use std::collections::HashMap;
use std::borrow::Cow;
+use std::rc::Rc;
use rand::rngs::StdRng;
use rand::SeedableRng;
pub use crate::stacked_borrows::{EvalContextExt as StackedBorEvalContextExt};
// Used by priroda.
-pub use crate::stacked_borrows::{Borrow, Stack, Stacks, BorStackItem};
+pub use crate::stacked_borrows::{Tag, Permission, Stack, Stacks, Item};
/// Insert rustc arguments at the beginning of the argument list that Miri wants to be
/// set per default, for maximal validation power.
// Don't forget `0` terminator.
cmd.push(std::char::from_u32(0).unwrap());
// Collect the pointers to the individual strings.
- let mut argvs = Vec::<Pointer<Borrow>>::new();
+ let mut argvs = Vec::<Pointer<Tag>>::new();
for arg in config.args {
// Add `0` terminator.
let mut arg = arg.into_bytes();
Size::from_bytes(cmd_utf16.len() as u64 * 2),
Align::from_bytes(2).unwrap(),
MiriMemoryKind::Env.into(),
- ).with_default_tag();
+ );
ecx.machine.cmd_line = Some(cmd_ptr);
// Store the UTF-16 string.
let char_size = Size::from_bytes(2);
main_id: DefId,
config: MiriConfig,
) {
- let mut ecx = create_ecx(tcx, main_id, config).expect("couldn't create ecx");
+ let mut ecx = match create_ecx(tcx, main_id, config) {
+ Ok(ecx) => ecx,
+ Err(mut err) => {
+ err.print_backtrace();
+ panic!("Miri initialziation error: {}", err.kind)
+ }
+ };
// Perform the main execution.
let res: EvalResult = (|| {
pub struct Evaluator<'tcx> {
/// Environment variables set by `setenv`.
/// Miri does not expose env vars from the host to the emulated program.
- pub(crate) env_vars: HashMap<Vec<u8>, Pointer<Borrow>>,
+ pub(crate) env_vars: HashMap<Vec<u8>, Pointer<Tag>>,
/// Program arguments (`Option` because we can only initialize them after creating the ecx).
/// These are *pointers* to argc/argv because macOS.
/// We also need the full command line as one string because of Windows.
- pub(crate) argc: Option<Pointer<Borrow>>,
- pub(crate) argv: Option<Pointer<Borrow>>,
- pub(crate) cmd_line: Option<Pointer<Borrow>>,
+ pub(crate) argc: Option<Pointer<Tag>>,
+ pub(crate) argv: Option<Pointer<Tag>>,
+ pub(crate) cmd_line: Option<Pointer<Tag>>,
/// Last OS error.
pub(crate) last_error: u32,
/// Whether to enforce the validity invariant.
pub(crate) validate: bool,
- /// Stacked Borrows state.
- pub(crate) stacked_borrows: stacked_borrows::State,
-
/// The random number generator to use if Miri
/// is running in non-deterministic mode
pub(crate) rng: Option<StdRng>
last_error: 0,
tls: TlsData::default(),
validate,
- stacked_borrows: stacked_borrows::State::default(),
rng: seed.map(|s| StdRng::seed_from_u64(s))
}
}
type FrameExtra = stacked_borrows::CallId;
type MemoryExtra = stacked_borrows::MemoryState;
type AllocExtra = stacked_borrows::Stacks;
- type PointerTag = Borrow;
+ type PointerTag = Tag;
- type MemoryMap = MonoHashMap<AllocId, (MemoryKind<MiriMemoryKind>, Allocation<Borrow, Self::AllocExtra>)>;
+ type MemoryMap = MonoHashMap<AllocId, (MemoryKind<MiriMemoryKind>, Allocation<Tag, Self::AllocExtra>)>;
const STATIC_KIND: Option<MiriMemoryKind> = Some(MiriMemoryKind::MutStatic);
fn find_fn(
ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
instance: ty::Instance<'tcx>,
- args: &[OpTy<'tcx, Borrow>],
- dest: Option<PlaceTy<'tcx, Borrow>>,
+ args: &[OpTy<'tcx, Tag>],
+ dest: Option<PlaceTy<'tcx, Tag>>,
ret: Option<mir::BasicBlock>,
) -> EvalResult<'tcx, Option<&'mir mir::Mir<'tcx>>> {
ecx.find_fn(instance, args, dest, ret)
fn call_intrinsic(
ecx: &mut rustc_mir::interpret::InterpretCx<'a, 'mir, 'tcx, Self>,
instance: ty::Instance<'tcx>,
- args: &[OpTy<'tcx, Borrow>],
- dest: PlaceTy<'tcx, Borrow>,
+ args: &[OpTy<'tcx, Tag>],
+ dest: PlaceTy<'tcx, Tag>,
) -> EvalResult<'tcx> {
ecx.call_intrinsic(instance, args, dest)
}
fn ptr_op(
ecx: &rustc_mir::interpret::InterpretCx<'a, 'mir, 'tcx, Self>,
bin_op: mir::BinOp,
- left: ImmTy<'tcx, Borrow>,
- right: ImmTy<'tcx, Borrow>,
- ) -> EvalResult<'tcx, (Scalar<Borrow>, bool)> {
+ left: ImmTy<'tcx, Tag>,
+ right: ImmTy<'tcx, Tag>,
+ ) -> EvalResult<'tcx, (Scalar<Tag>, bool)> {
ecx.ptr_op(bin_op, left, right)
}
fn box_alloc(
ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
- dest: PlaceTy<'tcx, Borrow>,
+ dest: PlaceTy<'tcx, Tag>,
) -> EvalResult<'tcx> {
trace!("box_alloc for {:?}", dest.layout.ty);
// Call the `exchange_malloc` lang item.
def_id: DefId,
tcx: TyCtxtAt<'a, 'tcx, 'tcx>,
memory_extra: &Self::MemoryExtra,
- ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Borrow, Self::AllocExtra>>> {
+ ) -> EvalResult<'tcx, Cow<'tcx, Allocation<Tag, Self::AllocExtra>>> {
let attrs = tcx.get_attrs(def_id);
let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
Some(name) => name.as_str(),
// This should be all-zero, pointer-sized.
let size = tcx.data_layout.pointer_size;
let data = vec![0; size.bytes() as usize];
- let extra = AllocationExtra::memory_allocated(size, memory_extra);
+ let extra = Stacks::new(size, Tag::default(), Rc::clone(memory_extra));
Allocation::from_bytes(&data, tcx.data_layout.pointer_align.abi, extra)
}
_ => return err!(Unimplemented(
fn adjust_static_allocation<'b>(
alloc: &'b Allocation,
memory_extra: &Self::MemoryExtra,
- ) -> Cow<'b, Allocation<Borrow, Self::AllocExtra>> {
- let extra = AllocationExtra::memory_allocated(
+ ) -> Cow<'b, Allocation<Tag, Self::AllocExtra>> {
+ let extra = Stacks::new(
Size::from_bytes(alloc.bytes.len() as u64),
- memory_extra,
+ Tag::default(),
+ Rc::clone(memory_extra),
);
- let alloc: Allocation<Borrow, Self::AllocExtra> = Allocation {
+ let alloc: Allocation<Tag, Self::AllocExtra> = Allocation {
bytes: alloc.bytes.clone(),
relocations: Relocations::from_presorted(
alloc.relocations.iter()
- .map(|&(offset, ((), alloc))| (offset, (Borrow::default(), alloc)))
+ .map(|&(offset, ((), alloc))| (offset, (Tag::default(), alloc)))
.collect()
),
undef_mask: alloc.undef_mask.clone(),
Cow::Owned(alloc)
}
- fn tag_dereference(
- ecx: &InterpretCx<'a, 'mir, 'tcx, Self>,
- place: MPlaceTy<'tcx, Borrow>,
- mutability: Option<hir::Mutability>,
- ) -> EvalResult<'tcx, Scalar<Borrow>> {
- let size = ecx.size_and_align_of_mplace(place)?.map(|(size, _)| size)
- // For extern types, just cover what we can.
- .unwrap_or_else(|| place.layout.size);
- if !ecx.tcx.sess.opts.debugging_opts.mir_emit_retag ||
- !Self::enforce_validity(ecx) || size == Size::ZERO
- {
- // No tracking.
- Ok(place.ptr)
- } else {
- ecx.ptr_dereference(place, size, mutability.into())?;
- // We never change the pointer.
- Ok(place.ptr)
- }
+ #[inline(always)]
+ fn new_allocation(
+ size: Size,
+ extra: &Self::MemoryExtra,
+ kind: MemoryKind<MiriMemoryKind>,
+ ) -> (Self::AllocExtra, Self::PointerTag) {
+ Stacks::new_allocation(size, extra, kind)
}
#[inline(always)]
- fn tag_new_allocation(
- ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
- ptr: Pointer,
- kind: MemoryKind<Self::MemoryKinds>,
- ) -> Pointer<Borrow> {
- if !ecx.machine.validate {
- // No tracking.
- ptr.with_default_tag()
- } else {
- let tag = ecx.tag_new_allocation(ptr.alloc_id, kind);
- Pointer::new_with_tag(ptr.alloc_id, ptr.offset, tag)
- }
+ fn tag_dereference(
+ _ecx: &InterpretCx<'a, 'mir, 'tcx, Self>,
+ place: MPlaceTy<'tcx, Tag>,
+ _mutability: Option<hir::Mutability>,
+ ) -> EvalResult<'tcx, Scalar<Tag>> {
+ // Nothing happens.
+ Ok(place.ptr)
}
#[inline(always)]
fn retag(
ecx: &mut InterpretCx<'a, 'mir, 'tcx, Self>,
kind: mir::RetagKind,
- place: PlaceTy<'tcx, Borrow>,
+ place: PlaceTy<'tcx, Tag>,
) -> EvalResult<'tcx> {
if !ecx.tcx.sess.opts.debugging_opts.mir_emit_retag || !Self::enforce_validity(ecx) {
// No tracking, or no retagging. The latter is possible because a dependency of ours
use std::cell::RefCell;
use std::collections::HashSet;
use std::rc::Rc;
+use std::fmt;
+use std::num::NonZeroU64;
use rustc::ty::{self, layout::Size};
use rustc::hir::{Mutability, MutMutable, MutImmutable};
use crate::{
EvalResult, InterpError, MiriEvalContext, HelpersEvalContextExt, Evaluator, MutValueVisitor,
- MemoryKind, MiriMemoryKind, RangeMap, AllocId, Allocation, AllocationExtra,
+ MemoryKind, MiriMemoryKind, RangeMap, Allocation, AllocationExtra,
Pointer, Immediate, ImmTy, PlaceTy, MPlaceTy,
};
-pub type Timestamp = u64;
+pub type PtrId = NonZeroU64;
pub type CallId = u64;
-/// Information about which kind of borrow was used to create the reference this is tagged with.
+/// Tracking pointer provenance
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-pub enum Borrow {
- /// A unique (mutable) reference.
- Uniq(Timestamp),
- /// An aliasing reference. This is also used by raw pointers, which do not track details
- /// of how or when they were created, hence the timestamp is optional.
- /// `Shr(Some(_))` does *not* mean that the destination of this reference is frozen;
- /// that depends on the type! Only those parts outside of an `UnsafeCell` are actually
- /// frozen.
- Alias(Option<Timestamp>),
+pub enum Tag {
+ Tagged(PtrId),
+ Untagged,
}
-impl Borrow {
- #[inline(always)]
- pub fn is_aliasing(self) -> bool {
- match self {
- Borrow::Alias(_) => true,
- _ => false,
- }
- }
-
- #[inline(always)]
- pub fn is_unique(self) -> bool {
+impl fmt::Display for Tag {
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
- Borrow::Uniq(_) => true,
- _ => false,
+ Tag::Tagged(id) => write!(f, "{}", id),
+ Tag::Untagged => write!(f, "<untagged>"),
}
}
}
-impl Default for Borrow {
- fn default() -> Self {
- Borrow::Alias(None)
- }
+/// Indicates which permission is granted (by this item to some pointers)
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+pub enum Permission {
+ /// Grants unique mutable access.
+ Unique,
+ /// Grants shared mutable access.
+ SharedReadWrite,
+ /// Greants shared read-only access.
+ SharedReadOnly,
}
/// An item in the per-location borrow stack.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-pub enum BorStackItem {
- /// Indicates the unique reference that may mutate.
- Uniq(Timestamp),
- /// Indicates that the location has been mutably shared. Used for raw pointers as
- /// well as for unfrozen shared references.
- Raw,
+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)
+ FnBarrier(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),
+ }
+ }
}
/// Extra per-location state.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Stack {
- /// Used as the stack; never empty.
- borrows: Vec<BorStackItem>,
- /// A virtual frozen "item" on top of the stack.
- frozen_since: Option<Timestamp>,
+ /// 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`.
+ borrows: Vec<Item>,
}
-impl Stack {
- #[inline(always)]
- pub fn is_frozen(&self) -> bool {
- self.frozen_since.is_some()
- }
+
+/// 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,
}
-/// Indicates which kind of reference is being used.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
-pub enum RefKind {
- /// `&mut`.
- Unique,
- /// `&` without interior mutability.
- Frozen,
- /// `*` (raw pointer) or `&` to `UnsafeCell`.
- Raw,
+/// Extra global state, available to the memory access hooks.
+#[derive(Debug)]
+pub struct GlobalState {
+ next_ptr_id: PtrId,
+ next_call_id: CallId,
+ active_calls: HashSet<CallId>,
}
+pub type MemoryState = Rc<RefCell<GlobalState>>;
/// Indicates which kind of access is being performed.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
pub enum AccessKind {
Read,
- Write,
- Dealloc,
+ Write { dealloc: bool },
}
-/// Extra global state in the memory, available to the memory access hooks.
-#[derive(Debug)]
-pub struct BarrierTracking {
- next_id: CallId,
- active_calls: HashSet<CallId>,
+// "Fake" constructors
+impl AccessKind {
+ fn write() -> AccessKind {
+ AccessKind::Write { dealloc: false }
+ }
+
+ fn dealloc() -> AccessKind {
+ AccessKind::Write { dealloc: true }
+ }
+}
+
+impl fmt::Display for AccessKind {
+ 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"),
+ }
+ }
+}
+
+/// Indicates which kind of reference is being created.
+/// Used by `reborrow` to compute which permissions to grant to the
+/// new pointer.
+#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+pub enum RefKind {
+ /// `&mut`.
+ Mutable,
+ /// `&` with or without interior mutability.
+ Shared { frozen: bool },
+ /// `*` (raw pointer).
+ Raw,
+}
+
+impl fmt::Display for RefKind {
+ 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"),
+ }
+ }
}
-pub type MemoryState = Rc<RefCell<BarrierTracking>>;
-impl Default for BarrierTracking {
+/// Utilities for initialization and ID generation
+impl Default for GlobalState {
fn default() -> Self {
- BarrierTracking {
- next_id: 0,
+ GlobalState {
+ next_ptr_id: NonZeroU64::new(1).unwrap(),
+ next_call_id: 0,
active_calls: HashSet::default(),
}
}
}
-impl BarrierTracking {
+impl GlobalState {
+ pub fn new_ptr(&mut self) -> PtrId {
+ let id = self.next_ptr_id;
+ self.next_ptr_id = NonZeroU64::new(id.get() + 1).unwrap();
+ id
+ }
+
pub fn new_call(&mut self) -> CallId {
- let id = self.next_id;
+ let id = self.next_call_id;
trace!("new_call: Assigning ID {}", id);
self.active_calls.insert(id);
- self.next_id += 1;
+ self.next_call_id = id+1;
id
}
}
}
-/// Extra global machine state.
-#[derive(Clone, Debug)]
-pub struct State {
- clock: Timestamp
-}
-
-impl Default for State {
- fn default() -> Self {
- State { clock: 0 }
- }
-}
+// # Stacked Borrows Core Begin
-impl State {
- fn increment_clock(&mut self) -> Timestamp {
- let val = self.clock;
- self.clock = val + 1;
- val
- }
-}
-
-/// 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>>,
- barrier_tracking: MemoryState,
-}
-
-/// Core per-location operations: deref, access, create.
/// We need to make at least the following things true:
///
/// U1: After creating a `Uniq`, it is at the top (and unfrozen).
/// U2: If the top is `Uniq` (and unfrozen), accesses must be through that `Uniq` or pop it.
-/// U3: If an access (deref sufficient?) happens with a `Uniq`, it requires the `Uniq` to be in the stack.
+/// U3: If an access happens with a `Uniq`, it requires the `Uniq` to be in the stack.
///
/// F1: After creating a `&`, the parts outside `UnsafeCell` are frozen.
/// F2: If a write access happens, it unfreezes.
-/// F3: If an access (well, a deref) happens with an `&` outside `UnsafeCell`,
+/// F3: If an access happens with an `&` outside `UnsafeCell`,
/// it requires the location to still be frozen.
-impl<'tcx> Stack {
- /// Deref `bor`: check if the location is frozen and the tag in the stack.
- /// This dos *not* constitute an access! "Deref" refers to the `*` operator
- /// in Rust, and includs cases like `&*x` or `(*x).foo` where no or only part
- /// of the memory actually gets accessed. Also we cannot know if we are
- /// going to read or write.
- /// Returns the index of the item we matched, `None` if it was the frozen one.
- /// `kind` indicates which kind of reference is being dereferenced.
- fn deref(
- &self,
- bor: Borrow,
- kind: RefKind,
- ) -> Result<Option<usize>, String> {
- // Exclude unique ref with frozen tag.
- if let (RefKind::Unique, Borrow::Alias(Some(_))) = (kind, bor) {
- return Err(format!("encountered mutable reference with frozen tag ({:?})", bor));
+
+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.
+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,
}
- // Checks related to freezing.
- match bor {
- Borrow::Alias(Some(bor_t)) if kind == RefKind::Frozen => {
- // We need the location to be frozen. This ensures F3.
- let frozen = self.frozen_since.map_or(false, |itm_t| itm_t <= bor_t);
- return if frozen { Ok(None) } else {
- Err(format!("location is not frozen long enough"))
- }
- }
- Borrow::Alias(_) if self.frozen_since.is_some() => {
- // Shared deref to frozen location; looking good.
- return Ok(None)
- }
- // Not sufficient; go on looking.
- _ => {}
+ }
+
+ /// This defines for a given permission, which other items 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: Item) -> bool {
+ use self::Permission::*;
+
+ let other = match other {
+ Item::Permission(perm, _) => perm,
+ Item::FnBarrier(_) => return false, // Remove all barriers -- if they are active, cause UB.
+ };
+
+ 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.
+ (_, 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 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.
}
- // If we got here, we have to look for our item in the stack.
- for (idx, &itm) in self.borrows.iter().enumerate().rev() {
- match (itm, bor) {
- (BorStackItem::Uniq(itm_t), Borrow::Uniq(bor_t)) if itm_t == bor_t => {
- // Found matching unique item. This satisfies U3.
- return Ok(Some(idx))
- }
- (BorStackItem::Raw, Borrow::Alias(_)) => {
- // Found matching aliasing/raw item.
- return Ok(Some(idx))
- }
- // Go on looking. We ignore barriers! When an `&mut` and an `&` alias,
- // dereferencing the `&` is still possible (to reborrow), but doing
- // an access is not.
- _ => {}
- }
+ }
+}
+
+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.
}
- // If we got here, we did not find our item. We have to error to satisfy U3.
- Err(format!("Borrow being dereferenced ({:?}) does not exist on the borrow stack", bor))
}
- /// Performs an actual memory access using `bor`. We do not know any types here
- /// or whether things should be frozen, but we *do* know if this is reading
- /// or writing.
+ /// 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.
+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()
+ .enumerate() // we also need to know *where* in the stack
+ .rev() // search top-to-bottom
+ // Return permission of first item that grants access.
+ .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,
- bor: Borrow,
- kind: AccessKind,
- barrier_tracking: &BarrierTracking,
- ) -> EvalResult<'tcx> {
- // Check if we can match the frozen "item".
- // Not possible on writes!
- if self.is_frozen() {
- if kind == AccessKind::Read {
- // When we are frozen, we just accept all reads. No harm in this.
- // The deref already checked that `Uniq` items are in the stack, and that
- // the location is frozen if it should be.
- return Ok(());
- }
- trace!("access: unfreezing");
- }
- // Unfreeze on writes. This ensures F2.
- self.frozen_since = None;
- // Pop the stack until we have something matching.
- while let Some(&itm) = self.borrows.last() {
- match (itm, bor) {
- (BorStackItem::FnBarrier(call), _) if barrier_tracking.is_active(call) => {
- return err!(MachineError(format!(
- "stopping looking for borrow being accessed ({:?}) because of barrier ({})",
- bor, call
- )))
- }
- (BorStackItem::Uniq(itm_t), Borrow::Uniq(bor_t)) if itm_t == bor_t => {
- // Found matching unique item. Continue after the match.
- }
- (BorStackItem::Raw, _) if kind == AccessKind::Read => {
- // When reading, everything can use a raw item!
- // We do not want to do this when writing: Writing to an `&mut`
- // should reaffirm its exclusivity (i.e., make sure it is
- // on top of the stack). Continue after the match.
- }
- (BorStackItem::Raw, Borrow::Alias(_)) => {
- // Found matching raw item. Continue after the match.
- }
- _ => {
- // Pop this, go on. This ensures U2.
- let itm = self.borrows.pop().unwrap();
- trace!("access: Popping {:?}", itm);
- continue
- }
- }
- // 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 kind == AccessKind::Dealloc {
- for &itm in self.borrows.iter().rev() {
- match itm {
- BorStackItem::FnBarrier(call) if barrier_tracking.is_active(call) => {
+ access: AccessKind,
+ tag: Tag,
+ global: &GlobalState,
+ ) -> EvalResult<'tcx, usize> {
+ // Two main steps: Find granting item, remove all incompatible items above.
+ // 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.
+ // 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;
+ while let Some(item) = self.borrows.get(cur) {
+ if granting_perm.compatible_with(access, *item) {
+ // Keep this, check next.
+ cur += 1;
+ } else {
+ // Aha! This is a bad one, remove it, and if it is an *active* barrier
+ // we have a problem.
+ match self.borrows.remove(cur) {
+ Item::FnBarrier(call) if global.is_active(call) => {
return err!(MachineError(format!(
- "deallocating with active barrier ({})", call
- )))
+ "not granting access because of barrier ({})", call
+ )));
}
- _ => {},
+ _ => {}
}
}
}
- // Now we are done.
- return Ok(())
}
- // If we got here, we did not find our item.
- err!(MachineError(format!(
- "borrow being accessed ({:?}) does not exist on the borrow stack",
- bor
- )))
- }
-
- /// Initiate `bor`; mostly this means pushing.
- /// This operation cannot fail; it is up to the caller to ensure that the precondition
- /// is met: We cannot push `Uniq` onto frozen stacks.
- /// `kind` indicates which kind of reference is being created.
- fn create(&mut self, bor: Borrow, kind: RefKind) {
- // When creating a frozen reference, freeze. This ensures F1.
- // We also do *not* push anything else to the stack, making sure that no nother kind
- // of access (like writing through raw pointers) is permitted.
- if kind == RefKind::Frozen {
- let bor_t = match bor {
- Borrow::Alias(Some(t)) => t,
- _ => bug!("Creating illegal borrow {:?} for frozen ref", bor),
- };
- // It is possible that we already are frozen (e.g., if we just pushed a barrier,
- // the redundancy check would not have kicked in).
- match self.frozen_since {
- Some(loc_t) => assert!(
- loc_t <= bor_t,
- "trying to freeze location for longer than it was already frozen"
- ),
- None => {
- trace!("create: Freezing");
- self.frozen_since = Some(bor_t);
+
+ // 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
+ )))
+ }
+ _ => {},
}
}
- return;
}
- assert!(
- self.frozen_since.is_none(),
- "trying to create non-frozen reference to frozen location"
- );
- // Push new item to the stack.
- let itm = match bor {
- Borrow::Uniq(t) => BorStackItem::Uniq(t),
- Borrow::Alias(_) => BorStackItem::Raw,
- };
- if *self.borrows.last().unwrap() == itm {
- // This is just an optimization, no functional change: Avoid stacking
- // multiple `Shr` on top of each other.
- assert!(bor.is_aliasing());
- trace!("create: sharing a shared location is a NOP");
- } else {
- // This ensures U1.
- trace!("create: pushing {:?}", itm);
- self.borrows.push(itm);
+ // Done.
+ return Ok(granting_idx);
+ }
+
+ /// `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);
}
+ /// `reborrow` helper function.
/// Adds a barrier.
fn barrier(&mut self, call: CallId) {
- let itm = BorStackItem::FnBarrier(call);
+ 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!("barrier: avoiding redundant extra barrier");
+ trace!("reborrow: avoiding redundant extra barrier");
} else {
- trace!("barrier: pushing barrier for call {}", call);
+ trace!("reborrow: pushing barrier for call {}", call);
self.borrows.push(itm);
}
}
+
+ /// `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);
+ }
+ _ => {}
+ }
+ }
+ }
+
+ /// 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();
+ 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,
+ )))?;
+ // With this we can compute the permission for the new pointer.
+ let new_perm = new_kind.new_perm(derived_from_perm)?;
+
+ // 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!
+ 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!
+ 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>
+ } 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.
+ let check_idx = self.access(access, derived_from, global)?;
+ assert_eq!(check_idx, derived_from_idx, "somehow we saw different items??");
+
+ // Now is a good time to add the barrier.
+ if let Some(call) = barrier {
+ self.barrier(call);
+ }
+
+ // 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.
+ self.grant(new_perm, new_tag, self.borrows.len());
+ }
+
+ // Make sure that after all this, the stack's invariant is still maintained.
+ if cfg!(debug_assertions) {
+ self.test_invariants();
+ }
+
+ Ok(())
+ }
}
/// Higher-level per-location operations: deref, access, reborrow.
impl<'tcx> Stacks {
- /// Checks that this stack is fine with being dereferenced.
- fn deref(
- &self,
- ptr: Pointer<Borrow>,
+ /// Creates new stack with initial tag.
+ pub(crate) fn new(
size: Size,
- kind: RefKind,
- ) -> EvalResult<'tcx> {
- trace!("deref for tag {:?} as {:?}: {:?}, size {}",
- ptr.tag, kind, ptr, size.bytes());
- let stacks = self.stacks.borrow();
- for stack in stacks.iter(ptr.offset, size) {
- stack.deref(ptr.tag, kind).map_err(InterpError::MachineError)?;
+ 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,
}
- Ok(())
}
/// `ptr` got used, reflect that in the stack.
fn access(
&self,
- ptr: Pointer<Borrow>,
+ ptr: Pointer<Tag>,
size: Size,
kind: AccessKind,
) -> EvalResult<'tcx> {
- trace!("{:?} access of tag {:?}: {:?}, size {}", kind, ptr.tag, ptr, size.bytes());
+ 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 barrier_tracking = self.barrier_tracking.borrow();
+ let global = self.global.borrow();
let mut stacks = self.stacks.borrow_mut();
for stack in stacks.iter_mut(ptr.offset, size) {
- stack.access(ptr.tag, kind, &*barrier_tracking)?;
+ stack.access(kind, ptr.tag, &*global)?;
}
Ok(())
}
/// This works on `&self` because we might encounter references to constant memory.
fn reborrow(
&self,
- ptr: Pointer<Borrow>,
+ ptr: Pointer<Tag>,
size: Size,
- mut barrier: Option<CallId>,
- new_bor: Borrow,
+ barrier: Option<CallId>,
new_kind: RefKind,
+ new_tag: Tag,
) -> EvalResult<'tcx> {
- assert_eq!(new_bor.is_unique(), new_kind == RefKind::Unique);
trace!(
- "reborrow for tag {:?} to {:?} as {:?}: {:?}, size {}",
- ptr.tag, new_bor, new_kind, ptr, size.bytes(),
+ "{} reborrow for tag {} to {}: {:?}, size {}",
+ new_kind, ptr.tag, new_tag, ptr, size.bytes(),
);
- if new_kind == RefKind::Raw {
- // No barrier for raw, including `&UnsafeCell`. 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>
- barrier = None;
- }
- let barrier_tracking = self.barrier_tracking.borrow();
+ let global = self.global.borrow();
let mut stacks = self.stacks.borrow_mut();
for stack in stacks.iter_mut(ptr.offset, size) {
- // Access source `ptr`, create new ref.
- let ptr_idx = stack.deref(ptr.tag, new_kind).map_err(InterpError::MachineError)?;
- // If we can deref the new tag already, and if that tag lives higher on
- // the stack than the one we come from, just use that.
- // That is, we check if `new_bor` *already* is "derived from" `ptr.tag`.
- // This also checks frozenness, if required.
- let bor_redundant = barrier.is_none() &&
- match (ptr_idx, stack.deref(new_bor, new_kind)) {
- // If the new borrow works with the frozen item, or else if it lives
- // above the old one in the stack, our job here is done.
- (_, Ok(None)) => true,
- (Some(ptr_idx), Ok(Some(new_idx))) if new_idx >= ptr_idx => true,
- // Otherwise, we need to create a new borrow.
- _ => false,
- };
- if bor_redundant {
- assert!(new_bor.is_aliasing(), "a unique reborrow can never be redundant");
- trace!("reborrow is redundant");
- continue;
- }
- // We need to do some actual work.
- let access_kind = if new_kind == RefKind::Unique {
- AccessKind::Write
- } else {
- AccessKind::Read
- };
- stack.access(ptr.tag, access_kind, &*barrier_tracking)?;
- if let Some(call) = barrier {
- stack.barrier(call);
- }
- stack.create(new_bor, new_kind);
+ stack.reborrow(ptr.tag, barrier, new_kind, new_tag, &*global)?;
}
Ok(())
}
}
-/// Hooks and glue.
-impl AllocationExtra<Borrow, MemoryState> for Stacks {
- #[inline(always)]
- fn memory_allocated<'tcx>(size: Size, extra: &MemoryState) -> Self {
- let stack = Stack {
- borrows: vec![BorStackItem::Raw],
- frozen_since: None,
+// # Stacked Borrows Core End
+
+// Glue code to connect with Miri Machine Hooks
+
+impl Stacks {
+ pub fn new_allocation(
+ size: Size,
+ extra: &MemoryState,
+ 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())
+ }
+ _ => {
+ Tag::Untagged
+ }
};
- Stacks {
- stacks: RefCell::new(RangeMap::new(size, stack)),
- barrier_tracking: Rc::clone(extra),
- }
+ let stack = Stacks::new(size, tag, Rc::clone(extra));
+ (stack, tag)
}
+}
+impl AllocationExtra<Tag> for Stacks {
#[inline(always)]
fn memory_read<'tcx>(
- alloc: &Allocation<Borrow, Stacks>,
- ptr: Pointer<Borrow>,
+ alloc: &Allocation<Tag, Stacks>,
+ ptr: Pointer<Tag>,
size: Size,
) -> EvalResult<'tcx> {
alloc.extra.access(ptr, size, AccessKind::Read)
#[inline(always)]
fn memory_written<'tcx>(
- alloc: &mut Allocation<Borrow, Stacks>,
- ptr: Pointer<Borrow>,
+ alloc: &mut Allocation<Tag, Stacks>,
+ ptr: Pointer<Tag>,
size: Size,
) -> EvalResult<'tcx> {
- alloc.extra.access(ptr, size, AccessKind::Write)
+ alloc.extra.access(ptr, size, AccessKind::write())
}
#[inline(always)]
fn memory_deallocated<'tcx>(
- alloc: &mut Allocation<Borrow, Stacks>,
- ptr: Pointer<Borrow>,
+ alloc: &mut Allocation<Tag, Stacks>,
+ ptr: Pointer<Tag>,
size: Size,
) -> EvalResult<'tcx> {
- alloc.extra.access(ptr, size, AccessKind::Dealloc)
- }
-}
-
-impl<'tcx> Stacks {
- /// Pushes the first item to the stacks.
- pub(crate) fn first_item(
- &mut self,
- itm: BorStackItem,
- size: Size
- ) {
- for stack in self.stacks.get_mut().iter_mut(Size::ZERO, size) {
- assert!(stack.borrows.len() == 1);
- assert_eq!(stack.borrows.pop().unwrap(), BorStackItem::Raw);
- stack.borrows.push(itm);
- }
+ alloc.extra.access(ptr, size, AccessKind::dealloc())
}
}
trait EvalContextPrivExt<'a, 'mir, 'tcx: 'a+'mir>: crate::MiriEvalContextExt<'a, 'mir, 'tcx> {
fn reborrow(
&mut self,
- place: MPlaceTy<'tcx, Borrow>,
+ place: MPlaceTy<'tcx, Tag>,
size: Size,
+ mutbl: Option<Mutability>,
+ new_tag: Tag,
fn_barrier: bool,
- new_bor: Borrow
) -> EvalResult<'tcx> {
let this = self.eval_context_mut();
- let ptr = place.ptr.to_ptr()?;
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_bor);
+ ptr, place.layout.ty, new_tag);
// 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)?;
// Update the stacks.
- if let Borrow::Alias(Some(_)) = new_bor {
+ 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 kind = if frozen { RefKind::Frozen } else { RefKind::Raw };
- alloc.extra.reborrow(cur_ptr, size, barrier, new_bor, kind)
+ 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 kind = if new_bor.is_unique() { RefKind::Unique } else { RefKind::Raw };
- alloc.extra.reborrow(ptr, size, barrier, new_bor, kind)?;
+ let new_kind = if mutbl == Some(MutMutable) { RefKind::Mutable } else { RefKind::Raw };
+ alloc.extra.reborrow(ptr, size, barrier, new_kind, new_tag)?;
}
Ok(())
}
/// `mutbl` can be `None` to make this a raw pointer.
fn retag_reference(
&mut self,
- val: ImmTy<'tcx, Borrow>,
+ val: ImmTy<'tcx, Tag>,
mutbl: Option<Mutability>,
fn_barrier: bool,
two_phase: bool,
- ) -> EvalResult<'tcx, Immediate<Borrow>> {
+ ) -> EvalResult<'tcx, Immediate<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)?;
}
// Compute new borrow.
- let time = this.machine.stacked_borrows.increment_clock();
- let new_bor = match mutbl {
- Some(MutMutable) => Borrow::Uniq(time),
- Some(MutImmutable) => Borrow::Alias(Some(time)),
- None => Borrow::default(),
+ let new_tag = match mutbl {
+ Some(_) => Tag::Tagged(this.memory().extra.borrow_mut().new_ptr()),
+ None => Tag::Untagged,
};
// Reborrow.
- this.reborrow(place, size, fn_barrier, new_bor)?;
- let new_place = place.with_tag(new_bor);
+ this.reborrow(place, size, mutbl, new_tag, fn_barrier)?;
+ 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");
- // We immediately share it, to allow read accesses
- let two_phase_time = this.machine.stacked_borrows.increment_clock();
- let two_phase_bor = Borrow::Alias(Some(two_phase_time));
- this.reborrow(new_place, size, false /* fn_barrier */, two_phase_bor)?;
+ // 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.
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 tag_new_allocation(
- &mut self,
- id: AllocId,
- kind: MemoryKind<MiriMemoryKind>,
- ) -> Borrow {
- let this = self.eval_context_mut();
- let time = 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>
- this.machine.stacked_borrows.increment_clock()
- }
- _ => {
- // Nothing to do for everything else.
- return Borrow::default()
- }
- };
- // Make this the active borrow for this allocation.
- let alloc = this
- .memory_mut()
- .get_mut(id)
- .expect("this is a new allocation; it must still exist");
- let size = Size::from_bytes(alloc.bytes.len() as u64);
- alloc.extra.first_item(BorStackItem::Uniq(time), size);
- Borrow::Uniq(time)
- }
-
- /// Called for value-to-place conversion. `mutability` is `None` for raw pointers.
- ///
- /// Note that this does *not* mean that all this memory will actually get accessed/referenced!
- /// We could be in the middle of `&(*var).1`.
- fn ptr_dereference(
- &self,
- place: MPlaceTy<'tcx, Borrow>,
- size: Size,
- mutability: Option<Mutability>,
- ) -> EvalResult<'tcx> {
- let this = self.eval_context_ref();
- trace!(
- "ptr_dereference: Accessing {} reference for {:?} (pointee {})",
- if let Some(mutability) = mutability {
- format!("{:?}", mutability)
- } else {
- format!("raw")
- },
- place.ptr, place.layout.ty
- );
- let ptr = place.ptr.to_ptr()?;
- if mutability.is_none() {
- // No further checks on raw derefs -- only the access itself will be checked.
- return Ok(());
- }
-
- // Get the allocation
- let alloc = this.memory().get(ptr.alloc_id)?;
- alloc.check_bounds(this, ptr, size)?;
- // If we got here, we do some checking, *but* we leave the tag unchanged.
- if let Borrow::Alias(Some(_)) = ptr.tag {
- assert_eq!(mutability, Some(MutImmutable));
- // We need a frozen-sensitive check.
- this.visit_freeze_sensitive(place, size, |cur_ptr, size, frozen| {
- let kind = if frozen { RefKind::Frozen } else { RefKind::Raw };
- alloc.extra.deref(cur_ptr, size, kind)
- })?;
- } else {
- // Just treat this as one big chunk.
- let kind = if mutability == Some(MutMutable) { RefKind::Unique } else { RefKind::Raw };
- alloc.extra.deref(ptr, size, kind)?;
- }
-
- // All is good.
- Ok(())
- }
-
fn retag(
&mut self,
kind: RetagKind,
- place: PlaceTy<'tcx, Borrow>
+ place: PlaceTy<'tcx, Tag>
) -> EvalResult<'tcx> {
let this = self.eval_context_mut();
// Determine mutability and whether to add a barrier.
for
RetagVisitor<'ecx, 'a, 'mir, 'tcx>
{
- type V = MPlaceTy<'tcx, Borrow>;
+ type V = MPlaceTy<'tcx, Tag>;
#[inline(always)]
fn ecx(&mut self) -> &mut MiriEvalContext<'a, 'mir, 'tcx> {
}
// Primitives of reference type, that is the one thing we are interested in.
- fn visit_primitive(&mut self, place: MPlaceTy<'tcx, Borrow>) -> EvalResult<'tcx>
+ fn visit_primitive(&mut self, place: MPlaceTy<'tcx, Tag>) -> EvalResult<'tcx>
{
// Cannot use `builtin_deref` because that reports *immutable* for `Box`,
// making it useless.
projects / rust.git / commitdiff