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::symbol::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::BinOp;
  13 use rustc::mir::interpret::{InterpResult, Scalar, GlobalId, ConstValue};
  14
  15 use super::{
  16     Machine, PlaceTy, OpTy, InterpCx, ImmTy,
  17 };
  18
  19 mod caller_location;
  20 mod type_name;
  21
  22 fn numeric_intrinsic<'tcx, Tag>(
  23     name: &str,
  24     bits: u128,
  25     kind: Primitive,
  26 ) -> InterpResult<'tcx, Scalar<Tag>> {
  27     let size = match kind {
  28         Primitive::Int(integer, _) => integer.size(),
  29         _ => bug!("invalid `{}` argument: {:?}", name, bits),
  30     };
  31     let extra = 128 - size.bits() as u128;
  32     let bits_out = match name {
  33         "ctpop" => bits.count_ones() as u128,
  34         "ctlz" => bits.leading_zeros() as u128 - extra,
  35         "cttz" => (bits << extra).trailing_zeros() as u128 - extra,
  36         "bswap" => (bits << extra).swap_bytes(),
  37         "bitreverse" => (bits << extra).reverse_bits(),
  38         _ => bug!("not a numeric intrinsic: {}", name),
  39     };
  40     Ok(Scalar::from_uint(bits_out, size))
  41 }
  42
  43 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
  44 /// inside an `InterpCx` and instead have their value computed directly from rustc internal info.
  45 crate fn eval_nullary_intrinsic<'tcx>(
  46     tcx: TyCtxt<'tcx>,
  47     param_env: ty::ParamEnv<'tcx>,
  48     def_id: DefId,
  49     substs: SubstsRef<'tcx>,
  50 ) -> InterpResult<'tcx, &'tcx ty::Const<'tcx>> {
  51     let tp_ty = substs.type_at(0);
  52     let name = &*tcx.item_name(def_id).as_str();
  53     Ok(match name {
  54         "type_name" => {
  55             let alloc = type_name::alloc_type_name(tcx, tp_ty);
  56             tcx.mk_const(ty::Const {
  57                 val: ConstValue::Slice {
  58                     data: alloc,
  59                     start: 0,
  60                     end: alloc.len(),
  61                 },
  62                 ty: tcx.mk_static_str(),
  63             })
  64         },
  65         "needs_drop" => ty::Const::from_bool(tcx, tp_ty.needs_drop(tcx, param_env)),
  66         "size_of" |
  67         "min_align_of" |
  68         "pref_align_of" => {
  69             let layout = tcx.layout_of(param_env.and(tp_ty)).map_err(|e| err_inval!(Layout(e)))?;
  70             let n = match name {
  71                 "pref_align_of" => layout.align.pref.bytes(),
  72                 "min_align_of" => layout.align.abi.bytes(),
  73                 "size_of" => layout.size.bytes(),
  74                 _ => bug!(),
  75             };
  76             ty::Const::from_usize(tcx, n)
  77         },
  78         "type_id" => ty::Const::from_bits(
  79             tcx,
  80             tcx.type_id_hash(tp_ty).into(),
  81             param_env.and(tcx.types.u64),
  82         ),
  83         other => bug!("`{}` is not a zero arg intrinsic", other),
  84     })
  85 }
  86
  87 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  88     /// Returns `true` if emulation happened.
  89     pub fn emulate_intrinsic(
  90         &mut self,
  91         span: Span,
  92         instance: ty::Instance<'tcx>,
  93         args: &[OpTy<'tcx, M::PointerTag>],
  94         dest: Option<PlaceTy<'tcx, M::PointerTag>>,
  95     ) -> InterpResult<'tcx, bool> {
  96         let substs = instance.substs;
  97
  98         // The intrinsic itself cannot diverge, so if we got here without a return
  99         // place... (can happen e.g., for transmute returning `!`)
 100         let dest = match dest {
 101             Some(dest) => dest,
 102             None => throw_ub!(Unreachable)
 103         };
 104         let intrinsic_name = &self.tcx.item_name(instance.def_id()).as_str();
 105
 106         match intrinsic_name {
 107             "caller_location" => {
 108                 let topmost = span.ctxt().outer_expn().expansion_cause().unwrap_or(span);
 109                 let caller = self.tcx.sess.source_map().lookup_char_pos(topmost.lo());
 110                 let location = self.alloc_caller_location(
 111                     Symbol::intern(&caller.file.name.to_string()),
 112                     caller.line as u32,
 113                     caller.col_display as u32 + 1,
 114                 )?;
 115                 self.write_scalar(location.ptr, dest)?;
 116             }
 117
 118             "min_align_of" |
 119             "pref_align_of" |
 120             "needs_drop" |
 121             "size_of" |
 122             "type_id" |
 123             "type_name" => {
 124                 let gid = GlobalId {
 125                     instance,
 126                     promoted: None,
 127                 };
 128                 let val = self.tcx.const_eval(self.param_env.and(gid))?;
 129                 let val = self.eval_const_to_op(val, None)?;
 130                 self.copy_op(val, dest)?;
 131             }
 132
 133             | "ctpop"
 134             | "cttz"
 135             | "cttz_nonzero"
 136             | "ctlz"
 137             | "ctlz_nonzero"
 138             | "bswap"
 139             | "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 out_val = if intrinsic_name.ends_with("_nonzero") {
 149                     if bits == 0 {
 150                         throw_ub_format!("`{}` called on 0", intrinsic_name);
 151                     }
 152                     numeric_intrinsic(intrinsic_name.trim_end_matches("_nonzero"), bits, kind)?
 153                 } else {
 154                     numeric_intrinsic(intrinsic_name, bits, kind)?
 155                 };
 156                 self.write_scalar(out_val, dest)?;
 157             }
 158             | "wrapping_add"
 159             | "wrapping_sub"
 160             | "wrapping_mul"
 161             | "add_with_overflow"
 162             | "sub_with_overflow"
 163             | "mul_with_overflow" => {
 164                 let lhs = self.read_immediate(args[0])?;
 165                 let rhs = self.read_immediate(args[1])?;
 166                 let (bin_op, ignore_overflow) = match intrinsic_name {
 167                     "wrapping_add" => (BinOp::Add, true),
 168                     "wrapping_sub" => (BinOp::Sub, true),
 169                     "wrapping_mul" => (BinOp::Mul, true),
 170                     "add_with_overflow" => (BinOp::Add, false),
 171                     "sub_with_overflow" => (BinOp::Sub, false),
 172                     "mul_with_overflow" => (BinOp::Mul, false),
 173                     _ => bug!("Already checked for int ops")
 174                 };
 175                 if ignore_overflow {
 176                     self.binop_ignore_overflow(bin_op, lhs, rhs, dest)?;
 177                 } else {
 178                     self.binop_with_overflow(bin_op, lhs, rhs, dest)?;
 179                 }
 180             }
 181             "saturating_add" | "saturating_sub" => {
 182                 let l = self.read_immediate(args[0])?;
 183                 let r = self.read_immediate(args[1])?;
 184                 let is_add = intrinsic_name == "saturating_add";
 185                 let (val, overflowed, _ty) = self.overflowing_binary_op(if is_add {
 186                     BinOp::Add
 187                 } else {
 188                     BinOp::Sub
 189                 }, l, r)?;
 190                 let val = if overflowed {
 191                     let num_bits = l.layout.size.bits();
 192                     if l.layout.abi.is_signed() {
 193                         // For signed ints the saturated value depends on the sign of the first
 194                         // term since the sign of the second term can be inferred from this and
 195                         // the fact that the operation has overflowed (if either is 0 no
 196                         // overflow can occur)
 197                         let first_term: u128 = self.force_bits(l.to_scalar()?, l.layout.size)?;
 198                         let first_term_positive = first_term & (1 << (num_bits-1)) == 0;
 199                         if first_term_positive {
 200                             // Negative overflow not possible since the positive first term
 201                             // can only increase an (in range) negative term for addition
 202                             // or corresponding negated positive term for subtraction
 203                             Scalar::from_uint((1u128 << (num_bits - 1)) - 1,  // max positive
 204                                 Size::from_bits(num_bits))
 205                         } else {
 206                             // Positive overflow not possible for similar reason
 207                             // max negative
 208                             Scalar::from_uint(1u128 << (num_bits - 1), Size::from_bits(num_bits))
 209                         }
 210                     } else {  // unsigned
 211                         if is_add {
 212                             // max unsigned
 213                             Scalar::from_uint(u128::max_value() >> (128 - num_bits),
 214                                 Size::from_bits(num_bits))
 215                         } else {  // underflow to 0
 216                             Scalar::from_uint(0u128, Size::from_bits(num_bits))
 217                         }
 218                     }
 219                 } else {
 220                     val
 221                 };
 222                 self.write_scalar(val, dest)?;
 223             }
 224             "unchecked_shl" | "unchecked_shr" => {
 225                 let l = self.read_immediate(args[0])?;
 226                 let r = self.read_immediate(args[1])?;
 227                 let bin_op = match intrinsic_name {
 228                     "unchecked_shl" => BinOp::Shl,
 229                     "unchecked_shr" => BinOp::Shr,
 230                     _ => bug!("Already checked for int ops")
 231                 };
 232                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, l, r)?;
 233                 if overflowed {
 234                     let layout = self.layout_of(substs.type_at(0))?;
 235                     let r_val = self.force_bits(r.to_scalar()?, layout.size)?;
 236                     throw_ub_format!("Overflowing shift by {} in `{}`", r_val, intrinsic_name);
 237                 }
 238                 self.write_scalar(val, dest)?;
 239             }
 240             "rotate_left" | "rotate_right" => {
 241                 // rotate_left: (X << (S % BW)) | (X >> ((BW - S) % BW))
 242                 // rotate_right: (X << ((BW - S) % BW)) | (X >> (S % BW))
 243                 let layout = self.layout_of(substs.type_at(0))?;
 244                 let val = self.read_scalar(args[0])?.not_undef()?;
 245                 let val_bits = self.force_bits(val, layout.size)?;
 246                 let raw_shift = self.read_scalar(args[1])?.not_undef()?;
 247                 let raw_shift_bits = self.force_bits(raw_shift, layout.size)?;
 248                 let width_bits = layout.size.bits() as u128;
 249                 let shift_bits = raw_shift_bits % width_bits;
 250                 let inv_shift_bits = (width_bits - shift_bits) % width_bits;
 251                 let result_bits = if intrinsic_name == "rotate_left" {
 252                     (val_bits << shift_bits) | (val_bits >> inv_shift_bits)
 253                 } else {
 254                     (val_bits >> shift_bits) | (val_bits << inv_shift_bits)
 255                 };
 256                 let truncated_bits = self.truncate(result_bits, layout);
 257                 let result = Scalar::from_uint(truncated_bits, layout.size);
 258                 self.write_scalar(result, dest)?;
 259             }
 260
 261             "ptr_offset_from" => {
 262                 let isize_layout = self.layout_of(self.tcx.types.isize)?;
 263                 let a = self.read_immediate(args[0])?.to_scalar()?;
 264                 let b = self.read_immediate(args[1])?.to_scalar()?;
 265
 266                 // Special case: if both scalars are *equal integers*
 267                 // and not NULL, we pretend there is an allocation of size 0 right there,
 268                 // and their offset is 0. (There's never a valid object at NULL, making it an
 269                 // exception from the exception.)
 270                 // This is the dual to the special exception for offset-by-0
 271                 // in the inbounds pointer offset operation (see the Miri code, `src/operator.rs`).
 272                 if a.is_bits() && b.is_bits() {
 273                     let a = a.to_machine_usize(self)?;
 274                     let b = b.to_machine_usize(self)?;
 275                     if a == b && a != 0 {
 276                         self.write_scalar(Scalar::from_int(0, isize_layout.size), dest)?;
 277                         return Ok(true);
 278                     }
 279                 }
 280
 281                 // General case: we need two pointers.
 282                 let a = self.force_ptr(a)?;
 283                 let b = self.force_ptr(b)?;
 284                 if a.alloc_id != b.alloc_id {
 285                     throw_ub_format!(
 286                         "ptr_offset_from cannot compute offset of pointers into different \
 287                         allocations.",
 288                     );
 289                 }
 290                 let usize_layout = self.layout_of(self.tcx.types.usize)?;
 291                 let a_offset = ImmTy::from_uint(a.offset.bytes(), usize_layout);
 292                 let b_offset = ImmTy::from_uint(b.offset.bytes(), usize_layout);
 293                 let (val, _overflowed, _ty) = self.overflowing_binary_op(
 294                     BinOp::Sub, a_offset, b_offset,
 295                 )?;
 296                 let pointee_layout = self.layout_of(substs.type_at(0))?;
 297                 let val = ImmTy::from_scalar(val, isize_layout);
 298                 let size = ImmTy::from_int(pointee_layout.size.bytes(), isize_layout);
 299                 self.exact_div(val, size, dest)?;
 300             }
 301
 302             "transmute" => {
 303                 self.copy_op_transmute(args[0], dest)?;
 304             }
 305             "simd_insert" => {
 306                 let index = self.read_scalar(args[1])?.to_u32()? as u64;
 307                 let scalar = args[2];
 308                 let input = args[0];
 309                 let (len, e_ty) = self.read_vector_ty(input);
 310                 assert!(
 311                     index < len,
 312                     "Index `{}` must be in bounds of vector type `{}`: `[0, {})`",
 313                     index, e_ty, len
 314                 );
 315                 assert_eq!(
 316                     input.layout, dest.layout,
 317                     "Return type `{}` must match vector type `{}`",
 318                     dest.layout.ty, input.layout.ty
 319                 );
 320                 assert_eq!(
 321                     scalar.layout.ty, e_ty,
 322                     "Scalar type `{}` must match vector element type `{}`",
 323                     scalar.layout.ty, e_ty
 324                 );
 325
 326                 for i in 0..len {
 327                     let place = self.place_field(dest, i)?;
 328                     let value = if i == index {
 329                         scalar
 330                     } else {
 331                         self.operand_field(input, i)?
 332                     };
 333                     self.copy_op(value, place)?;
 334                 }
 335             }
 336             "simd_extract" => {
 337                 let index = self.read_scalar(args[1])?.to_u32()? as _;
 338                 let (len, e_ty) = self.read_vector_ty(args[0]);
 339                 assert!(
 340                     index < len,
 341                     "index `{}` is out-of-bounds of vector type `{}` with length `{}`",
 342                     index, e_ty, len
 343                 );
 344                 assert_eq!(
 345                     e_ty, dest.layout.ty,
 346                     "Return type `{}` must match vector element type `{}`",
 347                     dest.layout.ty, e_ty
 348                 );
 349                 self.copy_op(self.operand_field(args[0], index)?, dest)?;
 350             }
 351             _ => return Ok(false),
 352         }
 353
 354         Ok(true)
 355     }
 356
 357     /// "Intercept" a function call because we have something special to do for it.
 358     /// Returns `true` if an intercept happened.
 359     pub fn hook_fn(
 360         &mut self,
 361         instance: ty::Instance<'tcx>,
 362         args: &[OpTy<'tcx, M::PointerTag>],
 363         _dest: Option<PlaceTy<'tcx, M::PointerTag>>,
 364     ) -> InterpResult<'tcx, bool> {
 365         let def_id = instance.def_id();
 366         if Some(def_id) == self.tcx.lang_items().panic_fn() {
 367             // &'static str, &core::panic::Location { &'static str, u32, u32 }
 368             assert!(args.len() == 2);
 369
 370             let msg_place = self.deref_operand(args[0])?;
 371             let msg = Symbol::intern(self.read_str(msg_place)?);
 372
 373             let location = self.deref_operand(args[1])?;
 374             let (file, line, col) = (
 375                 self.mplace_field(location, 0)?,
 376                 self.mplace_field(location, 1)?,
 377                 self.mplace_field(location, 2)?,
 378             );
 379
 380             let file_place = self.deref_operand(file.into())?;
 381             let file = Symbol::intern(self.read_str(file_place)?);
 382             let line = self.read_scalar(line.into())?.to_u32()?;
 383             let col = self.read_scalar(col.into())?.to_u32()?;
 384             throw_panic!(Panic { msg, file, line, col })
 385         } else if Some(def_id) == self.tcx.lang_items().begin_panic_fn() {
 386             assert!(args.len() == 2);
 387             // &'static str, &(&'static str, u32, u32)
 388             let msg = args[0];
 389             let place = self.deref_operand(args[1])?;
 390             let (file, line, col) = (
 391                 self.mplace_field(place, 0)?,
 392                 self.mplace_field(place, 1)?,
 393                 self.mplace_field(place, 2)?,
 394             );
 395
 396             let msg_place = self.deref_operand(msg.into())?;
 397             let msg = Symbol::intern(self.read_str(msg_place)?);
 398             let file_place = self.deref_operand(file.into())?;
 399             let file = Symbol::intern(self.read_str(file_place)?);
 400             let line = self.read_scalar(line.into())?.to_u32()?;
 401             let col = self.read_scalar(col.into())?.to_u32()?;
 402             throw_panic!(Panic { msg, file, line, col })
 403         } else {
 404             return Ok(false);
 405         }
 406     }
 407
 408     pub fn exact_div(
 409         &mut self,
 410         a: ImmTy<'tcx, M::PointerTag>,
 411         b: ImmTy<'tcx, M::PointerTag>,
 412         dest: PlaceTy<'tcx, M::PointerTag>,
 413     ) -> InterpResult<'tcx> {
 414         // Performs an exact division, resulting in undefined behavior where
 415         // `x % y != 0` or `y == 0` or `x == T::min_value() && y == -1`.
 416         // First, check x % y != 0.
 417         if self.binary_op(BinOp::Rem, a, b)?.to_bits()? != 0 {
 418             // Then, check if `b` is -1, which is the "min_value / -1" case.
 419             let minus1 = Scalar::from_int(-1, dest.layout.size);
 420             let b = b.to_scalar().unwrap();
 421             if b == minus1 {
 422                 throw_ub_format!("exact_div: result of dividing MIN by -1 cannot be represented")
 423             } else {
 424                 throw_ub_format!(
 425                     "exact_div: {} cannot be divided by {} without remainder",
 426                     a.to_scalar().unwrap(),
 427                     b,
 428                 )
 429             }
 430         }
 431         self.binop_ignore_overflow(BinOp::Div, a, b, dest)
 432     }
 433 }