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
//! This module is responsible for managing the absolute addresses that allocations are located at,
//! and for casting between pointers and integers based on those addresses.

mod reuse_pool;

use std::cell::RefCell;
use std::cmp::max;
use std::collections::hash_map::Entry;

use rand::Rng;

use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_span::Span;
use rustc_target::abi::{Align, HasDataLayout, Size};

use crate::{concurrency::VClock, *};

use self::reuse_pool::ReusePool;

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum ProvenanceMode {
    /// We support `expose_provenance`/`with_exposed_provenance` via "wildcard" provenance.
    /// However, we warn on `with_exposed_provenance` to alert the user of the precision loss.
    Default,
    /// Like `Default`, but without the warning.
    Permissive,
    /// We error on `with_exposed_provenance`, ensuring no precision loss.
    Strict,
}

pub type GlobalState = RefCell<GlobalStateInner>;

#[derive(Debug)]
pub struct GlobalStateInner {
    /// This is used as a map between the address of each allocation and its `AllocId`. It is always
    /// sorted by address. We cannot use a `HashMap` since we can be given an address that is offset
    /// from the base address, and we need to find the `AllocId` it belongs to. This is not the
    /// *full* inverse of `base_addr`; dead allocations have been removed.
    int_to_ptr_map: Vec<(u64, AllocId)>,
    /// The base address for each allocation.  We cannot put that into
    /// `AllocExtra` because function pointers also have a base address, and
    /// they do not have an `AllocExtra`.
    /// This is the inverse of `int_to_ptr_map`.
    base_addr: FxHashMap<AllocId, u64>,
    /// A pool of addresses we can reuse for future allocations.
    reuse: ReusePool,
    /// Whether an allocation has been exposed or not. This cannot be put
    /// into `AllocExtra` for the same reason as `base_addr`.
    exposed: FxHashSet<AllocId>,
    /// This is used as a memory address when a new pointer is casted to an integer. It
    /// is always larger than any address that was previously made part of a block.
    next_base_addr: u64,
    /// The provenance to use for int2ptr casts
    provenance_mode: ProvenanceMode,
}

impl VisitProvenance for GlobalStateInner {
    fn visit_provenance(&self, _visit: &mut VisitWith<'_>) {
        let GlobalStateInner {
            int_to_ptr_map: _,
            base_addr: _,
            reuse: _,
            exposed: _,
            next_base_addr: _,
            provenance_mode: _,
        } = self;
        // Though base_addr, int_to_ptr_map, and exposed contain AllocIds, we do not want to visit them.
        // int_to_ptr_map and exposed must contain only live allocations, and those
        // are never garbage collected.
        // base_addr is only relevant if we have a pointer to an AllocId and need to look up its
        // base address; so if an AllocId is not reachable from somewhere else we can remove it
        // here.
    }
}

impl GlobalStateInner {
    pub fn new(config: &MiriConfig, stack_addr: u64) -> Self {
        GlobalStateInner {
            int_to_ptr_map: Vec::default(),
            base_addr: FxHashMap::default(),
            reuse: ReusePool::new(config),
            exposed: FxHashSet::default(),
            next_base_addr: stack_addr,
            provenance_mode: config.provenance_mode,
        }
    }

    pub fn remove_unreachable_allocs(&mut self, allocs: &LiveAllocs<'_, '_>) {
        // `exposed` and `int_to_ptr_map` are cleared immediately when an allocation
        // is freed, so `base_addr` is the only one we have to clean up based on the GC.
        self.base_addr.retain(|id, _| allocs.is_live(*id));
    }
}

/// Shifts `addr` to make it aligned with `align` by rounding `addr` to the smallest multiple
/// of `align` that is larger or equal to `addr`
fn align_addr(addr: u64, align: u64) -> u64 {
    match addr % align {
        0 => addr,
        rem => addr.strict_add(align) - rem,
    }
}

impl<'tcx> EvalContextExtPriv<'tcx> for crate::MiriInterpCx<'tcx> {}
trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
    // Returns the exposed `AllocId` that corresponds to the specified addr,
    // or `None` if the addr is out of bounds
    fn alloc_id_from_addr(&self, addr: u64) -> Option<AllocId> {
        let ecx = self.eval_context_ref();
        let global_state = ecx.machine.alloc_addresses.borrow();
        assert!(global_state.provenance_mode != ProvenanceMode::Strict);

        let pos = global_state.int_to_ptr_map.binary_search_by_key(&addr, |(addr, _)| *addr);

        // Determine the in-bounds provenance for this pointer.
        // (This is only called on an actual access, so in-bounds is the only possible kind of provenance.)
        let alloc_id = match pos {
            Ok(pos) => Some(global_state.int_to_ptr_map[pos].1),
            Err(0) => None,
            Err(pos) => {
                // This is the largest of the addresses smaller than `int`,
                // i.e. the greatest lower bound (glb)
                let (glb, alloc_id) = global_state.int_to_ptr_map[pos - 1];
                // This never overflows because `addr >= glb`
                let offset = addr - glb;
                // We require this to be strict in-bounds of the allocation. This arm is only
                // entered for addresses that are not the base address, so even zero-sized
                // allocations will get recognized at their base address -- but all other
                // allocations will *not* be recognized at their "end" address.
                let size = ecx.get_alloc_info(alloc_id).0;
                if offset < size.bytes() { Some(alloc_id) } else { None }
            }
        }?;

        // We only use this provenance if it has been exposed.
        if global_state.exposed.contains(&alloc_id) {
            // This must still be live, since we remove allocations from `int_to_ptr_map` when they get freed.
            debug_assert!(ecx.is_alloc_live(alloc_id));
            Some(alloc_id)
        } else {
            None
        }
    }

    fn addr_from_alloc_id(
        &self,
        alloc_id: AllocId,
        memory_kind: MemoryKind,
    ) -> InterpResult<'tcx, u64> {
        let ecx = self.eval_context_ref();
        let mut global_state = ecx.machine.alloc_addresses.borrow_mut();
        let global_state = &mut *global_state;

        Ok(match global_state.base_addr.entry(alloc_id) {
            Entry::Occupied(entry) => *entry.get(),
            Entry::Vacant(entry) => {
                let mut rng = ecx.machine.rng.borrow_mut();
                let (size, align, kind) = ecx.get_alloc_info(alloc_id);
                // This is either called immediately after allocation (and then cached), or when
                // adjusting `tcx` pointers (which never get freed). So assert that we are looking
                // at a live allocation. This also ensures that we never re-assign an address to an
                // allocation that previously had an address, but then was freed and the address
                // information was removed.
                assert!(!matches!(kind, AllocKind::Dead));

                // This allocation does not have a base address yet, pick or reuse one.
                let base_addr = if let Some((reuse_addr, clock)) = global_state.reuse.take_addr(
                    &mut *rng,
                    size,
                    align,
                    memory_kind,
                    ecx.active_thread(),
                ) {
                    if let Some(clock) = clock {
                        ecx.acquire_clock(&clock);
                    }
                    reuse_addr
                } else {
                    // We have to pick a fresh address.
                    // Leave some space to the previous allocation, to give it some chance to be less aligned.
                    // We ensure that `(global_state.next_base_addr + slack) % 16` is uniformly distributed.
                    let slack = rng.gen_range(0..16);
                    // From next_base_addr + slack, round up to adjust for alignment.
                    let base_addr = global_state
                        .next_base_addr
                        .checked_add(slack)
                        .ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
                    let base_addr = align_addr(base_addr, align.bytes());

                    // Remember next base address.  If this allocation is zero-sized, leave a gap
                    // of at least 1 to avoid two allocations having the same base address.
                    // (The logic in `alloc_id_from_addr` assumes unique addresses, and different
                    // function/vtable pointers need to be distinguishable!)
                    global_state.next_base_addr = base_addr
                        .checked_add(max(size.bytes(), 1))
                        .ok_or_else(|| err_exhaust!(AddressSpaceFull))?;
                    // Even if `Size` didn't overflow, we might still have filled up the address space.
                    if global_state.next_base_addr > ecx.target_usize_max() {
                        throw_exhaust!(AddressSpaceFull);
                    }

                    base_addr
                };
                trace!(
                    "Assigning base address {:#x} to allocation {:?} (size: {}, align: {})",
                    base_addr,
                    alloc_id,
                    size.bytes(),
                    align.bytes(),
                );

                // Store address in cache.
                entry.insert(base_addr);

                // Also maintain the opposite mapping in `int_to_ptr_map`, ensuring we keep it sorted.
                // We have a fast-path for the common case that this address is bigger than all previous ones.
                let pos = if global_state
                    .int_to_ptr_map
                    .last()
                    .is_some_and(|(last_addr, _)| *last_addr < base_addr)
                {
                    global_state.int_to_ptr_map.len()
                } else {
                    global_state
                        .int_to_ptr_map
                        .binary_search_by_key(&base_addr, |(addr, _)| *addr)
                        .unwrap_err()
                };
                global_state.int_to_ptr_map.insert(pos, (base_addr, alloc_id));

                base_addr
            }
        })
    }
}

impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
    fn expose_ptr(&mut self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
        let ecx = self.eval_context_mut();
        let global_state = ecx.machine.alloc_addresses.get_mut();
        // In strict mode, we don't need this, so we can save some cycles by not tracking it.
        if global_state.provenance_mode == ProvenanceMode::Strict {
            return Ok(());
        }
        // Exposing a dead alloc is a no-op, because it's not possible to get a dead allocation
        // via int2ptr.
        if !ecx.is_alloc_live(alloc_id) {
            return Ok(());
        }
        trace!("Exposing allocation id {alloc_id:?}");
        let global_state = ecx.machine.alloc_addresses.get_mut();
        global_state.exposed.insert(alloc_id);
        if ecx.machine.borrow_tracker.is_some() {
            ecx.expose_tag(alloc_id, tag)?;
        }
        Ok(())
    }

    fn ptr_from_addr_cast(&self, addr: u64) -> InterpResult<'tcx, Pointer> {
        trace!("Casting {:#x} to a pointer", addr);

        let ecx = self.eval_context_ref();
        let global_state = ecx.machine.alloc_addresses.borrow();

        // Potentially emit a warning.
        match global_state.provenance_mode {
            ProvenanceMode::Default => {
                // The first time this happens at a particular location, print a warning.
                thread_local! {
                    // `Span` is non-`Send`, so we use a thread-local instead.
                    static PAST_WARNINGS: RefCell<FxHashSet<Span>> = RefCell::default();
                }
                PAST_WARNINGS.with_borrow_mut(|past_warnings| {
                    let first = past_warnings.is_empty();
                    if past_warnings.insert(ecx.cur_span()) {
                        // Newly inserted, so first time we see this span.
                        ecx.emit_diagnostic(NonHaltingDiagnostic::Int2Ptr { details: first });
                    }
                });
            }
            ProvenanceMode::Strict => {
                throw_machine_stop!(TerminationInfo::Int2PtrWithStrictProvenance);
            }
            ProvenanceMode::Permissive => {}
        }

        // We do *not* look up the `AllocId` here! This is a `ptr as usize` cast, and it is
        // completely legal to do a cast and then `wrapping_offset` to another allocation and only
        // *then* do a memory access. So the allocation that the pointer happens to point to on a
        // cast is fairly irrelevant. Instead we generate this as a "wildcard" pointer, such that
        // *every time the pointer is used*, we do an `AllocId` lookup to find the (exposed)
        // allocation it might be referencing.
        Ok(Pointer::new(Some(Provenance::Wildcard), Size::from_bytes(addr)))
    }

    /// Convert a relative (tcx) pointer to a Miri pointer.
    fn adjust_alloc_root_pointer(
        &self,
        ptr: interpret::Pointer<CtfeProvenance>,
        tag: BorTag,
        kind: MemoryKind,
    ) -> InterpResult<'tcx, interpret::Pointer<Provenance>> {
        let ecx = self.eval_context_ref();

        let (prov, offset) = ptr.into_parts(); // offset is relative (AllocId provenance)
        let alloc_id = prov.alloc_id();
        let base_addr = ecx.addr_from_alloc_id(alloc_id, kind)?;

        // Add offset with the right kind of pointer-overflowing arithmetic.
        let dl = ecx.data_layout();
        let absolute_addr = dl.overflowing_offset(base_addr, offset.bytes()).0;
        Ok(interpret::Pointer::new(
            Provenance::Concrete { alloc_id, tag },
            Size::from_bytes(absolute_addr),
        ))
    }

    /// When a pointer is used for a memory access, this computes where in which allocation the
    /// access is going.
    fn ptr_get_alloc(&self, ptr: interpret::Pointer<Provenance>) -> Option<(AllocId, Size)> {
        let ecx = self.eval_context_ref();

        let (tag, addr) = ptr.into_parts(); // addr is absolute (Tag provenance)

        let alloc_id = if let Provenance::Concrete { alloc_id, .. } = tag {
            alloc_id
        } else {
            // A wildcard pointer.
            ecx.alloc_id_from_addr(addr.bytes())?
        };

        // This cannot fail: since we already have a pointer with that provenance, adjust_alloc_root_pointer
        // must have been called in the past, so we can just look up the address in the map.
        let base_addr = *ecx.machine.alloc_addresses.borrow().base_addr.get(&alloc_id).unwrap();

        // Wrapping "addr - base_addr"
        #[allow(clippy::cast_possible_wrap)] // we want to wrap here
        let neg_base_addr = (base_addr as i64).wrapping_neg();
        Some((
            alloc_id,
            Size::from_bytes(ecx.overflowing_signed_offset(addr.bytes(), neg_base_addr).0),
        ))
    }
}

impl<'tcx> MiriMachine<'tcx> {
    pub fn free_alloc_id(&mut self, dead_id: AllocId, size: Size, align: Align, kind: MemoryKind) {
        let global_state = self.alloc_addresses.get_mut();
        let rng = self.rng.get_mut();

        // We can *not* remove this from `base_addr`, since the interpreter design requires that we
        // be able to retrieve an AllocId + offset for any memory access *before* we check if the
        // access is valid. Specifically, `ptr_get_alloc` is called on each attempt at a memory
        // access to determine the allocation ID and offset -- and there can still be pointers with
        // `dead_id` that one can attempt to use for a memory access. `ptr_get_alloc` may return
        // `None` only if the pointer truly has no provenance (this ensures consistent error
        // messages).
        // However, we *can* remove it from `int_to_ptr_map`, since any wildcard pointers that exist
        // can no longer actually be accessing that address. This ensures `alloc_id_from_addr` never
        // returns a dead allocation.
        // To avoid a linear scan we first look up the address in `base_addr`, and then find it in
        // `int_to_ptr_map`.
        let addr = *global_state.base_addr.get(&dead_id).unwrap();
        let pos =
            global_state.int_to_ptr_map.binary_search_by_key(&addr, |(addr, _)| *addr).unwrap();
        let removed = global_state.int_to_ptr_map.remove(pos);
        assert_eq!(removed, (addr, dead_id)); // double-check that we removed the right thing
        // We can also remove it from `exposed`, since this allocation can anyway not be returned by
        // `alloc_id_from_addr` any more.
        global_state.exposed.remove(&dead_id);
        // Also remember this address for future reuse.
        let thread = self.threads.active_thread();
        global_state.reuse.add_addr(rng, addr, size, align, kind, thread, || {
            if let Some(data_race) = &self.data_race {
                data_race.release_clock(&self.threads).clone()
            } else {
                VClock::default()
            }
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_align_addr() {
        assert_eq!(align_addr(37, 4), 40);
        assert_eq!(align_addr(44, 4), 44);
    }
}