compiler/rustc_const_eval/src/interpret/terminator.rs

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