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