src/librustc_mir/interpret/terminator.rs

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