1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
use std::borrow::Cow;

use either::Either;

use rustc_middle::{
    mir,
    ty::{
        self,
        layout::{FnAbiOf, IntegerExt, LayoutOf, TyAndLayout},
        AdtDef, Instance, Ty,
    },
};
use rustc_span::{source_map::Spanned, sym};
use rustc_target::abi::{self, FieldIdx};
use rustc_target::abi::{
    call::{ArgAbi, FnAbi, PassMode},
    Integer,
};
use rustc_target::spec::abi::Abi;

use super::{
    CtfeProvenance, FnVal, ImmTy, InterpCx, InterpResult, MPlaceTy, Machine, OpTy, PlaceTy,
    Projectable, Provenance, Scalar, StackPopCleanup,
};
use crate::fluent_generated as fluent;

/// An argment passed to a function.
#[derive(Clone, Debug)]
pub enum FnArg<'tcx, Prov: Provenance = CtfeProvenance> {
    /// Pass a copy of the given operand.
    Copy(OpTy<'tcx, Prov>),
    /// Allow for the argument to be passed in-place: destroy the value originally stored at that place and
    /// make the place inaccessible for the duration of the function call.
    InPlace(MPlaceTy<'tcx, Prov>),
}

impl<'tcx, Prov: Provenance> FnArg<'tcx, Prov> {
    pub fn layout(&self) -> &TyAndLayout<'tcx> {
        match self {
            FnArg::Copy(op) => &op.layout,
            FnArg::InPlace(mplace) => &mplace.layout,
        }
    }
}

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
    /// Make a copy of the given fn_arg. Any `InPlace` are degenerated to copies, no protection of the
    /// original memory occurs.
    pub fn copy_fn_arg(&self, arg: &FnArg<'tcx, M::Provenance>) -> OpTy<'tcx, M::Provenance> {
        match arg {
            FnArg::Copy(op) => op.clone(),
            FnArg::InPlace(mplace) => mplace.clone().into(),
        }
    }

    /// Make a copy of the given fn_args. Any `InPlace` are degenerated to copies, no protection of the
    /// original memory occurs.
    pub fn copy_fn_args(
        &self,
        args: &[FnArg<'tcx, M::Provenance>],
    ) -> Vec<OpTy<'tcx, M::Provenance>> {
        args.iter().map(|fn_arg| self.copy_fn_arg(fn_arg)).collect()
    }

    pub fn fn_arg_field(
        &self,
        arg: &FnArg<'tcx, M::Provenance>,
        field: usize,
    ) -> InterpResult<'tcx, FnArg<'tcx, M::Provenance>> {
        Ok(match arg {
            FnArg::Copy(op) => FnArg::Copy(self.project_field(op, field)?),
            FnArg::InPlace(mplace) => FnArg::InPlace(self.project_field(mplace, field)?),
        })
    }

    pub(super) fn eval_terminator(
        &mut self,
        terminator: &mir::Terminator<'tcx>,
    ) -> InterpResult<'tcx> {
        use rustc_middle::mir::TerminatorKind::*;
        match terminator.kind {
            Return => {
                self.pop_stack_frame(/* unwinding */ false)?
            }

            Goto { target } => self.go_to_block(target),

            SwitchInt { ref discr, ref targets } => {
                let discr = self.read_immediate(&self.eval_operand(discr, None)?)?;
                trace!("SwitchInt({:?})", *discr);

                // Branch to the `otherwise` case by default, if no match is found.
                let mut target_block = targets.otherwise();

                for (const_int, target) in targets.iter() {
                    // Compare using MIR BinOp::Eq, to also support pointer values.
                    // (Avoiding `self.binary_op` as that does some redundant layout computation.)
                    let res = self.wrapping_binary_op(
                        mir::BinOp::Eq,
                        &discr,
                        &ImmTy::from_uint(const_int, discr.layout),
                    )?;
                    if res.to_scalar().to_bool()? {
                        target_block = target;
                        break;
                    }
                }

                self.go_to_block(target_block);
            }

            Call {
                ref func,
                ref args,
                destination,
                target,
                unwind,
                call_source: _,
                fn_span: _,
            } => {
                let old_stack = self.frame_idx();
                let old_loc = self.frame().loc;
                let func = self.eval_operand(func, None)?;
                let args = self.eval_fn_call_arguments(args)?;

                let fn_sig_binder = func.layout.ty.fn_sig(*self.tcx);
                let fn_sig =
                    self.tcx.normalize_erasing_late_bound_regions(self.param_env, fn_sig_binder);
                let extra_args = &args[fn_sig.inputs().len()..];
                let extra_args =
                    self.tcx.mk_type_list_from_iter(extra_args.iter().map(|arg| arg.layout().ty));

                let (fn_val, fn_abi, with_caller_location) = match *func.layout.ty.kind() {
                    ty::FnPtr(_sig) => {
                        let fn_ptr = self.read_pointer(&func)?;
                        let fn_val = self.get_ptr_fn(fn_ptr)?;
                        (fn_val, self.fn_abi_of_fn_ptr(fn_sig_binder, extra_args)?, false)
                    }
                    ty::FnDef(def_id, args) => {
                        let instance = self.resolve(def_id, args)?;
                        (
                            FnVal::Instance(instance),
                            self.fn_abi_of_instance(instance, extra_args)?,
                            instance.def.requires_caller_location(*self.tcx),
                        )
                    }
                    _ => span_bug!(
                        terminator.source_info.span,
                        "invalid callee of type {}",
                        func.layout.ty
                    ),
                };

                let destination = self.force_allocation(&self.eval_place(destination)?)?;
                self.eval_fn_call(
                    fn_val,
                    (fn_sig.abi, fn_abi),
                    &args,
                    with_caller_location,
                    &destination,
                    target,
                    if fn_abi.can_unwind { unwind } else { mir::UnwindAction::Unreachable },
                )?;
                // Sanity-check that `eval_fn_call` either pushed a new frame or
                // did a jump to another block.
                if self.frame_idx() == old_stack && self.frame().loc == old_loc {
                    span_bug!(terminator.source_info.span, "evaluating this call made no progress");
                }
            }

            Drop { place, target, unwind, replace: _ } => {
                let frame = self.frame();
                let ty = place.ty(&frame.body.local_decls, *self.tcx).ty;
                let ty = self.instantiate_from_frame_and_normalize_erasing_regions(frame, ty)?;
                let instance = Instance::resolve_drop_in_place(*self.tcx, ty);
                if let ty::InstanceDef::DropGlue(_, None) = instance.def {
                    // This is the branch we enter if and only if the dropped type has no drop glue
                    // whatsoever. This can happen as a result of monomorphizing a drop of a
                    // generic. In order to make sure that generic and non-generic code behaves
                    // roughly the same (and in keeping with Mir semantics) we do nothing here.
                    self.go_to_block(target);
                    return Ok(());
                }
                let place = self.eval_place(place)?;
                trace!("TerminatorKind::drop: {:?}, type {}", place, ty);
                self.drop_in_place(&place, instance, target, unwind)?;
            }

            Assert { ref cond, expected, ref msg, target, unwind } => {
                let ignored =
                    M::ignore_optional_overflow_checks(self) && msg.is_optional_overflow_check();
                let cond_val = self.read_scalar(&self.eval_operand(cond, None)?)?.to_bool()?;
                if ignored || expected == cond_val {
                    self.go_to_block(target);
                } else {
                    M::assert_panic(self, msg, unwind)?;
                }
            }

            UnwindTerminate(reason) => {
                M::unwind_terminate(self, reason)?;
            }

            // When we encounter Resume, we've finished unwinding
            // cleanup for the current stack frame. We pop it in order
            // to continue unwinding the next frame
            UnwindResume => {
                trace!("unwinding: resuming from cleanup");
                // By definition, a Resume terminator means
                // that we're unwinding
                self.pop_stack_frame(/* unwinding */ true)?;
                return Ok(());
            }

            // It is UB to ever encounter this.
            Unreachable => throw_ub!(Unreachable),

            // These should never occur for MIR we actually run.
            FalseEdge { .. } | FalseUnwind { .. } | Yield { .. } | CoroutineDrop => span_bug!(
                terminator.source_info.span,
                "{:#?} should have been eliminated by MIR pass",
                terminator.kind
            ),

            InlineAsm { template, ref operands, options, ref targets, .. } => {
                M::eval_inline_asm(self, template, operands, options, targets)?;
            }
        }

        Ok(())
    }

    /// Evaluate the arguments of a function call
    pub(super) fn eval_fn_call_arguments(
        &self,
        ops: &[Spanned<mir::Operand<'tcx>>],
    ) -> InterpResult<'tcx, Vec<FnArg<'tcx, M::Provenance>>> {
        ops.iter()
            .map(|op| {
                let arg = match &op.node {
                    mir::Operand::Copy(_) | mir::Operand::Constant(_) => {
                        // Make a regular copy.
                        let op = self.eval_operand(&op.node, None)?;
                        FnArg::Copy(op)
                    }
                    mir::Operand::Move(place) => {
                        // If this place lives in memory, preserve its location.
                        // We call `place_to_op` which will be an `MPlaceTy` whenever there exists
                        // an mplace for this place. (This is in contrast to `PlaceTy::as_mplace_or_local`
                        // which can return a local even if that has an mplace.)
                        let place = self.eval_place(*place)?;
                        let op = self.place_to_op(&place)?;

                        match op.as_mplace_or_imm() {
                            Either::Left(mplace) => FnArg::InPlace(mplace),
                            Either::Right(_imm) => {
                                // This argument doesn't live in memory, so there's no place
                                // to make inaccessible during the call.
                                // We rely on there not being any stray `PlaceTy` that would let the
                                // caller directly access this local!
                                // This is also crucial for tail calls, where we want the `FnArg` to
                                // stay valid when the old stack frame gets popped.
                                FnArg::Copy(op)
                            }
                        }
                    }
                };

                Ok(arg)
            })
            .collect()
    }

    /// Find the wrapped inner type of a transparent wrapper.
    /// Must not be called on 1-ZST (as they don't have a uniquely defined "wrapped field").
    ///
    /// We work with `TyAndLayout` here since that makes it much easier to iterate over all fields.
    fn unfold_transparent(
        &self,
        layout: TyAndLayout<'tcx>,
        may_unfold: impl Fn(AdtDef<'tcx>) -> bool,
    ) -> TyAndLayout<'tcx> {
        match layout.ty.kind() {
            ty::Adt(adt_def, _) if adt_def.repr().transparent() && may_unfold(*adt_def) => {
                assert!(!adt_def.is_enum());
                // Find the non-1-ZST field, and recurse.
                let (_, field) = layout.non_1zst_field(self).unwrap();
                self.unfold_transparent(field, may_unfold)
            }
            // Not a transparent type, no further unfolding.
            _ => layout,
        }
    }

    /// Unwrap types that are guaranteed a null-pointer-optimization
    fn unfold_npo(&self, layout: TyAndLayout<'tcx>) -> InterpResult<'tcx, TyAndLayout<'tcx>> {
        // Check if this is `Option` wrapping some type.
        let inner = match layout.ty.kind() {
            ty::Adt(def, args) if self.tcx.is_diagnostic_item(sym::Option, def.did()) => {
                args[0].as_type().unwrap()
            }
            _ => {
                // Not an `Option`.
                return Ok(layout);
            }
        };
        let inner = self.layout_of(inner)?;
        // Check if the inner type is one of the NPO-guaranteed ones.
        // For that we first unpeel transparent *structs* (but not unions).
        let is_npo = |def: AdtDef<'tcx>| {
            self.tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
        };
        let inner = self.unfold_transparent(inner, /* may_unfold */ |def| {
            // Stop at NPO tpyes so that we don't miss that attribute in the check below!
            def.is_struct() && !is_npo(def)
        });
        Ok(match inner.ty.kind() {
            ty::Ref(..) | ty::FnPtr(..) => {
                // Option<&T> behaves like &T, and same for fn()
                inner
            }
            ty::Adt(def, _) if is_npo(*def) => {
                // Once we found a `nonnull_optimization_guaranteed` type, further strip off
                // newtype structs from it to find the underlying ABI type.
                self.unfold_transparent(inner, /* may_unfold */ |def| def.is_struct())
            }
            _ => {
                // Everything else we do not unfold.
                layout
            }
        })
    }

    /// Check if these two layouts look like they are fn-ABI-compatible.
    /// (We also compare the `PassMode`, so this doesn't have to check everything. But it turns out
    /// that only checking the `PassMode` is insufficient.)
    fn layout_compat(
        &self,
        caller: TyAndLayout<'tcx>,
        callee: TyAndLayout<'tcx>,
    ) -> InterpResult<'tcx, bool> {
        // Fast path: equal types are definitely compatible.
        if caller.ty == callee.ty {
            return Ok(true);
        }
        // 1-ZST are compatible with all 1-ZST (and with nothing else).
        if caller.is_1zst() || callee.is_1zst() {
            return Ok(caller.is_1zst() && callee.is_1zst());
        }
        // Unfold newtypes and NPO optimizations.
        let unfold = |layout: TyAndLayout<'tcx>| {
            self.unfold_npo(self.unfold_transparent(layout, /* may_unfold */ |_def| true))
        };
        let caller = unfold(caller)?;
        let callee = unfold(callee)?;
        // Now see if these inner types are compatible.

        // Compatible pointer types. For thin pointers, we have to accept even non-`repr(transparent)`
        // things as compatible due to `DispatchFromDyn`. For instance, `Rc<i32>` and `*mut i32`
        // must be compatible. So we just accept everything with Pointer ABI as compatible,
        // even if this will accept some code that is not stably guaranteed to work.
        // This also handles function pointers.
        let thin_pointer = |layout: TyAndLayout<'tcx>| match layout.abi {
            abi::Abi::Scalar(s) => match s.primitive() {
                abi::Primitive::Pointer(addr_space) => Some(addr_space),
                _ => None,
            },
            _ => None,
        };
        if let (Some(caller), Some(callee)) = (thin_pointer(caller), thin_pointer(callee)) {
            return Ok(caller == callee);
        }
        // For wide pointers we have to get the pointee type.
        let pointee_ty = |ty: Ty<'tcx>| -> InterpResult<'tcx, Option<Ty<'tcx>>> {
            // We cannot use `builtin_deref` here since we need to reject `Box<T, MyAlloc>`.
            Ok(Some(match ty.kind() {
                ty::Ref(_, ty, _) => *ty,
                ty::RawPtr(mt) => mt.ty,
                // We only accept `Box` with the default allocator.
                _ if ty.is_box_global(*self.tcx) => ty.boxed_ty(),
                _ => return Ok(None),
            }))
        };
        if let (Some(caller), Some(callee)) = (pointee_ty(caller.ty)?, pointee_ty(callee.ty)?) {
            // This is okay if they have the same metadata type.
            let meta_ty = |ty: Ty<'tcx>| {
                // Even if `ty` is normalized, the search for the unsized tail will project
                // to fields, which can yield non-normalized types. So we need to provide a
                // normalization function.
                let normalize = |ty| self.tcx.normalize_erasing_regions(self.param_env, ty);
                ty.ptr_metadata_ty(*self.tcx, normalize)
            };
            return Ok(meta_ty(caller) == meta_ty(callee));
        }

        // Compatible integer types (in particular, usize vs ptr-sized-u32/u64).
        // `char` counts as `u32.`
        let int_ty = |ty: Ty<'tcx>| {
            Some(match ty.kind() {
                ty::Int(ity) => (Integer::from_int_ty(&self.tcx, *ity), /* signed */ true),
                ty::Uint(uty) => (Integer::from_uint_ty(&self.tcx, *uty), /* signed */ false),
                ty::Char => (Integer::I32, /* signed */ false),
                _ => return None,
            })
        };
        if let (Some(caller), Some(callee)) = (int_ty(caller.ty), int_ty(callee.ty)) {
            // This is okay if they are the same integer type.
            return Ok(caller == callee);
        }

        // Fall back to exact equality.
        // FIXME: We are missing the rules for "repr(C) wrapping compatible types".
        Ok(caller == callee)
    }

    fn check_argument_compat(
        &self,
        caller_abi: &ArgAbi<'tcx, Ty<'tcx>>,
        callee_abi: &ArgAbi<'tcx, Ty<'tcx>>,
    ) -> InterpResult<'tcx, bool> {
        // We do not want to accept things as ABI-compatible that just "happen to be" compatible on the current target,
        // so we implement a type-based check that reflects the guaranteed rules for ABI compatibility.
        if self.layout_compat(caller_abi.layout, callee_abi.layout)? {
            // Ensure that our checks imply actual ABI compatibility for this concrete call.
            assert!(caller_abi.eq_abi(callee_abi));
            return Ok(true);
        } else {
            trace!(
                "check_argument_compat: incompatible ABIs:\ncaller: {:?}\ncallee: {:?}",
                caller_abi,
                callee_abi
            );
            return Ok(false);
        }
    }

    /// Initialize a single callee argument, checking the types for compatibility.
    fn pass_argument<'x, 'y>(
        &mut self,
        caller_args: &mut impl Iterator<
            Item = (&'x FnArg<'tcx, M::Provenance>, &'y ArgAbi<'tcx, Ty<'tcx>>),
        >,
        callee_abi: &ArgAbi<'tcx, Ty<'tcx>>,
        callee_arg: &mir::Place<'tcx>,
        callee_ty: Ty<'tcx>,
        already_live: bool,
    ) -> InterpResult<'tcx>
    where
        'tcx: 'x,
        'tcx: 'y,
    {
        assert_eq!(callee_ty, callee_abi.layout.ty);
        if matches!(callee_abi.mode, PassMode::Ignore) {
            // This one is skipped. Still must be made live though!
            if !already_live {
                self.storage_live(callee_arg.as_local().unwrap())?;
            }
            return Ok(());
        }
        // Find next caller arg.
        let Some((caller_arg, caller_abi)) = caller_args.next() else {
            throw_ub_custom!(fluent::const_eval_not_enough_caller_args);
        };
        assert_eq!(caller_arg.layout().layout, caller_abi.layout.layout);
        // Sadly we cannot assert that `caller_arg.layout().ty` and `caller_abi.layout.ty` are
        // equal; in closures the types sometimes differ. We just hope that `caller_abi` is the
        // right type to print to the user.

        // Check compatibility
        if !self.check_argument_compat(caller_abi, callee_abi)? {
            throw_ub!(AbiMismatchArgument {
                caller_ty: caller_abi.layout.ty,
                callee_ty: callee_abi.layout.ty
            });
        }
        // We work with a copy of the argument for now; if this is in-place argument passing, we
        // will later protect the source it comes from. This means the callee cannot observe if we
        // did in-place of by-copy argument passing, except for pointer equality tests.
        let caller_arg_copy = self.copy_fn_arg(caller_arg);
        if !already_live {
            let local = callee_arg.as_local().unwrap();
            let meta = caller_arg_copy.meta();
            // `check_argument_compat` ensures that if metadata is needed, both have the same type,
            // so we know they will use the metadata the same way.
            assert!(!meta.has_meta() || caller_arg_copy.layout.ty == callee_ty);

            self.storage_live_dyn(local, meta)?;
        }
        // Now we can finally actually evaluate the callee place.
        let callee_arg = self.eval_place(*callee_arg)?;
        // We allow some transmutes here.
        // FIXME: Depending on the PassMode, this should reset some padding to uninitialized. (This
        // is true for all `copy_op`, but there are a lot of special cases for argument passing
        // specifically.)
        self.copy_op_allow_transmute(&caller_arg_copy, &callee_arg)?;
        // If this was an in-place pass, protect the place it comes from for the duration of the call.
        if let FnArg::InPlace(mplace) = caller_arg {
            M::protect_in_place_function_argument(self, mplace)?;
        }
        Ok(())
    }

    /// Call this function -- pushing the stack frame and initializing the arguments.
    ///
    /// `caller_fn_abi` is used to determine if all the arguments are passed the proper way.
    /// However, we also need `caller_abi` to determine if we need to do untupling of arguments.
    ///
    /// `with_caller_location` indicates whether the caller passed a caller location. Miri
    /// implements caller locations without argument passing, but to match `FnAbi` we need to know
    /// when those arguments are present.
    pub(crate) fn eval_fn_call(
        &mut self,
        fn_val: FnVal<'tcx, M::ExtraFnVal>,
        (caller_abi, caller_fn_abi): (Abi, &FnAbi<'tcx, Ty<'tcx>>),
        args: &[FnArg<'tcx, M::Provenance>],
        with_caller_location: bool,
        destination: &MPlaceTy<'tcx, M::Provenance>,
        target: Option<mir::BasicBlock>,
        mut unwind: mir::UnwindAction,
    ) -> InterpResult<'tcx> {
        trace!("eval_fn_call: {:#?}", fn_val);

        let instance = match fn_val {
            FnVal::Instance(instance) => instance,
            FnVal::Other(extra) => {
                return M::call_extra_fn(
                    self,
                    extra,
                    caller_abi,
                    args,
                    destination,
                    target,
                    unwind,
                );
            }
        };

        match instance.def {
            ty::InstanceDef::Intrinsic(def_id) => {
                assert!(self.tcx.intrinsic(def_id).is_some());
                // FIXME: Should `InPlace` arguments be reset to uninit?
                M::call_intrinsic(
                    self,
                    instance,
                    &self.copy_fn_args(args),
                    destination,
                    target,
                    unwind,
                )
            }
            ty::InstanceDef::VTableShim(..)
            | ty::InstanceDef::ReifyShim(..)
            | ty::InstanceDef::ClosureOnceShim { .. }
            | ty::InstanceDef::ConstructCoroutineInClosureShim { .. }
            | ty::InstanceDef::CoroutineKindShim { .. }
            | ty::InstanceDef::FnPtrShim(..)
            | ty::InstanceDef::DropGlue(..)
            | ty::InstanceDef::CloneShim(..)
            | ty::InstanceDef::FnPtrAddrShim(..)
            | ty::InstanceDef::ThreadLocalShim(..)
            | ty::InstanceDef::Item(_) => {
                // We need MIR for this fn
                let Some((body, instance)) = M::find_mir_or_eval_fn(
                    self,
                    instance,
                    caller_abi,
                    args,
                    destination,
                    target,
                    unwind,
                )?
                else {
                    return Ok(());
                };

                // Compute callee information using the `instance` returned by
                // `find_mir_or_eval_fn`.
                // FIXME: for variadic support, do we have to somehow determine callee's extra_args?
                let callee_fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;

                if callee_fn_abi.c_variadic || caller_fn_abi.c_variadic {
                    throw_unsup_format!("calling a c-variadic function is not supported");
                }

                if M::enforce_abi(self) {
                    if caller_fn_abi.conv != callee_fn_abi.conv {
                        throw_ub_custom!(
                            fluent::const_eval_incompatible_calling_conventions,
                            callee_conv = format!("{:?}", callee_fn_abi.conv),
                            caller_conv = format!("{:?}", caller_fn_abi.conv),
                        )
                    }
                }

                // Check that all target features required by the callee (i.e., from
                // the attribute `#[target_feature(enable = ...)]`) are enabled at
                // compile time.
                self.check_fn_target_features(instance)?;

                if !callee_fn_abi.can_unwind {
                    // The callee cannot unwind, so force the `Unreachable` unwind handling.
                    unwind = mir::UnwindAction::Unreachable;
                }

                self.push_stack_frame(
                    instance,
                    body,
                    destination,
                    StackPopCleanup::Goto { ret: target, unwind },
                )?;

                // If an error is raised here, pop the frame again to get an accurate backtrace.
                // To this end, we wrap it all in a `try` block.
                let res: InterpResult<'tcx> = try {
                    trace!(
                        "caller ABI: {:?}, args: {:#?}",
                        caller_abi,
                        args.iter()
                            .map(|arg| (
                                arg.layout().ty,
                                match arg {
                                    FnArg::Copy(op) => format!("copy({op:?})"),
                                    FnArg::InPlace(mplace) => format!("in-place({mplace:?})"),
                                }
                            ))
                            .collect::<Vec<_>>()
                    );
                    trace!(
                        "spread_arg: {:?}, locals: {:#?}",
                        body.spread_arg,
                        body.args_iter()
                            .map(|local| (
                                local,
                                self.layout_of_local(self.frame(), local, None).unwrap().ty,
                            ))
                            .collect::<Vec<_>>()
                    );

                    // In principle, we have two iterators: Where the arguments come from, and where
                    // they go to.

                    // For where they come from: If the ABI is RustCall, we untuple the
                    // last incoming argument. These two iterators do not have the same type,
                    // so to keep the code paths uniform we accept an allocation
                    // (for RustCall ABI only).
                    let caller_args: Cow<'_, [FnArg<'tcx, M::Provenance>]> =
                        if caller_abi == Abi::RustCall && !args.is_empty() {
                            // Untuple
                            let (untuple_arg, args) = args.split_last().unwrap();
                            trace!("eval_fn_call: Will pass last argument by untupling");
                            Cow::from(
                                args.iter()
                                    .map(|a| Ok(a.clone()))
                                    .chain(
                                        (0..untuple_arg.layout().fields.count())
                                            .map(|i| self.fn_arg_field(untuple_arg, i)),
                                    )
                                    .collect::<InterpResult<'_, Vec<_>>>()?,
                            )
                        } else {
                            // Plain arg passing
                            Cow::from(args)
                        };
                    // If `with_caller_location` is set we pretend there is an extra argument (that
                    // we will not pass).
                    assert_eq!(
                        caller_args.len() + if with_caller_location { 1 } else { 0 },
                        caller_fn_abi.args.len(),
                        "mismatch between caller ABI and caller arguments",
                    );
                    let mut caller_args = caller_args
                        .iter()
                        .zip(caller_fn_abi.args.iter())
                        .filter(|arg_and_abi| !matches!(arg_and_abi.1.mode, PassMode::Ignore));

                    // Now we have to spread them out across the callee's locals,
                    // taking into account the `spread_arg`. If we could write
                    // this is a single iterator (that handles `spread_arg`), then
                    // `pass_argument` would be the loop body. It takes care to
                    // not advance `caller_iter` for ignored arguments.
                    let mut callee_args_abis = callee_fn_abi.args.iter();
                    for local in body.args_iter() {
                        // Construct the destination place for this argument. At this point all
                        // locals are still dead, so we cannot construct a `PlaceTy`.
                        let dest = mir::Place::from(local);
                        // `layout_of_local` does more than just the instantiation we need to get the
                        // type, but the result gets cached so this avoids calling the instantiation
                        // query *again* the next time this local is accessed.
                        let ty = self.layout_of_local(self.frame(), local, None)?.ty;
                        if Some(local) == body.spread_arg {
                            // Make the local live once, then fill in the value field by field.
                            self.storage_live(local)?;
                            // Must be a tuple
                            let ty::Tuple(fields) = ty.kind() else {
                                span_bug!(self.cur_span(), "non-tuple type for `spread_arg`: {ty}")
                            };
                            for (i, field_ty) in fields.iter().enumerate() {
                                let dest = dest.project_deeper(
                                    &[mir::ProjectionElem::Field(
                                        FieldIdx::from_usize(i),
                                        field_ty,
                                    )],
                                    *self.tcx,
                                );
                                let callee_abi = callee_args_abis.next().unwrap();
                                self.pass_argument(
                                    &mut caller_args,
                                    callee_abi,
                                    &dest,
                                    field_ty,
                                    /* already_live */ true,
                                )?;
                            }
                        } else {
                            // Normal argument. Cannot mark it as live yet, it might be unsized!
                            let callee_abi = callee_args_abis.next().unwrap();
                            self.pass_argument(
                                &mut caller_args,
                                callee_abi,
                                &dest,
                                ty,
                                /* already_live */ false,
                            )?;
                        }
                    }
                    // If the callee needs a caller location, pretend we consume one more argument from the ABI.
                    if instance.def.requires_caller_location(*self.tcx) {
                        callee_args_abis.next().unwrap();
                    }
                    // Now we should have no more caller args or callee arg ABIs
                    assert!(
                        callee_args_abis.next().is_none(),
                        "mismatch between callee ABI and callee body arguments"
                    );
                    if caller_args.next().is_some() {
                        throw_ub_custom!(fluent::const_eval_too_many_caller_args);
                    }
                    // Don't forget to check the return type!
                    if !self.check_argument_compat(&caller_fn_abi.ret, &callee_fn_abi.ret)? {
                        throw_ub!(AbiMismatchReturn {
                            caller_ty: caller_fn_abi.ret.layout.ty,
                            callee_ty: callee_fn_abi.ret.layout.ty
                        });
                    }

                    // Protect return place for in-place return value passing.
                    M::protect_in_place_function_argument(self, &destination)?;

                    // Don't forget to mark "initially live" locals as live.
                    self.storage_live_for_always_live_locals()?;
                };
                match res {
                    Err(err) => {
                        self.stack_mut().pop();
                        Err(err)
                    }
                    Ok(()) => Ok(()),
                }
            }
            // `InstanceDef::Virtual` does not have callable MIR. Calls to `Virtual` instances must be
            // codegen'd / interpreted as virtual calls through the vtable.
            ty::InstanceDef::Virtual(def_id, idx) => {
                let mut args = args.to_vec();
                // We have to implement all "object safe receivers". So we have to go search for a
                // pointer or `dyn Trait` type, but it could be wrapped in newtypes. So recursively
                // unwrap those newtypes until we are there.
                // An `InPlace` does nothing here, we keep the original receiver intact. We can't
                // really pass the argument in-place anyway, and we are constructing a new
                // `Immediate` receiver.
                let mut receiver = self.copy_fn_arg(&args[0]);
                let receiver_place = loop {
                    match receiver.layout.ty.kind() {
                        ty::Ref(..) | ty::RawPtr(..) => {
                            // We do *not* use `deref_pointer` here: we don't want to conceptually
                            // create a place that must be dereferenceable, since the receiver might
                            // be a raw pointer and (for `*const dyn Trait`) we don't need to
                            // actually access memory to resolve this method.
                            // Also see <https://github.com/rust-lang/miri/issues/2786>.
                            let val = self.read_immediate(&receiver)?;
                            break self.ref_to_mplace(&val)?;
                        }
                        ty::Dynamic(.., ty::Dyn) => break receiver.assert_mem_place(), // no immediate unsized values
                        ty::Dynamic(.., ty::DynStar) => {
                            // Not clear how to handle this, so far we assume the receiver is always a pointer.
                            span_bug!(
                                self.cur_span(),
                                "by-value calls on a `dyn*`... are those a thing?"
                            );
                        }
                        _ => {
                            // Not there yet, search for the only non-ZST field.
                            // (The rules for `DispatchFromDyn` ensure there's exactly one such field.)
                            let (idx, _) = receiver.layout.non_1zst_field(self).expect(
                                "not exactly one non-1-ZST field in a `DispatchFromDyn` type",
                            );
                            receiver = self.project_field(&receiver, idx)?;
                        }
                    }
                };

                // Obtain the underlying trait we are working on, and the adjusted receiver argument.
                let (vptr, dyn_ty, adjusted_receiver) = if let ty::Dynamic(data, _, ty::DynStar) =
                    receiver_place.layout.ty.kind()
                {
                    let (recv, vptr) = self.unpack_dyn_star(&receiver_place)?;
                    let (dyn_ty, dyn_trait) = self.get_ptr_vtable(vptr)?;
                    if dyn_trait != data.principal() {
                        throw_ub_custom!(fluent::const_eval_dyn_star_call_vtable_mismatch);
                    }

                    (vptr, dyn_ty, recv.ptr())
                } else {
                    // Doesn't have to be a `dyn Trait`, but the unsized tail must be `dyn Trait`.
                    // (For that reason we also cannot use `unpack_dyn_trait`.)
                    let receiver_tail = self
                        .tcx
                        .struct_tail_erasing_lifetimes(receiver_place.layout.ty, self.param_env);
                    let ty::Dynamic(data, _, ty::Dyn) = receiver_tail.kind() else {
                        span_bug!(
                            self.cur_span(),
                            "dynamic call on non-`dyn` type {}",
                            receiver_tail
                        )
                    };
                    assert!(receiver_place.layout.is_unsized());

                    // Get the required information from the vtable.
                    let vptr = receiver_place.meta().unwrap_meta().to_pointer(self)?;
                    let (dyn_ty, dyn_trait) = self.get_ptr_vtable(vptr)?;
                    if dyn_trait != data.principal() {
                        throw_ub_custom!(fluent::const_eval_dyn_call_vtable_mismatch);
                    }

                    // It might be surprising that we use a pointer as the receiver even if this
                    // is a by-val case; this works because by-val passing of an unsized `dyn
                    // Trait` to a function is actually desugared to a pointer.
                    (vptr, dyn_ty, receiver_place.ptr())
                };

                // Now determine the actual method to call. We can do that in two different ways and
                // compare them to ensure everything fits.
                let Some(ty::VtblEntry::Method(fn_inst)) =
                    self.get_vtable_entries(vptr)?.get(idx).copied()
                else {
                    // FIXME(fee1-dead) these could be variants of the UB info enum instead of this
                    throw_ub_custom!(fluent::const_eval_dyn_call_not_a_method);
                };
                trace!("Virtual call dispatches to {fn_inst:#?}");
                if cfg!(debug_assertions) {
                    let tcx = *self.tcx;

                    let trait_def_id = tcx.trait_of_item(def_id).unwrap();
                    let virtual_trait_ref =
                        ty::TraitRef::from_method(tcx, trait_def_id, instance.args);
                    let existential_trait_ref =
                        ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
                    let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);

                    let concrete_method = Instance::resolve_for_vtable(
                        tcx,
                        self.param_env,
                        def_id,
                        instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
                    )
                    .unwrap();
                    assert_eq!(fn_inst, concrete_method);
                }

                // Adjust receiver argument. Layout can be any (thin) ptr.
                let receiver_ty = Ty::new_mut_ptr(self.tcx.tcx, dyn_ty);
                args[0] = FnArg::Copy(
                    ImmTy::from_immediate(
                        Scalar::from_maybe_pointer(adjusted_receiver, self).into(),
                        self.layout_of(receiver_ty)?,
                    )
                    .into(),
                );
                trace!("Patched receiver operand to {:#?}", args[0]);
                // Need to also adjust the type in the ABI. Strangely, the layout there is actually
                // already fine! Just the type is bogus. This is due to what `force_thin_self_ptr`
                // does in `fn_abi_new_uncached`; supposedly, codegen relies on having the bogus
                // type, so we just patch this up locally.
                let mut caller_fn_abi = caller_fn_abi.clone();
                caller_fn_abi.args[0].layout.ty = receiver_ty;

                // recurse with concrete function
                self.eval_fn_call(
                    FnVal::Instance(fn_inst),
                    (caller_abi, &caller_fn_abi),
                    &args,
                    with_caller_location,
                    destination,
                    target,
                    unwind,
                )
            }
        }
    }

    fn check_fn_target_features(&self, instance: ty::Instance<'tcx>) -> InterpResult<'tcx, ()> {
        // Calling functions with `#[target_feature]` is not unsafe on WASM, see #84988
        let attrs = self.tcx.codegen_fn_attrs(instance.def_id());
        if !self.tcx.sess.target.is_like_wasm
            && attrs
                .target_features
                .iter()
                .any(|feature| !self.tcx.sess.target_features.contains(feature))
        {
            throw_ub_custom!(
                fluent::const_eval_unavailable_target_features_for_fn,
                unavailable_feats = attrs
                    .target_features
                    .iter()
                    .filter(|&feature| !self.tcx.sess.target_features.contains(feature))
                    .fold(String::new(), |mut s, feature| {
                        if !s.is_empty() {
                            s.push_str(", ");
                        }
                        s.push_str(feature.as_str());
                        s
                    }),
            );
        }
        Ok(())
    }

    fn drop_in_place(
        &mut self,
        place: &PlaceTy<'tcx, M::Provenance>,
        instance: ty::Instance<'tcx>,
        target: mir::BasicBlock,
        unwind: mir::UnwindAction,
    ) -> InterpResult<'tcx> {
        trace!("drop_in_place: {:?},\n  instance={:?}", place, instance);
        // We take the address of the object. This may well be unaligned, which is fine
        // for us here. However, unaligned accesses will probably make the actual drop
        // implementation fail -- a problem shared by rustc.
        let place = self.force_allocation(place)?;

        let place = match place.layout.ty.kind() {
            ty::Dynamic(_, _, ty::Dyn) => {
                // Dropping a trait object. Need to find actual drop fn.
                self.unpack_dyn_trait(&place)?.0
            }
            ty::Dynamic(_, _, ty::DynStar) => {
                // Dropping a `dyn*`. Need to find actual drop fn.
                self.unpack_dyn_star(&place)?.0
            }
            _ => {
                debug_assert_eq!(
                    instance,
                    ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty)
                );
                place
            }
        };
        let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
        let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;

        let arg = self.mplace_to_ref(&place)?;
        let ret = MPlaceTy::fake_alloc_zst(self.layout_of(self.tcx.types.unit)?);

        self.eval_fn_call(
            FnVal::Instance(instance),
            (Abi::Rust, fn_abi),
            &[FnArg::Copy(arg.into())],
            false,
            &ret.into(),
            Some(target),
            unwind,
        )
    }
}