).trailing_zeros() as u128 - 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, &'tcx ty::Const<'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             tcx.mk_const(ty::Const {
  59                 val: ty::ConstKind::Value(ConstValue::Slice {
  60                     data: alloc,
  61                     start: 0,
  62                     end: alloc.len(),
  63                 }),
  64                 ty: tcx.mk_static_str(),
  65             })
  66         },
  67         sym::needs_drop => ty::Const::from_bool(tcx, tp_ty.needs_drop(tcx, param_env)),
  68         sym::size_of |
  69         sym::min_align_of |
  70         sym::pref_align_of => {
  71             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  72             let n = match name {
  73                 sym::pref_align_of => layout.align.pref.bytes(),
  74                 sym::min_align_of => layout.align.abi.bytes(),
  75                 sym::size_of => layout.size.bytes(),
  76                 _ => bug!(),
  77             };
  78             ty::Const::from_usize(tcx, n)
  79         },
  80         sym::type_id => ty::Const::from_bits(
  81             tcx,
  82             tcx.type_id_hash(tp_ty).into(),
  83             param_env.and(tcx.types.u64),
  84         ),
  85         other => bug!("`{}` is not a zero arg intrinsic", other),
  86     })
  87 }
  88
  89 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  90     /// Returns `true` if emulation happened.
  91     pub fn emulate_intrinsic(
  92         &mut self,
  93         span: Span,
  94         instance: ty::Instance<'tcx>,
  95         args: &[OpTy<'tcx, M::PointerTag>],
  96         ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
  97     ) -> InterpResult<'tcx, bool> {
  98         let substs = instance.substs;
  99         let intrinsic_name = self.tcx.item_name(instance.def_id());
 100
 101         // We currently do not handle any intrinsics that are *allowed* to diverge,
 102         // but `transmute` could lack a return place in case of UB.
 103         let (dest, ret) = match ret {
 104             Some(p) => p,
 105             None => match intrinsic_name {
 106                 sym::transmute => throw_ub!(Unreachable),
 107                 _ => return Ok(false),
 108             }
 109         };
 110
 111         // Keep the patterns in this match ordered the same as the list in
 112         // `src/librustc/ty/constness.rs`
 113         match intrinsic_name {
 114             sym::caller_location => {
 115                 let location = self.alloc_caller_location_for_span(span);
 116                 self.write_scalar(location.ptr, dest)?;
 117             }
 118
 119             sym::min_align_of |
 120             sym::pref_align_of |
 121             sym::needs_drop |
 122             sym::size_of |
 123             sym::type_id |
 124             sym::type_name => {
 125                 let gid = GlobalId {
 126                     instance,
 127                     promoted: None,
 128                 };
 129                 let val = self.tcx.const_eval(self.param_env.and(gid))?;
 130                 let val = self.eval_const_to_op(val, None)?;
 131                 self.copy_op(val, dest)?;
 132             }
 133
 134             | sym::ctpop
 135             | sym::cttz
 136             | sym::cttz_nonzero
 137             | sym::ctlz
 138             | sym::ctlz_nonzero
 139             | sym::bswap
 140             | sym::bitreverse => {
 141                 let ty = substs.type_at(0);
 142                 let layout_of = self.layout_of(ty)?;
 143                 let val = self.read_scalar(args[0])?.not_undef()?;
 144                 let bits = self.force_bits(val, layout_of.size)?;
 145                 let kind = match layout_of.abi {
 146                     ty::layout::Abi::Scalar(ref scalar) => scalar.value,
 147                     _ => throw_unsup!(TypeNotPrimitive(ty)),
 148                 };
 149                 let (nonzero, intrinsic_name) = match intrinsic_name {
 150                     sym::cttz_nonzero => (true, sym::cttz),
 151                     sym::ctlz_nonzero => (true, sym::ctlz),
 152                     other => (false, other),
 153                 };
 154                 if nonzero && bits == 0 {
 155                     throw_ub_format!("`{}_nonzero` called on 0", intrinsic_name);
 156                 }
 157                 let out_val = numeric_intrinsic(intrinsic_name, bits, kind)?;
 158                 self.write_scalar(out_val, dest)?;
 159             }
 160             | sym::wrapping_add
 161             | sym::wrapping_sub
 162             | sym::wrapping_mul
 163             | sym::add_with_overflow
 164             | sym::sub_with_overflow
 165             | sym::mul_with_overflow => {
 166                 let lhs = self.read_immediate(args[0])?;
 167                 let rhs = self.read_immediate(args[1])?;
 168                 let (bin_op, ignore_overflow) = match intrinsic_name {
 169                     sym::wrapping_add => (BinOp::Add, true),
 170                     sym::wrapping_sub => (BinOp::Sub, true),
 171                     sym::wrapping_mul => (BinOp::Mul, true),
 172                     sym::add_with_overflow => (BinOp::Add, false),
 173                     sym::sub_with_overflow => (BinOp::Sub, false),
 174                     sym::mul_with_overflow => (BinOp::Mul, false),
 175                     _ => bug!("Already checked for int ops")
 176                 };
 177                 if ignore_overflow {
 178                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 179                 } else {
 180                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 181                 }
 182             }
 183             sym::saturating_add | sym::saturating_sub => {
 184                 let l = self.read_immediate(args[0])?;
 185                 let r = self.read_immediate(args[1])?;
 186                 let is_add = intrinsic_name == sym::saturating_add;
 187                 let (val, overflowed, _ty) = self.overflowing_binary_op(if is_add {
 188                     BinOp::Add
 189                 } else {
 190                     BinOp::Sub
 191                 }, l, r)?;
 192                 let val = if overflowed {
 193                     let num_bits = l.layout.size.bits();
 194                     if l.layout.abi.is_signed() {
 195                         // For signed ints the saturated value depends on the sign of the first
 196                         // term since the sign of the second term can be inferred from this and
 197                         // the fact that the operation has overflowed (if either is 0 no
 198                         // overflow can occur)
 199                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 200                         let first_term_positive = first_term & (1 << (num_bits-1)) == 0;
 201                         if first_term_positive {
 202                             // Negative overflow not possible since the positive first term
 203                             // can only increase an (in range) negative term for addition
 204                             // or corresponding negated positive term for subtraction
 205                             Scalar::from_uint((1u128 << (num_bits - 1)) - 1,  // max positive
 206                                 Size::from_bits(num_bits))
 207                         } else {
 208                             // Positive overflow not possible for similar reason
 209                             // max negative
 210                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 211                         }
 212                     } else {  // unsigned
 213                         if is_add {
 214                             // max unsigned
 215                             Scalar::from_uint(u128::max_value() >> (128 - num_bits),
 216                                 Size::from_bits(num_bits))
 217                         } else {  // underflow to 0
 218                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 219                         }
 220                     }
 221                 } else {
 222                     val
 223                 };
 224                 self.write_scalar(val, dest)?;
 225             }
 226             sym::unchecked_shl | sym::unchecked_shr => {
 227                 let l = self.read_immediate(args[0])?;
 228                 let r = self.read_immediate(args[1])?;
 229                 let bin_op = match intrinsic_name {
 230                     sym::unchecked_shl => BinOp::Shl,
 231                     sym::unchecked_shr => BinOp::Shr,
 232                     _ => bug!("Already checked for int ops")
 233                 };
 234                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 235                 if overflowed {
 236                     let layout = self.layout_of(substs.type_at(0))?;
 237                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 238                     throw_ub_format!("Overflowing shift by {} in `{}`", r_val, intrinsic_name);
 239                 }
 240                 self.write_scalar(val, dest)?;
 241             }
 242             sym::rotate_left | sym::rotate_right => {
 243                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 244                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 245                 let layout = self.layout_of(substs.type_at(0))?;
 246                 let val = self.read_scalar(args[0])?.not_undef()?;
 247                 let val_bits = self.force_bits(val, layout.size)?;
 248                 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
 249                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 250                 let width_bits = layout.size.bits() as u128;
 251                 let shift_bits = raw_shift_bits % width_bits;
 252                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 253                 let result_bits = if intrinsic_name == sym::rotate_left {
 254                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 255                 } else {
 256                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 257                 };
 258                 let truncated_bits = self.truncate(result_bits, layout);
 259                 let result = Scalar::from_uint(truncated_bits, layout.size);
 260                 self.write_scalar(result, dest)?;
 261             }
 262
 263             sym::ptr_offset_from => {
 264                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 265                 let a = self.read_immediate(args[0])?.to_scalar()?;
 266                 let b = self.read_immediate(args[1])?.to_scalar()?;
 267
 268                 // Special case: if both scalars are *equal integers*
 269                 // and not NULL, we pretend there is an allocation of size 0 right there,
 270                 // and their offset is 0. (There's never a valid object at NULL, making it an
 271                 // exception from the exception.)
 272                 // This is the dual to the special exception for offset-by-0
 273                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 274                 //
 275                 // Control flow is weird because we cannot early-return (to reach the
 276                 // `go_to_block` at the end).
 277                 let done = if a.is_bits() && b.is_bits() {
 278                     let a = a.to_machine_usize(self)?;
 279                     let b = b.to_machine_usize(self)?;
 280                     if a == b && a != 0 {
 281                         self.write_scalar(Scalar::from_int(0, isize_layout.size), dest)?;
 282                         true
 283                     } else { false }
 284                 } else { false };
 285
 286                 if !done {
 287                     // General case: we need two pointers.
 288                     let a = self.force_ptr(a)?;
 289                     let b = self.force_ptr(b)?;
 290                     if a.alloc_id != b.alloc_id {
 291                         throw_ub_format!(
 292                             "ptr_offset_from cannot compute offset of pointers into different \
 293                             allocations.",
 294                         );
 295                     }
 296                     let usize_layout = self.layout_of(self.tcx.types.usize)?;
 297                     let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 298                     let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 299                     let (val, _overflowed, _ty) = self.overflowing_binary_op(
 300                         BinOp::Sub, a_offset, b_offset,
 301                     )?;
 302                     let pointee_layout = self.layout_of(substs.type_at(0))?;
 303                     let val = ImmTy::from_scalar(val, isize_layout);
 304                     let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 305                     self.exact_div(val, size, dest)?;
 306                 }
 307             }
 308
 309             sym::transmute => {
 310                 self.copy_op_transmute(args[0], dest)?;
 311             }
 312             sym::simd_insert => {
 313                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 314                 let elem = args[2];
 315                 let input = args[0];
 316                 let (len, e_ty) = input.layout.ty.simd_size_and_type(self.tcx.tcx);
 317                 assert!(
 318                     index < len,
 319                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 320                     index, e_ty, len
 321                 );
 322                 assert_eq!(
 323                     input.layout, dest.layout,
 324                     "Return type `{}` must match vector type `{}`",
 325                     dest.layout.ty, input.layout.ty
 326                 );
 327                 assert_eq!(
 328                     elem.layout.ty, e_ty,
 329                     "Scalar element type `{}` must match vector element type `{}`",
 330                     elem.layout.ty, e_ty
 331                 );
 332
 333                 for i in 0..len {
 334                     let place = self.place_field(dest, i)?;
 335                     let value = if i == index {
 336                         elem
 337                     } else {
 338                         self.operand_field(input, i)?
 339                     };
 340                     self.copy_op(value, place)?;
 341                 }
 342             }
 343             sym::simd_extract => {
 344                 let index = u64::from(self.read_scalar(args[1])?.to_u32()?);
 345                 let (len, e_ty) = args[0].layout.ty.simd_size_and_type(self.tcx.tcx);
 346                 assert!(
 347                     index < len,
 348                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 349                     index, e_ty, len
 350                 );
 351                 assert_eq!(
 352                     e_ty, dest.layout.ty,
 353                     "Return type `{}` must match vector element type `{}`",
 354                     dest.layout.ty, e_ty
 355                 );
 356                 self.copy_op(self.operand_field(args[0], index)?, dest)?;
 357             }
 358             _ => return Ok(false),
 359         }
 360
 361         self.dump_place(*dest);
 362         self.go_to_block(ret);
 363         Ok(true)
 364     }
 365
 366     /// "Intercept" a function call to a panic-related function
 367     /// because we have something special to do for it.
 368     /// Returns `true` if an intercept happened.
 369     pub fn hook_panic_fn(
 370         &mut self,
 371         instance: ty::Instance<'tcx>,
 372         args: &[OpTy<'tcx, M::PointerTag>],
 373         _ret: Option<(PlaceTy<'tcx, M::PointerTag>, mir::BasicBlock)>,
 374     ) -> InterpResult<'tcx, bool> {
 375         let def_id = instance.def_id();
 376         if Some(def_id) == self.tcx.lang_items().panic_fn() {
 377             // &'static str, &core::panic::Location { &'static str, u32, u32 }
 378             assert!(args.len() == 2);
 379
 380             let msg_place = self.deref_operand(args[0])?;
 381             let msg = Symbol::intern(self.read_str(msg_place)?);
 382
 383             let location = self.deref_operand(args[1])?;
 384             let (file, line, col) = (
 385                 self.mplace_field(location, 0)?,
 386                 self.mplace_field(location, 1)?,
 387                 self.mplace_field(location, 2)?,
 388             );
 389
 390             let file_place = self.deref_operand(file.into())?;
 391             let file = Symbol::intern(self.read_str(file_place)?);
 392             let line = self.read_scalar(line.into())?.to_u32()?;
 393             let col = self.read_scalar(col.into())?.to_u32()?;
 394             throw_panic!(Panic { msg, file, line, col })
 395         } else if Some(def_id) == self.tcx.lang_items().begin_panic_fn() {
 396             assert!(args.len() == 2);
 397             // &'static str, &(&'static str, u32, u32)
 398             let msg = args[0];
 399             let place = self.deref_operand(args[1])?;
 400             let (file, line, col) = (
 401                 self.mplace_field(place, 0)?,
 402                 self.mplace_field(place, 1)?,
 403                 self.mplace_field(place, 2)?,
 404             );
 405
 406             let msg_place = self.deref_operand(msg.into())?;
 407             let msg = Symbol::intern(self.read_str(msg_place)?);
 408             let file_place = self.deref_operand(file.into())?;
 409             let file = Symbol::intern(self.read_str(file_place)?);
 410             let line = self.read_scalar(line.into())?.to_u32()?;
 411             let col = self.read_scalar(col.into())?.to_u32()?;
 412             throw_panic!(Panic { msg, file, line, col })
 413         } else {
 414             return Ok(false);
 415         }
 416     }
 417
 418     pub fn exact_div(
 419         &mut self,
 420         a: ImmTy<'tcx, M::PointerTag>,
 421         b: ImmTy<'tcx, M::PointerTag>,
 422         dest: PlaceTy<'tcx, M::PointerTag>,
 423     ) -> InterpResult<'tcx> {
 424         // Performs an exact division, resulting in undefined behavior where
 425         // `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`.
 426         // First, check x % y != 0.
 427         if self.binary_op(BinOp::Rem, a, b)?.to_bits()? != 0 {
 428             // Then, check if `b` is -1, which is the "min_value / -1" case.
 429             let minus1 = Scalar::from_int(-1, dest.layout.size);
 430             let b_scalar = b.to_scalar().unwrap();
 431             if b_scalar == minus1 {
 432                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 433             } else {
 434                 throw_ub_format!(
 435                     "exact_div: {} cannot be divided by {} without remainder",
 436                     a,
 437                     b,
 438                 )
 439             }
 440         }
 441         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 442     }
 443 }