Enum Provenance

pub enum Provenance {
    Concrete {
        alloc_id: AllocId,
        tag: BorTag,
    },
    Wildcard,
}

Pointer provenance.

Variants

Concrete

For pointers with concrete provenance. we exactly know which allocation they are attached to and what their borrow tag is.

Fields

alloc_id: AllocId

tag: BorTag

Borrow Tracker tag.

Wildcard

Pointers with wildcard provenance are created on int-to-ptr casts. According to the specification, we should at that point angelically “guess” a provenance that will make all future uses of this pointer work, if at all possible. Of course such a semantics cannot be actually implemented in Miri. So instead, we approximate this, erroring on the side of accepting too much code rather than rejecting correct code: a pointer with wildcard provenance “acts like” any previously exposed pointer. Each time it is used, we check whether some exposed pointer could have done what we want to do, and if the answer is yes then we allow the access. This allows too much code in two ways:

• The same wildcard pointer can “take the role” of multiple different exposed pointers on subsequent memory accesses.
• In the aliasing model, we don’t just have to know the borrow tag of the pointer used for the access, we also have to update the aliasing state – and that update can be very different depending on which borrow tag we pick! Stacked Borrows has support for this by switching to a stack that is only approximately known, i.e. we over-approximate the effect of using any exposed pointer for this access, and only keep information about the borrow stack that would be true with all possible choices.

Trait Implementations

impl Clone for Provenance

fn clone(&self) -> Provenance

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Provenance

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Hash for Provenance

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for Provenance

fn eq(&self, other: &Provenance) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Provenance for Provenance

const OFFSET_IS_ADDR: bool = true

We use absolute addresses in the offset of a StrictPointer.

const WILDCARD: Option<Self>

Miri implements wildcard provenance.

fn get_alloc_id(self) -> Option<AllocId>

If OFFSET_IS_ADDR == false, provenance must always be able to identify the allocation this ptr points to (i.e., this must return Some). Otherwise this function is best-effort (but must agree with Machine::ptr_get_alloc). (Identifying the offset in that allocation, however, is harder – use Memory::ptr_get_alloc for that.)

fn fmt(ptr: &Pointer<Self>, f: &mut Formatter<'_>) -> Result

Determines how a pointer should be printed.

fn join(left: Option<Self>, right: Option<Self>) -> Option<Self>

Defines the ‘join’ of provenance: what happens when doing a pointer load and different bytes have different provenance.

impl VisitProvenance for Provenance

fn visit_provenance(&self, visit: &mut VisitWith<'_>)

impl Copy for Provenance

impl Eq for Provenance

impl StructuralPartialEq for Provenance

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 16 bytes

Size for each variant:

• Concrete: 16 bytes
• Wildcard: 0 bytes