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 rustc::mir::interpret::{InterpResult, PointerArithmetic, InterpError, Scalar};
  10 use super::{
  11     InterpretCx, Machine, Immediate, OpTy, ImmTy, PlaceTy, MPlaceTy, StackPopCleanup
  12 };
  13
  14 impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> InterpretCx<'a, '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!(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_def, abi) = match func.layout.ty.sty {
  80                     ty::FnPtr(sig) => {
  81                         let caller_abi = sig.abi();
  82                         let fn_ptr = self.read_scalar(func)?.to_ptr()?;
  83                         let instance = self.memory.get_fn(fn_ptr)?;
  84                         (instance, caller_abi)
  85                     }
  86                     ty::FnDef(def_id, substs) => {
  87                         let sig = func.layout.ty.fn_sig(*self.tcx);
  88                         (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_def,
  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::InterpError::*;
 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!(BoundsCheck { len, index })
 148                         }
 149                         Overflow(op) => Err(Overflow(op).into()),
 150                         OverflowNeg => Err(OverflowNeg.into()),
 151                         DivisionByZero => Err(DivisionByZero.into()),
 152                         RemainderByZero => Err(RemainderByZero.into()),
 153                         GeneratorResumedAfterReturn |
 154                         GeneratorResumedAfterPanic => unimplemented!(),
 155                         _ => bug!(),
 156                     };
 157                 }
 158             }
 159
 160             Yield { .. } |
 161             GeneratorDrop |
 162             DropAndReplace { .. } |
 163             Resume |
 164             Abort => unimplemented!("{:#?}", terminator.kind),
 165             FalseEdges { .. } => bug!("should have been eliminated by\
 166                                       `simplify_branches` mir pass"),
 167             FalseUnwind { .. } => bug!("should have been eliminated by\
 168                                        `simplify_branches` mir pass"),
 169             Unreachable => return err!(Unreachable),
 170         }
 171
 172         Ok(())
 173     }
 174
 175     fn check_argument_compat(
 176         rust_abi: bool,
 177         caller: TyLayout<'tcx>,
 178         callee: TyLayout<'tcx>,
 179     ) -> bool {
 180         if caller.ty == callee.ty {
 181             // No question
 182             return true;
 183         }
 184         if !rust_abi {
 185             // Don't risk anything
 186             return false;
 187         }
 188         // Compare layout
 189         match (&caller.abi, &callee.abi) {
 190             // Different valid ranges are okay (once we enforce validity,
 191             // that will take care to make it UB to leave the range, just
 192             // like for transmute).
 193             (layout::Abi::Scalar(ref caller), layout::Abi::Scalar(ref callee)) =>
 194                 caller.value == callee.value,
 195             (layout::Abi::ScalarPair(ref caller1, ref caller2),
 196              layout::Abi::ScalarPair(ref callee1, ref callee2)) =>
 197                 caller1.value == callee1.value && caller2.value == callee2.value,
 198             // Be conservative
 199             _ => false
 200         }
 201     }
 202
 203     /// Pass a single argument, checking the types for compatibility.
 204     fn pass_argument(
 205         &mut self,
 206         rust_abi: bool,
 207         caller_arg: &mut impl Iterator<Item=OpTy<'tcx, M::PointerTag>>,
 208         callee_arg: PlaceTy<'tcx, M::PointerTag>,
 209     ) -> InterpResult<'tcx> {
 210         if rust_abi && callee_arg.layout.is_zst() {
 211             // Nothing to do.
 212             trace!("Skipping callee ZST");
 213             return Ok(());
 214         }
 215         let caller_arg = caller_arg.next()
 216             .ok_or_else(|| InterpError::FunctionArgCountMismatch)?;
 217         if rust_abi {
 218             debug_assert!(!caller_arg.layout.is_zst(), "ZSTs must have been already filtered out");
 219         }
 220         // Now, check
 221         if !Self::check_argument_compat(rust_abi, caller_arg.layout, callee_arg.layout) {
 222             return err!(FunctionArgMismatch(caller_arg.layout.ty, callee_arg.layout.ty));
 223         }
 224         // We allow some transmutes here
 225         self.copy_op_transmute(caller_arg, callee_arg)
 226     }
 227
 228     /// Call this function -- pushing the stack frame and initializing the arguments.
 229     fn eval_fn_call(
 230         &mut self,
 231         instance: ty::Instance<'tcx>,
 232         span: Span,
 233         caller_abi: Abi,
 234         args: &[OpTy<'tcx, M::PointerTag>],
 235         dest: Option<PlaceTy<'tcx, M::PointerTag>>,
 236         ret: Option<mir::BasicBlock>,
 237     ) -> InterpResult<'tcx> {
 238         trace!("eval_fn_call: {:#?}", instance);
 239
 240         match instance.def {
 241             ty::InstanceDef::Intrinsic(..) => {
 242                 if caller_abi != Abi::RustIntrinsic {
 243                     return err!(FunctionAbiMismatch(caller_abi, Abi::RustIntrinsic));
 244                 }
 245                 // The intrinsic itself cannot diverge, so if we got here without a return
 246                 // place... (can happen e.g., for transmute returning `!`)
 247                 let dest = match dest {
 248                     Some(dest) => dest,
 249                     None => return err!(Unreachable)
 250                 };
 251                 M::call_intrinsic(self, instance, args, dest)?;
 252                 // No stack frame gets pushed, the main loop will just act as if the
 253                 // call completed.
 254                 self.goto_block(ret)?;
 255                 self.dump_place(*dest);
 256                 Ok(())
 257             }
 258             ty::InstanceDef::VtableShim(..) |
 259             ty::InstanceDef::ClosureOnceShim { .. } |
 260             ty::InstanceDef::FnPtrShim(..) |
 261             ty::InstanceDef::DropGlue(..) |
 262             ty::InstanceDef::CloneShim(..) |
 263             ty::InstanceDef::Item(_) => {
 264                 // ABI check
 265                 {
 266                     let callee_abi = {
 267                         let instance_ty = instance.ty(*self.tcx);
 268                         match instance_ty.sty {
 269                             ty::FnDef(..) =>
 270                                 instance_ty.fn_sig(*self.tcx).abi(),
 271                             ty::Closure(..) => Abi::RustCall,
 272                             ty::Generator(..) => Abi::Rust,
 273                             _ => bug!("unexpected callee ty: {:?}", instance_ty),
 274                         }
 275                     };
 276                     // Rust and RustCall are compatible
 277                     let normalize_abi = |abi| if abi == Abi::RustCall { Abi::Rust } else { abi };
 278                     if normalize_abi(caller_abi) != normalize_abi(callee_abi) {
 279                         return err!(FunctionAbiMismatch(caller_abi, callee_abi));
 280                     }
 281                 }
 282
 283                 // We need MIR for this fn
 284                 let mir = match M::find_fn(self, instance, args, dest, ret)? {
 285                     Some(mir) => mir,
 286                     None => return Ok(()),
 287                 };
 288
 289                 self.push_stack_frame(
 290                     instance,
 291                     span,
 292                     mir,
 293                     dest,
 294                     StackPopCleanup::Goto(ret),
 295                 )?;
 296
 297                 // We want to pop this frame again in case there was an error, to put
 298                 // the blame in the right location.  Until the 2018 edition is used in
 299                 // the compiler, we have to do this with an immediately invoked function.
 300                 let res = (||{
 301                     trace!(
 302                         "caller ABI: {:?}, args: {:#?}",
 303                         caller_abi,
 304                         args.iter()
 305                             .map(|arg| (arg.layout.ty, format!("{:?}", **arg)))
 306                             .collect::<Vec<_>>()
 307                     );
 308                     trace!(
 309                         "spread_arg: {:?}, locals: {:#?}",
 310                         mir.spread_arg,
 311                         mir.args_iter()
 312                             .map(|local|
 313                                 (local, self.layout_of_local(self.frame(), local, None).unwrap().ty)
 314                             )
 315                             .collect::<Vec<_>>()
 316                     );
 317
 318                     // Figure out how to pass which arguments.
 319                     // The Rust ABI is special: ZST get skipped.
 320                     let rust_abi = match caller_abi {
 321                         Abi::Rust | Abi::RustCall => true,
 322                         _ => false
 323                     };
 324                     // We have two iterators: Where the arguments come from,
 325                     // and where they go to.
 326
 327                     // For where they come from: If the ABI is RustCall, we untuple the
 328                     // last incoming argument.  These two iterators do not have the same type,
 329                     // so to keep the code paths uniform we accept an allocation
 330                     // (for RustCall ABI only).
 331                     let caller_args : Cow<'_, [OpTy<'tcx, M::PointerTag>]> =
 332                         if caller_abi == Abi::RustCall && !args.is_empty() {
 333                             // Untuple
 334                             let (&untuple_arg, args) = args.split_last().unwrap();
 335                             trace!("eval_fn_call: Will pass last argument by untupling");
 336                             Cow::from(args.iter().map(|&a| Ok(a))
 337                                 .chain((0..untuple_arg.layout.fields.count()).into_iter()
 338                                     .map(|i| self.operand_field(untuple_arg, i as u64))
 339                                 )
 340                                 .collect::<InterpResult<'_, Vec<OpTy<'tcx, M::PointerTag>>>>()?)
 341                         } else {
 342                             // Plain arg passing
 343                             Cow::from(args)
 344                         };
 345                     // Skip ZSTs
 346                     let mut caller_iter = caller_args.iter()
 347                         .filter(|op| !rust_abi || !op.layout.is_zst())
 348                         .map(|op| *op);
 349
 350                     // Now we have to spread them out across the callee's locals,
 351                     // taking into account the `spread_arg`.  If we could write
 352                     // this is a single iterator (that handles `spread_arg`), then
 353                     // `pass_argument` would be the loop body. It takes care to
 354                     // not advance `caller_iter` for ZSTs.
 355                     let mut locals_iter = mir.args_iter();
 356                     while let Some(local) = locals_iter.next() {
 357                         let dest = self.eval_place(
 358                             &mir::Place::Base(mir::PlaceBase::Local(local))
 359                         )?;
 360                         if Some(local) == mir.spread_arg {
 361                             // Must be a tuple
 362                             for i in 0..dest.layout.fields.count() {
 363                                 let dest = self.place_field(dest, i as u64)?;
 364                                 self.pass_argument(rust_abi, &mut caller_iter, dest)?;
 365                             }
 366                         } else {
 367                             // Normal argument
 368                             self.pass_argument(rust_abi, &mut caller_iter, dest)?;
 369                         }
 370                     }
 371                     // Now we should have no more caller args
 372                     if caller_iter.next().is_some() {
 373                         trace!("Caller has passed too many args");
 374                         return err!(FunctionArgCountMismatch);
 375                     }
 376                     // Don't forget to check the return type!
 377                     if let Some(caller_ret) = dest {
 378                         let callee_ret = self.eval_place(
 379                             &mir::Place::RETURN_PLACE
 380                         )?;
 381                         if !Self::check_argument_compat(
 382                             rust_abi,
 383                             caller_ret.layout,
 384                             callee_ret.layout,
 385                         ) {
 386                             return err!(FunctionRetMismatch(
 387                                 caller_ret.layout.ty, callee_ret.layout.ty
 388                             ));
 389                         }
 390                     } else {
 391                         let callee_layout =
 392                             self.layout_of_local(self.frame(), mir::RETURN_PLACE, None)?;
 393                         if !callee_layout.abi.is_uninhabited() {
 394                             return err!(FunctionRetMismatch(
 395                                 self.tcx.types.never, callee_layout.ty
 396                             ));
 397                         }
 398                     }
 399                     Ok(())
 400                 })();
 401                 match res {
 402                     Err(err) => {
 403                         self.stack.pop();
 404                         Err(err)
 405                     }
 406                     Ok(v) => Ok(v)
 407                 }
 408             }
 409             // cannot use the shim here, because that will only result in infinite recursion
 410             ty::InstanceDef::Virtual(_, idx) => {
 411                 let mut args = args.to_vec();
 412                 let ptr_size = self.pointer_size();
 413                 // We have to implement all "object safe receivers".  Currently we
 414                 // support built-in pointers (&, &mut, Box) as well as unsized-self.  We do
 415                 // not yet support custom self types.
 416                 // Also see librustc_codegen_llvm/abi.rs and librustc_codegen_llvm/mir/block.rs.
 417                 let receiver_place = match args[0].layout.ty.builtin_deref(true) {
 418                     Some(_) => {
 419                         // Built-in pointer.
 420                         self.deref_operand(args[0])?
 421                     }
 422                     None => {
 423                         // Unsized self.
 424                         args[0].to_mem_place()
 425                     }
 426                 };
 427                 // Find and consult vtable
 428                 let vtable = receiver_place.vtable()?;
 429                 self.memory.check_align(vtable.into(), self.tcx.data_layout.pointer_align.abi)?;
 430                 let fn_ptr = self.memory.get(vtable.alloc_id)?.read_ptr_sized(
 431                     self,
 432                     vtable.offset(ptr_size * (idx as u64 + 3), self)?,
 433                 )?.to_ptr()?;
 434                 let instance = self.memory.get_fn(fn_ptr)?;
 435
 436                 // `*mut receiver_place.layout.ty` is almost the layout that we
 437                 // want for args[0]: We have to project to field 0 because we want
 438                 // a thin pointer.
 439                 assert!(receiver_place.layout.is_unsized());
 440                 let receiver_ptr_ty = self.tcx.mk_mut_ptr(receiver_place.layout.ty);
 441                 let this_receiver_ptr = self.layout_of(receiver_ptr_ty)?.field(self, 0)?;
 442                 // Adjust receiver argument.
 443                 args[0] = OpTy::from(ImmTy {
 444                     layout: this_receiver_ptr,
 445                     imm: Immediate::Scalar(receiver_place.ptr.into())
 446                 });
 447                 trace!("Patched self operand to {:#?}", args[0]);
 448                 // recurse with concrete function
 449                 self.eval_fn_call(instance, span, caller_abi, &args, dest, ret)
 450             }
 451         }
 452     }
 453
 454     fn drop_in_place(
 455         &mut self,
 456         place: PlaceTy<'tcx, M::PointerTag>,
 457         instance: ty::Instance<'tcx>,
 458         span: Span,
 459         target: mir::BasicBlock,
 460     ) -> InterpResult<'tcx> {
 461         trace!("drop_in_place: {:?},\n  {:?}, {:?}", *place, place.layout.ty, instance);
 462         // We take the address of the object.  This may well be unaligned, which is fine
 463         // for us here.  However, unaligned accesses will probably make the actual drop
 464         // implementation fail -- a problem shared by rustc.
 465         let place = self.force_allocation(place)?;
 466
 467         let (instance, place) = match place.layout.ty.sty {
 468             ty::Dynamic(..) => {
 469                 // Dropping a trait object.
 470                 self.unpack_dyn_trait(place)?
 471             }
 472             _ => (instance, place),
 473         };
 474
 475         let arg = ImmTy {
 476             imm: place.to_ref(),
 477             layout: self.layout_of(self.tcx.mk_mut_ptr(place.layout.ty))?,
 478         };
 479
 480         let ty = self.tcx.mk_unit(); // return type is ()
 481         let dest = MPlaceTy::dangling(self.layout_of(ty)?, self);
 482
 483         self.eval_fn_call(
 484             instance,
 485             span,
 486             Abi::Rust,
 487             &[arg.into()],
 488             Some(dest.into()),
 489             Some(target),
 490         )
 491     }
 492 }