src/librustc_mir/interpret/terminator.rs

   1 // Copyright 2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use std::borrow::Cow;
  12
  13 use rustc::{mir, ty};
  14 use rustc::ty::layout::{self, TyLayout, LayoutOf};
  15 use syntax::source_map::Span;
  16 use rustc_target::spec::abi::Abi;
  17
  18 use rustc::mir::interpret::{EvalResult, PointerArithmetic, EvalErrorKind, Scalar};
  19 use super::{
  20     EvalContext, Machine, Immediate, OpTy, PlaceTy, MPlaceTy, Operand, StackPopCleanup
  21 };
  22
  23 impl<'a, 'mir, 'tcx, M: Machine<'a, 'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
  24     #[inline]
  25     pub fn goto_block(&mut self, target: Option<mir::BasicBlock>) -> EvalResult<'tcx> {
  26         if let Some(target) = target {
  27             self.frame_mut().block = target;
  28             self.frame_mut().stmt = 0;
  29             Ok(())
  30         } else {
  31             err!(Unreachable)
  32         }
  33     }
  34
  35     pub(super) fn eval_terminator(
  36         &mut self,
  37         terminator: &mir::Terminator<'tcx>,
  38     ) -> EvalResult<'tcx> {
  39         use rustc::mir::TerminatorKind::*;
  40         match terminator.kind {
  41             Return => {
  42                 self.frame().return_place.map(|r| self.dump_place(*r));
  43                 self.pop_stack_frame()?
  44             }
  45
  46             Goto { target } => self.goto_block(Some(target))?,
  47
  48             SwitchInt {
  49                 ref discr,
  50                 ref values,
  51                 ref targets,
  52                 ..
  53             } => {
  54                 let discr = self.read_immediate(self.eval_operand(discr, None)?)?;
  55                 trace!("SwitchInt({:?})", *discr);
  56
  57                 // Branch to the `otherwise` case by default, if no match is found.
  58                 let mut target_block = targets[targets.len() - 1];
  59
  60                 for (index, &const_int) in values.iter().enumerate() {
  61                     // Compare using binary_op, to also support pointer values
  62                     let const_int = Scalar::from_uint(const_int, discr.layout.size);
  63                     let (res, _) = self.binary_op(mir::BinOp::Eq,
  64                         discr.to_scalar()?, discr.layout,
  65                         const_int, discr.layout,
  66                     )?;
  67                     if res.to_bool()? {
  68                         target_block = targets[index];
  69                         break;
  70                     }
  71                 }
  72
  73                 self.goto_block(Some(target_block))?;
  74             }
  75
  76             Call {
  77                 ref func,
  78                 ref args,
  79                 ref destination,
  80                 ..
  81             } => {
  82                 let (dest, ret) = match *destination {
  83                     Some((ref lv, target)) => (Some(self.eval_place(lv)?), Some(target)),
  84                     None => (None, None),
  85                 };
  86
  87                 let func = self.eval_operand(func, None)?;
  88                 let (fn_def, abi) = match func.layout.ty.sty {
  89                     ty::FnPtr(sig) => {
  90                         let caller_abi = sig.abi();
  91                         let fn_ptr = self.read_scalar(func)?.to_ptr()?;
  92                         let instance = self.memory.get_fn(fn_ptr)?;
  93                         (instance, caller_abi)
  94                     }
  95                     ty::FnDef(def_id, substs) => {
  96                         let sig = func.layout.ty.fn_sig(*self.tcx);
  97                         (self.resolve(def_id, substs)?, sig.abi())
  98                     },
  99                     _ => {
 100                         let msg = format!("can't handle callee of type {:?}", func.layout.ty);
 101                         return err!(Unimplemented(msg));
 102                     }
 103                 };
 104                 let args = self.eval_operands(args)?;
 105                 self.eval_fn_call(
 106                     fn_def,
 107                     terminator.source_info.span,
 108                     abi,
 109                     &args[..],
 110                     dest,
 111                     ret,
 112                 )?;
 113             }
 114
 115             Drop {
 116                 ref location,
 117                 target,
 118                 ..
 119             } => {
 120                 // FIXME(CTFE): forbid drop in const eval
 121                 let place = self.eval_place(location)?;
 122                 let ty = place.layout.ty;
 123                 trace!("TerminatorKind::drop: {:?}, type {}", location, ty);
 124
 125                 let instance = ::monomorphize::resolve_drop_in_place(*self.tcx, ty);
 126                 self.drop_in_place(
 127                     place,
 128                     instance,
 129                     terminator.source_info.span,
 130                     target,
 131                 )?;
 132             }
 133
 134             Assert {
 135                 ref cond,
 136                 expected,
 137                 ref msg,
 138                 target,
 139                 ..
 140             } => {
 141                 let cond_val = self.read_immediate(self.eval_operand(cond, None)?)?
 142                     .to_scalar()?.to_bool()?;
 143                 if expected == cond_val {
 144                     self.goto_block(Some(target))?;
 145                 } else {
 146                     // Compute error message
 147                     use rustc::mir::interpret::EvalErrorKind::*;
 148                     return match *msg {
 149                         BoundsCheck { ref len, ref index } => {
 150                             let len = self.read_immediate(self.eval_operand(len, None)?)
 151                                 .expect("can't eval len").to_scalar()?
 152                                 .to_bits(self.memory().pointer_size())? as u64;
 153                             let index = self.read_immediate(self.eval_operand(index, None)?)
 154                                 .expect("can't eval index").to_scalar()?
 155                                 .to_bits(self.memory().pointer_size())? as u64;
 156                             err!(BoundsCheck { len, index })
 157                         }
 158                         Overflow(op) => Err(Overflow(op).into()),
 159                         OverflowNeg => Err(OverflowNeg.into()),
 160                         DivisionByZero => Err(DivisionByZero.into()),
 161                         RemainderByZero => Err(RemainderByZero.into()),
 162                         GeneratorResumedAfterReturn |
 163                         GeneratorResumedAfterPanic => unimplemented!(),
 164                         _ => bug!(),
 165                     };
 166                 }
 167             }
 168
 169             Yield { .. } |
 170             GeneratorDrop |
 171             DropAndReplace { .. } |
 172             Resume |
 173             Abort => unimplemented!("{:#?}", terminator.kind),
 174             FalseEdges { .. } => bug!("should have been eliminated by\
 175                                       `simplify_branches` mir pass"),
 176             FalseUnwind { .. } => bug!("should have been eliminated by\
 177                                        `simplify_branches` mir pass"),
 178             Unreachable => return err!(Unreachable),
 179         }
 180
 181         Ok(())
 182     }
 183
 184     fn check_argument_compat(
 185         caller: TyLayout<'tcx>,
 186         callee: TyLayout<'tcx>,
 187     ) -> bool {
 188         if caller.ty == callee.ty {
 189             // No question
 190             return true;
 191         }
 192         // Compare layout
 193         match (&caller.abi, &callee.abi) {
 194             (layout::Abi::Scalar(ref caller), layout::Abi::Scalar(ref callee)) =>
 195                 // Different valid ranges are okay (once we enforce validity,
 196                 // that will take care to make it UB to leave the range, just
 197                 // like for transmute).
 198                 caller.value == callee.value,
 199             (layout::Abi::ScalarPair(ref caller1, ref caller2),
 200              layout::Abi::ScalarPair(ref callee1, ref callee2)) =>
 201                 caller1.value == callee1.value && caller2.value == callee2.value,
 202             // Be conservative
 203             _ => false
 204         }
 205     }
 206
 207     /// Pass a single argument, checking the types for compatibility.
 208     fn pass_argument(
 209         &mut self,
 210         skip_zst: bool,
 211         caller_arg: &mut impl Iterator<Item=OpTy<'tcx, M::PointerTag>>,
 212         callee_arg: PlaceTy<'tcx, M::PointerTag>,
 213     ) -> EvalResult<'tcx> {
 214         if skip_zst && callee_arg.layout.is_zst() {
 215             // Nothing to do.
 216             trace!("Skipping callee ZST");
 217             return Ok(());
 218         }
 219         let caller_arg = caller_arg.next()
 220             .ok_or_else(|| EvalErrorKind::FunctionArgCountMismatch)?;
 221         if skip_zst {
 222             debug_assert!(!caller_arg.layout.is_zst(), "ZSTs must have been already filtered out");
 223         }
 224         // Now, check
 225         if !Self::check_argument_compat(caller_arg.layout, callee_arg.layout) {
 226             return err!(FunctionArgMismatch(caller_arg.layout.ty, callee_arg.layout.ty));
 227         }
 228         // We allow some transmutes here
 229         self.copy_op_transmute(caller_arg, callee_arg)
 230     }
 231
 232     /// Call this function -- pushing the stack frame and initializing the arguments.
 233     fn eval_fn_call(
 234         &mut self,
 235         instance: ty::Instance<'tcx>,
 236         span: Span,
 237         caller_abi: Abi,
 238         args: &[OpTy<'tcx, M::PointerTag>],
 239         dest: Option<PlaceTy<'tcx, M::PointerTag>>,
 240         ret: Option<mir::BasicBlock>,
 241     ) -> EvalResult<'tcx> {
 242         trace!("eval_fn_call: {:#?}", instance);
 243
 244         match instance.def {
 245             ty::InstanceDef::Intrinsic(..) => {
 246                 if caller_abi != Abi::RustIntrinsic {
 247                     return err!(FunctionAbiMismatch(caller_abi, Abi::RustIntrinsic));
 248                 }
 249                 // The intrinsic itself cannot diverge, so if we got here without a return
 250                 // place... (can happen e.g. for transmute returning `!`)
 251                 let dest = match dest {
 252                     Some(dest) => dest,
 253                     None => return err!(Unreachable)
 254                 };
 255                 M::call_intrinsic(self, instance, args, dest)?;
 256                 // No stack frame gets pushed, the main loop will just act as if the
 257                 // call completed.
 258                 self.goto_block(ret)?;
 259                 self.dump_place(*dest);
 260                 Ok(())
 261             }
 262             ty::InstanceDef::VtableShim(..) |
 263             ty::InstanceDef::ClosureOnceShim { .. } |
 264             ty::InstanceDef::FnPtrShim(..) |
 265             ty::InstanceDef::DropGlue(..) |
 266             ty::InstanceDef::CloneShim(..) |
 267             ty::InstanceDef::Item(_) => {
 268                 // ABI check
 269                 {
 270                     let callee_abi = {
 271                         let instance_ty = instance.ty(*self.tcx);
 272                         match instance_ty.sty {
 273                             ty::FnDef(..) =>
 274                                 instance_ty.fn_sig(*self.tcx).abi(),
 275                             ty::Closure(..) => Abi::RustCall,
 276                             ty::Generator(..) => Abi::Rust,
 277                             _ => bug!("unexpected callee ty: {:?}", instance_ty),
 278                         }
 279                     };
 280                     // Rust and RustCall are compatible
 281                     let normalize_abi = |abi| if abi == Abi::RustCall { Abi::Rust } else { abi };
 282                     if normalize_abi(caller_abi) != normalize_abi(callee_abi) {
 283                         return err!(FunctionAbiMismatch(caller_abi, callee_abi));
 284                     }
 285                 }
 286
 287                 // We need MIR for this fn
 288                 let mir = match M::find_fn(self, instance, args, dest, ret)? {
 289                     Some(mir) => mir,
 290                     None => return Ok(()),
 291                 };
 292
 293                 self.push_stack_frame(
 294                     instance,
 295                     span,
 296                     mir,
 297                     dest,
 298                     StackPopCleanup::Goto(ret),
 299                 )?;
 300
 301                 // We want to pop this frame again in case there was an error, to put
 302                 // the blame in the right location.  Until the 2018 edition is used in
 303                 // the compiler, we have to do this with an immediately invoked function.
 304                 let res = (||{
 305                     trace!(
 306                         "caller ABI: {:?}, args: {:#?}",
 307                         caller_abi,
 308                         args.iter()
 309                             .map(|arg| (arg.layout.ty, format!("{:?}", **arg)))
 310                             .collect::<Vec<_>>()
 311                     );
 312                     trace!(
 313                         "spread_arg: {:?}, locals: {:#?}",
 314                         mir.spread_arg,
 315                         mir.args_iter()
 316                             .map(|local|
 317                                 (local, self.layout_of_local(self.frame(), local).unwrap().ty)
 318                             )
 319                             .collect::<Vec<_>>()
 320                     );
 321
 322                     // Figure out how to pass which arguments.
 323                     // We have two iterators: Where the arguments come from,
 324                     // and where they go to.
 325                     let skip_zst = match caller_abi {
 326                         Abi::Rust | Abi::RustCall => true,
 327                         _ => false
 328                     };
 329
 330                     // For where they come from: If the ABI is RustCall, we untuple the
 331                     // last incoming argument.  These two iterators do not have the same type,
 332                     // so to keep the code paths uniform we accept an allocation
 333                     // (for RustCall ABI only).
 334                     let caller_args : Cow<[OpTy<'tcx, M::PointerTag>]> =
 335                         if caller_abi == Abi::RustCall && !args.is_empty() {
 336                             // Untuple
 337                             let (&untuple_arg, args) = args.split_last().unwrap();
 338                             trace!("eval_fn_call: Will pass last argument by untupling");
 339                             Cow::from(args.iter().map(|&a| Ok(a))
 340                                 .chain((0..untuple_arg.layout.fields.count()).into_iter()
 341                                     .map(|i| self.operand_field(untuple_arg, i as u64))
 342                                 )
 343                                 .collect::<EvalResult<Vec<OpTy<'tcx, M::PointerTag>>>>()?)
 344                         } else {
 345                             // Plain arg passing
 346                             Cow::from(args)
 347                         };
 348                     // Skip ZSTs
 349                     let mut caller_iter = caller_args.iter()
 350                         .filter(|op| !skip_zst || !op.layout.is_zst())
 351                         .map(|op| *op);
 352
 353                     // Now we have to spread them out across the callee's locals,
 354                     // taking into account the `spread_arg`.  If we could write
 355                     // this is a single iterator (that handles `spread_arg`), then
 356                     // `pass_argument` would be the loop body. It takes care to
 357                     // not advance `caller_iter` for ZSTs.
 358                     let mut locals_iter = mir.args_iter();
 359                     while let Some(local) = locals_iter.next() {
 360                         let dest = self.eval_place(&mir::Place::Local(local))?;
 361                         if Some(local) == mir.spread_arg {
 362                             // Must be a tuple
 363                             for i in 0..dest.layout.fields.count() {
 364                                 let dest = self.place_field(dest, i as u64)?;
 365                                 self.pass_argument(skip_zst, &mut caller_iter, dest)?;
 366                             }
 367                         } else {
 368                             // Normal argument
 369                             self.pass_argument(skip_zst, &mut caller_iter, dest)?;
 370                         }
 371                     }
 372                     // Now we should have no more caller args
 373                     if caller_iter.next().is_some() {
 374                         trace!("Caller has too many args over");
 375                         return err!(FunctionArgCountMismatch);
 376                     }
 377                     // Don't forget to check the return type!
 378                     if let Some(caller_ret) = dest {
 379                         let callee_ret = self.eval_place(&mir::Place::Local(mir::RETURN_PLACE))?;
 380                         if !Self::check_argument_compat(caller_ret.layout, callee_ret.layout) {
 381                             return err!(FunctionRetMismatch(
 382                                 caller_ret.layout.ty, callee_ret.layout.ty
 383                             ));
 384                         }
 385                     } else {
 386                         let callee_layout =
 387                             self.layout_of_local(self.frame(), mir::RETURN_PLACE)?;
 388                         if !callee_layout.abi.is_uninhabited() {
 389                             return err!(FunctionRetMismatch(
 390                                 self.tcx.types.never, callee_layout.ty
 391                             ));
 392                         }
 393                     }
 394                     Ok(())
 395                 })();
 396                 match res {
 397                     Err(err) => {
 398                         self.stack.pop();
 399                         Err(err)
 400                     }
 401                     Ok(v) => Ok(v)
 402                 }
 403             }
 404             // cannot use the shim here, because that will only result in infinite recursion
 405             ty::InstanceDef::Virtual(_, idx) => {
 406                 let ptr_size = self.pointer_size();
 407                 let ptr_align = self.tcx.data_layout.pointer_align;
 408                 let ptr = self.deref_operand(args[0])?;
 409                 let vtable = ptr.vtable()?;
 410                 let fn_ptr = self.memory.read_ptr_sized(
 411                     vtable.offset(ptr_size * (idx as u64 + 3), self)?,
 412                     ptr_align
 413                 )?.to_ptr()?;
 414                 let instance = self.memory.get_fn(fn_ptr)?;
 415
 416                 // We have to patch the self argument, in particular get the layout
 417                 // expected by the actual function. Cannot just use "field 0" due to
 418                 // Box<self>.
 419                 let mut args = args.to_vec();
 420                 let pointee = args[0].layout.ty.builtin_deref(true).unwrap().ty;
 421                 let fake_fat_ptr_ty = self.tcx.mk_mut_ptr(pointee);
 422                 args[0].layout = self.layout_of(fake_fat_ptr_ty)?.field(self, 0)?;
 423                 args[0].op = Operand::Immediate(Immediate::Scalar(ptr.ptr.into())); // strip vtable
 424                 trace!("Patched self operand to {:#?}", args[0]);
 425                 // recurse with concrete function
 426                 self.eval_fn_call(instance, span, caller_abi, &args, dest, ret)
 427             }
 428         }
 429     }
 430
 431     fn drop_in_place(
 432         &mut self,
 433         place: PlaceTy<'tcx, M::PointerTag>,
 434         instance: ty::Instance<'tcx>,
 435         span: Span,
 436         target: mir::BasicBlock,
 437     ) -> EvalResult<'tcx> {
 438         trace!("drop_in_place: {:?},\n  {:?}, {:?}", *place, place.layout.ty, instance);
 439         // We take the address of the object.  This may well be unaligned, which is fine
 440         // for us here.  However, unaligned accesses will probably make the actual drop
 441         // implementation fail -- a problem shared by rustc.
 442         let place = self.force_allocation(place)?;
 443
 444         let (instance, place) = match place.layout.ty.sty {
 445             ty::Dynamic(..) => {
 446                 // Dropping a trait object.
 447                 self.unpack_dyn_trait(place)?
 448             }
 449             _ => (instance, place),
 450         };
 451
 452         let arg = OpTy {
 453             op: Operand::Immediate(place.to_ref()),
 454             layout: self.layout_of(self.tcx.mk_mut_ptr(place.layout.ty))?,
 455         };
 456
 457         let ty = self.tcx.mk_unit(); // return type is ()
 458         let dest = MPlaceTy::dangling(self.layout_of(ty)?, self);
 459
 460         self.eval_fn_call(
 461             instance,
 462             span,
 463             Abi::Rust,
 464             &[arg],
 465             Some(dest.into()),
 466             Some(target),
 467         )
 468     }
 469 }