+//! Implements "Stacked Borrows". See <https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md>
+//! for further information.
+
use std::cell::RefCell;
-use std::collections::HashSet;
-use std::rc::Rc;
use std::fmt;
use std::num::NonZeroU64;
+use std::rc::Rc;
-use rustc::ty::{self, layout::Size};
-use rustc::hir::{Mutability, MutMutable, MutImmutable};
-use rustc::mir::RetagKind;
+use log::trace;
-use crate::{
- EvalResult, InterpError, MiriEvalContext, HelpersEvalContextExt, Evaluator, MutValueVisitor,
- MemoryKind, MiriMemoryKind, RangeMap, Allocation, AllocationExtra,
- Pointer, Immediate, ImmTy, PlaceTy, MPlaceTy,
-};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_middle::mir::RetagKind;
+use rustc_middle::ty;
+use rustc_target::abi::{Align, LayoutOf, Size};
+use rustc_hir::Mutability;
+
+use crate::*;
pub type PtrId = NonZeroU64;
-pub type CallId = u64;
+pub type CallId = NonZeroU64;
+pub type AllocExtra = Stacks;
/// Tracking pointer provenance
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Hash, PartialEq, Eq)]
pub enum Tag {
Tagged(PtrId),
Untagged,
}
-impl fmt::Display for Tag {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+impl fmt::Debug for Tag {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
- Tag::Tagged(id) => write!(f, "{}", id),
+ Tag::Tagged(id) => write!(f, "<{}>", id),
Tag::Untagged => write!(f, "<untagged>"),
}
}
Unique,
/// Grants shared mutable access.
SharedReadWrite,
- /// Greants shared read-only access.
+ /// Grants shared read-only access.
SharedReadOnly,
+ /// Grants no access, but separates two groups of SharedReadWrite so they are not
+ /// all considered mutually compatible.
+ Disabled,
}
/// An item in the per-location borrow stack.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-pub enum Item {
- /// Grants the given permission for pointers with this tag.
- Permission(Permission, Tag),
- /// A barrier, tracking the function it belongs to by its index on the call stack.
- FnBarrier(CallId),
+#[derive(Copy, Clone, Hash, PartialEq, Eq)]
+pub struct Item {
+ /// The permission this item grants.
+ perm: Permission,
+ /// The pointers the permission is granted to.
+ tag: Tag,
+ /// An optional protector, ensuring the item cannot get popped until `CallId` is over.
+ protector: Option<CallId>,
}
-impl fmt::Display for Item {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- match self {
- Item::Permission(perm, tag) => write!(f, "[{:?} for {}]", perm, tag),
- Item::FnBarrier(call) => write!(f, "[barrier {}]", call),
+impl fmt::Debug for Item {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ write!(f, "[{:?} for {:?}", self.perm, self.tag)?;
+ if let Some(call) = self.protector {
+ write!(f, " (call {})", call)?;
}
+ write!(f, "]")?;
+ Ok(())
}
}
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Stack {
/// Used *mostly* as a stack; never empty.
- /// We sometimes push into the middle but never remove from the middle.
- /// The same tag may occur multiple times, e.g. from a two-phase borrow.
/// Invariants:
- /// * Above a `SharedReadOnly` there can only be barriers and more `SharedReadOnly`.
+ /// * Above a `SharedReadOnly` there can only be more `SharedReadOnly`.
+ /// * Except for `Untagged`, no tag occurs in the stack more than once.
borrows: Vec<Item>,
}
-
/// Extra per-allocation state.
#[derive(Clone, Debug)]
pub struct Stacks {
// Even reading memory can have effects on the stack, so we need a `RefCell` here.
stacks: RefCell<RangeMap<Stack>>,
// Pointer to global state
- global: MemoryState,
+ global: MemoryExtra,
}
/// Extra global state, available to the memory access hooks.
#[derive(Debug)]
pub struct GlobalState {
+ /// Next unused pointer ID (tag).
next_ptr_id: PtrId,
+ /// 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.
+ base_ptr_ids: FxHashMap<AllocId, Tag>,
+ /// Next unused call ID (for protectors).
next_call_id: CallId,
- active_calls: HashSet<CallId>,
+ /// Those call IDs corresponding to functions that are still running.
+ active_calls: FxHashSet<CallId>,
+ /// The pointer id to trace
+ tracked_pointer_tag: Option<PtrId>,
+ /// The call id to trace
+ tracked_call_id: Option<CallId>,
+ /// Whether to track raw pointers.
+ track_raw: bool,
}
-pub type MemoryState = Rc<RefCell<GlobalState>>;
+/// Memory extra state gives us interior mutable access to the global state.
+pub type MemoryExtra = Rc<RefCell<GlobalState>>;
/// Indicates which kind of access is being performed.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Hash, PartialEq, Eq)]
pub enum AccessKind {
Read,
- Write { dealloc: bool },
-}
-
-// "Fake" constructors
-impl AccessKind {
- fn write() -> AccessKind {
- AccessKind::Write { dealloc: false }
- }
-
- fn dealloc() -> AccessKind {
- AccessKind::Write { dealloc: true }
- }
+ Write,
}
impl fmt::Display for AccessKind {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
- AccessKind::Read => write!(f, "read"),
- AccessKind::Write { dealloc: false } => write!(f, "write"),
- AccessKind::Write { dealloc: true } => write!(f, "deallocation"),
+ AccessKind::Read => write!(f, "read access"),
+ AccessKind::Write => write!(f, "write access"),
}
}
}
/// Indicates which kind of reference is being created.
-/// Used by `reborrow` to compute which permissions to grant to the
+/// Used by high-level `reborrow` to compute which permissions to grant to the
/// new pointer.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Hash, PartialEq, Eq)]
pub enum RefKind {
- /// `&mut`.
- Mutable,
+ /// `&mut` and `Box`.
+ Unique { two_phase: bool },
/// `&` with or without interior mutability.
- Shared { frozen: bool },
- /// `*` (raw pointer).
- Raw,
+ Shared,
+ /// `*mut`/`*const` (raw pointers).
+ Raw { mutable: bool },
}
impl fmt::Display for RefKind {
- fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
- RefKind::Mutable => write!(f, "mutable"),
- RefKind::Shared { frozen: true } => write!(f, "shared (frozen)"),
- RefKind::Shared { frozen: false } => write!(f, "shared (mutable)"),
- RefKind::Raw => write!(f, "raw"),
+ RefKind::Unique { two_phase: false } => write!(f, "unique"),
+ RefKind::Unique { two_phase: true } => write!(f, "unique (two-phase)"),
+ RefKind::Shared => write!(f, "shared"),
+ RefKind::Raw { mutable: true } => write!(f, "raw (mutable)"),
+ RefKind::Raw { mutable: false } => write!(f, "raw (constant)"),
}
}
}
/// Utilities for initialization and ID generation
-impl Default for GlobalState {
- fn default() -> Self {
+impl GlobalState {
+ pub fn new(tracked_pointer_tag: Option<PtrId>, tracked_call_id: Option<CallId>, track_raw: bool) -> Self {
GlobalState {
next_ptr_id: NonZeroU64::new(1).unwrap(),
- next_call_id: 0,
- active_calls: HashSet::default(),
+ base_ptr_ids: FxHashMap::default(),
+ next_call_id: NonZeroU64::new(1).unwrap(),
+ active_calls: FxHashSet::default(),
+ tracked_pointer_tag,
+ tracked_call_id,
+ track_raw,
}
}
-}
-impl GlobalState {
- pub fn new_ptr(&mut self) -> PtrId {
+ fn new_ptr(&mut self) -> PtrId {
let id = self.next_ptr_id;
+ if Some(id) == self.tracked_pointer_tag {
+ register_diagnostic(NonHaltingDiagnostic::CreatedPointerTag(id));
+ }
self.next_ptr_id = NonZeroU64::new(id.get() + 1).unwrap();
id
}
pub fn new_call(&mut self) -> CallId {
let id = self.next_call_id;
trace!("new_call: Assigning ID {}", id);
- self.active_calls.insert(id);
- self.next_call_id = id+1;
+ if Some(id) == self.tracked_call_id {
+ register_diagnostic(NonHaltingDiagnostic::CreatedCallId(id));
+ }
+ assert!(self.active_calls.insert(id));
+ self.next_call_id = NonZeroU64::new(id.get() + 1).unwrap();
id
}
fn is_active(&self, id: CallId) -> bool {
self.active_calls.contains(&id)
}
+
+ pub fn global_base_ptr(&mut self, id: AllocId) -> Tag {
+ self.base_ptr_ids.get(&id).copied().unwrap_or_else(|| {
+ let tag = Tag::Tagged(self.new_ptr());
+ trace!("New allocation {:?} has base tag {:?}", id, tag);
+ self.base_ptr_ids.insert(id, tag).unwrap_none();
+ tag
+ })
+ }
+}
+
+/// Error reporting
+fn err_sb_ub(msg: String) -> InterpError<'static> {
+ err_machine_stop!(TerminationInfo::ExperimentalUb {
+ msg,
+ url: format!("https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md"),
+ })
}
// # Stacked Borrows Core Begin
/// F3: If an access happens with an `&` outside `UnsafeCell`,
/// it requires the `SharedReadOnly` to still be in the stack.
-impl Default for Tag {
- #[inline(always)]
- fn default() -> Tag {
- Tag::Untagged
- }
-}
-
-/// Core relations on `Permission` define which accesses are allowed:
-/// On every access, we try to find a *granting* item, and then we remove all
-/// *incompatible* items above it.
+/// Core relation on `Permission` to define which accesses are allowed
impl Permission {
/// This defines for a given permission, whether it permits the given kind of access.
fn grants(self, access: AccessKind) -> bool {
- match (self, access) {
- // Unique and SharedReadWrite allow any kind of access.
- (Permission::Unique, _) |
- (Permission::SharedReadWrite, _) =>
- true,
- // SharedReadOnly only permits read access.
- (Permission::SharedReadOnly, AccessKind::Read) =>
- true,
- (Permission::SharedReadOnly, AccessKind::Write { .. }) =>
- false,
- }
- }
-
- /// This defines for a given permission, which other permissions it can tolerate "above" itself
- /// for which kinds of accesses.
- /// If true, then `other` is allowed to remain on top of `self` when `access` happens.
- fn compatible_with(self, access: AccessKind, other: Permission) -> bool {
- use self::Permission::*;
-
- match (self, access, other) {
- // Some cases are impossible.
- (SharedReadOnly, _, SharedReadWrite) |
- (SharedReadOnly, _, Unique) =>
- bug!("There can never be a SharedReadWrite or a Unique on top of a SharedReadOnly"),
- // When `other` is `SharedReadOnly`, that is NEVER compatible with
- // write accesses.
- // This makes sure read-only pointers become invalid on write accesses (ensures F2a).
- (_, AccessKind::Write { .. }, SharedReadOnly) =>
- false,
- // When `other` is `Unique`, that is compatible with nothing.
- // This makes sure unique pointers become invalid on incompatible accesses (ensures U2).
- (_, _, Unique) =>
- false,
- // When we are unique and this is a write/dealloc, we tolerate nothing.
- // This makes sure we re-assert uniqueness ("being on top") on write accesses.
- // (This is particularily important such that when a new mutable ref gets created, it gets
- // pushed into the right item -- this behaves like a write and we assert uniqueness of the
- // pointer from which this comes, *if* it was a unique pointer.)
- (Unique, AccessKind::Write { .. }, _) =>
- false,
- // `SharedReadWrite` items can tolerate any other akin items for any kind of access.
- (SharedReadWrite, _, SharedReadWrite) =>
- true,
- // Any item can tolerate read accesses for shared items.
- // This includes unique items! Reads from unique pointers do not invalidate
- // other pointers.
- (_, AccessKind::Read, SharedReadWrite) |
- (_, AccessKind::Read, SharedReadOnly) =>
- true,
- // That's it.
- }
+ // Disabled grants nothing. Otherwise, all items grant read access, and except for SharedReadOnly they grant write access.
+ self != Permission::Disabled
+ && (access == AccessKind::Read || self != Permission::SharedReadOnly)
}
}
-impl<'tcx> RefKind {
- /// Defines which kind of access the "parent" must grant to create this reference.
- fn access(self) -> AccessKind {
- match self {
- RefKind::Mutable | RefKind::Shared { frozen: false } => AccessKind::write(),
- RefKind::Raw | RefKind::Shared { frozen: true } => AccessKind::Read,
- // FIXME: Just requiring read-only access for raw means that a raw ptr might not be writeable
- // even when we think it should be! Think about this some more.
- }
- }
-
- /// This defines the new permission used when a pointer gets created: For raw pointers, whether these are read-only
- /// or read-write depends on the permission from which they derive.
- fn new_perm(self, derived_from: Permission) -> EvalResult<'tcx, Permission> {
- Ok(match (self, derived_from) {
- // Do not derive writable safe pointer from read-only pointer!
- (RefKind::Mutable, Permission::SharedReadOnly) =>
- return err!(MachineError(format!(
- "deriving mutable reference from read-only pointer"
- ))),
- (RefKind::Shared { frozen: false }, Permission::SharedReadOnly) =>
- return err!(MachineError(format!(
- "deriving shared reference with interior mutability from read-only pointer"
- ))),
- // Safe pointer cases.
- (RefKind::Mutable, _) => Permission::Unique,
- (RefKind::Shared { frozen: true }, _) => Permission::SharedReadOnly,
- (RefKind::Shared { frozen: false }, _) => Permission::SharedReadWrite,
- // Raw pointer cases.
- (RefKind::Raw, Permission::SharedReadOnly) => Permission::SharedReadOnly,
- (RefKind::Raw, _) => Permission::SharedReadWrite,
- })
- }
-}
-
-/// Core per-location operations: access, create.
+/// Core per-location operations: access, dealloc, reborrow.
impl<'tcx> Stack {
- /// Find the item granting the given kind of access to the given tag, and where that item is in the stack.
- fn find_granting(&self, access: AccessKind, tag: Tag) -> Option<(usize, Permission)> {
- self.borrows.iter()
+ /// Find the item granting the given kind of access to the given tag, and return where
+ /// it is on the stack.
+ fn find_granting(&self, access: AccessKind, tag: Tag) -> Option<usize> {
+ self.borrows
+ .iter()
.enumerate() // we also need to know *where* in the stack
.rev() // search top-to-bottom
// Return permission of first item that grants access.
// We require a permission with the right tag, ensuring U3 and F3.
- .filter_map(|(idx, item)| match item {
- &Item::Permission(perm, item_tag) if perm.grants(access) && tag == item_tag =>
- Some((idx, perm)),
- _ => None,
- })
- .next()
- }
-
- /// Test if a memory `access` using pointer tagged `tag` is granted.
- /// If yes, return the index of the item that granted it.
- fn access(
- &mut self,
- access: AccessKind,
- tag: Tag,
- global: &GlobalState,
- ) -> EvalResult<'tcx, usize> {
- // Two main steps: Find granting item, remove all incompatible items above.
- // The second step is where barriers get implemented: they "protect" the items
- // below them, meaning that if we remove an item and then further up encounter a barrier,
- // we raise an error.
- // Afterwards we just do some post-processing for deallocation accesses.
-
- // Step 1: Find granting item.
- let (granting_idx, granting_perm) = self.find_granting(access, tag)
- .ok_or_else(|| InterpError::MachineError(format!(
- "no item granting {} access to tag {} found in borrow stack",
- access, tag,
- )))?;
-
- // Step 2: Remove everything incompatible above them.
- // Items below an active barrier however may not be removed, so we check that as well.
- // We do *not* maintain a stack discipline here. We could, in principle, decide to only
- // keep the items immediately above `granting_idx` that are compatible, and then pop the rest.
- // However, that kills off entire "branches" of pointer derivation too easily:
- // in `let raw = &mut *x as *mut _; let _val = *x;`, the second statement would pop the `Unique`
- // from the reborrow of the first statement, and subequently also pop the `SharedReadWrite` for `raw`.
- {
- // Implemented with indices because there does not seem to be a nice iterator and range-based
- // API for this.
- let mut cur = granting_idx + 1;
- let mut removed_item = None;
- while let Some(item) = self.borrows.get(cur) {
- match *item {
- Item::Permission(perm, _) => {
- if granting_perm.compatible_with(access, perm) {
- // Keep this, check next.
- cur += 1;
- } else {
- // Aha! This is a bad one, remove it.
- let item = self.borrows.remove(cur);
- trace!("access: popping item {}", item);
- removed_item = Some(item);
- }
- }
- Item::FnBarrier(call) if !global.is_active(call) => {
- // An inactive barrier, just get rid of it. (Housekeeping.)
- self.borrows.remove(cur);
- }
- Item::FnBarrier(call) => {
- // We hit an active barrier! If we have already removed an item,
- // we got a problem! The barrier was supposed to protect this item.
- if let Some(removed_item) = removed_item {
- return err!(MachineError(format!(
- "not granting {} access to tag {} because barrier ({}) protects incompatible item {}",
- access, tag, call, removed_item
- )));
- }
- // Keep this, check next.
- cur += 1;
+ .find_map(
+ |(idx, item)| {
+ if tag == item.tag && item.perm.grants(access) { Some(idx) } else { None }
+ },
+ )
+ }
+
+ /// Find the first write-incompatible item above the given one --
+ /// i.e, find the height to which the stack will be truncated when writing to `granting`.
+ fn find_first_write_incompatible(&self, granting: usize) -> usize {
+ let perm = self.borrows[granting].perm;
+ match perm {
+ Permission::SharedReadOnly => bug!("Cannot use SharedReadOnly for writing"),
+ Permission::Disabled => bug!("Cannot use Disabled for anything"),
+ // On a write, everything above us is incompatible.
+ Permission::Unique => granting + 1,
+ Permission::SharedReadWrite => {
+ // The SharedReadWrite *just* above us are compatible, to skip those.
+ let mut idx = granting + 1;
+ while let Some(item) = self.borrows.get(idx) {
+ if item.perm == Permission::SharedReadWrite {
+ // Go on.
+ idx += 1;
+ } else {
+ // Found first incompatible!
+ break;
}
}
+ idx
}
}
+ }
- // Post-processing.
- // If we got here, we found a matching item. Congratulations!
- // However, we are not done yet: If this access is deallocating, we must make sure
- // there are no active barriers remaining on the stack.
- if access == AccessKind::dealloc() {
- for &itm in self.borrows.iter().rev() {
- match itm {
- Item::FnBarrier(call) if global.is_active(call) => {
- return err!(MachineError(format!(
- "deallocating with active barrier ({})", call
- )))
- }
- _ => {},
+ /// Check if the given item is protected.
+ fn check_protector(item: &Item, tag: Option<Tag>, global: &GlobalState) -> InterpResult<'tcx> {
+ if let Tag::Tagged(id) = item.tag {
+ if Some(id) == global.tracked_pointer_tag {
+ register_diagnostic(NonHaltingDiagnostic::PoppedPointerTag(item.clone()));
+ }
+ }
+ if let Some(call) = item.protector {
+ if global.is_active(call) {
+ if let Some(tag) = tag {
+ Err(err_sb_ub(format!(
+ "not granting access to tag {:?} because incompatible item is protected: {:?}",
+ tag, item
+ )))?
+ } else {
+ Err(err_sb_ub(format!(
+ "deallocating while item is protected: {:?}",
+ item
+ )))?
}
}
}
-
- // Done.
- return Ok(granting_idx);
+ Ok(())
}
- /// `reborrow` helper function.
- /// Grant `permisson` to new pointer tagged `tag`, added at `position` in the stack.
- fn grant(&mut self, perm: Permission, tag: Tag, position: usize) {
- // Simply add it to the "stack" -- this might add in the middle.
- // As an optimization, do nothing if the new item is identical to one of its neighbors.
- let item = Item::Permission(perm, tag);
- if self.borrows[position-1] == item || self.borrows.get(position) == Some(&item) {
- // Optimization applies, done.
- trace!("reborrow: avoiding redundant item {}", item);
- return;
- }
- trace!("reborrow: pushing item {}", item);
- self.borrows.insert(position, item);
- }
+ /// Test if a memory `access` using pointer tagged `tag` is granted.
+ /// If yes, return the index of the item that granted it.
+ fn access(&mut self, access: AccessKind, ptr: Pointer<Tag>, global: &GlobalState) -> InterpResult<'tcx> {
+ // Two main steps: Find granting item, remove incompatible items above.
- /// `reborrow` helper function.
- /// Adds a barrier.
- fn barrier(&mut self, call: CallId) {
- let itm = Item::FnBarrier(call);
- if *self.borrows.last().unwrap() == itm {
- // This is just an optimization, no functional change: Avoid stacking
- // multiple identical barriers on top of each other.
- // This can happen when a function receives several shared references
- // that overlap.
- trace!("reborrow: avoiding redundant extra barrier");
+ // Step 1: Find granting item.
+ let granting_idx = self.find_granting(access, ptr.tag).ok_or_else(|| {
+ err_sb_ub(format!(
+ "no item granting {} to tag {:?} at {} found in borrow stack.",
+ access, ptr.tag, ptr.erase_tag(),
+ ))
+ })?;
+
+ // Step 2: Remove incompatible items above them. Make sure we do not remove protected
+ // items. Behavior differs for reads and writes.
+ if access == AccessKind::Write {
+ // Remove everything above the write-compatible items, like a proper stack. This makes sure read-only and unique
+ // pointers become invalid on write accesses (ensures F2a, and ensures U2 for write accesses).
+ let first_incompatible_idx = self.find_first_write_incompatible(granting_idx);
+ for item in self.borrows.drain(first_incompatible_idx..).rev() {
+ trace!("access: popping item {:?}", item);
+ Stack::check_protector(&item, Some(ptr.tag), global)?;
+ }
} else {
- trace!("reborrow: pushing barrier for call {}", call);
- self.borrows.push(itm);
+ // On a read, *disable* all `Unique` above the granting item. This ensures U2 for read accesses.
+ // The reason this is not following the stack discipline (by removing the first Unique and
+ // everything on top of it) is that in `let raw = &mut *x as *mut _; let _val = *x;`, the second statement
+ // would pop the `Unique` from the reborrow of the first statement, and subsequently also pop the
+ // `SharedReadWrite` for `raw`.
+ // This pattern occurs a lot in the standard library: create a raw pointer, then also create a shared
+ // reference and use that.
+ // We *disable* instead of removing `Unique` to avoid "connecting" two neighbouring blocks of SRWs.
+ for idx in ((granting_idx + 1)..self.borrows.len()).rev() {
+ let item = &mut self.borrows[idx];
+ if item.perm == Permission::Unique {
+ trace!("access: disabling item {:?}", item);
+ Stack::check_protector(item, Some(ptr.tag), global)?;
+ item.perm = Permission::Disabled;
+ }
+ }
}
+
+ // Done.
+ Ok(())
}
- /// `reborrow` helper function: test that the stack invariants are still maintained.
- fn test_invariants(&self) {
- let mut saw_shared_read_only = false;
- for item in self.borrows.iter() {
- match item {
- Item::Permission(Permission::SharedReadOnly, _) => {
- saw_shared_read_only = true;
- }
- Item::Permission(perm, _) if saw_shared_read_only => {
- panic!("Found {:?} on top of a SharedReadOnly!", perm);
- }
- _ => {}
- }
+ /// Deallocate a location: Like a write access, but also there must be no
+ /// active protectors at all because we will remove all items.
+ fn dealloc(&mut self, ptr: Pointer<Tag>, global: &GlobalState) -> InterpResult<'tcx> {
+ // Step 1: Find granting item.
+ self.find_granting(AccessKind::Write, ptr.tag).ok_or_else(|| {
+ err_sb_ub(format!(
+ "no item granting write access for deallocation to tag {:?} at {} found in borrow stack",
+ ptr.tag, ptr.erase_tag(),
+ ))
+ })?;
+
+ // Step 2: Remove all items. Also checks for protectors.
+ for item in self.borrows.drain(..).rev() {
+ Stack::check_protector(&item, None, global)?;
}
+
+ Ok(())
}
- /// Derived a new pointer from one with the given tag.
- fn reborrow(
- &mut self,
- derived_from: Tag,
- barrier: Option<CallId>,
- new_kind: RefKind,
- new_tag: Tag,
- global: &GlobalState,
- ) -> EvalResult<'tcx> {
- // Find the permission "from which we derive". To this end we first have to decide
- // if we derive from a permission that grants writes or just reads.
- let access = new_kind.access();
- // Now we figure out which item grants our parent (`derived_from`) permission.
- // We use that to determine (a) where to put the new item, and for raw pointers
- // (b) whether to given read-only or read-write access.
- // FIXME: This handling of raw pointers is fragile, very fragile. What if we do
- // not get "the right one", like when there are multiple items granting `derived_from`
- // and we accidentally create a read-only pointer? This can happen for two-phase borrows
- // (then there's a `Unique` and a `SharedReadOnly` for the same tag), and for raw pointers
- // (which currently all are `Untagged`).
- let (derived_from_idx, derived_from_perm) = self.find_granting(access, derived_from)
- .ok_or_else(|| InterpError::MachineError(format!(
- "no item to reborrow as {} from tag {} found in borrow stack", new_kind, derived_from,
+ /// Derive a new pointer from one with the given tag.
+ /// `weak` controls whether this operation is weak or strong: weak granting does not act as
+ /// an access, and they add the new item directly on top of the one it is derived
+ /// from instead of all the way at the top of the stack.
+ fn grant(&mut self, derived_from: Pointer<Tag>, new: Item, global: &GlobalState) -> InterpResult<'tcx> {
+ // Figure out which access `perm` corresponds to.
+ let access =
+ if new.perm.grants(AccessKind::Write) { AccessKind::Write } else { AccessKind::Read };
+ // Now we figure out which item grants our parent (`derived_from`) this kind of access.
+ // We use that to determine where to put the new item.
+ let granting_idx = self.find_granting(access, derived_from.tag)
+ .ok_or_else(|| err_sb_ub(format!(
+ "trying to reborrow for {:?} at {}, but parent tag {:?} does not have an appropriate item in the borrow stack",
+ new.perm, derived_from.erase_tag(), derived_from.tag,
)))?;
- // With this we can compute the permission for the new pointer.
- let new_perm = new_kind.new_perm(derived_from_perm).expect("this should never fail");
-
- // We behave very differently for the "unsafe" case of a shared-read-write pointer
- // ("unsafe" because this also applies to shared references with interior mutability).
- // This is because such pointers may be reborrowed to unique pointers that actually
- // remain valid when their "parents" get further reborrows!
- // However, either way, we ensure that we insert the new item in a way that between
+
+ // Compute where to put the new item.
+ // Either way, we ensure that we insert the new item in a way such that between
// `derived_from` and the new one, there are only items *compatible with* `derived_from`.
- if new_perm == Permission::SharedReadWrite {
- // A very liberal reborrow because the new pointer does not expect any kind of aliasing guarantee.
- // Just insert new permission as child of old permission, and maintain everything else.
- // This inserts "as far down as possible", which is good because it makes this pointer as
- // long-lived as possible *and* we want all the items that are incompatible with this
- // to actually get removed from the stack. If we pushed a `SharedReadWrite` on top of
- // a `SharedReadOnly`, we'd violate the invariant that `SaredReadOnly` are at the top
- // and we'd allow write access without invalidating frozen shared references!
- // This ensures F2b for `SharedReadWrite` by adding the new item below any
- // potentially existing `SharedReadOnly`.
- self.grant(new_perm, new_tag, derived_from_idx+1);
-
- // No barrier. They can rightfully alias with `&mut`.
- // FIXME: This means that the `dereferencable` attribute on non-frozen shared references
- // is incorrect! They are dereferencable when the function is called, but might become
- // non-dereferencable during the course of execution.
- // Also see [1], [2].
- //
- // [1]: <https://internals.rust-lang.org/t/
- // is-it-possible-to-be-memory-safe-with-deallocated-self/8457/8>,
- // [2]: <https://lists.llvm.org/pipermail/llvm-dev/2018-July/124555.html>
+ let new_idx = if new.perm == Permission::SharedReadWrite {
+ assert!(
+ access == AccessKind::Write,
+ "this case only makes sense for stack-like accesses"
+ );
+ // SharedReadWrite can coexist with "existing loans", meaning they don't act like a write
+ // access. Instead of popping the stack, we insert the item at the place the stack would
+ // be popped to (i.e., we insert it above all the write-compatible items).
+ // This ensures F2b by adding the new item below any potentially existing `SharedReadOnly`.
+ self.find_first_write_incompatible(granting_idx)
} else {
// A "safe" reborrow for a pointer that actually expects some aliasing guarantees.
- // Here, creating a reference actually counts as an access, and pops incompatible
- // stuff off the stack.
+ // Here, creating a reference actually counts as an access.
// This ensures F2b for `Unique`, by removing offending `SharedReadOnly`.
- let check_idx = self.access(access, derived_from, global)?;
- assert_eq!(check_idx, derived_from_idx, "somehow we saw different items??");
+ self.access(access, derived_from, global)?;
// We insert "as far up as possible": We know only compatible items are remaining
// on top of `derived_from`, and we want the new item at the top so that we
// get the strongest possible guarantees.
// This ensures U1 and F1.
- self.grant(new_perm, new_tag, self.borrows.len());
-
- // Now is a good time to add the barrier, protecting the item we just added.
- if let Some(call) = barrier {
- self.barrier(call);
- }
- }
+ self.borrows.len()
+ };
- // Make sure that after all this, the stack's invariant is still maintained.
- if cfg!(debug_assertions) {
- self.test_invariants();
+ // Put the new item there. As an optimization, deduplicate if it is equal to one of its new neighbors.
+ if self.borrows[new_idx - 1] == new || self.borrows.get(new_idx) == Some(&new) {
+ // Optimization applies, done.
+ trace!("reborrow: avoiding adding redundant item {:?}", new);
+ } else {
+ trace!("reborrow: adding item {:?}", new);
+ self.borrows.insert(new_idx, new);
}
Ok(())
}
}
+// # Stacked Borrows Core End
-/// Higher-level per-location operations: deref, access, reborrow.
+/// Map per-stack operations to higher-level per-location-range operations.
impl<'tcx> Stacks {
/// Creates new stack with initial tag.
- pub(crate) fn new(
- size: Size,
- tag: Tag,
- extra: MemoryState,
- ) -> Self {
- let item = Item::Permission(Permission::Unique, tag);
- let stack = Stack {
- borrows: vec![item],
- };
- Stacks {
- stacks: RefCell::new(RangeMap::new(size, stack)),
- global: extra,
- }
- }
+ fn new(size: Size, perm: Permission, tag: Tag, extra: MemoryExtra) -> Self {
+ let item = Item { perm, tag, protector: None };
+ let stack = Stack { borrows: vec![item] };
- /// `ptr` got used, reflect that in the stack.
- fn access(
- &self,
- ptr: Pointer<Tag>,
- size: Size,
- kind: AccessKind,
- ) -> EvalResult<'tcx> {
- trace!("{} access of tag {}: {:?}, size {}", kind, ptr.tag, ptr, size.bytes());
- // Even reads can have a side-effect, by invalidating other references.
- // This is fundamentally necessary since `&mut` asserts that there
- // are no accesses through other references, not even reads.
- let global = self.global.borrow();
- let mut stacks = self.stacks.borrow_mut();
- for stack in stacks.iter_mut(ptr.offset, size) {
- stack.access(kind, ptr.tag, &*global)?;
- }
- Ok(())
+ Stacks { stacks: RefCell::new(RangeMap::new(size, stack)), global: extra }
}
- /// Reborrow the given pointer to the new tag for the given kind of reference.
- /// This works on `&self` because we might encounter references to constant memory.
- fn reborrow(
+ /// Call `f` on every stack in the range.
+ fn for_each(
&self,
ptr: Pointer<Tag>,
size: Size,
- barrier: Option<CallId>,
- new_kind: RefKind,
- new_tag: Tag,
- ) -> EvalResult<'tcx> {
- trace!(
- "{} reborrow for tag {} to {}: {:?}, size {}",
- new_kind, ptr.tag, new_tag, ptr, size.bytes(),
- );
+ f: impl Fn(Pointer<Tag>, &mut Stack, &GlobalState) -> InterpResult<'tcx>,
+ ) -> InterpResult<'tcx> {
let global = self.global.borrow();
let mut stacks = self.stacks.borrow_mut();
- for stack in stacks.iter_mut(ptr.offset, size) {
- stack.reborrow(ptr.tag, barrier, new_kind, new_tag, &*global)?;
+ for (offset, stack) in stacks.iter_mut(ptr.offset, size) {
+ let mut cur_ptr = ptr;
+ cur_ptr.offset = offset;
+ f(cur_ptr, stack, &*global)?;
}
Ok(())
}
}
-// # Stacked Borrows Core End
-
-// Glue code to connect with Miri Machine Hooks
-
+/// Glue code to connect with Miri Machine Hooks
impl Stacks {
pub fn new_allocation(
+ id: AllocId,
size: Size,
- extra: &MemoryState,
+ extra: MemoryExtra,
kind: MemoryKind<MiriMemoryKind>,
) -> (Self, Tag) {
- let tag = match kind {
- MemoryKind::Stack => {
- // New unique borrow. This `Uniq` is not accessible by the program,
- // so it will only ever be used when using the local directly (i.e.,
- // not through a pointer). That is, whenever we directly use a local, this will pop
- // everything else off the stack, invalidating all previous pointers,
- // and in particular, *all* raw pointers. This subsumes the explicit
- // `reset` which the blog post [1] says to perform when accessing a local.
- //
- // [1]: <https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html>
- Tag::Tagged(extra.borrow_mut().new_ptr())
- }
+ let (tag, perm) = match kind {
+ // New unique borrow. This tag is not accessible by the program,
+ // so it will only ever be used when using the local directly (i.e.,
+ // not through a pointer). That is, whenever we directly write to a local, this will pop
+ // everything else off the stack, invalidating all previous pointers,
+ // and in particular, *all* raw pointers.
+ MemoryKind::Stack => (Tag::Tagged(extra.borrow_mut().new_ptr()), Permission::Unique),
+ // `Global` memory can be referenced by global pointers from `tcx`.
+ // Thus we call `global_base_ptr` such that the global pointers get the same tag
+ // as what we use here.
+ // `ExternStatic` is used for extern statics, and thus must also be listed here.
+ // `Env` we list because we can get away with precise tracking there.
+ // The base pointer is not unique, so the base permission is `SharedReadWrite`.
+ MemoryKind::Machine(MiriMemoryKind::Global | MiriMemoryKind::ExternStatic | MiriMemoryKind::Tls | MiriMemoryKind::Env) =>
+ (extra.borrow_mut().global_base_ptr(id), Permission::SharedReadWrite),
+ // Everything else we handle like raw pointers for now.
_ => {
- Tag::Untagged
+ let mut extra = extra.borrow_mut();
+ let tag = if extra.track_raw { Tag::Tagged(extra.new_ptr()) } else { Tag::Untagged };
+ (tag, Permission::SharedReadWrite)
}
};
- let stack = Stacks::new(size, tag, Rc::clone(extra));
- (stack, tag)
+ (Stacks::new(size, perm, tag, extra), tag)
}
-}
-impl AllocationExtra<Tag> for Stacks {
#[inline(always)]
- fn memory_read<'tcx>(
- alloc: &Allocation<Tag, Stacks>,
- ptr: Pointer<Tag>,
- size: Size,
- ) -> EvalResult<'tcx> {
- alloc.extra.access(ptr, size, AccessKind::Read)
+ pub fn memory_read<'tcx>(&self, ptr: Pointer<Tag>, size: Size) -> InterpResult<'tcx> {
+ trace!("read access with tag {:?}: {:?}, size {}", ptr.tag, ptr.erase_tag(), size.bytes());
+ self.for_each(ptr, size, |ptr, stack, global| stack.access(AccessKind::Read, ptr, global))
}
#[inline(always)]
- fn memory_written<'tcx>(
- alloc: &mut Allocation<Tag, Stacks>,
- ptr: Pointer<Tag>,
- size: Size,
- ) -> EvalResult<'tcx> {
- alloc.extra.access(ptr, size, AccessKind::write())
+ pub fn memory_written<'tcx>(&mut self, ptr: Pointer<Tag>, size: Size) -> InterpResult<'tcx> {
+ trace!("write access with tag {:?}: {:?}, size {}", ptr.tag, ptr.erase_tag(), size.bytes());
+ self.for_each(ptr, size, |ptr, stack, global| stack.access(AccessKind::Write, ptr, global))
}
#[inline(always)]
- fn memory_deallocated<'tcx>(
- alloc: &mut Allocation<Tag, Stacks>,
+ pub fn memory_deallocated<'tcx>(
+ &mut self,
ptr: Pointer<Tag>,
size: Size,
- ) -> EvalResult<'tcx> {
- alloc.extra.access(ptr, size, AccessKind::dealloc())
+ ) -> InterpResult<'tcx> {
+ trace!("deallocation with tag {:?}: {:?}, size {}", ptr.tag, ptr.erase_tag(), size.bytes());
+ self.for_each(ptr, size, |ptr, stack, global| stack.dealloc(ptr, global))
}
}
-impl<'a, 'mir, 'tcx> EvalContextPrivExt<'a, 'mir, 'tcx> for crate::MiriEvalContext<'a, 'mir, 'tcx> {}
-trait EvalContextPrivExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a, 'mir, 'tcx> {
+/// Retagging/reborrowing. There is some policy in here, such as which permissions
+/// to grant for which references, and when to add protectors.
+impl<'mir, 'tcx: 'mir> EvalContextPrivExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
+trait EvalContextPrivExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
fn reborrow(
&mut self,
place: MPlaceTy<'tcx, Tag>,
size: Size,
- mutbl: Option<Mutability>,
+ kind: RefKind,
new_tag: Tag,
- fn_barrier: bool,
- ) -> EvalResult<'tcx> {
+ protect: bool,
+ ) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
- let barrier = if fn_barrier { Some(this.frame().extra) } else { None };
- let ptr = place.ptr.to_ptr()?;
- trace!("reborrow: creating new reference for {:?} (pointee {}): {:?}",
- ptr, place.layout.ty, new_tag);
+ let protector = if protect { Some(this.frame().extra.call_id) } else { None };
+ let ptr = place.ptr.assert_ptr();
+ trace!(
+ "reborrow: {} reference {:?} derived from {:?} (pointee {}): {:?}, size {}",
+ kind,
+ new_tag,
+ ptr.tag,
+ place.layout.ty,
+ ptr.erase_tag(),
+ size.bytes()
+ );
// Get the allocation. It might not be mutable, so we cannot use `get_mut`.
- let alloc = this.memory().get(ptr.alloc_id)?;
- alloc.check_bounds(this, ptr, size)?;
+ let extra = &this.memory.get_raw(ptr.alloc_id)?.extra;
+ let stacked_borrows =
+ extra.stacked_borrows.as_ref().expect("we should have Stacked Borrows data");
// Update the stacks.
- if mutbl == Some(MutImmutable) {
- // Reference that cares about freezing. We need a frozen-sensitive reborrow.
- this.visit_freeze_sensitive(place, size, |cur_ptr, size, frozen| {
- let new_kind = RefKind::Shared { frozen };
- alloc.extra.reborrow(cur_ptr, size, barrier, new_kind, new_tag)
- })?;
- } else {
- // Just treat this as one big chunk.
- let new_kind = if mutbl == Some(MutMutable) { RefKind::Mutable } else { RefKind::Raw };
- alloc.extra.reborrow(ptr, size, barrier, new_kind, new_tag)?;
- }
- Ok(())
+ // Make sure that raw pointers and mutable shared references are reborrowed "weak":
+ // There could be existing unique pointers reborrowed from them that should remain valid!
+ let perm = match kind {
+ RefKind::Unique { two_phase: false } => Permission::Unique,
+ RefKind::Unique { two_phase: true } => Permission::SharedReadWrite,
+ RefKind::Raw { mutable: true } => Permission::SharedReadWrite,
+ RefKind::Shared | RefKind::Raw { mutable: false } => {
+ // Shared references and *const are a whole different kind of game, the
+ // permission is not uniform across the entire range!
+ // We need a frozen-sensitive reborrow.
+ return this.visit_freeze_sensitive(place, size, |cur_ptr, size, frozen| {
+ // We are only ever `SharedReadOnly` inside the frozen bits.
+ let perm = if frozen {
+ Permission::SharedReadOnly
+ } else {
+ Permission::SharedReadWrite
+ };
+ let item = Item { perm, tag: new_tag, protector };
+ stacked_borrows.for_each(cur_ptr, size, |cur_ptr, stack, global| {
+ stack.grant(cur_ptr, item, global)
+ })
+ });
+ }
+ };
+ let item = Item { perm, tag: new_tag, protector };
+ stacked_borrows.for_each(ptr, size, |ptr, stack, global| stack.grant(ptr, item, global))
}
/// Retags an indidual pointer, returning the retagged version.
fn retag_reference(
&mut self,
val: ImmTy<'tcx, Tag>,
- mutbl: Option<Mutability>,
- fn_barrier: bool,
- two_phase: bool,
- ) -> EvalResult<'tcx, Immediate<Tag>> {
+ kind: RefKind,
+ protect: bool,
+ ) -> InterpResult<'tcx, ImmTy<'tcx, Tag>> {
let this = self.eval_context_mut();
// We want a place for where the ptr *points to*, so we get one.
let place = this.ref_to_mplace(val)?;
- let size = this.size_and_align_of_mplace(place)?
+ let size = this
+ .size_and_align_of_mplace(place)?
.map(|(size, _)| size)
.unwrap_or_else(|| place.layout.size);
+ // `reborrow` relies on getting a `Pointer` and everything being in-bounds,
+ // so let's ensure that. However, we do not care about alignment.
+ // We can see dangling ptrs in here e.g. after a Box's `Unique` was
+ // updated using "self.0 = ..." (can happen in Box::from_raw) so we cannot ICE; see miri#1050.
+ let place = this.mplace_access_checked(place, Some(Align::from_bytes(1).unwrap()))?;
+ // Nothing to do for ZSTs.
if size == Size::ZERO {
- // Nothing to do for ZSTs.
- return Ok(*val);
+ return Ok(val);
}
// Compute new borrow.
- let new_tag = match mutbl {
- Some(_) => Tag::Tagged(this.memory().extra.borrow_mut().new_ptr()),
- None => Tag::Untagged,
+ let new_tag = {
+ let mut mem_extra = this.memory.extra.stacked_borrows.as_ref().unwrap().borrow_mut();
+ match kind {
+ // Give up tracking for raw pointers.
+ RefKind::Raw { .. } if !mem_extra.track_raw => Tag::Untagged,
+ // All other pointers are properly tracked.
+ _ => Tag::Tagged(mem_extra.new_ptr()),
+ }
};
// Reborrow.
- this.reborrow(place, size, mutbl, new_tag, fn_barrier)?;
+ this.reborrow(place, size, kind, new_tag, protect)?;
let new_place = place.replace_tag(new_tag);
- // Handle two-phase borrows.
- if two_phase {
- assert!(mutbl == Some(MutMutable), "two-phase shared borrows make no sense");
- // Grant read access *to the parent pointer* with the old tag. This means the same pointer
- // has multiple items in the stack now!
- // FIXME: Think about this some more, in particular about the interaction with cast-to-raw.
- // Maybe find a better way to express 2-phase, now that we have a "more expressive language"
- // in the stack.
- let old_tag = place.ptr.to_ptr().unwrap().tag;
- this.reborrow(new_place, size, Some(MutImmutable), old_tag, /* fn_barrier: */ false)?;
- }
// Return new pointer.
- Ok(new_place.to_ref())
+ Ok(ImmTy::from_immediate(new_place.to_ref(), val.layout))
}
}
-impl<'a, 'mir, 'tcx> EvalContextExt<'a, 'mir, 'tcx> for crate::MiriEvalContext<'a, 'mir, 'tcx> {}
-pub trait EvalContextExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a, 'mir, 'tcx> {
- fn retag(
- &mut self,
- kind: RetagKind,
- place: PlaceTy<'tcx, Tag>
- ) -> EvalResult<'tcx> {
+impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
+pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
+ fn retag(&mut self, kind: RetagKind, place: PlaceTy<'tcx, Tag>) -> InterpResult<'tcx> {
let this = self.eval_context_mut();
- // Determine mutability and whether to add a barrier.
+ // Determine mutability and whether to add a protector.
// Cannot use `builtin_deref` because that reports *immutable* for `Box`,
// making it useless.
- fn qualify(ty: ty::Ty<'_>, kind: RetagKind) -> Option<(Option<Mutability>, bool)> {
- match ty.sty {
+ fn qualify(ty: ty::Ty<'_>, kind: RetagKind) -> Option<(RefKind, bool)> {
+ match ty.kind() {
// References are simple.
- ty::Ref(_, _, mutbl) => Some((Some(mutbl), kind == RetagKind::FnEntry)),
+ ty::Ref(_, _, Mutability::Mut) => Some((
+ RefKind::Unique { two_phase: kind == RetagKind::TwoPhase },
+ kind == RetagKind::FnEntry,
+ )),
+ ty::Ref(_, _, Mutability::Not) =>
+ Some((RefKind::Shared, kind == RetagKind::FnEntry)),
// Raw pointers need to be enabled.
- ty::RawPtr(..) if kind == RetagKind::Raw => Some((None, false)),
- // Boxes do not get a barrier: barriers reflect that references outlive the call
+ ty::RawPtr(tym) if kind == RetagKind::Raw =>
+ Some((RefKind::Raw { mutable: tym.mutbl == Mutability::Mut }, false)),
+ // Boxes do not get a protector: protectors reflect that references outlive the call
// they were passed in to; that's just not the case for boxes.
- ty::Adt(..) if ty.is_box() => Some((Some(MutMutable), false)),
+ ty::Adt(..) if ty.is_box() => Some((RefKind::Unique { two_phase: false }, false)),
_ => None,
}
}
- // We need a visitor to visit all references. However, that requires
- // a `MemPlace`, so we have a fast path for reference types that
- // avoids allocating.
- if let Some((mutbl, barrier)) = qualify(place.layout.ty, kind) {
+ // We only reborrow "bare" references/boxes.
+ // Not traversing into fields helps with <https://github.com/rust-lang/unsafe-code-guidelines/issues/125>,
+ // but might also cost us optimization and analyses. We will have to experiment more with this.
+ if let Some((mutbl, protector)) = qualify(place.layout.ty, kind) {
// Fast path.
let val = this.read_immediate(this.place_to_op(place)?)?;
- let val = this.retag_reference(val, mutbl, barrier, kind == RetagKind::TwoPhase)?;
- this.write_immediate(val, place)?;
- return Ok(());
+ let val = this.retag_reference(val, mutbl, protector)?;
+ this.write_immediate(*val, place)?;
}
- let place = this.force_allocation(place)?;
- let mut visitor = RetagVisitor { ecx: this, kind };
- visitor.visit_value(place)?;
-
- // The actual visitor.
- struct RetagVisitor<'ecx, 'a, 'mir, 'tcx> {
- ecx: &'ecx mut MiriEvalContext<'a, 'mir, 'tcx>,
- kind: RetagKind,
- }
- impl<'ecx, 'a, 'mir, 'tcx>
- MutValueVisitor<'a, 'mir, 'tcx, Evaluator<'tcx>>
- for
- RetagVisitor<'ecx, 'a, 'mir, 'tcx>
- {
- type V = MPlaceTy<'tcx, Tag>;
-
- #[inline(always)]
- fn ecx(&mut self) -> &mut MiriEvalContext<'a, 'mir, 'tcx> {
- &mut self.ecx
- }
+ Ok(())
+ }
- // Primitives of reference type, that is the one thing we are interested in.
- fn visit_primitive(&mut self, place: MPlaceTy<'tcx, Tag>) -> EvalResult<'tcx>
- {
- // Cannot use `builtin_deref` because that reports *immutable* for `Box`,
- // making it useless.
- if let Some((mutbl, barrier)) = qualify(place.layout.ty, self.kind) {
- let val = self.ecx.read_immediate(place.into())?;
- let val = self.ecx.retag_reference(
- val,
- mutbl,
- barrier,
- self.kind == RetagKind::TwoPhase
- )?;
- self.ecx.write_immediate(val, place.into())?;
- }
- Ok(())
- }
+ /// After a stack frame got pushed, retag the return place so that we are sure
+ /// it does not alias with anything.
+ ///
+ /// This is a HACK because there is nothing in MIR that would make the retag
+ /// explicit. Also see https://github.com/rust-lang/rust/issues/71117.
+ fn retag_return_place(&mut self) -> InterpResult<'tcx> {
+ let this = self.eval_context_mut();
+ let return_place = if let Some(return_place) = this.frame_mut().return_place {
+ return_place
+ } else {
+ // No return place, nothing to do.
+ return Ok(());
+ };
+ if return_place.layout.is_zst() {
+ // There may not be any memory here, nothing to do.
+ return Ok(());
}
+ // We need this to be in-memory to use tagged pointers.
+ let return_place = this.force_allocation(return_place)?;
+
+ // We have to turn the place into a pointer to use the existing code.
+ // (The pointer type does not matter, so we use a raw pointer.)
+ let ptr_layout = this.layout_of(this.tcx.mk_mut_ptr(return_place.layout.ty))?;
+ let val = ImmTy::from_immediate(return_place.to_ref(), ptr_layout);
+ // Reborrow it.
+ let val = this.retag_reference(val, RefKind::Unique { two_phase: false }, /*protector*/ true)?;
+ // And use reborrowed pointer for return place.
+ let return_place = this.ref_to_mplace(val)?;
+ this.frame_mut().return_place = Some(return_place.into());
Ok(())
}
projects / rust.git / blobdiff