Struct Tree

pub struct Tree {
    pub(super) tag_mapping: UniKeyMap<BorTag>,
    pub(super) nodes: UniValMap<Node>,
    pub(super) rperms: RangeMap<UniValMap<LocationState>>,
    pub(super) root: UniIndex,
}

Tree structure with both parents and children since we want to be able to traverse the tree efficiently in both directions.

Fields

tag_mapping: UniKeyMap<BorTag>

Mapping from tags to keys. The key obtained can then be used in any of the UniValMap relative to this allocation, i.e. both the nodes and rperms of the same Tree. The parent-child relationship in Node is encoded in terms of these same keys, so traversing the entire tree needs exactly one access to tag_mapping.

nodes: UniValMap<Node>

All nodes of this tree.

rperms: RangeMap<UniValMap<LocationState>>

Maps a tag and a location to a perm, with possible lazy initialization.

NOTE: not all tags registered in nodes are necessarily in all ranges of rperms, because rperms is in part lazily initialized. Just because nodes.get(key) is Some(_) does not mean you can safely unwrap any perm.get(key).

We do uphold the fact that keys(perms) is a subset of keys(nodes)

root: UniIndex

The index of the root node.

Implementations

impl<'tcx> Tree

fn nth_parent(&self, tag: BorTag, nth_parent: u8) -> Option<BorTag>

Climb the tree to get the tag of a distant ancestor. Allows operations on tags that are unreachable by the program but still exist in the tree. Not guaranteed to perform consistently if provenance-gc=1.

pub fn give_pointer_debug_name( &mut self, tag: BorTag, nth_parent: u8, name: &str, ) -> InterpResult<'tcx>

Debug helper: assign name to tag.

pub fn is_allocation_of(&self, tag: BorTag) -> bool

Debug helper: determines if the tree contains a tag.

impl<'tcx> Tree

pub fn print_tree( &self, protected_tags: &FxHashMap<BorTag, ProtectorKind>, show_unnamed: bool, ) -> InterpResult<'tcx>

Display the contents of the tree.

impl Tree

pub fn new(root_tag: BorTag, size: Size, span: Span) -> Self

Create a new tree, with only a root pointer.

impl<'tcx> Tree

pub fn new_child( &mut self, parent_tag: BorTag, new_tag: BorTag, default_initial_perm: Permission, reborrow_range: AllocRange, span: Span, ) -> InterpResult<'tcx>

Insert a new tag in the tree

pub fn dealloc( &mut self, tag: BorTag, access_range: AllocRange, global: &RefCell<GlobalStateInner>, alloc_id: AllocId, span: Span, ) -> InterpResult<'tcx>

Deallocation requires

• a pointer that permits write accesses
• the absence of Strong Protectors anywhere in the allocation

pub fn perform_access( &mut self, tag: BorTag, access_range_and_kind: Option<(AllocRange, AccessKind, AccessCause)>, global: &RefCell<GlobalStateInner>, alloc_id: AllocId, span: Span, ) -> InterpResult<'tcx>

Map the per-node and per-location LocationState::perform_access to each location of the first component of access_range_and_kind, on every tag of the allocation.

If access_range_and_kind is None, this is interpreted as the special access that is applied on protector release:

• the access will be applied only to initialized locations of the allocation,
• it will not be visible to children,
• it will be recorded as a FnExit diagnostic access
• and it will be a read except if the location is Active, i.e. has been written to, in which case it will be a write.

LocationState::perform_access will take care of raising transition errors and updating the initialized status of each location, this traversal adds to that:

• inserting into the map locations that do not exist yet,
• trimming the traversal,
• recording the history.

impl Tree

Integration with the BorTag garbage collector

pub fn remove_unreachable_tags(&mut self, live_tags: &FxHashSet<BorTag>)

fn is_useless(&self, idx: UniIndex, live: &FxHashSet<BorTag>) -> bool

Checks if a node is useless and should be GC’ed. A node is useless if it has no children and also the tag is no longer live.

fn can_be_replaced_by_single_child( &self, idx: UniIndex, live: &FxHashSet<BorTag>, ) -> Option<UniIndex>

Checks whether a node can be replaced by its only child. If so, returns the index of said only child. If not, returns none.

fn remove_useless_node(&mut self, this: UniIndex)

Properly removes a node. The node to be removed should not otherwise be usable. It also should have no children, but this is not checked, so that nodes whose children were rotated somewhere else can be deleted without having to first modify them to clear that array.

fn remove_useless_children(&mut self, root: UniIndex, live: &FxHashSet<BorTag>)

Traverses the entire tree looking for useless tags. Removes from the tree all useless child nodes of root. It will not delete the root itself.

NOTE: This leaves in the middle of the tree tags that are unreachable but have reachable children. There is a potential for compacting the tree by reassigning children of dead tags to the nearest live parent, but it must be done with care not to remove UB.

Example: Consider the tree root - parent - child, with parent: Frozen and child: Reserved. This tree can exist. If we blindly delete parent and reassign child to be a direct child of root then Writes to child are now permitted whereas they were not when parent was still there.

impl<'tcx> Tree

pub fn new_allocation( id: AllocId, size: Size, state: &mut GlobalStateInner, _kind: MemoryKind, machine: &MiriMachine<'tcx>, ) -> Self

Create a new allocation, i.e. a new tree

pub fn before_memory_access( &mut self, access_kind: AccessKind, alloc_id: AllocId, prov: ProvenanceExtra, range: AllocRange, machine: &MiriMachine<'tcx>, ) -> InterpResult<'tcx>

Check that an access on the entire range is permitted, and update the tree.

pub fn before_memory_deallocation( &mut self, alloc_id: AllocId, prov: ProvenanceExtra, size: Size, machine: &MiriMachine<'tcx>, ) -> InterpResult<'tcx>

Check that this pointer has permission to deallocate this range.

pub fn expose_tag(&mut self, _tag: BorTag)

pub fn release_protector( &mut self, machine: &MiriMachine<'tcx>, global: &RefCell<GlobalStateInner>, tag: BorTag, alloc_id: AllocId, ) -> InterpResult<'tcx>

A tag just lost its protector.

This emits a special kind of access that is only applied to initialized locations, as a protection against other tags not having been made aware of the existence of this protector.

Trait Implementations

impl Clone for Tree

fn clone(&self) -> Tree

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for Tree

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

Formats the value using the given formatter.

impl VisitProvenance for Tree

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

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: 112 bytes