1a0493946d
This change makes the storage of `Table` more internally consistent. Elements are stored as raw pointers for both static and dynamic table storage. Explicitly storing elements as pointers removes assumptions being made by the pooling allocator in terms of the size and default representation of the elements. However, care must be made to properly clone externrefs for table operations.
1256 lines
47 KiB
Rust
1256 lines
47 KiB
Rust
//! # `VMExternRef`
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//!
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//! `VMExternRef` is a reference-counted box for any kind of data that is
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//! external and opaque to running Wasm. Sometimes it might hold a Wasmtime
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//! thing, other times it might hold something from a Wasmtime embedder and is
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//! opaque even to us. It is morally equivalent to `Rc<dyn Any>` in Rust, but
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//! additionally always fits in a pointer-sized word. `VMExternRef` is
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//! non-nullable, but `Option<VMExternRef>` is a null pointer.
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//!
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//! The one part of `VMExternRef` that can't ever be opaque to us is the
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//! reference count. Even when we don't know what's inside an `VMExternRef`, we
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//! need to be able to manipulate its reference count as we add and remove
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//! references to it. And we need to do this from compiled Wasm code, so it must
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//! be `repr(C)`!
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//!
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//! ## Memory Layout
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//!
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//! `VMExternRef` itself is just a pointer to an `VMExternData`, which holds the
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//! opaque, boxed value, its reference count, and its vtable pointer.
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//!
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//! The `VMExternData` struct is *preceded* by the dynamically-sized value boxed
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//! up and referenced by one or more `VMExternRef`s:
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//!
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//! ```text
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//! ,-------------------------------------------------------.
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//! | |
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//! V |
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//! +----------------------------+-----------+-----------+ |
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//! | dynamically-sized value... | ref_count | value_ptr |---'
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//! +----------------------------+-----------+-----------+
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//! | VMExternData |
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//! +-----------------------+
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//! ^
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//! +-------------+ |
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//! | VMExternRef |-------------------+
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//! +-------------+ |
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//! |
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//! +-------------+ |
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//! | VMExternRef |-------------------+
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//! +-------------+ |
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//! |
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//! ... ===
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//! |
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//! +-------------+ |
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//! | VMExternRef |-------------------'
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//! +-------------+
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//! ```
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//!
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//! The `value_ptr` member always points backwards to the start of the
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//! dynamically-sized value (which is also the start of the heap allocation for
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//! this value-and-`VMExternData` pair). Because it is a `dyn` pointer, it is
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//! fat, and also points to the value's `Any` vtable.
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//!
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//! The boxed value and the `VMExternRef` footer are held a single heap
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//! allocation. The layout described above is used to make satisfying the
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//! value's alignment easy: we just need to ensure that the heap allocation used
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//! to hold everything satisfies its alignment. It also ensures that we don't
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//! need a ton of excess padding between the `VMExternData` and the value for
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//! values with large alignment.
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//!
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//! ## Reference Counting, Wasm Functions, and Garbage Collection
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//!
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//! For host VM code, we use plain reference counting, where cloning increments
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//! the reference count, and dropping decrements it. We can avoid many of the
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//! on-stack increment/decrement operations that typically plague the
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//! performance of reference counting via Rust's ownership and borrowing system.
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//! Moving a `VMExternRef` avoids mutating its reference count, and borrowing it
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//! either avoids the reference count increment or delays it until if/when the
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//! `VMExternRef` is cloned.
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//!
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//! When passing a `VMExternRef` into compiled Wasm code, we don't want to do
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//! reference count mutations for every compiled `local.{get,set}`, nor for
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//! every function call. Therefore, we use a variation of **deferred reference
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//! counting**, where we only mutate reference counts when storing
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//! `VMExternRef`s somewhere that outlives the activation: into a global or
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//! table. Simultaneously, we over-approximate the set of `VMExternRef`s that
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//! are inside Wasm function activations. Periodically, we walk the stack at GC
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//! safe points, and use stack map information to precisely identify the set of
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//! `VMExternRef`s inside Wasm activations. Then we take the difference between
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//! this precise set and our over-approximation, and decrement the reference
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//! count for each of the `VMExternRef`s that are in our over-approximation but
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//! not in the precise set. Finally, the over-approximation is replaced with the
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//! precise set.
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//!
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//! The `VMExternRefActivationsTable` implements the over-approximized set of
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//! `VMExternRef`s referenced by Wasm activations. Calling a Wasm function and
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//! passing it a `VMExternRef` moves the `VMExternRef` into the table, and the
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//! compiled Wasm function logically "borrows" the `VMExternRef` from the
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//! table. Similarly, `global.get` and `table.get` operations clone the gotten
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//! `VMExternRef` into the `VMExternRefActivationsTable` and then "borrow" the
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//! reference out of the table.
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//!
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//! When a `VMExternRef` is returned to host code from a Wasm function, the host
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//! increments the reference count (because the reference is logically
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//! "borrowed" from the `VMExternRefActivationsTable` and the reference count
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//! from the table will be dropped at the next GC).
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//!
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//! For more general information on deferred reference counting, see *An
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//! Examination of Deferred Reference Counting and Cycle Detection* by Quinane:
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//! <https://openresearch-repository.anu.edu.au/bitstream/1885/42030/2/hon-thesis.pdf>
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use std::alloc::Layout;
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use std::any::Any;
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use std::cell::{Cell, RefCell, UnsafeCell};
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use std::cmp::Ordering;
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use std::collections::BTreeMap;
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use std::collections::HashSet;
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use std::hash::{Hash, Hasher};
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use std::mem;
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use std::ops::Deref;
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use std::ptr::{self, NonNull};
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use std::rc::Rc;
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use wasmtime_environ::{ir::StackMap, StackMapInformation};
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/// An external reference to some opaque data.
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///
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/// `VMExternRef`s dereference to their underlying opaque data as `dyn Any`.
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///
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/// Unlike the `externref` in the Wasm spec, `VMExternRef`s are non-nullable,
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/// and always point to a valid value. You may use `Option<VMExternRef>` to
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/// represent nullable references, and `Option<VMExternRef>` is guaranteed to
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/// have the same size and alignment as a raw pointer, with `None` represented
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/// with the null pointer.
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///
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/// `VMExternRef`s are reference counted, so cloning is a cheap, shallow
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/// operation. It also means they are inherently shared, so you may not get a
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/// mutable, exclusive reference to their inner contents, only a shared,
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/// immutable reference. You may use interior mutability with `RefCell` or
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/// `Mutex` to work around this restriction, if necessary.
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///
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/// `VMExternRef`s have pointer-equality semantics, not structural-equality
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/// semantics. Given two `VMExternRef`s `a` and `b`, `a == b` only if `a` and
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/// `b` point to the same allocation. `a` and `b` are considered not equal, even
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/// if `a` and `b` are two different identical copies of the same data, if they
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/// are in two different allocations. The hashing and ordering implementations
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/// also only operate on the pointer.
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///
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/// # Example
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///
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/// ```
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/// # fn foo() -> Result<(), Box<dyn std::error::Error>> {
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/// use std::cell::RefCell;
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/// use wasmtime_runtime::VMExternRef;
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///
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/// // Open a file. Wasm doesn't know about files, but we can let Wasm instances
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/// // work with files via opaque `externref` handles.
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/// let file = std::fs::File::create("some/file/path")?;
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///
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/// // Wrap the file up as an `VMExternRef` that can be passed to Wasm.
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/// let extern_ref_to_file = VMExternRef::new(RefCell::new(file));
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///
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/// // `VMExternRef`s dereference to `dyn Any`, so you can use `Any` methods to
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/// // perform runtime type checks and downcasts.
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///
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/// assert!(extern_ref_to_file.is::<RefCell<std::fs::File>>());
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/// assert!(!extern_ref_to_file.is::<String>());
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///
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/// if let Some(file) = extern_ref_to_file.downcast_ref::<RefCell<std::fs::File>>() {
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/// use std::io::Write;
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/// let mut file = file.borrow_mut();
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/// writeln!(&mut file, "Hello, `VMExternRef`!")?;
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/// }
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/// # Ok(())
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/// # }
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/// ```
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#[derive(Debug)]
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#[repr(transparent)]
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pub struct VMExternRef(NonNull<VMExternData>);
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#[repr(C)]
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pub(crate) struct VMExternData {
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// Implicit, dynamically-sized member that always preceded an
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// `VMExternData`.
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//
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// value: [u8],
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//
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/// The reference count for this `VMExternData` and value. When it reaches
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/// zero, we can safely destroy the value and free this heap
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/// allocation. This is an `UnsafeCell`, rather than plain `Cell`, because
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/// it can be modified by compiled Wasm code.
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///
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/// Note: this field's offset must be kept in sync with
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/// `wasmtime_environ::VMOffsets::vm_extern_data_ref_count()` which is
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/// currently always zero.
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ref_count: UnsafeCell<usize>,
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/// Always points to the implicit, dynamically-sized `value` member that
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/// precedes this `VMExternData`.
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value_ptr: NonNull<dyn Any>,
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}
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impl Clone for VMExternRef {
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#[inline]
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fn clone(&self) -> VMExternRef {
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self.extern_data().increment_ref_count();
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VMExternRef(self.0)
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}
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}
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impl Drop for VMExternRef {
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#[inline]
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fn drop(&mut self) {
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let data = self.extern_data();
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data.decrement_ref_count();
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if data.get_ref_count() == 0 {
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// Drop our live reference to `data` before we drop it itself.
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drop(data);
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unsafe {
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VMExternData::drop_and_dealloc(self.0);
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}
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}
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}
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}
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impl VMExternData {
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/// Get the `Layout` for a value with the given size and alignment, and the
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/// offset within that layout where the `VMExternData` footer resides.
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///
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/// This doesn't take a `value: &T` because `VMExternRef::new_with` hasn't
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/// constructed a `T` value yet, and it isn't generic over `T` because
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/// `VMExternData::drop_and_dealloc` doesn't know what `T` to use, and has
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/// to use `std::mem::{size,align}_of_val` instead.
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unsafe fn layout_for(value_size: usize, value_align: usize) -> (Layout, usize) {
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let extern_data_size = mem::size_of::<VMExternData>();
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let extern_data_align = mem::align_of::<VMExternData>();
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let value_and_padding_size = round_up_to_align(value_size, extern_data_align).unwrap();
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let alloc_align = std::cmp::max(value_align, extern_data_align);
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let alloc_size = value_and_padding_size + extern_data_size;
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debug_assert!(Layout::from_size_align(alloc_size, alloc_align).is_ok());
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(
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Layout::from_size_align_unchecked(alloc_size, alloc_align),
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value_and_padding_size,
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)
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}
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/// Drop the inner value and then free this `VMExternData` heap allocation.
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pub(crate) unsafe fn drop_and_dealloc(mut data: NonNull<VMExternData>) {
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// Note: we introduce a block scope so that we drop the live
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// reference to the data before we free the heap allocation it
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// resides within after this block.
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let (alloc_ptr, layout) = {
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let data = data.as_mut();
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debug_assert_eq!(data.get_ref_count(), 0);
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// Same thing, but for the dropping the reference to `value` before
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// we drop it itself.
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let (layout, _) = {
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let value = data.value_ptr.as_ref();
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Self::layout_for(mem::size_of_val(value), mem::align_of_val(value))
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};
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ptr::drop_in_place(data.value_ptr.as_ptr());
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let alloc_ptr = data.value_ptr.cast::<u8>();
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(alloc_ptr, layout)
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};
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ptr::drop_in_place(data.as_ptr());
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std::alloc::dealloc(alloc_ptr.as_ptr(), layout);
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}
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#[inline]
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fn get_ref_count(&self) -> usize {
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unsafe { *self.ref_count.get() }
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}
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#[inline]
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fn increment_ref_count(&self) {
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unsafe {
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let count = self.ref_count.get();
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*count += 1;
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}
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}
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#[inline]
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fn decrement_ref_count(&self) {
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unsafe {
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let count = self.ref_count.get();
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*count -= 1;
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}
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}
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}
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#[inline]
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fn round_up_to_align(n: usize, align: usize) -> Option<usize> {
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debug_assert!(align.is_power_of_two());
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let align_minus_one = align - 1;
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Some(n.checked_add(align_minus_one)? & !align_minus_one)
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}
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impl VMExternRef {
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/// Wrap the given value inside an `VMExternRef`.
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pub fn new<T>(value: T) -> VMExternRef
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where
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T: 'static + Any,
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{
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VMExternRef::new_with(|| value)
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}
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/// Construct a new `VMExternRef` in place by invoking `make_value`.
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pub fn new_with<T>(make_value: impl FnOnce() -> T) -> VMExternRef
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where
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T: 'static + Any,
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{
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unsafe {
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let (layout, footer_offset) =
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VMExternData::layout_for(mem::size_of::<T>(), mem::align_of::<T>());
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let alloc_ptr = std::alloc::alloc(layout);
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let alloc_ptr = NonNull::new(alloc_ptr).unwrap_or_else(|| {
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std::alloc::handle_alloc_error(layout);
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});
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let value_ptr = alloc_ptr.cast::<T>();
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ptr::write(value_ptr.as_ptr(), make_value());
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let value_ref: &T = value_ptr.as_ref();
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let value_ref: &dyn Any = value_ref as _;
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let value_ptr: *const dyn Any = value_ref as _;
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let value_ptr: *mut dyn Any = value_ptr as _;
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let value_ptr = NonNull::new_unchecked(value_ptr);
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let extern_data_ptr =
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alloc_ptr.cast::<u8>().as_ptr().add(footer_offset) as *mut VMExternData;
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ptr::write(
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extern_data_ptr,
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VMExternData {
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ref_count: UnsafeCell::new(1),
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value_ptr,
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},
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);
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VMExternRef(NonNull::new_unchecked(extern_data_ptr))
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}
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}
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/// Turn this `VMExternRef` into a raw, untyped pointer.
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///
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/// Unlike `into_raw`, this does not consume and forget `self`. It is *not*
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/// safe to use `from_raw` on pointers returned from this method; only use
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/// `clone_from_raw`!
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///
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/// Nor does this method increment the reference count. You must ensure
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/// that `self` (or some other clone of `self`) stays alive until
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/// `clone_from_raw` is called.
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pub fn as_raw(&self) -> *mut u8 {
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let ptr = self.0.cast::<u8>().as_ptr();
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ptr
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}
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/// Consume this `VMExternRef` into a raw, untyped pointer.
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///
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|
/// # Safety
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///
|
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/// This method forgets self, so it is possible to create a leak of the
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/// underlying reference counted data if not used carefully.
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///
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/// Use `from_raw` to recreate the `VMExternRef`.
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pub unsafe fn into_raw(self) -> *mut u8 {
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let ptr = self.0.cast::<u8>().as_ptr();
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std::mem::forget(self);
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ptr
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}
|
|
|
|
/// Recreate a `VMExternRef` from a pointer returned from a previous call to
|
|
/// `as_raw`.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// Unlike `clone_from_raw`, this does not increment the reference count of the
|
|
/// underlying data. It is not safe to continue to use the pointer passed to this
|
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/// function.
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|
pub unsafe fn from_raw(ptr: *mut u8) -> Self {
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debug_assert!(!ptr.is_null());
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VMExternRef(NonNull::new_unchecked(ptr).cast())
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|
}
|
|
|
|
/// Recreate a `VMExternRef` from a pointer returned from a previous call to
|
|
/// `as_raw`.
|
|
///
|
|
/// # Safety
|
|
///
|
|
/// Wildly unsafe to use with anything other than the result of a previous
|
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/// `as_raw` call!
|
|
///
|
|
/// Additionally, it is your responsibility to ensure that this raw
|
|
/// `VMExternRef`'s reference count has not dropped to zero. Failure to do
|
|
/// so will result in use after free!
|
|
pub unsafe fn clone_from_raw(ptr: *mut u8) -> Self {
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|
debug_assert!(!ptr.is_null());
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let x = VMExternRef(NonNull::new_unchecked(ptr).cast());
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x.extern_data().increment_ref_count();
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x
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}
|
|
|
|
/// Get the strong reference count for this `VMExternRef`.
|
|
pub fn strong_count(&self) -> usize {
|
|
self.extern_data().get_ref_count()
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|
}
|
|
|
|
#[inline]
|
|
fn extern_data(&self) -> &VMExternData {
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unsafe { self.0.as_ref() }
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}
|
|
}
|
|
|
|
/// Methods that would normally be trait implementations, but aren't to avoid
|
|
/// potential footguns around `VMExternRef`'s pointer-equality semantics.
|
|
///
|
|
/// Note that none of these methods are on `&self`, they all require a
|
|
/// fully-qualified `VMExternRef::foo(my_ref)` invocation.
|
|
impl VMExternRef {
|
|
/// Check whether two `VMExternRef`s point to the same inner allocation.
|
|
///
|
|
/// Note that this uses pointer-equality semantics, not structural-equality
|
|
/// semantics, and so only pointers are compared, and doesn't use any `Eq`
|
|
/// or `PartialEq` implementation of the pointed-to values.
|
|
#[inline]
|
|
pub fn eq(a: &Self, b: &Self) -> bool {
|
|
ptr::eq(a.0.as_ptr() as *const _, b.0.as_ptr() as *const _)
|
|
}
|
|
|
|
/// Hash a given `VMExternRef`.
|
|
///
|
|
/// Note that this just hashes the pointer to the inner value, it does *not*
|
|
/// use the inner value's `Hash` implementation (if any).
|
|
#[inline]
|
|
pub fn hash<H>(externref: &Self, hasher: &mut H)
|
|
where
|
|
H: Hasher,
|
|
{
|
|
ptr::hash(externref.0.as_ptr() as *const _, hasher);
|
|
}
|
|
|
|
/// Compare two `VMExternRef`s.
|
|
///
|
|
/// Note that this uses pointer-equality semantics, not structural-equality
|
|
/// semantics, and so only pointers are compared, and doesn't use any `Cmp`
|
|
/// or `PartialCmp` implementation of the pointed-to values.
|
|
#[inline]
|
|
pub fn cmp(a: &Self, b: &Self) -> Ordering {
|
|
let a = a.0.as_ptr() as usize;
|
|
let b = b.0.as_ptr() as usize;
|
|
a.cmp(&b)
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|
}
|
|
}
|
|
|
|
impl Deref for VMExternRef {
|
|
type Target = dyn Any;
|
|
|
|
fn deref(&self) -> &dyn Any {
|
|
unsafe { self.extern_data().value_ptr.as_ref() }
|
|
}
|
|
}
|
|
|
|
/// A wrapper around a `VMExternRef` that implements `Eq` and `Hash` with
|
|
/// pointer semantics.
|
|
///
|
|
/// We use this so that we can morally put `VMExternRef`s inside of `HashSet`s
|
|
/// even though they don't implement `Eq` and `Hash` to avoid foot guns.
|
|
#[derive(Clone)]
|
|
struct VMExternRefWithTraits(VMExternRef);
|
|
|
|
impl Hash for VMExternRefWithTraits {
|
|
fn hash<H>(&self, hasher: &mut H)
|
|
where
|
|
H: Hasher,
|
|
{
|
|
VMExternRef::hash(&self.0, hasher)
|
|
}
|
|
}
|
|
|
|
impl PartialEq for VMExternRefWithTraits {
|
|
fn eq(&self, other: &Self) -> bool {
|
|
VMExternRef::eq(&self.0, &other.0)
|
|
}
|
|
}
|
|
|
|
impl Eq for VMExternRefWithTraits {}
|
|
|
|
type TableElem = UnsafeCell<Option<VMExternRef>>;
|
|
|
|
/// A table that over-approximizes the set of `VMExternRef`s that any Wasm
|
|
/// activation on this thread is currently using.
|
|
///
|
|
/// Under the covers, this is a simple bump allocator that allows duplicate
|
|
/// entries. Deduplication happens at GC time.
|
|
#[repr(C)]
|
|
pub struct VMExternRefActivationsTable {
|
|
/// Bump-allocation finger within the `chunk`.
|
|
///
|
|
/// NB: this is an `UnsafeCell` because it is written to by compiled Wasm
|
|
/// code.
|
|
next: UnsafeCell<NonNull<TableElem>>,
|
|
|
|
/// Pointer to just after the `chunk`.
|
|
///
|
|
/// This is *not* within the current chunk and therefore is not a valid
|
|
/// place to insert a reference!
|
|
end: NonNull<TableElem>,
|
|
|
|
/// Bump allocation chunk that stores fast-path insertions.
|
|
chunk: Box<[TableElem]>,
|
|
|
|
/// When unioned with `chunk`, this is an over-approximation of the GC roots
|
|
/// on the stack, inside Wasm frames.
|
|
///
|
|
/// This is used by slow-path insertion, and when a GC cycle finishes, is
|
|
/// re-initialized to the just-discovered precise set of stack roots (which
|
|
/// immediately becomes an over-approximation again as soon as Wasm runs and
|
|
/// potentially drops references).
|
|
over_approximated_stack_roots: RefCell<HashSet<VMExternRefWithTraits>>,
|
|
|
|
/// The precise set of on-stack, inside-Wasm GC roots that we discover via
|
|
/// walking the stack and interpreting stack maps.
|
|
///
|
|
/// This is *only* used inside the `gc` function, and is empty otherwise. It
|
|
/// is just part of this struct so that we can reuse the allocation, rather
|
|
/// than create a new hash set every GC.
|
|
precise_stack_roots: RefCell<HashSet<VMExternRefWithTraits>>,
|
|
|
|
/// A pointer to a `u8` on the youngest host stack frame before we called
|
|
/// into Wasm for the first time. When walking the stack in garbage
|
|
/// collection, if we don't find this frame, then we failed to walk every
|
|
/// Wasm stack frame, which means we failed to find all on-stack,
|
|
/// inside-a-Wasm-frame roots, and doing a GC could lead to freeing one of
|
|
/// those missed roots, and use after free.
|
|
stack_canary: Cell<Option<NonNull<u8>>>,
|
|
}
|
|
|
|
impl VMExternRefActivationsTable {
|
|
const CHUNK_SIZE: usize = 4096 / mem::size_of::<usize>();
|
|
|
|
/// Create a new `VMExternRefActivationsTable`.
|
|
pub fn new() -> Self {
|
|
let chunk = Self::new_chunk(Self::CHUNK_SIZE);
|
|
let next = chunk.as_ptr() as *mut TableElem;
|
|
let end = unsafe { next.add(chunk.len()) };
|
|
|
|
VMExternRefActivationsTable {
|
|
next: UnsafeCell::new(NonNull::new(next).unwrap()),
|
|
end: NonNull::new(end).unwrap(),
|
|
chunk,
|
|
over_approximated_stack_roots: RefCell::new(HashSet::with_capacity(Self::CHUNK_SIZE)),
|
|
precise_stack_roots: RefCell::new(HashSet::with_capacity(Self::CHUNK_SIZE)),
|
|
stack_canary: Cell::new(None),
|
|
}
|
|
}
|
|
|
|
fn new_chunk(size: usize) -> Box<[UnsafeCell<Option<VMExternRef>>]> {
|
|
assert!(size >= Self::CHUNK_SIZE);
|
|
(0..size).map(|_| UnsafeCell::new(None)).collect()
|
|
}
|
|
|
|
/// Try and insert a `VMExternRef` into this table.
|
|
///
|
|
/// This is a fast path that only succeeds when the bump chunk has the
|
|
/// capacity for the requested insertion.
|
|
///
|
|
/// If the insertion fails, then the `VMExternRef` is given back. Callers
|
|
/// may attempt a GC to free up space and try again, or may call
|
|
/// `insert_slow_path` to infallibly insert the reference (potentially
|
|
/// allocating additional space in the table to hold it).
|
|
#[inline]
|
|
pub fn try_insert(&self, externref: VMExternRef) -> Result<(), VMExternRef> {
|
|
unsafe {
|
|
let next = *self.next.get();
|
|
if next == self.end {
|
|
return Err(externref);
|
|
}
|
|
|
|
debug_assert!(
|
|
(*next.as_ref().get()).is_none(),
|
|
"slots >= the `next` bump finger are always `None`"
|
|
);
|
|
ptr::write(next.as_ptr(), UnsafeCell::new(Some(externref)));
|
|
|
|
let next = NonNull::new_unchecked(next.as_ptr().add(1));
|
|
debug_assert!(next <= self.end);
|
|
*self.next.get() = next;
|
|
|
|
Ok(())
|
|
}
|
|
}
|
|
|
|
/// Insert a reference into the table, falling back on a GC to clear up
|
|
/// space if the table is already full.
|
|
///
|
|
/// # Unsafety
|
|
///
|
|
/// The same as `gc`.
|
|
#[inline]
|
|
pub unsafe fn insert_with_gc(
|
|
&self,
|
|
externref: VMExternRef,
|
|
stack_maps_registry: &StackMapRegistry,
|
|
) {
|
|
if let Err(externref) = self.try_insert(externref) {
|
|
self.gc_and_insert_slow(externref, stack_maps_registry);
|
|
}
|
|
}
|
|
|
|
#[inline(never)]
|
|
unsafe fn gc_and_insert_slow(
|
|
&self,
|
|
externref: VMExternRef,
|
|
stack_maps_registry: &StackMapRegistry,
|
|
) {
|
|
gc(stack_maps_registry, self);
|
|
|
|
// Might as well insert right into the hash set, rather than the bump
|
|
// chunk, since we are already on a slow path and we get de-duplication
|
|
// this way.
|
|
let mut roots = self.over_approximated_stack_roots.borrow_mut();
|
|
roots.insert(VMExternRefWithTraits(externref));
|
|
}
|
|
|
|
fn num_filled_in_bump_chunk(&self) -> usize {
|
|
let next = unsafe { *self.next.get() };
|
|
let bytes_unused = (self.end.as_ptr() as usize) - (next.as_ptr() as usize);
|
|
let slots_unused = bytes_unused / mem::size_of::<TableElem>();
|
|
self.chunk.len().saturating_sub(slots_unused)
|
|
}
|
|
|
|
fn elements(&self, mut f: impl FnMut(&VMExternRef)) {
|
|
let roots = self.over_approximated_stack_roots.borrow();
|
|
for elem in roots.iter() {
|
|
f(&elem.0);
|
|
}
|
|
|
|
// The bump chunk is not all the way full, so we only iterate over its
|
|
// filled-in slots.
|
|
let num_filled = self.num_filled_in_bump_chunk();
|
|
for slot in self.chunk.iter().take(num_filled) {
|
|
if let Some(elem) = unsafe { &*slot.get() } {
|
|
f(elem);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn insert_precise_stack_root(
|
|
precise_stack_roots: &mut HashSet<VMExternRefWithTraits>,
|
|
root: NonNull<VMExternData>,
|
|
) {
|
|
let root = unsafe { VMExternRef::clone_from_raw(root.as_ptr() as *mut _) };
|
|
precise_stack_roots.insert(VMExternRefWithTraits(root));
|
|
}
|
|
|
|
/// Sweep the bump allocation table after we've discovered our precise stack
|
|
/// roots.
|
|
fn sweep(&self, precise_stack_roots: &mut HashSet<VMExternRefWithTraits>) {
|
|
// Swap out the over-approximated set so we can distinguish between the
|
|
// over-approximation before we started sweeping, and any new elements
|
|
// we might insert into the table because of re-entering Wasm via an
|
|
// `externref`'s destructor. The new elements must be kept alive for
|
|
// memory safety, but we keep this set around because we likely want to
|
|
// reuse its allocation/capacity for the new `precise_stack_roots` in
|
|
// the next GC cycle.
|
|
let mut old_over_approximated = mem::replace(
|
|
&mut *self.over_approximated_stack_roots.borrow_mut(),
|
|
Default::default(),
|
|
);
|
|
|
|
// Sweep our bump chunk.
|
|
//
|
|
// Just in case an `externref` destructor calls back into Wasm, passing
|
|
// more `externref`s into that Wasm, which requires the `externref`s to
|
|
// be inserted into this `VMExternRefActivationsTable`, make sure `next
|
|
// == end` so that they go into the over-approximation hash set.
|
|
let num_filled = self.num_filled_in_bump_chunk();
|
|
unsafe {
|
|
*self.next.get() = self.end;
|
|
}
|
|
for slot in self.chunk.iter().take(num_filled) {
|
|
unsafe {
|
|
*slot.get() = None;
|
|
}
|
|
}
|
|
debug_assert!(
|
|
self.chunk
|
|
.iter()
|
|
.all(|slot| unsafe { (*slot.get()).as_ref().is_none() }),
|
|
"after sweeping the bump chunk, all slots should be `None`"
|
|
);
|
|
|
|
// Reset our `next` finger to the start of the bump allocation chunk.
|
|
unsafe {
|
|
let next = self.chunk.as_ptr() as *mut TableElem;
|
|
debug_assert!(!next.is_null());
|
|
*self.next.get() = NonNull::new_unchecked(next);
|
|
}
|
|
|
|
// The current `precise_stack_roots` becomes our new over-appoximated
|
|
// set for the next GC cycle.
|
|
let mut over_approximated = self.over_approximated_stack_roots.borrow_mut();
|
|
mem::swap(&mut *precise_stack_roots, &mut *over_approximated);
|
|
|
|
// And finally, the new `precise_stack_roots` should be cleared and
|
|
// remain empty until the next GC cycle.
|
|
//
|
|
// However, if an `externref` destructor called re-entered Wasm with
|
|
// more `externref`s, then the temp over-approximated set we were using
|
|
// during sweeping (now `precise_stack_roots`) is not empty, and we need
|
|
// to keep its references alive in our new over-approximated set.
|
|
over_approximated.extend(precise_stack_roots.drain());
|
|
|
|
// If we didn't re-enter Wasm during destructors (likely),
|
|
// `precise_stack_roots` has zero capacity, and the old
|
|
// over-approximated has a bunch of capacity. Reuse whichever set has
|
|
// most capacity.
|
|
if old_over_approximated.capacity() > precise_stack_roots.capacity() {
|
|
old_over_approximated.clear();
|
|
*precise_stack_roots = old_over_approximated;
|
|
}
|
|
}
|
|
|
|
/// Set the stack canary around a call into Wasm.
|
|
///
|
|
/// The return value should not be dropped until after the Wasm call has
|
|
/// returned.
|
|
///
|
|
/// While this method is always safe to call (or not call), it is unsafe to
|
|
/// call the `wasmtime_runtime::gc` function unless this method is called at
|
|
/// the proper times and its return value properly outlives its Wasm call.
|
|
///
|
|
/// For `gc` to be safe, this is only *strictly required* to surround the
|
|
/// oldest host-->Wasm stack frame transition on this thread, but repeatedly
|
|
/// calling it is idempotent and cheap, so it is recommended to call this
|
|
/// for every host-->Wasm call.
|
|
///
|
|
/// # Example
|
|
///
|
|
/// ```no_run
|
|
/// use wasmtime_runtime::*;
|
|
///
|
|
/// # let get_table_from_somewhere = || unimplemented!();
|
|
/// let table: &VMExternRefActivationsTable = get_table_from_somewhere();
|
|
///
|
|
/// // Set the canary before a Wasm call. The canary should always be a
|
|
/// // local on the stack.
|
|
/// let canary = 0;
|
|
/// let auto_reset_canary = table.set_stack_canary(&canary);
|
|
///
|
|
/// // Do the call into Wasm.
|
|
/// # let call_into_wasm = || unimplemented!();
|
|
/// call_into_wasm();
|
|
///
|
|
/// // Only drop the value returned by `set_stack_canary` after the Wasm
|
|
/// // call has returned.
|
|
/// drop(auto_reset_canary);
|
|
/// ```
|
|
pub fn set_stack_canary<'a>(&'a self, canary: &u8) -> impl Drop + 'a {
|
|
let should_reset = if self.stack_canary.get().is_none() {
|
|
let canary = canary as *const u8 as *mut u8;
|
|
self.stack_canary.set(Some(unsafe {
|
|
debug_assert!(!canary.is_null());
|
|
NonNull::new_unchecked(canary)
|
|
}));
|
|
true
|
|
} else {
|
|
false
|
|
};
|
|
|
|
return AutoResetCanary {
|
|
table: self,
|
|
should_reset,
|
|
};
|
|
|
|
struct AutoResetCanary<'a> {
|
|
table: &'a VMExternRefActivationsTable,
|
|
should_reset: bool,
|
|
}
|
|
|
|
impl Drop for AutoResetCanary<'_> {
|
|
fn drop(&mut self) {
|
|
if self.should_reset {
|
|
debug_assert!(self.table.stack_canary.get().is_some());
|
|
self.table.stack_canary.set(None);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// A registry of stack maps for currently active Wasm modules.
|
|
#[derive(Default)]
|
|
pub struct StackMapRegistry {
|
|
inner: RefCell<StackMapRegistryInner>,
|
|
}
|
|
|
|
#[derive(Default)]
|
|
struct StackMapRegistryInner {
|
|
/// A map from the highest pc in a module, to its stack maps.
|
|
///
|
|
/// For details, see the comment above `GlobalFrameInfo::ranges`.
|
|
ranges: BTreeMap<usize, ModuleStackMaps>,
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
struct ModuleStackMaps {
|
|
/// The range of PCs that this module covers. Different modules must always
|
|
/// have distinct ranges.
|
|
range: std::ops::Range<usize>,
|
|
|
|
/// A map from a PC in this module (that is a GC safepoint) to its
|
|
/// associated stack map. If `None` then it means that the PC is the start
|
|
/// of a range which has no stack map.
|
|
pc_to_stack_map: Vec<(usize, Option<Rc<StackMap>>)>,
|
|
}
|
|
|
|
impl StackMapRegistry {
|
|
/// Register the stack maps for a given module.
|
|
///
|
|
/// The stack maps should be given as an iterator over a function's PC range
|
|
/// in memory (that is, where the JIT actually allocated and emitted the
|
|
/// function's code at), and the stack maps and code offsets within that
|
|
/// range for each of its GC safepoints.
|
|
pub fn register_stack_maps<'a>(
|
|
&self,
|
|
stack_maps: impl IntoIterator<Item = (std::ops::Range<usize>, &'a [StackMapInformation])>,
|
|
) {
|
|
let mut min = usize::max_value();
|
|
let mut max = 0;
|
|
let mut pc_to_stack_map = vec![];
|
|
let mut last_is_none_marker = true;
|
|
|
|
for (range, infos) in stack_maps {
|
|
let len = range.end - range.start;
|
|
|
|
min = std::cmp::min(min, range.start);
|
|
max = std::cmp::max(max, range.end);
|
|
|
|
// Add a marker between functions indicating that this function's pc
|
|
// starts with no stack map so when our binary search later on finds
|
|
// a pc between the start of the function and the function's first
|
|
// stack map it doesn't think the previous stack map is our stack
|
|
// map.
|
|
//
|
|
// We skip this if the previous entry pushed was also a `None`
|
|
// marker, in which case the starting pc already has no stack map.
|
|
// This is also skipped if the first `code_offset` is zero since
|
|
// what we'll push applies for the first pc anyway.
|
|
if !last_is_none_marker && (infos.is_empty() || infos[0].code_offset > 0) {
|
|
pc_to_stack_map.push((range.start, None));
|
|
last_is_none_marker = true;
|
|
}
|
|
|
|
for info in infos {
|
|
assert!((info.code_offset as usize) < len);
|
|
pc_to_stack_map.push((
|
|
range.start + (info.code_offset as usize),
|
|
Some(Rc::new(info.stack_map.clone())),
|
|
));
|
|
last_is_none_marker = false;
|
|
}
|
|
}
|
|
|
|
if pc_to_stack_map.is_empty() {
|
|
// Nothing to register.
|
|
return;
|
|
}
|
|
|
|
let module_stack_maps = ModuleStackMaps {
|
|
range: min..max,
|
|
pc_to_stack_map,
|
|
};
|
|
|
|
let mut inner = self.inner.borrow_mut();
|
|
|
|
// Check if we've already registered this module.
|
|
if let Some(existing_module) = inner.ranges.get(&max) {
|
|
assert_eq!(existing_module.range, module_stack_maps.range);
|
|
debug_assert_eq!(
|
|
existing_module.pc_to_stack_map,
|
|
module_stack_maps.pc_to_stack_map,
|
|
);
|
|
return;
|
|
}
|
|
|
|
// Assert that this chunk of ranges doesn't collide with any other known
|
|
// chunks.
|
|
if let Some((_, prev)) = inner.ranges.range(max..).next() {
|
|
assert!(prev.range.start > max);
|
|
}
|
|
if let Some((prev_end, _)) = inner.ranges.range(..=min).next_back() {
|
|
assert!(*prev_end < min);
|
|
}
|
|
|
|
let old = inner.ranges.insert(max, module_stack_maps);
|
|
assert!(old.is_none());
|
|
}
|
|
|
|
/// Lookup the stack map for the given PC, if any.
|
|
pub fn lookup_stack_map(&self, pc: usize) -> Option<Rc<StackMap>> {
|
|
let inner = self.inner.borrow();
|
|
let stack_maps = inner.module_stack_maps(pc)?;
|
|
|
|
// Do a binary search to find the stack map for the given PC.
|
|
//
|
|
// Because GC safepoints are technically only associated with a single
|
|
// PC, we should ideally only care about `Ok(index)` values returned
|
|
// from the binary search. However, safepoints are inserted right before
|
|
// calls, and there are two things that can disturb the PC/offset
|
|
// associated with the safepoint versus the PC we actually use to query
|
|
// for the stack map:
|
|
//
|
|
// 1. The `backtrace` crate gives us the PC in a frame that will be
|
|
// *returned to*, and where execution will continue from, rather than
|
|
// the PC of the call we are currently at. So we would need to
|
|
// disassemble one instruction backwards to query the actual PC for
|
|
// the stack map.
|
|
//
|
|
// TODO: One thing we *could* do to make this a little less error
|
|
// prone, would be to assert/check that the nearest GC safepoint
|
|
// found is within `max_encoded_size(any kind of call instruction)`
|
|
// our queried PC for the target architecture.
|
|
//
|
|
// 2. Cranelift's stack maps only handle the stack, not
|
|
// registers. However, some references that are arguments to a call
|
|
// may need to be in registers. In these cases, what Cranelift will
|
|
// do is:
|
|
//
|
|
// a. spill all the live references,
|
|
// b. insert a GC safepoint for those references,
|
|
// c. reload the references into registers, and finally
|
|
// d. make the call.
|
|
//
|
|
// Step (c) adds drift between the GC safepoint and the location of
|
|
// the call, which is where we actually walk the stack frame and
|
|
// collect its live references.
|
|
//
|
|
// Luckily, the spill stack slots for the live references are still
|
|
// up to date, so we can still find all the on-stack roots.
|
|
// Furthermore, we do not have a moving GC, so we don't need to worry
|
|
// whether the following code will reuse the references in registers
|
|
// (which would not have been updated to point to the moved objects)
|
|
// or reload from the stack slots (which would have been updated to
|
|
// point to the moved objects).
|
|
let index = match stack_maps
|
|
.pc_to_stack_map
|
|
.binary_search_by_key(&pc, |(pc, _stack_map)| *pc)
|
|
{
|
|
// Exact hit.
|
|
Ok(i) => i,
|
|
|
|
// `Err(0)` means that the associated stack map would have been the
|
|
// first element in the array if this pc had an associated stack
|
|
// map, but this pc does not have an associated stack map. This can
|
|
// only happen inside a Wasm frame if there are no live refs at this
|
|
// pc.
|
|
Err(0) => return None,
|
|
|
|
Err(n) => n - 1,
|
|
};
|
|
|
|
let stack_map = stack_maps.pc_to_stack_map[index].1.as_ref()?.clone();
|
|
Some(stack_map)
|
|
}
|
|
}
|
|
|
|
impl StackMapRegistryInner {
|
|
fn module_stack_maps(&self, pc: usize) -> Option<&ModuleStackMaps> {
|
|
let (end, stack_maps) = self.ranges.range(pc..).next()?;
|
|
if pc < stack_maps.range.start || *end < pc {
|
|
None
|
|
} else {
|
|
Some(stack_maps)
|
|
}
|
|
}
|
|
}
|
|
|
|
#[derive(Debug, Default)]
|
|
struct DebugOnly<T> {
|
|
inner: T,
|
|
}
|
|
|
|
impl<T> std::ops::Deref for DebugOnly<T> {
|
|
type Target = T;
|
|
|
|
fn deref(&self) -> &T {
|
|
if cfg!(debug_assertions) {
|
|
&self.inner
|
|
} else {
|
|
panic!(
|
|
"only deref `DebugOnly` when `cfg(debug_assertions)` or \
|
|
inside a `debug_assert!(..)`"
|
|
)
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<T> std::ops::DerefMut for DebugOnly<T> {
|
|
fn deref_mut(&mut self) -> &mut T {
|
|
if cfg!(debug_assertions) {
|
|
&mut self.inner
|
|
} else {
|
|
panic!(
|
|
"only deref `DebugOnly` when `cfg(debug_assertions)` or \
|
|
inside a `debug_assert!(..)`"
|
|
)
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Perform garbage collection of `VMExternRef`s.
|
|
///
|
|
/// # Unsafety
|
|
///
|
|
/// You must have called `VMExternRefActivationsTable::set_stack_canary` for at
|
|
/// least the oldest host-->Wasm stack frame transition on this thread's stack
|
|
/// (it is idempotent to call it more than once) and keep its return value alive
|
|
/// across the duration of that host-->Wasm call.
|
|
///
|
|
/// Additionally, you must have registered the stack maps for every Wasm module
|
|
/// that has frames on the stack with the given `stack_maps_registry`.
|
|
pub unsafe fn gc(
|
|
stack_maps_registry: &StackMapRegistry,
|
|
externref_activations_table: &VMExternRefActivationsTable,
|
|
) {
|
|
// We borrow the precise stack roots `RefCell` for the whole duration of
|
|
// GC. Whether it is dynamically borrowed serves as a flag for detecting
|
|
// re-entrancy into GC. Re-entrancy can occur if we do a GC, drop an
|
|
// `externref`, and that `externref`'s destructor then triggers another
|
|
// GC. Whenever we detect re-entrancy, we return and give the first,
|
|
// outermost GC call priority.
|
|
let mut precise_stack_roots = match externref_activations_table
|
|
.precise_stack_roots
|
|
.try_borrow_mut()
|
|
{
|
|
Err(_) => return,
|
|
Ok(roots) => roots,
|
|
};
|
|
|
|
log::debug!("start GC");
|
|
|
|
debug_assert!({
|
|
// This set is only non-empty within this function. It is built up when
|
|
// walking the stack and interpreting stack maps, and then drained back
|
|
// into the activations table's bump-allocated space at the
|
|
// end. Therefore, it should always be empty upon entering this
|
|
// function.
|
|
precise_stack_roots.is_empty()
|
|
});
|
|
|
|
// Whenever we call into Wasm from host code for the first time, we set a
|
|
// stack canary. When we return to that host code, we unset the stack
|
|
// canary. If there is *not* a stack canary, then there must be zero Wasm
|
|
// frames on the stack. Therefore, we can simply reset the table without
|
|
// walking the stack.
|
|
let stack_canary = match externref_activations_table.stack_canary.get() {
|
|
None => {
|
|
if cfg!(debug_assertions) {
|
|
// Assert that there aren't any Wasm frames on the stack.
|
|
backtrace::trace(|frame| {
|
|
let stack_map = stack_maps_registry.lookup_stack_map(frame.ip() as usize);
|
|
assert!(stack_map.is_none());
|
|
true
|
|
});
|
|
}
|
|
externref_activations_table.sweep(&mut precise_stack_roots);
|
|
log::debug!("end GC");
|
|
return;
|
|
}
|
|
Some(canary) => canary.as_ptr() as usize,
|
|
};
|
|
|
|
// There is a stack canary, so there must be Wasm frames on the stack. The
|
|
// rest of this function consists of:
|
|
//
|
|
// * walking the stack,
|
|
//
|
|
// * finding the precise set of roots inside Wasm frames via our stack maps,
|
|
// and
|
|
//
|
|
// * resetting our bump-allocated table's over-approximation to the
|
|
// newly-discovered precise set.
|
|
|
|
// The SP of the previous (younger) frame we processed.
|
|
let mut last_sp = None;
|
|
|
|
// Whether we have found our stack canary or not yet.
|
|
let mut found_canary = false;
|
|
|
|
// The `activations_table_set` is used for `debug_assert!`s checking that
|
|
// every reference we read out from the stack via stack maps is actually in
|
|
// the table. If that weren't true, than either we forgot to insert a
|
|
// reference in the table when passing it into Wasm (a bug) or we are
|
|
// reading invalid references from the stack (another bug).
|
|
let mut activations_table_set: DebugOnly<HashSet<_>> = Default::default();
|
|
if cfg!(debug_assertions) {
|
|
externref_activations_table.elements(|elem| {
|
|
activations_table_set.insert(elem.as_raw() as *mut VMExternData);
|
|
});
|
|
}
|
|
|
|
backtrace::trace(|frame| {
|
|
let pc = frame.ip() as usize;
|
|
let sp = frame.sp() as usize;
|
|
|
|
if let Some(stack_map) = stack_maps_registry.lookup_stack_map(pc) {
|
|
debug_assert!(sp != 0, "we should always get a valid SP for Wasm frames");
|
|
|
|
for i in 0..(stack_map.mapped_words() as usize) {
|
|
if stack_map.get_bit(i) {
|
|
// Stack maps have one bit per word in the frame, and the
|
|
// zero^th bit is the *lowest* addressed word in the frame,
|
|
// i.e. the closest to the SP. So to get the `i`^th word in
|
|
// this frame, we add `i * sizeof(word)` to the SP.
|
|
let ptr_to_ref = sp + i * mem::size_of::<usize>();
|
|
|
|
let r = std::ptr::read(ptr_to_ref as *const *mut VMExternData);
|
|
debug_assert!(
|
|
r.is_null() || activations_table_set.contains(&r),
|
|
"every on-stack externref inside a Wasm frame should \
|
|
have an entry in the VMExternRefActivationsTable"
|
|
);
|
|
if let Some(r) = NonNull::new(r) {
|
|
VMExternRefActivationsTable::insert_precise_stack_root(
|
|
&mut precise_stack_roots,
|
|
r,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
if let Some(last_sp) = last_sp {
|
|
// We've found the stack canary when we walk over the frame that it
|
|
// is contained within.
|
|
found_canary |= last_sp <= stack_canary && stack_canary <= sp;
|
|
}
|
|
last_sp = Some(sp);
|
|
|
|
// Keep walking the stack until we've found the canary, which is the
|
|
// oldest frame before we ever called into Wasm. We can stop once we've
|
|
// found it because there won't be any more Wasm frames, and therefore
|
|
// there won't be anymore on-stack, inside-a-Wasm-frame roots.
|
|
!found_canary
|
|
});
|
|
|
|
// Only sweep and reset the table if we found the stack canary, and
|
|
// therefore know that we discovered all the on-stack, inside-a-Wasm-frame
|
|
// roots. If we did *not* find the stack canary, then `libunwind` failed to
|
|
// walk the whole stack, and we might be missing roots. Reseting the table
|
|
// would free those missing roots while they are still in use, leading to
|
|
// use-after-free.
|
|
if found_canary {
|
|
externref_activations_table.sweep(&mut precise_stack_roots);
|
|
} else {
|
|
log::warn!("did not find stack canary; skipping GC sweep");
|
|
precise_stack_roots.clear();
|
|
}
|
|
|
|
log::debug!("end GC");
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use super::*;
|
|
use std::convert::TryInto;
|
|
|
|
#[test]
|
|
fn extern_ref_is_pointer_sized_and_aligned() {
|
|
assert_eq!(mem::size_of::<VMExternRef>(), mem::size_of::<*mut ()>());
|
|
assert_eq!(mem::align_of::<VMExternRef>(), mem::align_of::<*mut ()>());
|
|
assert_eq!(
|
|
mem::size_of::<Option<VMExternRef>>(),
|
|
mem::size_of::<*mut ()>()
|
|
);
|
|
assert_eq!(
|
|
mem::align_of::<Option<VMExternRef>>(),
|
|
mem::align_of::<*mut ()>()
|
|
);
|
|
}
|
|
|
|
#[test]
|
|
fn ref_count_is_at_correct_offset() {
|
|
let s = "hi";
|
|
let s: &dyn Any = &s as _;
|
|
let s: *const dyn Any = s as _;
|
|
let s: *mut dyn Any = s as _;
|
|
|
|
let extern_data = VMExternData {
|
|
ref_count: UnsafeCell::new(0),
|
|
value_ptr: NonNull::new(s).unwrap(),
|
|
};
|
|
|
|
let extern_data_ptr = &extern_data as *const _;
|
|
let ref_count_ptr = &extern_data.ref_count as *const _;
|
|
|
|
let actual_offset = (ref_count_ptr as usize) - (extern_data_ptr as usize);
|
|
|
|
assert_eq!(
|
|
wasmtime_environ::VMOffsets::vm_extern_data_ref_count(),
|
|
actual_offset.try_into().unwrap(),
|
|
);
|
|
}
|
|
|
|
#[test]
|
|
fn table_next_is_at_correct_offset() {
|
|
let table = VMExternRefActivationsTable::new();
|
|
|
|
let table_ptr = &table as *const _;
|
|
let next_ptr = &table.next as *const _;
|
|
|
|
let actual_offset = (next_ptr as usize) - (table_ptr as usize);
|
|
|
|
let offsets = wasmtime_environ::VMOffsets {
|
|
pointer_size: 8,
|
|
num_signature_ids: 0,
|
|
num_imported_functions: 0,
|
|
num_imported_tables: 0,
|
|
num_imported_memories: 0,
|
|
num_imported_globals: 0,
|
|
num_defined_functions: 0,
|
|
num_defined_tables: 0,
|
|
num_defined_memories: 0,
|
|
num_defined_globals: 0,
|
|
};
|
|
assert_eq!(
|
|
offsets.vm_extern_ref_activation_table_next() as usize,
|
|
actual_offset
|
|
);
|
|
}
|
|
|
|
#[test]
|
|
fn table_end_is_at_correct_offset() {
|
|
let table = VMExternRefActivationsTable::new();
|
|
|
|
let table_ptr = &table as *const _;
|
|
let end_ptr = &table.end as *const _;
|
|
|
|
let actual_offset = (end_ptr as usize) - (table_ptr as usize);
|
|
|
|
let offsets = wasmtime_environ::VMOffsets {
|
|
pointer_size: 8,
|
|
num_signature_ids: 0,
|
|
num_imported_functions: 0,
|
|
num_imported_tables: 0,
|
|
num_imported_memories: 0,
|
|
num_imported_globals: 0,
|
|
num_defined_functions: 0,
|
|
num_defined_tables: 0,
|
|
num_defined_memories: 0,
|
|
num_defined_globals: 0,
|
|
};
|
|
assert_eq!(
|
|
offsets.vm_extern_ref_activation_table_end() as usize,
|
|
actual_offset
|
|
);
|
|
}
|
|
}
|