Auto merge of rust-lang#2697 - Vanille-N:borrow-tracking, r=RalfJung

Reorganizing `stacked_borrows` in anticipation of a different model

These commits reorganize all the code inside the former `stacked_borrows` module and extract the part that really is specific to Stacked Borrows inside the `borrow_tracker/stacked_borrows` submodule.
Everything not specific to SB is put in `borrow_tracker/mod.rs`.
This is so that the future Tree Borrows model can be later added as a second submodule and reuse all the contents of `borrow_tracker/mod.rs`.

This reorganization is accompanied by renamings, mostly from "stacked borrows" to "borrow tracking".

src/tools/miri/src/bin/miri.rs

@@ -317,7 +317,7 @@ fn main() {
         } else if arg == "-Zmiri-disable-validation" {
             miri_config.validate = false;
         } else if arg == "-Zmiri-disable-stacked-borrows" {
-            miri_config.stacked_borrows = false;
+            miri_config.borrow_tracker = None;
         } else if arg == "-Zmiri-disable-data-race-detector" {
             miri_config.data_race_detector = false;
             miri_config.weak_memory_emulation = false;
@@ -413,7 +413,7 @@ fn main() {
                         err
                     ),
             };
-            for id in ids.into_iter().map(miri::SbTag::new) {
+            for id in ids.into_iter().map(miri::BorTag::new) {
                 if let Some(id) = id {
                     miri_config.tracked_pointer_tags.insert(id);
                 } else {

src/tools/miri/src/borrow_tracker/mod.rs

@@ -0,0 +1,365 @@
+use std::cell::RefCell;
+use std::fmt;
+use std::num::NonZeroU64;
+
+use log::trace;
+use smallvec::SmallVec;
+
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_middle::mir::RetagKind;
+use rustc_target::abi::Size;
+
+use crate::*;
+pub mod stacked_borrows;
+use stacked_borrows::diagnostics::RetagCause;
+
+pub type CallId = NonZeroU64;
+
+/// Tracking pointer provenance
+#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct BorTag(NonZeroU64);
+
+impl BorTag {
+    pub fn new(i: u64) -> Option<Self> {
+        NonZeroU64::new(i).map(BorTag)
+    }
+
+    pub fn get(&self) -> u64 {
+        self.0.get()
+    }
+
+    pub fn inner(&self) -> NonZeroU64 {
+        self.0
+    }
+
+    pub fn succ(self) -> Option<Self> {
+        self.0.checked_add(1).map(Self)
+    }
+
+    /// The minimum representable tag
+    pub fn one() -> Self {
+        Self::new(1).unwrap()
+    }
+}
+
+impl std::default::Default for BorTag {
+    /// The default to be used when borrow tracking is disabled
+    fn default() -> Self {
+        Self::one()
+    }
+}
+
+impl fmt::Debug for BorTag {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "<{}>", self.0)
+    }
+}
+
+/// Per-frame data for borrow tracking
+#[derive(Debug)]
+pub struct FrameExtra {
+    /// The ID of the call this frame corresponds to.
+    pub call_id: CallId,
+
+    /// If this frame is protecting any tags, they are listed here. We use this list to do
+    /// incremental updates of the global list of protected tags stored in the
+    /// `stacked_borrows::GlobalState` upon function return, and if we attempt to pop a protected
+    /// tag, to identify which call is responsible for protecting the tag.
+    /// See `Stack::item_popped` for more explanation.
+    ///
+    /// This will contain one tag per reference passed to the function, so
+    /// a size of 2 is enough for the vast majority of functions.
+    pub protected_tags: SmallVec<[BorTag; 2]>,
+}
+
+impl VisitTags for FrameExtra {
+    fn visit_tags(&self, _visit: &mut dyn FnMut(BorTag)) {
+        // `protected_tags` are fine to GC.
+    }
+}
+
+/// Extra global state, available to the memory access hooks.
+#[derive(Debug)]
+pub struct GlobalStateInner {
+    /// Borrow tracker method currently in use.
+    pub borrow_tracker_method: BorrowTrackerMethod,
+    /// Next unused pointer ID (tag).
+    pub next_ptr_tag: BorTag,
+    /// Table storing the "base" tag for each allocation.
+    /// The base tag is the one used for the initial pointer.
+    /// We need this in a separate table to handle cyclic statics.
+    pub base_ptr_tags: FxHashMap<AllocId, BorTag>,
+    /// Next unused call ID (for protectors).
+    pub next_call_id: CallId,
+    /// All currently protected tags.
+    /// An item is protected if its tag is in this set, *and* it has the "protected" bit set.
+    /// We add tags to this when they are created with a protector in `reborrow`, and
+    /// we remove tags from this when the call which is protecting them returns, in
+    /// `GlobalStateInner::end_call`. See `Stack::item_popped` for more details.
+    pub protected_tags: FxHashMap<BorTag, ProtectorKind>,
+    /// The pointer ids to trace
+    pub tracked_pointer_tags: FxHashSet<BorTag>,
+    /// The call ids to trace
+    pub tracked_call_ids: FxHashSet<CallId>,
+    /// Whether to recurse into datatypes when searching for pointers to retag.
+    pub retag_fields: RetagFields,
+}
+
+impl VisitTags for GlobalStateInner {
+    fn visit_tags(&self, _visit: &mut dyn FnMut(BorTag)) {
+        // The only candidate is base_ptr_tags, and that does not need visiting since we don't ever
+        // GC the bottommost tag.
+    }
+}
+
+/// We need interior mutable access to the global state.
+pub type GlobalState = RefCell<GlobalStateInner>;
+
+/// Indicates which kind of access is being performed.
+#[derive(Copy, Clone, Hash, PartialEq, Eq, Debug)]
+pub enum AccessKind {
+    Read,
+    Write,
+}
+
+impl fmt::Display for AccessKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            AccessKind::Read => write!(f, "read access"),
+            AccessKind::Write => write!(f, "write access"),
+        }
+    }
+}
+
+/// Policy on whether to recurse into fields to retag
+#[derive(Copy, Clone, Debug)]
+pub enum RetagFields {
+    /// Don't retag any fields.
+    No,
+    /// Retag all fields.
+    Yes,
+    /// Only retag fields of types with Scalar and ScalarPair layout,
+    /// to match the LLVM `noalias` we generate.
+    OnlyScalar,
+}
+
+/// The flavor of the protector.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum ProtectorKind {
+    /// Protected against aliasing violations from other pointers.
+    ///
+    /// Items protected like this cause UB when they are invalidated, *but* the pointer itself may
+    /// still be used to issue a deallocation.
+    ///
+    /// This is required for LLVM IR pointers that are `noalias` but *not* `dereferenceable`.
+    WeakProtector,
+
+    /// Protected against any kind of invalidation.
+    ///
+    /// Items protected like this cause UB when they are invalidated or the memory is deallocated.
+    /// This is strictly stronger protection than `WeakProtector`.
+    ///
+    /// This is required for LLVM IR pointers that are `dereferenceable` (and also allows `noalias`).
+    StrongProtector,
+}
+
+/// Utilities for initialization and ID generation
+impl GlobalStateInner {
+    pub fn new(
+        borrow_tracker_method: BorrowTrackerMethod,
+        tracked_pointer_tags: FxHashSet<BorTag>,
+        tracked_call_ids: FxHashSet<CallId>,
+        retag_fields: RetagFields,
+    ) -> Self {
+        GlobalStateInner {
+            borrow_tracker_method,
+            next_ptr_tag: BorTag::one(),
+            base_ptr_tags: FxHashMap::default(),
+            next_call_id: NonZeroU64::new(1).unwrap(),
+            protected_tags: FxHashMap::default(),
+            tracked_pointer_tags,
+            tracked_call_ids,
+            retag_fields,
+        }
+    }
+
+    /// Generates a new pointer tag. Remember to also check track_pointer_tags and log its creation!
+    pub fn new_ptr(&mut self) -> BorTag {
+        let id = self.next_ptr_tag;
+        self.next_ptr_tag = id.succ().unwrap();
+        id
+    }
+
+    pub fn new_frame(&mut self, machine: &MiriMachine<'_, '_>) -> FrameExtra {
+        let call_id = self.next_call_id;
+        trace!("new_frame: Assigning call ID {}", call_id);
+        if self.tracked_call_ids.contains(&call_id) {
+            machine.emit_diagnostic(NonHaltingDiagnostic::CreatedCallId(call_id));
+        }
+        self.next_call_id = NonZeroU64::new(call_id.get() + 1).unwrap();
+        FrameExtra { call_id, protected_tags: SmallVec::new() }
+    }
+
+    pub fn end_call(&mut self, frame: &machine::FrameData<'_>) {
+        for tag in &frame
+            .borrow_tracker
+            .as_ref()
+            .expect("we should have borrow tracking data")
+            .protected_tags
+        {
+            self.protected_tags.remove(tag);
+        }
+    }
+
+    pub fn base_ptr_tag(&mut self, id: AllocId, machine: &MiriMachine<'_, '_>) -> BorTag {
+        self.base_ptr_tags.get(&id).copied().unwrap_or_else(|| {
+            let tag = self.new_ptr();
+            if self.tracked_pointer_tags.contains(&tag) {
+                machine.emit_diagnostic(NonHaltingDiagnostic::CreatedPointerTag(
+                    tag.inner(),
+                    None,
+                    None,
+                ));
+            }
+            trace!("New allocation {:?} has base tag {:?}", id, tag);
+            self.base_ptr_tags.try_insert(id, tag).unwrap();
+            tag
+        })
+    }
+}
+
+/// Which borrow tracking method to use
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub enum BorrowTrackerMethod {
+    /// Stacked Borrows, as implemented in borrow_tracker/stacked
+    StackedBorrows,
+}
+
+impl BorrowTrackerMethod {
+    pub fn instanciate_global_state(self, config: &MiriConfig) -> GlobalState {
+        RefCell::new(GlobalStateInner::new(
+            self,
+            config.tracked_pointer_tags.clone(),
+            config.tracked_call_ids.clone(),
+            config.retag_fields,
+        ))
+    }
+}
+
+impl GlobalStateInner {
+    pub fn new_allocation(
+        &mut self,
+        id: AllocId,
+        alloc_size: Size,
+        kind: MemoryKind<machine::MiriMemoryKind>,
+        machine: &MiriMachine<'_, '_>,
+    ) -> AllocExtra {
+        match self.borrow_tracker_method {
+            BorrowTrackerMethod::StackedBorrows =>
+                AllocExtra::StackedBorrows(Box::new(RefCell::new(Stacks::new_allocation(
+                    id, alloc_size, self, kind, machine,
+                )))),
+        }
+    }
+}
+
+impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
+pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
+    fn retag(&mut self, kind: RetagKind, place: &PlaceTy<'tcx, Provenance>) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+        let method = this.machine.borrow_tracker.as_ref().unwrap().borrow().borrow_tracker_method;
+        match method {
+            BorrowTrackerMethod::StackedBorrows => this.sb_retag(kind, place),
+        }
+    }
+
+    fn retag_return_place(&mut self) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+        let method = this.machine.borrow_tracker.as_ref().unwrap().borrow().borrow_tracker_method;
+        match method {
+            BorrowTrackerMethod::StackedBorrows => this.sb_retag_return_place(),
+        }
+    }
+
+    fn expose_tag(&mut self, alloc_id: AllocId, tag: BorTag) -> InterpResult<'tcx> {
+        let this = self.eval_context_mut();
+        let method = this.machine.borrow_tracker.as_ref().unwrap().borrow().borrow_tracker_method;
+        match method {
+            BorrowTrackerMethod::StackedBorrows => this.sb_expose_tag(alloc_id, tag),
+        }
+    }
+}
+
+/// Extra per-allocation data for borrow tracking
+#[derive(Debug, Clone)]
+pub enum AllocExtra {
+    /// Data corresponding to Stacked Borrows
+    StackedBorrows(Box<RefCell<stacked_borrows::AllocExtra>>),
+}
+
+impl AllocExtra {
+    pub fn assert_sb(&self) -> &RefCell<stacked_borrows::AllocExtra> {
+        match self {
+            AllocExtra::StackedBorrows(ref sb) => sb,
+        }
+    }
+
+    pub fn assert_sb_mut(&mut self) -> &mut RefCell<stacked_borrows::AllocExtra> {
+        match self {
+            AllocExtra::StackedBorrows(ref mut sb) => sb,
+        }
+    }
+
+    pub fn before_memory_read<'tcx>(
+        &self,
+        alloc_id: AllocId,
+        prov_extra: ProvenanceExtra,
+        range: AllocRange,
+        machine: &MiriMachine<'_, 'tcx>,
+    ) -> InterpResult<'tcx> {
+        match self {
+            AllocExtra::StackedBorrows(sb) =>
+                sb.borrow_mut().before_memory_read(alloc_id, prov_extra, range, machine),
+        }
+    }
+
+    pub fn before_memory_write<'tcx>(
+        &mut self,
+        alloc_id: AllocId,
+        prov_extra: ProvenanceExtra,
+        range: AllocRange,
+        machine: &mut MiriMachine<'_, 'tcx>,
+    ) -> InterpResult<'tcx> {
+        match self {
+            AllocExtra::StackedBorrows(sb) =>
+                sb.get_mut().before_memory_write(alloc_id, prov_extra, range, machine),
+        }
+    }
+
+    pub fn before_memory_deallocation<'tcx>(
+        &mut self,
+        alloc_id: AllocId,
+        prov_extra: ProvenanceExtra,
+        range: AllocRange,
+        machine: &mut MiriMachine<'_, 'tcx>,
+    ) -> InterpResult<'tcx> {
+        match self {
+            AllocExtra::StackedBorrows(sb) =>
+                sb.get_mut().before_memory_deallocation(alloc_id, prov_extra, range, machine),
+        }
+    }
+
+    pub fn remove_unreachable_tags(&self, tags: &FxHashSet<BorTag>) {
+        match self {
+            AllocExtra::StackedBorrows(sb) => sb.borrow_mut().remove_unreachable_tags(tags),
+        }
+    }
+}
+
+impl VisitTags for AllocExtra {
+    fn visit_tags(&self, visit: &mut dyn FnMut(BorTag)) {
+        match self {
+            AllocExtra::StackedBorrows(sb) => sb.visit_tags(visit),
+        }
+    }
+}