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