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
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
//! Check the validity invariant of a given value, and tell the user
//! where in the value it got violated.
//! In const context, this goes even further and tries to approximate const safety.
//! That's useful because it means other passes (e.g. promotion) can rely on `const`s
//! to be const-safe.

use std::fmt::Write;
use std::num::NonZero;

use either::{Left, Right};

use hir::def::DefKind;
use rustc_ast::Mutability;
use rustc_data_structures::fx::FxHashSet;
use rustc_hir as hir;
use rustc_middle::bug;
use rustc_middle::mir::interpret::{
    ExpectedKind, InterpError, InvalidMetaKind, Misalignment, PointerKind, Provenance,
    ValidationErrorInfo, ValidationErrorKind, ValidationErrorKind::*,
};
use rustc_middle::ty::layout::{LayoutOf, TyAndLayout};
use rustc_middle::ty::{self, Ty};
use rustc_span::symbol::{sym, Symbol};
use rustc_target::abi::{
    Abi, FieldIdx, Scalar as ScalarAbi, Size, VariantIdx, Variants, WrappingRange,
};

use std::hash::Hash;

use super::{
    err_ub, format_interp_error, machine::AllocMap, throw_ub, AllocId, CheckInAllocMsg,
    GlobalAlloc, ImmTy, Immediate, InterpCx, InterpResult, MPlaceTy, Machine, MemPlaceMeta, OpTy,
    Pointer, Projectable, Scalar, ValueVisitor,
};

// for the validation errors
use super::InterpError::UndefinedBehavior as Ub;
use super::InterpError::Unsupported as Unsup;
use super::UndefinedBehaviorInfo::*;
use super::UnsupportedOpInfo::*;

macro_rules! throw_validation_failure {
    ($where:expr, $kind: expr) => {{
        let where_ = &$where;
        let path = if !where_.is_empty() {
            let mut path = String::new();
            write_path(&mut path, where_);
            Some(path)
        } else {
            None
        };

        throw_ub!(ValidationError(ValidationErrorInfo { path, kind: $kind }))
    }};
}

/// If $e throws an error matching the pattern, throw a validation failure.
/// Other errors are passed back to the caller, unchanged -- and if they reach the root of
/// the visitor, we make sure only validation errors and `InvalidProgram` errors are left.
/// This lets you use the patterns as a kind of validation list, asserting which errors
/// can possibly happen:
///
/// ```ignore(illustrative)
/// let v = try_validation!(some_fn(), some_path, {
///     Foo | Bar | Baz => { "some failure" },
/// });
/// ```
///
/// The patterns must be of type `UndefinedBehaviorInfo`.
/// An additional expected parameter can also be added to the failure message:
///
/// ```ignore(illustrative)
/// let v = try_validation!(some_fn(), some_path, {
///     Foo | Bar | Baz => { "some failure" } expected { "something that wasn't a failure" },
/// });
/// ```
///
/// An additional nicety is that both parameters actually take format args, so you can just write
/// the format string in directly:
///
/// ```ignore(illustrative)
/// let v = try_validation!(some_fn(), some_path, {
///     Foo | Bar | Baz => { "{:?}", some_failure } expected { "{}", expected_value },
/// });
/// ```
///
macro_rules! try_validation {
    ($e:expr, $where:expr,
    $( $( $p:pat_param )|+ => $kind: expr ),+ $(,)?
    ) => {{
        match $e {
            Ok(x) => x,
            // We catch the error and turn it into a validation failure. We are okay with
            // allocation here as this can only slow down builds that fail anyway.
            Err(e) => match e.kind() {
                $(
                    $($p)|+ =>
                       throw_validation_failure!(
                            $where,
                            $kind
                        )
                ),+,
                #[allow(unreachable_patterns)]
                _ => Err::<!, _>(e)?,
            }
        }
    }};
}

/// We want to show a nice path to the invalid field for diagnostics,
/// but avoid string operations in the happy case where no error happens.
/// So we track a `Vec<PathElem>` where `PathElem` contains all the data we
/// need to later print something for the user.
#[derive(Copy, Clone, Debug)]
pub enum PathElem {
    Field(Symbol),
    Variant(Symbol),
    CoroutineState(VariantIdx),
    CapturedVar(Symbol),
    ArrayElem(usize),
    TupleElem(usize),
    Deref,
    EnumTag,
    CoroutineTag,
    DynDowncast,
}

/// Extra things to check for during validation of CTFE results.
#[derive(Copy, Clone)]
pub enum CtfeValidationMode {
    /// Validation of a `static`
    Static { mutbl: Mutability },
    /// Validation of a promoted.
    Promoted,
    /// Validation of a `const`.
    /// `allow_immutable_unsafe_cell` says whether we allow `UnsafeCell` in immutable memory (which is the
    /// case for the top-level allocation of a `const`, where this is fine because the allocation will be
    /// copied at each use site).
    Const { allow_immutable_unsafe_cell: bool },
}

impl CtfeValidationMode {
    fn allow_immutable_unsafe_cell(self) -> bool {
        match self {
            CtfeValidationMode::Static { .. } => false,
            CtfeValidationMode::Promoted { .. } => false,
            CtfeValidationMode::Const { allow_immutable_unsafe_cell, .. } => {
                allow_immutable_unsafe_cell
            }
        }
    }
}

/// State for tracking recursive validation of references
pub struct RefTracking<T, PATH = ()> {
    pub seen: FxHashSet<T>,
    pub todo: Vec<(T, PATH)>,
}

impl<T: Clone + Eq + Hash + std::fmt::Debug, PATH: Default> RefTracking<T, PATH> {
    pub fn empty() -> Self {
        RefTracking { seen: FxHashSet::default(), todo: vec![] }
    }
    pub fn new(op: T) -> Self {
        let mut ref_tracking_for_consts =
            RefTracking { seen: FxHashSet::default(), todo: vec![(op.clone(), PATH::default())] };
        ref_tracking_for_consts.seen.insert(op);
        ref_tracking_for_consts
    }

    pub fn track(&mut self, op: T, path: impl FnOnce() -> PATH) {
        if self.seen.insert(op.clone()) {
            trace!("Recursing below ptr {:#?}", op);
            let path = path();
            // Remember to come back to this later.
            self.todo.push((op, path));
        }
    }
}

// FIXME make this translatable as well?
/// Format a path
fn write_path(out: &mut String, path: &[PathElem]) {
    use self::PathElem::*;

    for elem in path.iter() {
        match elem {
            Field(name) => write!(out, ".{name}"),
            EnumTag => write!(out, ".<enum-tag>"),
            Variant(name) => write!(out, ".<enum-variant({name})>"),
            CoroutineTag => write!(out, ".<coroutine-tag>"),
            CoroutineState(idx) => write!(out, ".<coroutine-state({})>", idx.index()),
            CapturedVar(name) => write!(out, ".<captured-var({name})>"),
            TupleElem(idx) => write!(out, ".{idx}"),
            ArrayElem(idx) => write!(out, "[{idx}]"),
            // `.<deref>` does not match Rust syntax, but it is more readable for long paths -- and
            // some of the other items here also are not Rust syntax. Actually we can't
            // even use the usual syntax because we are just showing the projections,
            // not the root.
            Deref => write!(out, ".<deref>"),
            DynDowncast => write!(out, ".<dyn-downcast>"),
        }
        .unwrap()
    }
}

struct ValidityVisitor<'rt, 'mir, 'tcx, M: Machine<'mir, 'tcx>> {
    /// The `path` may be pushed to, but the part that is present when a function
    /// starts must not be changed!  `visit_fields` and `visit_array` rely on
    /// this stack discipline.
    path: Vec<PathElem>,
    ref_tracking: Option<&'rt mut RefTracking<MPlaceTy<'tcx, M::Provenance>, Vec<PathElem>>>,
    /// `None` indicates this is not validating for CTFE (but for runtime).
    ctfe_mode: Option<CtfeValidationMode>,
    ecx: &'rt InterpCx<'mir, 'tcx, M>,
}

impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, 'tcx, M> {
    fn aggregate_field_path_elem(&mut self, layout: TyAndLayout<'tcx>, field: usize) -> PathElem {
        // First, check if we are projecting to a variant.
        match layout.variants {
            Variants::Multiple { tag_field, .. } => {
                if tag_field == field {
                    return match layout.ty.kind() {
                        ty::Adt(def, ..) if def.is_enum() => PathElem::EnumTag,
                        ty::Coroutine(..) => PathElem::CoroutineTag,
                        _ => bug!("non-variant type {:?}", layout.ty),
                    };
                }
            }
            Variants::Single { .. } => {}
        }

        // Now we know we are projecting to a field, so figure out which one.
        match layout.ty.kind() {
            // coroutines, closures, and coroutine-closures all have upvars that may be named.
            ty::Closure(def_id, _) | ty::Coroutine(def_id, _) | ty::CoroutineClosure(def_id, _) => {
                let mut name = None;
                // FIXME this should be more descriptive i.e. CapturePlace instead of CapturedVar
                // https://github.com/rust-lang/project-rfc-2229/issues/46
                if let Some(local_def_id) = def_id.as_local() {
                    let captures = self.ecx.tcx.closure_captures(local_def_id);
                    if let Some(captured_place) = captures.get(field) {
                        // Sometimes the index is beyond the number of upvars (seen
                        // for a coroutine).
                        let var_hir_id = captured_place.get_root_variable();
                        let node = self.ecx.tcx.hir_node(var_hir_id);
                        if let hir::Node::Pat(pat) = node {
                            if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
                                name = Some(ident.name);
                            }
                        }
                    }
                }

                PathElem::CapturedVar(name.unwrap_or_else(|| {
                    // Fall back to showing the field index.
                    sym::integer(field)
                }))
            }

            // tuples
            ty::Tuple(_) => PathElem::TupleElem(field),

            // enums
            ty::Adt(def, ..) if def.is_enum() => {
                // we might be projecting *to* a variant, or to a field *in* a variant.
                match layout.variants {
                    Variants::Single { index } => {
                        // Inside a variant
                        PathElem::Field(def.variant(index).fields[FieldIdx::from_usize(field)].name)
                    }
                    Variants::Multiple { .. } => bug!("we handled variants above"),
                }
            }

            // other ADTs
            ty::Adt(def, _) => {
                PathElem::Field(def.non_enum_variant().fields[FieldIdx::from_usize(field)].name)
            }

            // arrays/slices
            ty::Array(..) | ty::Slice(..) => PathElem::ArrayElem(field),

            // dyn traits
            ty::Dynamic(..) => PathElem::DynDowncast,

            // nothing else has an aggregate layout
            _ => bug!("aggregate_field_path_elem: got non-aggregate type {:?}", layout.ty),
        }
    }

    fn with_elem<R>(
        &mut self,
        elem: PathElem,
        f: impl FnOnce(&mut Self) -> InterpResult<'tcx, R>,
    ) -> InterpResult<'tcx, R> {
        // Remember the old state
        let path_len = self.path.len();
        // Record new element
        self.path.push(elem);
        // Perform operation
        let r = f(self)?;
        // Undo changes
        self.path.truncate(path_len);
        // Done
        Ok(r)
    }

    fn read_immediate(
        &self,
        op: &OpTy<'tcx, M::Provenance>,
        expected: ExpectedKind,
    ) -> InterpResult<'tcx, ImmTy<'tcx, M::Provenance>> {
        Ok(try_validation!(
            self.ecx.read_immediate(op),
            self.path,
            Ub(InvalidUninitBytes(None)) =>
                Uninit { expected },
            // The `Unsup` cases can only occur during CTFE
            Unsup(ReadPointerAsInt(_)) =>
                PointerAsInt { expected },
            Unsup(ReadPartialPointer(_)) =>
                PartialPointer,
        ))
    }

    fn read_scalar(
        &self,
        op: &OpTy<'tcx, M::Provenance>,
        expected: ExpectedKind,
    ) -> InterpResult<'tcx, Scalar<M::Provenance>> {
        Ok(self.read_immediate(op, expected)?.to_scalar())
    }

    fn check_wide_ptr_meta(
        &mut self,
        meta: MemPlaceMeta<M::Provenance>,
        pointee: TyAndLayout<'tcx>,
    ) -> InterpResult<'tcx> {
        let tail = self.ecx.tcx.struct_tail_erasing_lifetimes(pointee.ty, self.ecx.param_env);
        match tail.kind() {
            ty::Dynamic(data, _, ty::Dyn) => {
                let vtable = meta.unwrap_meta().to_pointer(self.ecx)?;
                // Make sure it is a genuine vtable pointer.
                let (_dyn_ty, dyn_trait) = try_validation!(
                    self.ecx.get_ptr_vtable(vtable),
                    self.path,
                    Ub(DanglingIntPointer(..) | InvalidVTablePointer(..)) =>
                        InvalidVTablePtr { value: format!("{vtable}") }
                );
                // Make sure it is for the right trait.
                if dyn_trait != data.principal() {
                    throw_validation_failure!(
                        self.path,
                        InvalidMetaWrongTrait { expected_trait: data, vtable_trait: dyn_trait }
                    );
                }
            }
            ty::Slice(..) | ty::Str => {
                let _len = meta.unwrap_meta().to_target_usize(self.ecx)?;
                // We do not check that `len * elem_size <= isize::MAX`:
                // that is only required for references, and there it falls out of the
                // "dereferenceable" check performed by Stacked Borrows.
            }
            ty::Foreign(..) => {
                // Unsized, but not wide.
            }
            _ => bug!("Unexpected unsized type tail: {:?}", tail),
        }

        Ok(())
    }

    /// Check a reference or `Box`.
    fn check_safe_pointer(
        &mut self,
        value: &OpTy<'tcx, M::Provenance>,
        ptr_kind: PointerKind,
    ) -> InterpResult<'tcx> {
        // Not using `deref_pointer` since we want to use our `read_immediate` wrapper.
        let place = self.ecx.ref_to_mplace(&self.read_immediate(value, ptr_kind.into())?)?;
        // Handle wide pointers.
        // Check metadata early, for better diagnostics
        if place.layout.is_unsized() {
            self.check_wide_ptr_meta(place.meta(), place.layout)?;
        }
        // Make sure this is dereferenceable and all.
        let size_and_align = try_validation!(
            self.ecx.size_and_align_of_mplace(&place),
            self.path,
            Ub(InvalidMeta(msg)) => match msg {
                InvalidMetaKind::SliceTooBig => InvalidMetaSliceTooLarge { ptr_kind },
                InvalidMetaKind::TooBig => InvalidMetaTooLarge { ptr_kind },
            }
        );
        let (size, align) = size_and_align
            // for the purpose of validity, consider foreign types to have
            // alignment and size determined by the layout (size will be 0,
            // alignment should take attributes into account).
            .unwrap_or_else(|| (place.layout.size, place.layout.align.abi));
        // Direct call to `check_ptr_access_align` checks alignment even on CTFE machines.
        try_validation!(
            self.ecx.check_ptr_access(
                place.ptr(),
                size,
                CheckInAllocMsg::InboundsTest, // will anyway be replaced by validity message
            ),
            self.path,
            Ub(DanglingIntPointer(0, _)) => NullPtr { ptr_kind },
            Ub(DanglingIntPointer(i, _)) => DanglingPtrNoProvenance {
                ptr_kind,
                // FIXME this says "null pointer" when null but we need translate
                pointer: format!("{}", Pointer::<Option<AllocId>>::from_addr_invalid(*i))
            },
            Ub(PointerOutOfBounds { .. }) => DanglingPtrOutOfBounds {
                ptr_kind
            },
            // This cannot happen during const-eval (because interning already detects
            // dangling pointers), but it can happen in Miri.
            Ub(PointerUseAfterFree(..)) => DanglingPtrUseAfterFree {
                ptr_kind,
            },
        );
        try_validation!(
            self.ecx.check_ptr_align(
                place.ptr(),
                align,
            ),
            self.path,
            Ub(AlignmentCheckFailed(Misalignment { required, has }, _msg)) => UnalignedPtr {
                ptr_kind,
                required_bytes: required.bytes(),
                found_bytes: has.bytes()
            },
        );
        // Do not allow pointers to uninhabited types.
        if place.layout.abi.is_uninhabited() {
            let ty = place.layout.ty;
            throw_validation_failure!(self.path, PtrToUninhabited { ptr_kind, ty })
        }
        // Recursive checking
        if let Some(ref_tracking) = self.ref_tracking.as_deref_mut() {
            // Determine whether this pointer expects to be pointing to something mutable.
            let ptr_expected_mutbl = match ptr_kind {
                PointerKind::Box => Mutability::Mut,
                PointerKind::Ref(mutbl) => {
                    // We do not take into account interior mutability here since we cannot know if
                    // there really is an `UnsafeCell` inside `Option<UnsafeCell>` -- so we check
                    // that in the recursive descent behind this reference (controlled by
                    // `allow_immutable_unsafe_cell`).
                    mutbl
                }
            };
            // Proceed recursively even for ZST, no reason to skip them!
            // `!` is a ZST and we want to validate it.
            if let Ok((alloc_id, _offset, _prov)) = self.ecx.ptr_try_get_alloc_id(place.ptr()) {
                let mut skip_recursive_check = false;
                let alloc_actual_mutbl = mutability(self.ecx, alloc_id);
                if let GlobalAlloc::Static(did) = self.ecx.tcx.global_alloc(alloc_id) {
                    let DefKind::Static { nested, .. } = self.ecx.tcx.def_kind(did) else { bug!() };
                    // Special handling for pointers to statics (irrespective of their type).
                    assert!(!self.ecx.tcx.is_thread_local_static(did));
                    assert!(self.ecx.tcx.is_static(did));
                    // Mode-specific checks
                    match self.ctfe_mode {
                        Some(
                            CtfeValidationMode::Static { .. } | CtfeValidationMode::Promoted { .. },
                        ) => {
                            // We skip recursively checking other statics. These statics must be sound by
                            // themselves, and the only way to get broken statics here is by using
                            // unsafe code.
                            // The reasons we don't check other statics is twofold. For one, in all
                            // sound cases, the static was already validated on its own, and second, we
                            // trigger cycle errors if we try to compute the value of the other static
                            // and that static refers back to us (potentially through a promoted).
                            // This could miss some UB, but that's fine.
                            // We still walk nested allocations, as they are fundamentally part of this validation run.
                            // This means we will also recurse into nested statics of *other*
                            // statics, even though we do not recurse into other statics directly.
                            // That's somewhat inconsistent but harmless.
                            skip_recursive_check = !nested;
                        }
                        Some(CtfeValidationMode::Const { .. }) => {
                            // We can't recursively validate `extern static`, so we better reject them.
                            if self.ecx.tcx.is_foreign_item(did) {
                                throw_validation_failure!(self.path, ConstRefToExtern);
                            }
                        }
                        None => {}
                    }
                }

                // Mutability check.
                // If this allocation has size zero, there is no actual mutability here.
                let (size, _align, _alloc_kind) = self.ecx.get_alloc_info(alloc_id);
                if size != Size::ZERO {
                    // Mutable pointer to immutable memory is no good.
                    if ptr_expected_mutbl == Mutability::Mut
                        && alloc_actual_mutbl == Mutability::Not
                    {
                        throw_validation_failure!(self.path, MutableRefToImmutable);
                    }
                    // In a const, everything must be completely immutable.
                    if matches!(self.ctfe_mode, Some(CtfeValidationMode::Const { .. })) {
                        if ptr_expected_mutbl == Mutability::Mut
                            || alloc_actual_mutbl == Mutability::Mut
                        {
                            throw_validation_failure!(self.path, ConstRefToMutable);
                        }
                    }
                }
                // Potentially skip recursive check.
                if skip_recursive_check {
                    return Ok(());
                }
            }
            let path = &self.path;
            ref_tracking.track(place, || {
                // We need to clone the path anyway, make sure it gets created
                // with enough space for the additional `Deref`.
                let mut new_path = Vec::with_capacity(path.len() + 1);
                new_path.extend(path);
                new_path.push(PathElem::Deref);
                new_path
            });
        }
        Ok(())
    }

    /// Check if this is a value of primitive type, and if yes check the validity of the value
    /// at that type. Return `true` if the type is indeed primitive.
    ///
    /// Note that not all of these have `FieldsShape::Primitive`, e.g. wide references.
    fn try_visit_primitive(
        &mut self,
        value: &OpTy<'tcx, M::Provenance>,
    ) -> InterpResult<'tcx, bool> {
        // Go over all the primitive types
        let ty = value.layout.ty;
        match ty.kind() {
            ty::Bool => {
                let value = self.read_scalar(value, ExpectedKind::Bool)?;
                try_validation!(
                    value.to_bool(),
                    self.path,
                    Ub(InvalidBool(..)) => ValidationErrorKind::InvalidBool {
                        value: format!("{value:x}"),
                    }
                );
                Ok(true)
            }
            ty::Char => {
                let value = self.read_scalar(value, ExpectedKind::Char)?;
                try_validation!(
                    value.to_char(),
                    self.path,
                    Ub(InvalidChar(..)) => ValidationErrorKind::InvalidChar {
                        value: format!("{value:x}"),
                    }
                );
                Ok(true)
            }
            ty::Float(_) | ty::Int(_) | ty::Uint(_) => {
                // NOTE: Keep this in sync with the array optimization for int/float
                // types below!
                self.read_scalar(
                    value,
                    if matches!(ty.kind(), ty::Float(..)) {
                        ExpectedKind::Float
                    } else {
                        ExpectedKind::Int
                    },
                )?;
                Ok(true)
            }
            ty::RawPtr(..) => {
                let place =
                    self.ecx.ref_to_mplace(&self.read_immediate(value, ExpectedKind::RawPtr)?)?;
                if place.layout.is_unsized() {
                    self.check_wide_ptr_meta(place.meta(), place.layout)?;
                }
                Ok(true)
            }
            ty::Ref(_, _ty, mutbl) => {
                self.check_safe_pointer(value, PointerKind::Ref(*mutbl))?;
                Ok(true)
            }
            ty::FnPtr(_sig) => {
                let value = self.read_scalar(value, ExpectedKind::FnPtr)?;

                // If we check references recursively, also check that this points to a function.
                if let Some(_) = self.ref_tracking {
                    let ptr = value.to_pointer(self.ecx)?;
                    let _fn = try_validation!(
                        self.ecx.get_ptr_fn(ptr),
                        self.path,
                        Ub(DanglingIntPointer(..) | InvalidFunctionPointer(..)) =>
                            InvalidFnPtr { value: format!("{ptr}") },
                    );
                    // FIXME: Check if the signature matches
                } else {
                    // Otherwise (for standalone Miri), we have to still check it to be non-null.
                    if self.ecx.scalar_may_be_null(value)? {
                        throw_validation_failure!(self.path, NullFnPtr);
                    }
                }
                Ok(true)
            }
            ty::Never => throw_validation_failure!(self.path, NeverVal),
            ty::Foreign(..) | ty::FnDef(..) => {
                // Nothing to check.
                Ok(true)
            }
            // The above should be all the primitive types. The rest is compound, we
            // check them by visiting their fields/variants.
            ty::Adt(..)
            | ty::Tuple(..)
            | ty::Array(..)
            | ty::Slice(..)
            | ty::Str
            | ty::Dynamic(..)
            | ty::Closure(..)
            | ty::Pat(..)
            | ty::CoroutineClosure(..)
            | ty::Coroutine(..) => Ok(false),
            // Some types only occur during typechecking, they have no layout.
            // We should not see them here and we could not check them anyway.
            ty::Error(_)
            | ty::Infer(..)
            | ty::Placeholder(..)
            | ty::Bound(..)
            | ty::Param(..)
            | ty::Alias(..)
            | ty::CoroutineWitness(..) => bug!("Encountered invalid type {:?}", ty),
        }
    }

    fn visit_scalar(
        &mut self,
        scalar: Scalar<M::Provenance>,
        scalar_layout: ScalarAbi,
    ) -> InterpResult<'tcx> {
        let size = scalar_layout.size(self.ecx);
        let valid_range = scalar_layout.valid_range(self.ecx);
        let WrappingRange { start, end } = valid_range;
        let max_value = size.unsigned_int_max();
        assert!(end <= max_value);
        let bits = match scalar.try_to_int() {
            Ok(int) => int.assert_bits(size),
            Err(_) => {
                // So this is a pointer then, and casting to an int failed.
                // Can only happen during CTFE.
                // We support 2 kinds of ranges here: full range, and excluding zero.
                if start == 1 && end == max_value {
                    // Only null is the niche. So make sure the ptr is NOT null.
                    if self.ecx.scalar_may_be_null(scalar)? {
                        throw_validation_failure!(
                            self.path,
                            NullablePtrOutOfRange { range: valid_range, max_value }
                        )
                    } else {
                        return Ok(());
                    }
                } else if scalar_layout.is_always_valid(self.ecx) {
                    // Easy. (This is reachable if `enforce_number_validity` is set.)
                    return Ok(());
                } else {
                    // Conservatively, we reject, because the pointer *could* have a bad
                    // value.
                    throw_validation_failure!(
                        self.path,
                        PtrOutOfRange { range: valid_range, max_value }
                    )
                }
            }
        };
        // Now compare.
        if valid_range.contains(bits) {
            Ok(())
        } else {
            throw_validation_failure!(
                self.path,
                OutOfRange { value: format!("{bits}"), range: valid_range, max_value }
            )
        }
    }

    fn in_mutable_memory(&self, op: &OpTy<'tcx, M::Provenance>) -> bool {
        if let Some(mplace) = op.as_mplace_or_imm().left() {
            if let Some(alloc_id) = mplace.ptr().provenance.and_then(|p| p.get_alloc_id()) {
                return mutability(self.ecx, alloc_id).is_mut();
            }
        }
        false
    }
}

/// Returns whether the allocation is mutable, and whether it's actually a static.
/// For "root" statics we look at the type to account for interior
/// mutability; for nested statics we have no type and directly use the annotated mutability.
fn mutability<'mir, 'tcx: 'mir>(
    ecx: &InterpCx<'mir, 'tcx, impl Machine<'mir, 'tcx>>,
    alloc_id: AllocId,
) -> Mutability {
    // Let's see what kind of memory this points to.
    // We're not using `try_global_alloc` since dangling pointers have already been handled.
    match ecx.tcx.global_alloc(alloc_id) {
        GlobalAlloc::Static(did) => {
            let DefKind::Static { mutability, nested } = ecx.tcx.def_kind(did) else { bug!() };
            if nested {
                assert!(
                    ecx.memory.alloc_map.get(alloc_id).is_none(),
                    "allocations of nested statics are already interned: {alloc_id:?}, {did:?}"
                );
                // Nested statics in a `static` are never interior mutable,
                // so just use the declared mutability.
                mutability
            } else {
                let mutability = match mutability {
                    Mutability::Not
                        if !ecx
                            .tcx
                            .type_of(did)
                            .no_bound_vars()
                            .expect("statics should not have generic parameters")
                            .is_freeze(*ecx.tcx, ty::ParamEnv::reveal_all()) =>
                    {
                        Mutability::Mut
                    }
                    _ => mutability,
                };
                if let Some((_, alloc)) = ecx.memory.alloc_map.get(alloc_id) {
                    assert_eq!(alloc.mutability, mutability);
                }
                mutability
            }
        }
        GlobalAlloc::Memory(alloc) => alloc.inner().mutability,
        GlobalAlloc::Function(..) | GlobalAlloc::VTable(..) => {
            // These are immutable, we better don't allow mutable pointers here.
            Mutability::Not
        }
    }
}

impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueVisitor<'mir, 'tcx, M>
    for ValidityVisitor<'rt, 'mir, 'tcx, M>
{
    type V = OpTy<'tcx, M::Provenance>;

    #[inline(always)]
    fn ecx(&self) -> &InterpCx<'mir, 'tcx, M> {
        self.ecx
    }

    fn read_discriminant(
        &mut self,
        op: &OpTy<'tcx, M::Provenance>,
    ) -> InterpResult<'tcx, VariantIdx> {
        self.with_elem(PathElem::EnumTag, move |this| {
            Ok(try_validation!(
                this.ecx.read_discriminant(op),
                this.path,
                Ub(InvalidTag(val)) => InvalidEnumTag {
                    value: format!("{val:x}"),
                },
                Ub(UninhabitedEnumVariantRead(_)) => UninhabitedEnumVariant,
                // Uninit / bad provenance are not possible since the field was already previously
                // checked at its integer type.
            ))
        })
    }

    #[inline]
    fn visit_field(
        &mut self,
        old_op: &OpTy<'tcx, M::Provenance>,
        field: usize,
        new_op: &OpTy<'tcx, M::Provenance>,
    ) -> InterpResult<'tcx> {
        let elem = self.aggregate_field_path_elem(old_op.layout, field);
        self.with_elem(elem, move |this| this.visit_value(new_op))
    }

    #[inline]
    fn visit_variant(
        &mut self,
        old_op: &OpTy<'tcx, M::Provenance>,
        variant_id: VariantIdx,
        new_op: &OpTy<'tcx, M::Provenance>,
    ) -> InterpResult<'tcx> {
        let name = match old_op.layout.ty.kind() {
            ty::Adt(adt, _) => PathElem::Variant(adt.variant(variant_id).name),
            // Coroutines also have variants
            ty::Coroutine(..) => PathElem::CoroutineState(variant_id),
            _ => bug!("Unexpected type with variant: {:?}", old_op.layout.ty),
        };
        self.with_elem(name, move |this| this.visit_value(new_op))
    }

    #[inline(always)]
    fn visit_union(
        &mut self,
        op: &OpTy<'tcx, M::Provenance>,
        _fields: NonZero<usize>,
    ) -> InterpResult<'tcx> {
        // Special check for CTFE validation, preventing `UnsafeCell` inside unions in immutable memory.
        if self.ctfe_mode.is_some_and(|c| !c.allow_immutable_unsafe_cell()) {
            if !op.layout.is_zst() && !op.layout.ty.is_freeze(*self.ecx.tcx, self.ecx.param_env) {
                if !self.in_mutable_memory(op) {
                    throw_validation_failure!(self.path, UnsafeCellInImmutable);
                }
            }
        }
        Ok(())
    }

    #[inline]
    fn visit_box(
        &mut self,
        _box_ty: Ty<'tcx>,
        op: &OpTy<'tcx, M::Provenance>,
    ) -> InterpResult<'tcx> {
        self.check_safe_pointer(op, PointerKind::Box)?;
        Ok(())
    }

    #[inline]
    fn visit_value(&mut self, op: &OpTy<'tcx, M::Provenance>) -> InterpResult<'tcx> {
        trace!("visit_value: {:?}, {:?}", *op, op.layout);

        // Check primitive types -- the leaves of our recursive descent.
        if self.try_visit_primitive(op)? {
            return Ok(());
        }

        // Special check preventing `UnsafeCell` in the inner part of constants
        if self.ctfe_mode.is_some_and(|c| !c.allow_immutable_unsafe_cell()) {
            if !op.layout.is_zst()
                && let Some(def) = op.layout.ty.ty_adt_def()
                && def.is_unsafe_cell()
            {
                if !self.in_mutable_memory(op) {
                    throw_validation_failure!(self.path, UnsafeCellInImmutable);
                }
            }
        }

        // Recursively walk the value at its type. Apply optimizations for some large types.
        match op.layout.ty.kind() {
            ty::Str => {
                let mplace = op.assert_mem_place(); // strings are unsized and hence never immediate
                let len = mplace.len(self.ecx)?;
                try_validation!(
                    self.ecx.read_bytes_ptr_strip_provenance(mplace.ptr(), Size::from_bytes(len)),
                    self.path,
                    Ub(InvalidUninitBytes(..)) => Uninit { expected: ExpectedKind::Str },
                    Unsup(ReadPointerAsInt(_)) => PointerAsInt { expected: ExpectedKind::Str }
                );
            }
            ty::Array(tys, ..) | ty::Slice(tys)
                // This optimization applies for types that can hold arbitrary bytes (such as
                // integer and floating point types) or for structs or tuples with no fields.
                // FIXME(wesleywiser) This logic could be extended further to arbitrary structs
                // or tuples made up of integer/floating point types or inhabited ZSTs with no
                // padding.
                if matches!(tys.kind(), ty::Int(..) | ty::Uint(..) | ty::Float(..))
                =>
            {
                let expected = if tys.is_integral() { ExpectedKind::Int } else { ExpectedKind::Float };
                // Optimized handling for arrays of integer/float type.

                // This is the length of the array/slice.
                let len = op.len(self.ecx)?;
                // This is the element type size.
                let layout = self.ecx.layout_of(*tys)?;
                // This is the size in bytes of the whole array. (This checks for overflow.)
                let size = layout.size * len;
                // If the size is 0, there is nothing to check.
                // (`size` can only be 0 of `len` is 0, and empty arrays are always valid.)
                if size == Size::ZERO {
                    return Ok(());
                }
                // Now that we definitely have a non-ZST array, we know it lives in memory.
                let mplace = match op.as_mplace_or_imm() {
                    Left(mplace) => mplace,
                    Right(imm) => match *imm {
                        Immediate::Uninit =>
                            throw_validation_failure!(self.path, Uninit { expected }),
                        Immediate::Scalar(..) | Immediate::ScalarPair(..) =>
                            bug!("arrays/slices can never have Scalar/ScalarPair layout"),
                    }
                };

                // Optimization: we just check the entire range at once.
                // NOTE: Keep this in sync with the handling of integer and float
                // types above, in `visit_primitive`.
                // No need for an alignment check here, this is not an actual memory access.
                let alloc = self.ecx.get_ptr_alloc(mplace.ptr(), size)?.expect("we already excluded size 0");

                match alloc.get_bytes_strip_provenance() {
                    // In the happy case, we needn't check anything else.
                    Ok(_) => {}
                    // Some error happened, try to provide a more detailed description.
                    Err(err) => {
                        // For some errors we might be able to provide extra information.
                        // (This custom logic does not fit the `try_validation!` macro.)
                        match err.kind() {
                            Ub(InvalidUninitBytes(Some((_alloc_id, access)))) | Unsup(ReadPointerAsInt(Some((_alloc_id, access)))) => {
                                // Some byte was uninitialized, determine which
                                // element that byte belongs to so we can
                                // provide an index.
                                let i = usize::try_from(
                                    access.bad.start.bytes() / layout.size.bytes(),
                                )
                                .unwrap();
                                self.path.push(PathElem::ArrayElem(i));

                                if matches!(err.kind(), Ub(InvalidUninitBytes(_))) {
                                    throw_validation_failure!(self.path, Uninit { expected })
                                } else {
                                    throw_validation_failure!(self.path, PointerAsInt { expected })
                                }
                            }

                            // Propagate upwards (that will also check for unexpected errors).
                            _ => return Err(err),
                        }
                    }
                }
            }
            // Fast path for arrays and slices of ZSTs. We only need to check a single ZST element
            // of an array and not all of them, because there's only a single value of a specific
            // ZST type, so either validation fails for all elements or none.
            ty::Array(tys, ..) | ty::Slice(tys) if self.ecx.layout_of(*tys)?.is_zst() => {
                // Validate just the first element (if any).
                if op.len(self.ecx)? > 0 {
                    self.visit_field(op, 0, &self.ecx.project_index(op, 0)?)?;
                }
            }
            _ => {
                // default handler
                try_validation!(
                    self.walk_value(op),
                    self.path,
                    // It's not great to catch errors here, since we can't give a very good path,
                    // but it's better than ICEing.
                    Ub(InvalidVTableTrait { expected_trait, vtable_trait }) => {
                        InvalidMetaWrongTrait { expected_trait, vtable_trait: *vtable_trait }
                    },
                );
            }
        }

        // *After* all of this, check the ABI. We need to check the ABI to handle
        // types like `NonNull` where the `Scalar` info is more restrictive than what
        // the fields say (`rustc_layout_scalar_valid_range_start`).
        // But in most cases, this will just propagate what the fields say,
        // and then we want the error to point at the field -- so, first recurse,
        // then check ABI.
        //
        // FIXME: We could avoid some redundant checks here. For newtypes wrapping
        // scalars, we do the same check on every "level" (e.g., first we check
        // MyNewtype and then the scalar in there).
        match op.layout.abi {
            Abi::Uninhabited => {
                let ty = op.layout.ty;
                throw_validation_failure!(self.path, UninhabitedVal { ty });
            }
            Abi::Scalar(scalar_layout) => {
                if !scalar_layout.is_uninit_valid() {
                    // There is something to check here.
                    let scalar = self.read_scalar(op, ExpectedKind::InitScalar)?;
                    self.visit_scalar(scalar, scalar_layout)?;
                }
            }
            Abi::ScalarPair(a_layout, b_layout) => {
                // We can only proceed if *both* scalars need to be initialized.
                // FIXME: find a way to also check ScalarPair when one side can be uninit but
                // the other must be init.
                if !a_layout.is_uninit_valid() && !b_layout.is_uninit_valid() {
                    let (a, b) =
                        self.read_immediate(op, ExpectedKind::InitScalar)?.to_scalar_pair();
                    self.visit_scalar(a, a_layout)?;
                    self.visit_scalar(b, b_layout)?;
                }
            }
            Abi::Vector { .. } => {
                // No checks here, we assume layout computation gets this right.
                // (This is harder to check since Miri does not represent these as `Immediate`. We
                // also cannot use field projections since this might be a newtype around a vector.)
            }
            Abi::Aggregate { .. } => {
                // Nothing to do.
            }
        }

        Ok(())
    }
}

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
    fn validate_operand_internal(
        &self,
        op: &OpTy<'tcx, M::Provenance>,
        path: Vec<PathElem>,
        ref_tracking: Option<&mut RefTracking<MPlaceTy<'tcx, M::Provenance>, Vec<PathElem>>>,
        ctfe_mode: Option<CtfeValidationMode>,
    ) -> InterpResult<'tcx> {
        trace!("validate_operand_internal: {:?}, {:?}", *op, op.layout.ty);

        // Construct a visitor
        let mut visitor = ValidityVisitor { path, ref_tracking, ctfe_mode, ecx: self };

        // Run it.
        match self.run_for_validation(|| visitor.visit_value(op)) {
            Ok(()) => Ok(()),
            // Pass through validation failures and "invalid program" issues.
            Err(err)
                if matches!(
                    err.kind(),
                    err_ub!(ValidationError { .. }) | InterpError::InvalidProgram(_)
                ) =>
            {
                Err(err)
            }
            // Complain about any other kind of error -- those are bad because we'd like to
            // report them in a way that shows *where* in the value the issue lies.
            Err(err) => {
                bug!(
                    "Unexpected error during validation: {}",
                    format_interp_error(self.tcx.dcx(), err)
                );
            }
        }
    }

    /// This function checks the data at `op` to be const-valid.
    /// `op` is assumed to cover valid memory if it is an indirect operand.
    /// It will error if the bits at the destination do not match the ones described by the layout.
    ///
    /// `ref_tracking` is used to record references that we encounter so that they
    /// can be checked recursively by an outside driving loop.
    ///
    /// `constant` controls whether this must satisfy the rules for constants:
    /// - no pointers to statics.
    /// - no `UnsafeCell` or non-ZST `&mut`.
    #[inline(always)]
    pub(crate) fn const_validate_operand(
        &self,
        op: &OpTy<'tcx, M::Provenance>,
        path: Vec<PathElem>,
        ref_tracking: &mut RefTracking<MPlaceTy<'tcx, M::Provenance>, Vec<PathElem>>,
        ctfe_mode: CtfeValidationMode,
    ) -> InterpResult<'tcx> {
        self.validate_operand_internal(op, path, Some(ref_tracking), Some(ctfe_mode))
    }

    /// This function checks the data at `op` to be runtime-valid.
    /// `op` is assumed to cover valid memory if it is an indirect operand.
    /// It will error if the bits at the destination do not match the ones described by the layout.
    #[inline(always)]
    pub fn validate_operand(&self, op: &OpTy<'tcx, M::Provenance>) -> InterpResult<'tcx> {
        // Note that we *could* actually be in CTFE here with `-Zextra-const-ub-checks`, but it's
        // still correct to not use `ctfe_mode`: that mode is for validation of the final constant
        // value, it rules out things like `UnsafeCell` in awkward places. It also can make checking
        // recurse through references which, for now, we don't want here, either.
        self.validate_operand_internal(op, vec![], None, None)
    }
}