compiler/rustc_const_eval/src/interpret/terminator.rs

   1 use std::borrow::Cow;
   2
   3 use rustc_ast::ast::InlineAsmOptions;
   4 use rustc_middle::ty::layout::{FnAbiOf, LayoutOf};
   5 use rustc_middle::ty::Instance;
   6 use rustc_middle::{
   7     mir,
   8     ty::{self, Ty},
   9 };
  10 use rustc_target::abi;
  11 use rustc_target::abi::call::{ArgAbi, ArgAttribute, ArgAttributes, FnAbi, PassMode};
  12 use rustc_target::spec::abi::Abi;
  13
  14 use super::{
  15     FnVal, ImmTy, Immediate, InterpCx, InterpResult, MPlaceTy, Machine, MemoryKind, OpTy, Operand,
  16     PlaceTy, Scalar, StackPopCleanup, StackPopUnwind,
  17 };
  18
  19 impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
  20     pub(super) fn eval_terminator(
  21         &mut self,
  22         terminator: &mir::Terminator<'tcx>,
  23     ) -> InterpResult<'tcx> {
  24         use rustc_middle::mir::TerminatorKind::*;
  25         match terminator.kind {
  26             Return => {
  27                 self.pop_stack_frame(/* unwinding */ false)?
  28             }
  29
  30             Goto { target } => self.go_to_block(target),
  31
  32             SwitchInt { ref discr, ref targets } => {
  33                 let discr = self.read_immediate(&self.eval_operand(discr, None)?)?;
  34                 trace!("SwitchInt({:?})", *discr);
  35
  36                 // Branch to the `otherwise` case by default, if no match is found.
  37                 let mut target_block = targets.otherwise();
  38
  39                 for (const_int, target) in targets.iter() {
  40                     // Compare using MIR BinOp::Eq, to also support pointer values.
  41                     // (Avoiding `self.binary_op` as that does some redundant layout computation.)
  42                     let res = self
  43                         .overflowing_binary_op(
  44                             mir::BinOp::Eq,
  45                             &discr,
  46                             &ImmTy::from_uint(const_int, discr.layout),
  47                         )?
  48                         .0;
  49                     if res.to_bool()? {
  50                         target_block = target;
  51                         break;
  52                     }
  53                 }
  54
  55                 self.go_to_block(target_block);
  56             }
  57
  58             Call {
  59                 ref func,
  60                 ref args,
  61                 destination,
  62                 target,
  63                 ref cleanup,
  64                 from_hir_call: _,
  65                 fn_span: _,
  66             } => {
  67                 let old_stack = self.frame_idx();
  68                 let old_loc = self.frame().loc;
  69                 let func = self.eval_operand(func, None)?;
  70                 let args = self.eval_operands(args)?;
  71
  72                 let fn_sig_binder = func.layout.ty.fn_sig(*self.tcx);
  73                 let fn_sig =
  74                     self.tcx.normalize_erasing_late_bound_regions(self.param_env, fn_sig_binder);
  75                 let extra_args = &args[fn_sig.inputs().len()..];
  76                 let extra_args = self.tcx.mk_type_list(extra_args.iter().map(|arg| arg.layout.ty));
  77
  78                 let (fn_val, fn_abi, with_caller_location) = match *func.layout.ty.kind() {
  79                     ty::FnPtr(_sig) => {
  80                         let fn_ptr = self.read_pointer(&func)?;
  81                         let fn_val = self.get_ptr_fn(fn_ptr)?;
  82                         (fn_val, self.fn_abi_of_fn_ptr(fn_sig_binder, extra_args)?, false)
  83                     }
  84                     ty::FnDef(def_id, substs) => {
  85                         let instance =
  86                             self.resolve(ty::WithOptConstParam::unknown(def_id), substs)?;
  87                         (
  88                             FnVal::Instance(instance),
  89                             self.fn_abi_of_instance(instance, extra_args)?,
  90                             instance.def.requires_caller_location(*self.tcx),
  91                         )
  92                     }
  93                     _ => span_bug!(
  94                         terminator.source_info.span,
  95                         "invalid callee of type {:?}",
  96                         func.layout.ty
  97                     ),
  98                 };
  99
 100                 let destination = self.eval_place(destination)?;
 101                 self.eval_fn_call(
 102                     fn_val,
 103                     (fn_sig.abi, fn_abi),
 104                     &args,
 105                     with_caller_location,
 106                     &destination,
 107                     target,
 108                     match (cleanup, fn_abi.can_unwind) {
 109                         (Some(cleanup), true) => StackPopUnwind::Cleanup(*cleanup),
 110                         (None, true) => StackPopUnwind::Skip,
 111                         (_, false) => StackPopUnwind::NotAllowed,
 112                     },
 113                 )?;
 114                 // Sanity-check that `eval_fn_call` either pushed a new frame or
 115                 // did a jump to another block.
 116                 if self.frame_idx() == old_stack && self.frame().loc == old_loc {
 117                     span_bug!(terminator.source_info.span, "evaluating this call made no progress");
 118                 }
 119             }
 120
 121             Drop { place, target, unwind } => {
 122                 let place = self.eval_place(place)?;
 123                 let ty = place.layout.ty;
 124                 trace!("TerminatorKind::drop: {:?}, type {}", place, ty);
 125
 126                 let instance = Instance::resolve_drop_in_place(*self.tcx, ty);
 127                 self.drop_in_place(&place, instance, target, unwind)?;
 128             }
 129
 130             Assert { ref cond, expected, ref msg, target, cleanup } => {
 131                 let cond_val = self.read_scalar(&self.eval_operand(cond, None)?)?.to_bool()?;
 132                 if expected == cond_val {
 133                     self.go_to_block(target);
 134                 } else {
 135                     M::assert_panic(self, msg, cleanup)?;
 136                 }
 137             }
 138
 139             Abort => {
 140                 M::abort(self, "the program aborted execution".to_owned())?;
 141             }
 142
 143             // When we encounter Resume, we've finished unwinding
 144             // cleanup for the current stack frame. We pop it in order
 145             // to continue unwinding the next frame
 146             Resume => {
 147                 trace!("unwinding: resuming from cleanup");
 148                 // By definition, a Resume terminator means
 149                 // that we're unwinding
 150                 self.pop_stack_frame(/* unwinding */ true)?;
 151                 return Ok(());
 152             }
 153
 154             // It is UB to ever encounter this.
 155             Unreachable => throw_ub!(Unreachable),
 156
 157             // These should never occur for MIR we actually run.
 158             DropAndReplace { .. }
 159             | FalseEdge { .. }
 160             | FalseUnwind { .. }
 161             | Yield { .. }
 162             | GeneratorDrop => span_bug!(
 163                 terminator.source_info.span,
 164                 "{:#?} should have been eliminated by MIR pass",
 165                 terminator.kind
 166             ),
 167
 168             InlineAsm { template, ref operands, options, destination, .. } => {
 169                 M::eval_inline_asm(self, template, operands, options)?;
 170                 if options.contains(InlineAsmOptions::NORETURN) {
 171                     throw_ub_format!("returned from noreturn inline assembly");
 172                 }
 173                 self.go_to_block(
 174                     destination
 175                         .expect("InlineAsm terminators without noreturn must have a destination"),
 176                 )
 177             }
 178         }
 179
 180         Ok(())
 181     }
 182
 183     fn check_argument_compat(
 184         caller_abi: &ArgAbi<'tcx, Ty<'tcx>>,
 185         callee_abi: &ArgAbi<'tcx, Ty<'tcx>>,
 186     ) -> bool {
 187         // Heuristic for type comparison.
 188         let layout_compat = || {
 189             if caller_abi.layout.ty == callee_abi.layout.ty {
 190                 // No question
 191                 return true;
 192             }
 193             if caller_abi.layout.is_unsized() || callee_abi.layout.is_unsized() {
 194                 // No, no, no. We require the types to *exactly* match for unsized arguments. If
 195                 // these are somehow unsized "in a different way" (say, `dyn Trait` vs `[i32]`),
 196                 // then who knows what happens.
 197                 return false;
 198             }
 199             if caller_abi.layout.size != callee_abi.layout.size
 200                 || caller_abi.layout.align.abi != callee_abi.layout.align.abi
 201             {
 202                 // This cannot go well...
 203                 return false;
 204             }
 205             // The rest *should* be okay, but we are extra conservative.
 206             match (caller_abi.layout.abi, callee_abi.layout.abi) {
 207                 // Different valid ranges are okay (once we enforce validity,
 208                 // that will take care to make it UB to leave the range, just
 209                 // like for transmute).
 210                 (abi::Abi::Scalar(caller), abi::Abi::Scalar(callee)) => {
 211                     caller.primitive() == callee.primitive()
 212                 }
 213                 (
 214                     abi::Abi::ScalarPair(caller1, caller2),
 215                     abi::Abi::ScalarPair(callee1, callee2),
 216                 ) => {
 217                     caller1.primitive() == callee1.primitive()
 218                         && caller2.primitive() == callee2.primitive()
 219                 }
 220                 // Be conservative
 221                 _ => false,
 222             }
 223         };
 224         // When comparing the PassMode, we have to be smart about comparing the attributes.
 225         let arg_attr_compat = |a1: &ArgAttributes, a2: &ArgAttributes| {
 226             // There's only one regular attribute that matters for the call ABI: InReg.
 227             // Everything else is things like noalias, dereferenceable, nonnull, ...
 228             // (This also applies to pointee_size, pointee_align.)
 229             if a1.regular.contains(ArgAttribute::InReg) != a2.regular.contains(ArgAttribute::InReg)
 230             {
 231                 return false;
 232             }
 233             // We also compare the sign extension mode -- this could let the callee make assumptions
 234             // about bits that conceptually were not even passed.
 235             if a1.arg_ext != a2.arg_ext {
 236                 return false;
 237             }
 238             return true;
 239         };
 240         let mode_compat = || match (&caller_abi.mode, &callee_abi.mode) {
 241             (PassMode::Ignore, PassMode::Ignore) => true,
 242             (PassMode::Direct(a1), PassMode::Direct(a2)) => arg_attr_compat(a1, a2),
 243             (PassMode::Pair(a1, b1), PassMode::Pair(a2, b2)) => {
 244                 arg_attr_compat(a1, a2) && arg_attr_compat(b1, b2)
 245             }
 246             (PassMode::Cast(c1, pad1), PassMode::Cast(c2, pad2)) => c1 == c2 && pad1 == pad2,
 247             (
 248                 PassMode::Indirect { attrs: a1, extra_attrs: None, on_stack: s1 },
 249                 PassMode::Indirect { attrs: a2, extra_attrs: None, on_stack: s2 },
 250             ) => arg_attr_compat(a1, a2) && s1 == s2,
 251             (
 252                 PassMode::Indirect { attrs: a1, extra_attrs: Some(e1), on_stack: s1 },
 253                 PassMode::Indirect { attrs: a2, extra_attrs: Some(e2), on_stack: s2 },
 254             ) => arg_attr_compat(a1, a2) && arg_attr_compat(e1, e2) && s1 == s2,
 255             _ => false,
 256         };
 257
 258         if layout_compat() && mode_compat() {
 259             return true;
 260         }
 261         trace!(
 262             "check_argument_compat: incompatible ABIs:\ncaller: {:?}\ncallee: {:?}",
 263             caller_abi,
 264             callee_abi
 265         );
 266         return false;
 267     }
 268
 269     /// Initialize a single callee argument, checking the types for compatibility.
 270     fn pass_argument<'x, 'y>(
 271         &mut self,
 272         caller_args: &mut impl Iterator<
 273             Item = (&'x OpTy<'tcx, M::Provenance>, &'y ArgAbi<'tcx, Ty<'tcx>>),
 274         >,
 275         callee_abi: &ArgAbi<'tcx, Ty<'tcx>>,
 276         callee_arg: &PlaceTy<'tcx, M::Provenance>,
 277     ) -> InterpResult<'tcx>
 278     where
 279         'tcx: 'x,
 280         'tcx: 'y,
 281     {
 282         if matches!(callee_abi.mode, PassMode::Ignore) {
 283             // This one is skipped.
 284             return Ok(());
 285         }
 286         // Find next caller arg.
 287         let (caller_arg, caller_abi) = caller_args.next().ok_or_else(|| {
 288             err_ub_format!("calling a function with fewer arguments than it requires")
 289         })?;
 290         // Now, check
 291         if !Self::check_argument_compat(caller_abi, callee_abi) {
 292             throw_ub_format!(
 293                 "calling a function with argument of type {:?} passing data of type {:?}",
 294                 callee_arg.layout.ty,
 295                 caller_arg.layout.ty
 296             )
 297         }
 298         // Special handling for unsized parameters.
 299         if caller_arg.layout.is_unsized() {
 300             // `check_argument_compat` ensures that both have the same type, so we know they will use the metadata the same way.
 301             assert_eq!(caller_arg.layout.ty, callee_arg.layout.ty);
 302             // We have to properly pre-allocate the memory for the callee.
 303             // So let's tear down some wrappers.
 304             // This all has to be in memory, there are no immediate unsized values.
 305             let src = caller_arg.assert_mem_place();
 306             // The destination cannot be one of these "spread args".
 307             let (dest_frame, dest_local) = callee_arg.assert_local();
 308             // We are just initializing things, so there can't be anything here yet.
 309             assert!(matches!(
 310                 *self.local_to_op(&self.stack()[dest_frame], dest_local, None)?,
 311                 Operand::Immediate(Immediate::Uninit)
 312             ));
 313             // Allocate enough memory to hold `src`.
 314             let Some((size, align)) = self.size_and_align_of_mplace(&src)? else {
 315                 span_bug!(self.cur_span(), "unsized fn arg with `extern` type tail should not be allowed")
 316             };
 317             let ptr = self.allocate_ptr(size, align, MemoryKind::Stack)?;
 318             let dest_place =
 319                 MPlaceTy::from_aligned_ptr_with_meta(ptr.into(), callee_arg.layout, src.meta);
 320             // Update the local to be that new place.
 321             *M::access_local_mut(self, dest_frame, dest_local)? = Operand::Indirect(*dest_place);
 322         }
 323         // We allow some transmutes here.
 324         // FIXME: Depending on the PassMode, this should reset some padding to uninitialized. (This
 325         // is true for all `copy_op`, but there are a lot of special cases for argument passing
 326         // specifically.)
 327         self.copy_op(&caller_arg, callee_arg, /*allow_transmute*/ true)
 328     }
 329
 330     /// Call this function -- pushing the stack frame and initializing the arguments.
 331     ///
 332     /// `caller_fn_abi` is used to determine if all the arguments are passed the proper way.
 333     /// However, we also need `caller_abi` to determine if we need to do untupling of arguments.
 334     ///
 335     /// `with_caller_location` indicates whether the caller passed a caller location. Miri
 336     /// implements caller locations without argument passing, but to match `FnAbi` we need to know
 337     /// when those arguments are present.
 338     pub(crate) fn eval_fn_call(
 339         &mut self,
 340         fn_val: FnVal<'tcx, M::ExtraFnVal>,
 341         (caller_abi, caller_fn_abi): (Abi, &FnAbi<'tcx, Ty<'tcx>>),
 342         args: &[OpTy<'tcx, M::Provenance>],
 343         with_caller_location: bool,
 344         destination: &PlaceTy<'tcx, M::Provenance>,
 345         target: Option<mir::BasicBlock>,
 346         mut unwind: StackPopUnwind,
 347     ) -> InterpResult<'tcx> {
 348         trace!("eval_fn_call: {:#?}", fn_val);
 349
 350         let instance = match fn_val {
 351             FnVal::Instance(instance) => instance,
 352             FnVal::Other(extra) => {
 353                 return M::call_extra_fn(
 354                     self,
 355                     extra,
 356                     caller_abi,
 357                     args,
 358                     destination,
 359                     target,
 360                     unwind,
 361                 );
 362             }
 363         };
 364
 365         match instance.def {
 366             ty::InstanceDef::Intrinsic(def_id) => {
 367                 assert!(self.tcx.is_intrinsic(def_id));
 368                 // caller_fn_abi is not relevant here, we interpret the arguments directly for each intrinsic.
 369                 M::call_intrinsic(self, instance, args, destination, target, unwind)
 370             }
 371             ty::InstanceDef::VTableShim(..)
 372             | ty::InstanceDef::ReifyShim(..)
 373             | ty::InstanceDef::ClosureOnceShim { .. }
 374             | ty::InstanceDef::FnPtrShim(..)
 375             | ty::InstanceDef::DropGlue(..)
 376             | ty::InstanceDef::CloneShim(..)
 377             | ty::InstanceDef::Item(_) => {
 378                 // We need MIR for this fn
 379                 let Some((body, instance)) =
 380                     M::find_mir_or_eval_fn(self, instance, caller_abi, args, destination, target, unwind)? else {
 381                         return Ok(());
 382                     };
 383
 384                 // Compute callee information using the `instance` returned by
 385                 // `find_mir_or_eval_fn`.
 386                 // FIXME: for variadic support, do we have to somehow determine callee's extra_args?
 387                 let callee_fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
 388
 389                 if callee_fn_abi.c_variadic || caller_fn_abi.c_variadic {
 390                     throw_unsup_format!("calling a c-variadic function is not supported");
 391                 }
 392
 393                 if M::enforce_abi(self) {
 394                     if caller_fn_abi.conv != callee_fn_abi.conv {
 395                         throw_ub_format!(
 396                             "calling a function with calling convention {:?} using calling convention {:?}",
 397                             callee_fn_abi.conv,
 398                             caller_fn_abi.conv
 399                         )
 400                     }
 401                 }
 402
 403                 if !matches!(unwind, StackPopUnwind::NotAllowed) && !callee_fn_abi.can_unwind {
 404                     // The callee cannot unwind.
 405                     unwind = StackPopUnwind::NotAllowed;
 406                 }
 407
 408                 self.push_stack_frame(
 409                     instance,
 410                     body,
 411                     destination,
 412                     StackPopCleanup::Goto { ret: target, unwind },
 413                 )?;
 414
 415                 // If an error is raised here, pop the frame again to get an accurate backtrace.
 416                 // To this end, we wrap it all in a `try` block.
 417                 let res: InterpResult<'tcx> = try {
 418                     trace!(
 419                         "caller ABI: {:?}, args: {:#?}",
 420                         caller_abi,
 421                         args.iter()
 422                             .map(|arg| (arg.layout.ty, format!("{:?}", **arg)))
 423                             .collect::<Vec<_>>()
 424                     );
 425                     trace!(
 426                         "spread_arg: {:?}, locals: {:#?}",
 427                         body.spread_arg,
 428                         body.args_iter()
 429                             .map(|local| (
 430                                 local,
 431                                 self.layout_of_local(self.frame(), local, None).unwrap().ty
 432                             ))
 433                             .collect::<Vec<_>>()
 434                     );
 435
 436                     // In principle, we have two iterators: Where the arguments come from, and where
 437                     // they go to.
 438
 439                     // For where they come from: If the ABI is RustCall, we untuple the
 440                     // last incoming argument.  These two iterators do not have the same type,
 441                     // so to keep the code paths uniform we accept an allocation
 442                     // (for RustCall ABI only).
 443                     let caller_args: Cow<'_, [OpTy<'tcx, M::Provenance>]> =
 444                         if caller_abi == Abi::RustCall && !args.is_empty() {
 445                             // Untuple
 446                             let (untuple_arg, args) = args.split_last().unwrap();
 447                             trace!("eval_fn_call: Will pass last argument by untupling");
 448                             Cow::from(
 449                                 args.iter()
 450                                     .map(|a| Ok(a.clone()))
 451                                     .chain(
 452                                         (0..untuple_arg.layout.fields.count())
 453                                             .map(|i| self.operand_field(untuple_arg, i)),
 454                                     )
 455                                     .collect::<InterpResult<'_, Vec<OpTy<'tcx, M::Provenance>>>>(
 456                                     )?,
 457                             )
 458                         } else {
 459                             // Plain arg passing
 460                             Cow::from(args)
 461                         };
 462                     // If `with_caller_location` is set we pretend there is an extra argument (that
 463                     // we will not pass).
 464                     assert_eq!(
 465                         caller_args.len() + if with_caller_location { 1 } else { 0 },
 466                         caller_fn_abi.args.len(),
 467                         "mismatch between caller ABI and caller arguments",
 468                     );
 469                     let mut caller_args = caller_args
 470                         .iter()
 471                         .zip(caller_fn_abi.args.iter())
 472                         .filter(|arg_and_abi| !matches!(arg_and_abi.1.mode, PassMode::Ignore));
 473
 474                     // Now we have to spread them out across the callee's locals,
 475                     // taking into account the `spread_arg`.  If we could write
 476                     // this is a single iterator (that handles `spread_arg`), then
 477                     // `pass_argument` would be the loop body. It takes care to
 478                     // not advance `caller_iter` for ZSTs.
 479                     let mut callee_args_abis = callee_fn_abi.args.iter();
 480                     for local in body.args_iter() {
 481                         let dest = self.eval_place(mir::Place::from(local))?;
 482                         if Some(local) == body.spread_arg {
 483                             // Must be a tuple
 484                             for i in 0..dest.layout.fields.count() {
 485                                 let dest = self.place_field(&dest, i)?;
 486                                 let callee_abi = callee_args_abis.next().unwrap();
 487                                 self.pass_argument(&mut caller_args, callee_abi, &dest)?;
 488                             }
 489                         } else {
 490                             // Normal argument
 491                             let callee_abi = callee_args_abis.next().unwrap();
 492                             self.pass_argument(&mut caller_args, callee_abi, &dest)?;
 493                         }
 494                     }
 495                     // If the callee needs a caller location, pretend we consume one more argument from the ABI.
 496                     if instance.def.requires_caller_location(*self.tcx) {
 497                         callee_args_abis.next().unwrap();
 498                     }
 499                     // Now we should have no more caller args or callee arg ABIs
 500                     assert!(
 501                         callee_args_abis.next().is_none(),
 502                         "mismatch between callee ABI and callee body arguments"
 503                     );
 504                     if caller_args.next().is_some() {
 505                         throw_ub_format!("calling a function with more arguments than it expected")
 506                     }
 507                     // Don't forget to check the return type!
 508                     if !Self::check_argument_compat(&caller_fn_abi.ret, &callee_fn_abi.ret) {
 509                         throw_ub_format!(
 510                             "calling a function with return type {:?} passing \
 511                                     return place of type {:?}",
 512                             callee_fn_abi.ret.layout.ty,
 513                             caller_fn_abi.ret.layout.ty,
 514                         )
 515                     }
 516                 };
 517                 match res {
 518                     Err(err) => {
 519                         self.stack_mut().pop();
 520                         Err(err)
 521                     }
 522                     Ok(()) => Ok(()),
 523                 }
 524             }
 525             // cannot use the shim here, because that will only result in infinite recursion
 526             ty::InstanceDef::Virtual(def_id, idx) => {
 527                 let mut args = args.to_vec();
 528                 // We have to implement all "object safe receivers". So we have to go search for a
 529                 // pointer or `dyn Trait` type, but it could be wrapped in newtypes. So recursively
 530                 // unwrap those newtypes until we are there.
 531                 let mut receiver = args[0].clone();
 532                 let receiver_place = loop {
 533                     match receiver.layout.ty.kind() {
 534                         ty::Ref(..) | ty::RawPtr(..) => break self.deref_operand(&receiver)?,
 535                         ty::Dynamic(..) => break receiver.assert_mem_place(), // no immediate unsized values
 536                         _ => {
 537                             // Not there yet, search for the only non-ZST field.
 538                             let mut non_zst_field = None;
 539                             for i in 0..receiver.layout.fields.count() {
 540                                 let field = self.operand_field(&receiver, i)?;
 541                                 let zst =
 542                                     field.layout.is_zst() && field.layout.align.abi.bytes() == 1;
 543                                 if !zst {
 544                                     assert!(
 545                                         non_zst_field.is_none(),
 546                                         "multiple non-ZST fields in dyn receiver type {}",
 547                                         receiver.layout.ty
 548                                     );
 549                                     non_zst_field = Some(field);
 550                                 }
 551                             }
 552                             receiver = non_zst_field.unwrap_or_else(|| {
 553                                 panic!(
 554                                     "no non-ZST fields in dyn receiver type {}",
 555                                     receiver.layout.ty
 556                                 )
 557                             });
 558                         }
 559                     }
 560                 };
 561                 // Obtain the underlying trait we are working on.
 562                 let receiver_tail = self
 563                     .tcx
 564                     .struct_tail_erasing_lifetimes(receiver_place.layout.ty, self.param_env);
 565                 let ty::Dynamic(data, ..) = receiver_tail.kind() else {
 566                     span_bug!(self.cur_span(), "dynamic call on non-`dyn` type {}", receiver_tail)
 567                 };
 568
 569                 // Get the required information from the vtable.
 570                 let vptr = receiver_place.meta.unwrap_meta().to_pointer(self)?;
 571                 let (dyn_ty, dyn_trait) = self.get_ptr_vtable(vptr)?;
 572                 if dyn_trait != data.principal() {
 573                     throw_ub_format!(
 574                         "`dyn` call on a pointer whose vtable does not match its type"
 575                     );
 576                 }
 577
 578                 // Now determine the actual method to call. We can do that in two different ways and
 579                 // compare them to ensure everything fits.
 580                 let Some(ty::VtblEntry::Method(fn_inst)) = self.get_vtable_entries(vptr)?.get(idx).copied() else {
 581                     throw_ub_format!("`dyn` call trying to call something that is not a method")
 582                 };
 583                 if cfg!(debug_assertions) {
 584                     let tcx = *self.tcx;
 585
 586                     let trait_def_id = tcx.trait_of_item(def_id).unwrap();
 587                     let virtual_trait_ref =
 588                         ty::TraitRef::from_method(tcx, trait_def_id, instance.substs);
 589                     assert_eq!(
 590                         receiver_tail,
 591                         virtual_trait_ref.self_ty(),
 592                         "mismatch in underlying dyn trait computation within Miri and MIR building",
 593                     );
 594                     let existential_trait_ref =
 595                         ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
 596                     let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);
 597
 598                     let concrete_method = Instance::resolve_for_vtable(
 599                         tcx,
 600                         self.param_env,
 601                         def_id,
 602                         instance.substs.rebase_onto(tcx, trait_def_id, concrete_trait_ref.substs),
 603                     )
 604                     .unwrap();
 605                     assert_eq!(fn_inst, concrete_method);
 606                 }
 607
 608                 // `*mut receiver_place.layout.ty` is almost the layout that we
 609                 // want for args[0]: We have to project to field 0 because we want
 610                 // a thin pointer.
 611                 assert!(receiver_place.layout.is_unsized());
 612                 let receiver_ptr_ty = self.tcx.mk_mut_ptr(receiver_place.layout.ty);
 613                 let this_receiver_ptr = self.layout_of(receiver_ptr_ty)?.field(self, 0);
 614                 // Adjust receiver argument.
 615                 args[0] = OpTy::from(ImmTy::from_immediate(
 616                     Scalar::from_maybe_pointer(receiver_place.ptr, self).into(),
 617                     this_receiver_ptr,
 618                 ));
 619                 trace!("Patched receiver operand to {:#?}", args[0]);
 620                 // recurse with concrete function
 621                 self.eval_fn_call(
 622                     FnVal::Instance(fn_inst),
 623                     (caller_abi, caller_fn_abi),
 624                     &args,
 625                     with_caller_location,
 626                     destination,
 627                     target,
 628                     unwind,
 629                 )
 630             }
 631         }
 632     }
 633
 634     fn drop_in_place(
 635         &mut self,
 636         place: &PlaceTy<'tcx, M::Provenance>,
 637         instance: ty::Instance<'tcx>,
 638         target: mir::BasicBlock,
 639         unwind: Option<mir::BasicBlock>,
 640     ) -> InterpResult<'tcx> {
 641         trace!("drop_in_place: {:?},\n  {:?}, {:?}", *place, place.layout.ty, instance);
 642         // We take the address of the object.  This may well be unaligned, which is fine
 643         // for us here.  However, unaligned accesses will probably make the actual drop
 644         // implementation fail -- a problem shared by rustc.
 645         let place = self.force_allocation(place)?;
 646
 647         let (instance, place) = match place.layout.ty.kind() {
 648             ty::Dynamic(..) => {
 649                 // Dropping a trait object. Need to find actual drop fn.
 650                 let place = self.unpack_dyn_trait(&place)?;
 651                 let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
 652                 (instance, place)
 653             }
 654             _ => (instance, place),
 655         };
 656         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
 657
 658         let arg = ImmTy::from_immediate(
 659             place.to_ref(self),
 660             self.layout_of(self.tcx.mk_mut_ptr(place.layout.ty))?,
 661         );
 662         let ret = MPlaceTy::fake_alloc_zst(self.layout_of(self.tcx.types.unit)?);
 663
 664         self.eval_fn_call(
 665             FnVal::Instance(instance),
 666             (Abi::Rust, fn_abi),
 667             &[arg.into()],
 668             false,
 669             &ret.into(),
 670             Some(target),
 671             match unwind {
 672                 Some(cleanup) => StackPopUnwind::Cleanup(cleanup),
 673                 None => StackPopUnwind::Skip,
 674             },
 675         )
 676     }
 677 }