src/librustc_mir/interpret/terminator.rs

   1 use std::borrow::Cow;
   2
   3 use rustc::{mir, ty};
   4 use rustc::ty::Instance;
   5 use rustc::ty::layout::{self, TyLayout, LayoutOf};
   6 use syntax::source_map::Span;
   7 use rustc_target::spec::abi::Abi;
   8
   9 use super::{
  10     InterpResult, PointerArithmetic, Scalar,
  11     InterpCx, Machine, Immediate, OpTy, ImmTy, PlaceTy, MPlaceTy, StackPopCleanup, FnVal,
  12 };
  13
  14 impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  15     #[inline]
  16     pub fn goto_block(&mut self, target: Option<mir::BasicBlock>) -> InterpResult<'tcx> {
  17         if let Some(target) = target {
  18             self.frame_mut().block = target;
  19             self.frame_mut().stmt = 0;
  20             Ok(())
  21         } else {
  22             err_ub!(Unreachable)
  23         }
  24     }
  25
  26     pub(super) fn eval_terminator(
  27         &mut self,
  28         terminator: &mir::Terminator<'tcx>,
  29     ) -> InterpResult<'tcx> {
  30         use rustc::mir::TerminatorKind::*;
  31         match terminator.kind {
  32             Return => {
  33                 self.frame().return_place.map(|r| self.dump_place(*r));
  34                 self.pop_stack_frame()?
  35             }
  36
  37             Goto { target } => self.goto_block(Some(target))?,
  38
  39             SwitchInt {
  40                 ref discr,
  41                 ref values,
  42                 ref targets,
  43                 ..
  44             } => {
  45                 let discr = self.read_immediate(self.eval_operand(discr, None)?)?;
  46                 trace!("SwitchInt({:?})", *discr);
  47
  48                 // Branch to the `otherwise` case by default, if no match is found.
  49                 let mut target_block = targets[targets.len() - 1];
  50
  51                 for (index, &const_int) in values.iter().enumerate() {
  52                     // Compare using binary_op, to also support pointer values
  53                     let const_int = Scalar::from_uint(const_int, discr.layout.size);
  54                     let (res, _) = self.binary_op(mir::BinOp::Eq,
  55                         discr,
  56                         ImmTy::from_scalar(const_int, discr.layout),
  57                     )?;
  58                     if res.to_bool()? {
  59                         target_block = targets[index];
  60                         break;
  61                     }
  62                 }
  63
  64                 self.goto_block(Some(target_block))?;
  65             }
  66
  67             Call {
  68                 ref func,
  69                 ref args,
  70                 ref destination,
  71                 ..
  72             } => {
  73                 let (dest, ret) = match *destination {
  74                     Some((ref lv, target)) => (Some(self.eval_place(lv)?), Some(target)),
  75                     None => (None, None),
  76                 };
  77
  78                 let func = self.eval_operand(func, None)?;
  79                 let (fn_val, abi) = match func.layout.ty.sty {
  80                     ty::FnPtr(sig) => {
  81                         let caller_abi = sig.abi();
  82                         let fn_ptr = self.read_scalar(func)?.not_undef()?;
  83                         let fn_val = self.memory.get_fn(fn_ptr)?;
  84                         (fn_val, caller_abi)
  85                     }
  86                     ty::FnDef(def_id, substs) => {
  87                         let sig = func.layout.ty.fn_sig(*self.tcx);
  88                         (FnVal::Instance(self.resolve(def_id, substs)?), sig.abi())
  89                     },
  90                     _ => {
  91                         let msg = format!("can't handle callee of type {:?}", func.layout.ty);
  92                         return err!(Unimplemented(msg));
  93                     }
  94                 };
  95                 let args = self.eval_operands(args)?;
  96                 self.eval_fn_call(
  97                     fn_val,
  98                     terminator.source_info.span,
  99                     abi,
 100                     &args[..],
 101                     dest,
 102                     ret,
 103                 )?;
 104             }
 105
 106             Drop {
 107                 ref location,
 108                 target,
 109                 ..
 110             } => {
 111                 // FIXME(CTFE): forbid drop in const eval
 112                 let place = self.eval_place(location)?;
 113                 let ty = place.layout.ty;
 114                 trace!("TerminatorKind::drop: {:?}, type {}", location, ty);
 115
 116                 let instance = Instance::resolve_drop_in_place(*self.tcx, ty);
 117                 self.drop_in_place(
 118                     place,
 119                     instance,
 120                     terminator.source_info.span,
 121                     target,
 122                 )?;
 123             }
 124
 125             Assert {
 126                 ref cond,
 127                 expected,
 128                 ref msg,
 129                 target,
 130                 ..
 131             } => {
 132                 let cond_val = self.read_immediate(self.eval_operand(cond, None)?)?
 133                     .to_scalar()?.to_bool()?;
 134                 if expected == cond_val {
 135                     self.goto_block(Some(target))?;
 136                 } else {
 137                     // Compute error message
 138                     use rustc::mir::interpret::PanicInfo::*;
 139                     return match msg {
 140                         BoundsCheck { ref len, ref index } => {
 141                             let len = self.read_immediate(self.eval_operand(len, None)?)
 142                                 .expect("can't eval len").to_scalar()?
 143                                 .to_bits(self.memory().pointer_size())? as u64;
 144                             let index = self.read_immediate(self.eval_operand(index, None)?)
 145                                 .expect("can't eval index").to_scalar()?
 146                                 .to_bits(self.memory().pointer_size())? as u64;
 147                             err_panic!(BoundsCheck { len, index })
 148                         }
 149                         Overflow(op) =>
 150                             err_panic!(Overflow(*op)),
 151                         OverflowNeg =>
 152                             err_panic!(OverflowNeg),
 153                         DivisionByZero =>
 154                             err_panic!(DivisionByZero),
 155                         RemainderByZero =>
 156                             err_panic!(RemainderByZero),
 157                         GeneratorResumedAfterReturn =>
 158                             err_panic!(GeneratorResumedAfterReturn),
 159                         GeneratorResumedAfterPanic =>
 160                             err_panic!(GeneratorResumedAfterPanic),
 161                         Panic { .. } =>
 162                             bug!("`Panic` variant cannot occur in MIR"),
 163                     };
 164                 }
 165             }
 166
 167             Yield { .. } |
 168             GeneratorDrop |
 169             DropAndReplace { .. } |
 170             Resume |
 171             Abort => unimplemented!("{:#?}", terminator.kind),
 172             FalseEdges { .. } => bug!("should have been eliminated by\
 173                                       `simplify_branches` mir pass"),
 174             FalseUnwind { .. } => bug!("should have been eliminated by\
 175                                        `simplify_branches` mir pass"),
 176             Unreachable => return err_ub!(Unreachable),
 177         }
 178
 179         Ok(())
 180     }
 181
 182     fn check_argument_compat(
 183         rust_abi: bool,
 184         caller: TyLayout<'tcx>,
 185         callee: TyLayout<'tcx>,
 186     ) -> bool {
 187         if caller.ty == callee.ty {
 188             // No question
 189             return true;
 190         }
 191         if !rust_abi {
 192             // Don't risk anything
 193             return false;
 194         }
 195         // Compare layout
 196         match (&caller.abi, &callee.abi) {
 197             // Different valid ranges are okay (once we enforce validity,
 198             // that will take care to make it UB to leave the range, just
 199             // like for transmute).
 200             (layout::Abi::Scalar(ref caller), layout::Abi::Scalar(ref callee)) =>
 201                 caller.value == callee.value,
 202             (layout::Abi::ScalarPair(ref caller1, ref caller2),
 203              layout::Abi::ScalarPair(ref callee1, ref callee2)) =>
 204                 caller1.value == callee1.value && caller2.value == callee2.value,
 205             // Be conservative
 206             _ => false
 207         }
 208     }
 209
 210     /// Pass a single argument, checking the types for compatibility.
 211     fn pass_argument(
 212         &mut self,
 213         rust_abi: bool,
 214         caller_arg: &mut impl Iterator<Item=OpTy<'tcx, M::PointerTag>>,
 215         callee_arg: PlaceTy<'tcx, M::PointerTag>,
 216     ) -> InterpResult<'tcx> {
 217         if rust_abi && callee_arg.layout.is_zst() {
 218             // Nothing to do.
 219             trace!("Skipping callee ZST");
 220             return Ok(());
 221         }
 222         let caller_arg = caller_arg.next()
 223             .ok_or_else(|| unsup!(FunctionArgCountMismatch)) ?;
 224         if rust_abi {
 225             debug_assert!(!caller_arg.layout.is_zst(), "ZSTs must have been already filtered out");
 226         }
 227         // Now, check
 228         if !Self::check_argument_compat(rust_abi, caller_arg.layout, callee_arg.layout) {
 229             return err!(FunctionArgMismatch(caller_arg.layout.ty, callee_arg.layout.ty));
 230         }
 231         // We allow some transmutes here
 232         self.copy_op_transmute(caller_arg, callee_arg)
 233     }
 234
 235     /// Call this function -- pushing the stack frame and initializing the arguments.
 236     fn eval_fn_call(
 237         &mut self,
 238         fn_val: FnVal<'tcx, M::ExtraFnVal>,
 239         span: Span,
 240         caller_abi: Abi,
 241         args: &[OpTy<'tcx, M::PointerTag>],
 242         dest: Option<PlaceTy<'tcx, M::PointerTag>>,
 243         ret: Option<mir::BasicBlock>,
 244     ) -> InterpResult<'tcx> {
 245         trace!("eval_fn_call: {:#?}", fn_val);
 246
 247         let instance = match fn_val {
 248             FnVal::Instance(instance) => instance,
 249             FnVal::Other(extra) => {
 250                 return M::call_extra_fn(self, extra, args, dest, ret);
 251             }
 252         };
 253
 254         match instance.def {
 255             ty::InstanceDef::Intrinsic(..) => {
 256                 if caller_abi != Abi::RustIntrinsic {
 257                     return err!(FunctionAbiMismatch(caller_abi, Abi::RustIntrinsic));
 258                 }
 259                 // The intrinsic itself cannot diverge, so if we got here without a return
 260                 // place... (can happen e.g., for transmute returning `!`)
 261                 let dest = match dest {
 262                     Some(dest) => dest,
 263                     None => return err_ub!(Unreachable)
 264                 };
 265                 M::call_intrinsic(self, instance, args, dest)?;
 266                 // No stack frame gets pushed, the main loop will just act as if the
 267                 // call completed.
 268                 self.goto_block(ret)?;
 269                 self.dump_place(*dest);
 270                 Ok(())
 271             }
 272             ty::InstanceDef::VtableShim(..) |
 273             ty::InstanceDef::ClosureOnceShim { .. } |
 274             ty::InstanceDef::FnPtrShim(..) |
 275             ty::InstanceDef::DropGlue(..) |
 276             ty::InstanceDef::CloneShim(..) |
 277             ty::InstanceDef::Item(_) => {
 278                 // ABI check
 279                 {
 280                     let callee_abi = {
 281                         let instance_ty = instance.ty(*self.tcx);
 282                         match instance_ty.sty {
 283                             ty::FnDef(..) =>
 284                                 instance_ty.fn_sig(*self.tcx).abi(),
 285                             ty::Closure(..) => Abi::RustCall,
 286                             ty::Generator(..) => Abi::Rust,
 287                             _ => bug!("unexpected callee ty: {:?}", instance_ty),
 288                         }
 289                     };
 290                     let normalize_abi = |abi| match abi {
 291                         Abi::Rust | Abi::RustCall | Abi::RustIntrinsic | Abi::PlatformIntrinsic =>
 292                             // These are all the same ABI, really.
 293                             Abi::Rust,
 294                         abi =>
 295                             abi,
 296                     };
 297                     if normalize_abi(caller_abi) != normalize_abi(callee_abi) {
 298                         return err!(FunctionAbiMismatch(caller_abi, callee_abi));
 299                     }
 300                 }
 301
 302                 // We need MIR for this fn
 303                 let body = match M::find_fn(self, instance, args, dest, ret)? {
 304                     Some(body) => body,
 305                     None => return Ok(()),
 306                 };
 307
 308                 self.push_stack_frame(
 309                     instance,
 310                     span,
 311                     body,
 312                     dest,
 313                     StackPopCleanup::Goto(ret),
 314                 )?;
 315
 316                 // We want to pop this frame again in case there was an error, to put
 317                 // the blame in the right location.  Until the 2018 edition is used in
 318                 // the compiler, we have to do this with an immediately invoked function.
 319                 let res = (||{
 320                     trace!(
 321                         "caller ABI: {:?}, args: {:#?}",
 322                         caller_abi,
 323                         args.iter()
 324                             .map(|arg| (arg.layout.ty, format!("{:?}", **arg)))
 325                             .collect::<Vec<_>>()
 326                     );
 327                     trace!(
 328                         "spread_arg: {:?}, locals: {:#?}",
 329                         body.spread_arg,
 330                         body.args_iter()
 331                             .map(|local|
 332                                 (local, self.layout_of_local(self.frame(), local, None).unwrap().ty)
 333                             )
 334                             .collect::<Vec<_>>()
 335                     );
 336
 337                     // Figure out how to pass which arguments.
 338                     // The Rust ABI is special: ZST get skipped.
 339                     let rust_abi = match caller_abi {
 340                         Abi::Rust | Abi::RustCall => true,
 341                         _ => false
 342                     };
 343                     // We have two iterators: Where the arguments come from,
 344                     // and where they go to.
 345
 346                     // For where they come from: If the ABI is RustCall, we untuple the
 347                     // last incoming argument.  These two iterators do not have the same type,
 348                     // so to keep the code paths uniform we accept an allocation
 349                     // (for RustCall ABI only).
 350                     let caller_args : Cow<'_, [OpTy<'tcx, M::PointerTag>]> =
 351                         if caller_abi == Abi::RustCall && !args.is_empty() {
 352                             // Untuple
 353                             let (&untuple_arg, args) = args.split_last().unwrap();
 354                             trace!("eval_fn_call: Will pass last argument by untupling");
 355                             Cow::from(args.iter().map(|&a| Ok(a))
 356                                 .chain((0..untuple_arg.layout.fields.count()).into_iter()
 357                                     .map(|i| self.operand_field(untuple_arg, i as u64))
 358                                 )
 359                                 .collect::<InterpResult<'_, Vec<OpTy<'tcx, M::PointerTag>>>>()?)
 360                         } else {
 361                             // Plain arg passing
 362                             Cow::from(args)
 363                         };
 364                     // Skip ZSTs
 365                     let mut caller_iter = caller_args.iter()
 366                         .filter(|op| !rust_abi || !op.layout.is_zst())
 367                         .map(|op| *op);
 368
 369                     // Now we have to spread them out across the callee's locals,
 370                     // taking into account the `spread_arg`.  If we could write
 371                     // this is a single iterator (that handles `spread_arg`), then
 372                     // `pass_argument` would be the loop body. It takes care to
 373                     // not advance `caller_iter` for ZSTs.
 374                     let mut locals_iter = body.args_iter();
 375                     while let Some(local) = locals_iter.next() {
 376                         let dest = self.eval_place(
 377                             &mir::Place::from(local)
 378                         )?;
 379                         if Some(local) == body.spread_arg {
 380                             // Must be a tuple
 381                             for i in 0..dest.layout.fields.count() {
 382                                 let dest = self.place_field(dest, i as u64)?;
 383                                 self.pass_argument(rust_abi, &mut caller_iter, dest)?;
 384                             }
 385                         } else {
 386                             // Normal argument
 387                             self.pass_argument(rust_abi, &mut caller_iter, dest)?;
 388                         }
 389                     }
 390                     // Now we should have no more caller args
 391                     if caller_iter.next().is_some() {
 392                         trace!("Caller has passed too many args");
 393                         return err!(FunctionArgCountMismatch);
 394                     }
 395                     // Don't forget to check the return type!
 396                     if let Some(caller_ret) = dest {
 397                         let callee_ret = self.eval_place(
 398                             &mir::Place::RETURN_PLACE
 399                         )?;
 400                         if !Self::check_argument_compat(
 401                             rust_abi,
 402                             caller_ret.layout,
 403                             callee_ret.layout,
 404                         ) {
 405                             return err!(
 406                                 FunctionRetMismatch(caller_ret.layout.ty, callee_ret.layout.ty)
 407                             );
 408                         }
 409                     } else {
 410                         let local = mir::RETURN_PLACE;
 411                         let ty = self.frame().body.local_decls[local].ty;
 412                         if !self.tcx.is_ty_uninhabited_from_any_module(ty) {
 413                             return err!(FunctionRetMismatch(self.tcx.types.never, ty));
 414                         }
 415                     }
 416                     Ok(())
 417                 })();
 418                 match res {
 419                     Err(err) => {
 420                         self.stack.pop();
 421                         Err(err)
 422                     }
 423                     Ok(v) => Ok(v)
 424                 }
 425             }
 426             // cannot use the shim here, because that will only result in infinite recursion
 427             ty::InstanceDef::Virtual(_, idx) => {
 428                 let mut args = args.to_vec();
 429                 let ptr_size = self.pointer_size();
 430                 // We have to implement all "object safe receivers".  Currently we
 431                 // support built-in pointers (&, &mut, Box) as well as unsized-self.  We do
 432                 // not yet support custom self types.
 433                 // Also see librustc_codegen_llvm/abi.rs and librustc_codegen_llvm/mir/block.rs.
 434                 let receiver_place = match args[0].layout.ty.builtin_deref(true) {
 435                     Some(_) => {
 436                         // Built-in pointer.
 437                         self.deref_operand(args[0])?
 438                     }
 439                     None => {
 440                         // Unsized self.
 441                         args[0].assert_mem_place()
 442                     }
 443                 };
 444                 // Find and consult vtable
 445                 let vtable = receiver_place.vtable();
 446                 let vtable_slot = vtable.ptr_offset(ptr_size * (idx as u64 + 3), self)?;
 447                 let vtable_slot = self.memory.check_ptr_access(
 448                     vtable_slot,
 449                     ptr_size,
 450                     self.tcx.data_layout.pointer_align.abi,
 451                 )?.expect("cannot be a ZST");
 452                 let fn_ptr = self.memory.get(vtable_slot.alloc_id)?
 453                     .read_ptr_sized(self, vtable_slot)?.not_undef()?;
 454                 let drop_fn = self.memory.get_fn(fn_ptr)?;
 455
 456                 // `*mut receiver_place.layout.ty` is almost the layout that we
 457                 // want for args[0]: We have to project to field 0 because we want
 458                 // a thin pointer.
 459                 assert!(receiver_place.layout.is_unsized());
 460                 let receiver_ptr_ty = self.tcx.mk_mut_ptr(receiver_place.layout.ty);
 461                 let this_receiver_ptr = self.layout_of(receiver_ptr_ty)?.field(self, 0)?;
 462                 // Adjust receiver argument.
 463                 args[0] = OpTy::from(ImmTy {
 464                     layout: this_receiver_ptr,
 465                     imm: Immediate::Scalar(receiver_place.ptr.into())
 466                 });
 467                 trace!("Patched self operand to {:#?}", args[0]);
 468                 // recurse with concrete function
 469                 self.eval_fn_call(drop_fn, span, caller_abi, &args, dest, ret)
 470             }
 471         }
 472     }
 473
 474     fn drop_in_place(
 475         &mut self,
 476         place: PlaceTy<'tcx, M::PointerTag>,
 477         instance: ty::Instance<'tcx>,
 478         span: Span,
 479         target: mir::BasicBlock,
 480     ) -> InterpResult<'tcx> {
 481         trace!("drop_in_place: {:?},\n  {:?}, {:?}", *place, place.layout.ty, instance);
 482         // We take the address of the object.  This may well be unaligned, which is fine
 483         // for us here.  However, unaligned accesses will probably make the actual drop
 484         // implementation fail -- a problem shared by rustc.
 485         let place = self.force_allocation(place)?;
 486
 487         let (instance, place) = match place.layout.ty.sty {
 488             ty::Dynamic(..) => {
 489                 // Dropping a trait object.
 490                 self.unpack_dyn_trait(place)?
 491             }
 492             _ => (instance, place),
 493         };
 494
 495         let arg = ImmTy {
 496             imm: place.to_ref(),
 497             layout: self.layout_of(self.tcx.mk_mut_ptr(place.layout.ty))?,
 498         };
 499
 500         let ty = self.tcx.mk_unit(); // return type is ()
 501         let dest = MPlaceTy::dangling(self.layout_of(ty)?, self);
 502
 503         self.eval_fn_call(
 504             FnVal::Instance(instance),
 505             span,
 506             Abi::Rust,
 507             &[arg.into()],
 508             Some(dest.into()),
 509             Some(target),
 510         )
 511     }
 512 }