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