1898d52966
`VMExternRef` is a reference-counted box for any kind of data that is
external and opaque to running Wasm. Sometimes it might hold a Wasmtime
thing, other times it might hold something from a Wasmtime embedder and is
opaque even to us. It is morally equivalent to `Rc<dyn Any>` in Rust, but
additionally always fits in a pointer-sized word. `VMExternRef` is
non-nullable, but `Option<VMExternRef>` is a null pointer.
The one part of `VMExternRef` that can't ever be opaque to us is the
reference count. Even when we don't know what's inside an `VMExternRef`, we
need to be able to manipulate its reference count as we add and remove
references to it. And we need to do this from compiled Wasm code, so it must
be `repr(C)`!
`VMExternRef` itself is just a pointer to an `VMExternData`, which holds the
opaque, boxed value, its reference count, and its vtable pointer.
The `VMExternData` struct is *preceded* by the dynamically-sized value boxed
up and referenced by one or more `VMExternRef`s:
```ignore
,-------------------------------------------------------.
| |
V |
+----------------------------+-----------+-----------+ |
| dynamically-sized value... | ref_count | value_ptr |---'
+----------------------------+-----------+-----------+
| VMExternData |
+-----------------------+
^
+-------------+ |
| VMExternRef |-------------------+
+-------------+ |
|
+-------------+ |
| VMExternRef |-------------------+
+-------------+ |
|
... ===
|
+-------------+ |
| VMExternRef |-------------------'
+-------------+
```
The `value_ptr` member always points backwards to the start of the
dynamically-sized value (which is also the start of the heap allocation for
this value-and-`VMExternData` pair). Because it is a `dyn` pointer, it is
fat, and also points to the value's `Any` vtable.
The boxed value and the `VMExternRef` footer are held a single heap
allocation. The layout described above is used to make satisfying the
value's alignment easy: we just need to ensure that the heap allocation used
to hold everything satisfies its alignment. It also ensures that we don't
need a ton of excess padding between the `VMExternData` and the value for
values with large alignment.
625 lines
20 KiB
Rust
625 lines
20 KiB
Rust
//! Offsets and sizes of various structs in wasmtime-runtime's vmcontext
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//! module.
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// Currently the `VMContext` allocation by field looks like this:
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//
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// struct VMContext {
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// interrupts: *const VMInterrupts,
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// signature_ids: [VMSharedSignatureIndex; module.num_signature_ids],
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// imported_functions: [VMFunctionImport; module.num_imported_functions],
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// imported_tables: [VMTableImport; module.num_imported_tables],
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// imported_memories: [VMMemoryImport; module.num_imported_memories],
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// imported_globals: [VMGlobalImport; module.num_imported_globals],
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// tables: [VMTableDefinition; module.num_defined_tables],
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// memories: [VMMemoryDefinition; module.num_defined_memories],
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// globals: [VMGlobalDefinition; module.num_defined_globals],
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// builtins: VMBuiltinFunctionsArray,
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// }
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use crate::module::ModuleLocal;
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use crate::BuiltinFunctionIndex;
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use cranelift_codegen::ir;
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use cranelift_wasm::{
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DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex, FuncIndex, GlobalIndex, MemoryIndex,
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SignatureIndex, TableIndex,
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};
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use more_asserts::assert_lt;
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use std::convert::TryFrom;
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/// Sentinel value indicating that wasm has been interrupted.
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// Note that this has a bit of an odd definition. See the `insert_stack_check`
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// function in `cranelift/codegen/src/isa/x86/abi.rs` for more information
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pub const INTERRUPTED: usize = usize::max_value() - 32 * 1024;
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#[cfg(target_pointer_width = "32")]
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fn cast_to_u32(sz: usize) -> u32 {
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u32::try_from(sz).unwrap()
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}
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#[cfg(target_pointer_width = "64")]
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fn cast_to_u32(sz: usize) -> u32 {
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u32::try_from(sz).expect("overflow in cast from usize to u32")
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}
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/// Align an offset used in this module to a specific byte-width by rounding up
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fn align(offset: u32, width: u32) -> u32 {
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(offset + (width - 1)) / width * width
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}
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/// This class computes offsets to fields within `VMContext` and other
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/// related structs that JIT code accesses directly.
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pub struct VMOffsets {
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/// The size in bytes of a pointer on the target.
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pub pointer_size: u8,
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/// The number of signature declarations in the module.
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pub num_signature_ids: u32,
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/// The number of imported functions in the module.
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pub num_imported_functions: u32,
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/// The number of imported tables in the module.
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pub num_imported_tables: u32,
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/// The number of imported memories in the module.
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pub num_imported_memories: u32,
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/// The number of imported globals in the module.
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pub num_imported_globals: u32,
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/// The number of defined tables in the module.
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pub num_defined_tables: u32,
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/// The number of defined memories in the module.
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pub num_defined_memories: u32,
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/// The number of defined globals in the module.
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pub num_defined_globals: u32,
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}
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impl VMOffsets {
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/// Return a new `VMOffsets` instance, for a given pointer size.
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pub fn new(pointer_size: u8, module: &ModuleLocal) -> Self {
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Self {
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pointer_size,
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num_signature_ids: cast_to_u32(module.signatures.len()),
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num_imported_functions: cast_to_u32(module.num_imported_funcs),
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num_imported_tables: cast_to_u32(module.num_imported_tables),
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num_imported_memories: cast_to_u32(module.num_imported_memories),
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num_imported_globals: cast_to_u32(module.num_imported_globals),
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num_defined_tables: cast_to_u32(module.table_plans.len()),
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num_defined_memories: cast_to_u32(module.memory_plans.len()),
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num_defined_globals: cast_to_u32(module.globals.len()),
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}
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}
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}
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/// Offsets for `VMFunctionImport`.
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impl VMOffsets {
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/// The offset of the `body` field.
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#[allow(clippy::erasing_op)]
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pub fn vmfunction_import_body(&self) -> u8 {
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0 * self.pointer_size
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}
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/// The offset of the `vmctx` field.
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#[allow(clippy::identity_op)]
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pub fn vmfunction_import_vmctx(&self) -> u8 {
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1 * self.pointer_size
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}
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/// Return the size of `VMFunctionImport`.
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pub fn size_of_vmfunction_import(&self) -> u8 {
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2 * self.pointer_size
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}
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}
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/// Offsets for `*const VMFunctionBody`.
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impl VMOffsets {
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/// The size of the `current_elements` field.
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#[allow(clippy::identity_op)]
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pub fn size_of_vmfunction_body_ptr(&self) -> u8 {
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1 * self.pointer_size
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}
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}
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/// Offsets for `VMTableImport`.
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impl VMOffsets {
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/// The offset of the `from` field.
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#[allow(clippy::erasing_op)]
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pub fn vmtable_import_from(&self) -> u8 {
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0 * self.pointer_size
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}
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/// The offset of the `vmctx` field.
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#[allow(clippy::identity_op)]
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pub fn vmtable_import_vmctx(&self) -> u8 {
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1 * self.pointer_size
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}
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/// Return the size of `VMTableImport`.
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pub fn size_of_vmtable_import(&self) -> u8 {
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2 * self.pointer_size
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}
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}
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/// Offsets for `VMTableDefinition`.
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impl VMOffsets {
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/// The offset of the `base` field.
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#[allow(clippy::erasing_op)]
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pub fn vmtable_definition_base(&self) -> u8 {
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0 * self.pointer_size
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}
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/// The offset of the `current_elements` field.
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#[allow(clippy::identity_op)]
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pub fn vmtable_definition_current_elements(&self) -> u8 {
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1 * self.pointer_size
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}
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/// The size of the `current_elements` field.
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pub fn size_of_vmtable_definition_current_elements(&self) -> u8 {
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4
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}
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/// Return the size of `VMTableDefinition`.
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pub fn size_of_vmtable_definition(&self) -> u8 {
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2 * self.pointer_size
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}
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/// The type of the `current_elements` field.
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pub fn type_of_vmtable_definition_current_elements(&self) -> ir::Type {
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ir::Type::int(u16::from(self.size_of_vmtable_definition_current_elements()) * 8).unwrap()
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}
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}
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/// Offsets for `VMMemoryImport`.
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impl VMOffsets {
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/// The offset of the `from` field.
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#[allow(clippy::erasing_op)]
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pub fn vmmemory_import_from(&self) -> u8 {
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0 * self.pointer_size
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}
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/// The offset of the `vmctx` field.
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#[allow(clippy::identity_op)]
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pub fn vmmemory_import_vmctx(&self) -> u8 {
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1 * self.pointer_size
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}
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/// Return the size of `VMMemoryImport`.
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pub fn size_of_vmmemory_import(&self) -> u8 {
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2 * self.pointer_size
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}
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}
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/// Offsets for `VMMemoryDefinition`.
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impl VMOffsets {
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/// The offset of the `base` field.
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#[allow(clippy::erasing_op)]
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pub fn vmmemory_definition_base(&self) -> u8 {
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0 * self.pointer_size
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}
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/// The offset of the `current_length` field.
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#[allow(clippy::identity_op)]
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pub fn vmmemory_definition_current_length(&self) -> u8 {
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1 * self.pointer_size
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}
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/// The size of the `current_length` field.
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pub fn size_of_vmmemory_definition_current_length(&self) -> u8 {
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4
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}
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/// Return the size of `VMMemoryDefinition`.
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pub fn size_of_vmmemory_definition(&self) -> u8 {
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2 * self.pointer_size
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}
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/// The type of the `current_length` field.
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pub fn type_of_vmmemory_definition_current_length(&self) -> ir::Type {
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ir::Type::int(u16::from(self.size_of_vmmemory_definition_current_length()) * 8).unwrap()
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}
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}
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/// Offsets for `VMGlobalImport`.
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impl VMOffsets {
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/// The offset of the `from` field.
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#[allow(clippy::erasing_op)]
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pub fn vmglobal_import_from(&self) -> u8 {
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0 * self.pointer_size
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}
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/// Return the size of `VMGlobalImport`.
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#[allow(clippy::identity_op)]
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pub fn size_of_vmglobal_import(&self) -> u8 {
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1 * self.pointer_size
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}
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}
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/// Offsets for `VMGlobalDefinition`.
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impl VMOffsets {
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/// Return the size of `VMGlobalDefinition`; this is the size of the largest value type (i.e. a
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/// V128).
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pub fn size_of_vmglobal_definition(&self) -> u8 {
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16
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}
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}
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/// Offsets for `VMSharedSignatureIndex`.
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impl VMOffsets {
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/// Return the size of `VMSharedSignatureIndex`.
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pub fn size_of_vmshared_signature_index(&self) -> u8 {
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4
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}
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}
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/// Offsets for `VMInterrupts`.
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impl VMOffsets {
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/// Return the offset of the `stack_limit` field of `VMInterrupts`
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pub fn vminterrupts_stack_limit(&self) -> u8 {
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0
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}
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}
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/// Offsets for `VMCallerCheckedAnyfunc`.
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impl VMOffsets {
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/// The offset of the `func_ptr` field.
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#[allow(clippy::erasing_op)]
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pub fn vmcaller_checked_anyfunc_func_ptr(&self) -> u8 {
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0 * self.pointer_size
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}
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/// The offset of the `type_index` field.
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#[allow(clippy::identity_op)]
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pub fn vmcaller_checked_anyfunc_type_index(&self) -> u8 {
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1 * self.pointer_size
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}
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/// The offset of the `vmctx` field.
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pub fn vmcaller_checked_anyfunc_vmctx(&self) -> u8 {
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2 * self.pointer_size
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}
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/// Return the size of `VMCallerCheckedAnyfunc`.
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pub fn size_of_vmcaller_checked_anyfunc(&self) -> u8 {
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3 * self.pointer_size
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}
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}
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/// Offsets for `VMContext`.
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impl VMOffsets {
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/// Return the offset to the `VMInterrupts` structure
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pub fn vmctx_interrupts(&self) -> u32 {
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0
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}
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/// The offset of the `signature_ids` array.
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pub fn vmctx_signature_ids_begin(&self) -> u32 {
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self.vmctx_interrupts()
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.checked_add(u32::from(self.pointer_size))
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.unwrap()
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}
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/// The offset of the `tables` array.
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#[allow(clippy::erasing_op)]
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pub fn vmctx_imported_functions_begin(&self) -> u32 {
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self.vmctx_signature_ids_begin()
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.checked_add(
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self.num_signature_ids
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.checked_mul(u32::from(self.size_of_vmshared_signature_index()))
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.unwrap(),
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)
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.unwrap()
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}
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/// The offset of the `tables` array.
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#[allow(clippy::identity_op)]
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pub fn vmctx_imported_tables_begin(&self) -> u32 {
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self.vmctx_imported_functions_begin()
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.checked_add(
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self.num_imported_functions
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.checked_mul(u32::from(self.size_of_vmfunction_import()))
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.unwrap(),
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)
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.unwrap()
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}
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/// The offset of the `memories` array.
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pub fn vmctx_imported_memories_begin(&self) -> u32 {
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self.vmctx_imported_tables_begin()
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.checked_add(
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self.num_imported_tables
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.checked_mul(u32::from(self.size_of_vmtable_import()))
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.unwrap(),
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)
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.unwrap()
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}
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/// The offset of the `globals` array.
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pub fn vmctx_imported_globals_begin(&self) -> u32 {
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self.vmctx_imported_memories_begin()
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.checked_add(
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self.num_imported_memories
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.checked_mul(u32::from(self.size_of_vmmemory_import()))
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.unwrap(),
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)
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.unwrap()
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}
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/// The offset of the `tables` array.
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pub fn vmctx_tables_begin(&self) -> u32 {
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self.vmctx_imported_globals_begin()
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.checked_add(
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self.num_imported_globals
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.checked_mul(u32::from(self.size_of_vmglobal_import()))
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.unwrap(),
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)
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.unwrap()
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}
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/// The offset of the `memories` array.
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pub fn vmctx_memories_begin(&self) -> u32 {
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self.vmctx_tables_begin()
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.checked_add(
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self.num_defined_tables
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.checked_mul(u32::from(self.size_of_vmtable_definition()))
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.unwrap(),
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)
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.unwrap()
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}
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/// The offset of the `globals` array.
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pub fn vmctx_globals_begin(&self) -> u32 {
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let offset = self
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.vmctx_memories_begin()
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.checked_add(
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self.num_defined_memories
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.checked_mul(u32::from(self.size_of_vmmemory_definition()))
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.unwrap(),
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)
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.unwrap();
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align(offset, 16)
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}
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/// The offset of the builtin functions array.
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pub fn vmctx_builtin_functions_begin(&self) -> u32 {
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self.vmctx_globals_begin()
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.checked_add(
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self.num_defined_globals
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.checked_mul(u32::from(self.size_of_vmglobal_definition()))
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.unwrap(),
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)
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.unwrap()
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}
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/// Return the size of the `VMContext` allocation.
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pub fn size_of_vmctx(&self) -> u32 {
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self.vmctx_builtin_functions_begin()
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.checked_add(
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BuiltinFunctionIndex::builtin_functions_total_number()
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.checked_mul(u32::from(self.pointer_size))
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.unwrap(),
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)
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.unwrap()
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}
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/// Return the offset to `VMSharedSignatureId` index `index`.
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pub fn vmctx_vmshared_signature_id(&self, index: SignatureIndex) -> u32 {
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assert_lt!(index.as_u32(), self.num_signature_ids);
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self.vmctx_signature_ids_begin()
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.checked_add(
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index
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.as_u32()
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.checked_mul(u32::from(self.size_of_vmshared_signature_index()))
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.unwrap(),
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)
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.unwrap()
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}
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|
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/// Return the offset to `VMFunctionImport` index `index`.
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|
pub fn vmctx_vmfunction_import(&self, index: FuncIndex) -> u32 {
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|
assert_lt!(index.as_u32(), self.num_imported_functions);
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self.vmctx_imported_functions_begin()
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.checked_add(
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index
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|
.as_u32()
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.checked_mul(u32::from(self.size_of_vmfunction_import()))
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|
.unwrap(),
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)
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.unwrap()
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}
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|
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/// Return the offset to `VMTableImport` index `index`.
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|
pub fn vmctx_vmtable_import(&self, index: TableIndex) -> u32 {
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|
assert_lt!(index.as_u32(), self.num_imported_tables);
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|
self.vmctx_imported_tables_begin()
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|
.checked_add(
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|
index
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|
.as_u32()
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|
.checked_mul(u32::from(self.size_of_vmtable_import()))
|
|
.unwrap(),
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|
)
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|
.unwrap()
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|
}
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|
|
/// Return the offset to `VMMemoryImport` index `index`.
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|
pub fn vmctx_vmmemory_import(&self, index: MemoryIndex) -> u32 {
|
|
assert_lt!(index.as_u32(), self.num_imported_memories);
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|
self.vmctx_imported_memories_begin()
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|
.checked_add(
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|
index
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|
.as_u32()
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|
.checked_mul(u32::from(self.size_of_vmmemory_import()))
|
|
.unwrap(),
|
|
)
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|
.unwrap()
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|
}
|
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|
|
/// Return the offset to `VMGlobalImport` index `index`.
|
|
pub fn vmctx_vmglobal_import(&self, index: GlobalIndex) -> u32 {
|
|
assert_lt!(index.as_u32(), self.num_imported_globals);
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|
self.vmctx_imported_globals_begin()
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|
.checked_add(
|
|
index
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|
.as_u32()
|
|
.checked_mul(u32::from(self.size_of_vmglobal_import()))
|
|
.unwrap(),
|
|
)
|
|
.unwrap()
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|
}
|
|
|
|
/// Return the offset to `VMTableDefinition` index `index`.
|
|
pub fn vmctx_vmtable_definition(&self, index: DefinedTableIndex) -> u32 {
|
|
assert_lt!(index.as_u32(), self.num_defined_tables);
|
|
self.vmctx_tables_begin()
|
|
.checked_add(
|
|
index
|
|
.as_u32()
|
|
.checked_mul(u32::from(self.size_of_vmtable_definition()))
|
|
.unwrap(),
|
|
)
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to `VMMemoryDefinition` index `index`.
|
|
pub fn vmctx_vmmemory_definition(&self, index: DefinedMemoryIndex) -> u32 {
|
|
assert_lt!(index.as_u32(), self.num_defined_memories);
|
|
self.vmctx_memories_begin()
|
|
.checked_add(
|
|
index
|
|
.as_u32()
|
|
.checked_mul(u32::from(self.size_of_vmmemory_definition()))
|
|
.unwrap(),
|
|
)
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `VMGlobalDefinition` index `index`.
|
|
pub fn vmctx_vmglobal_definition(&self, index: DefinedGlobalIndex) -> u32 {
|
|
assert_lt!(index.as_u32(), self.num_defined_globals);
|
|
self.vmctx_globals_begin()
|
|
.checked_add(
|
|
index
|
|
.as_u32()
|
|
.checked_mul(u32::from(self.size_of_vmglobal_definition()))
|
|
.unwrap(),
|
|
)
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `body` field in `*const VMFunctionBody` index `index`.
|
|
pub fn vmctx_vmfunction_import_body(&self, index: FuncIndex) -> u32 {
|
|
self.vmctx_vmfunction_import(index)
|
|
.checked_add(u32::from(self.vmfunction_import_body()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `vmctx` field in `*const VMFunctionBody` index `index`.
|
|
pub fn vmctx_vmfunction_import_vmctx(&self, index: FuncIndex) -> u32 {
|
|
self.vmctx_vmfunction_import(index)
|
|
.checked_add(u32::from(self.vmfunction_import_vmctx()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `from` field in `VMTableImport` index `index`.
|
|
pub fn vmctx_vmtable_import_from(&self, index: TableIndex) -> u32 {
|
|
self.vmctx_vmtable_import(index)
|
|
.checked_add(u32::from(self.vmtable_import_from()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `base` field in `VMTableDefinition` index `index`.
|
|
pub fn vmctx_vmtable_definition_base(&self, index: DefinedTableIndex) -> u32 {
|
|
self.vmctx_vmtable_definition(index)
|
|
.checked_add(u32::from(self.vmtable_definition_base()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `current_elements` field in `VMTableDefinition` index `index`.
|
|
pub fn vmctx_vmtable_definition_current_elements(&self, index: DefinedTableIndex) -> u32 {
|
|
self.vmctx_vmtable_definition(index)
|
|
.checked_add(u32::from(self.vmtable_definition_current_elements()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `from` field in `VMMemoryImport` index `index`.
|
|
pub fn vmctx_vmmemory_import_from(&self, index: MemoryIndex) -> u32 {
|
|
self.vmctx_vmmemory_import(index)
|
|
.checked_add(u32::from(self.vmmemory_import_from()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `vmctx` field in `VMMemoryImport` index `index`.
|
|
pub fn vmctx_vmmemory_import_vmctx(&self, index: MemoryIndex) -> u32 {
|
|
self.vmctx_vmmemory_import(index)
|
|
.checked_add(u32::from(self.vmmemory_import_vmctx()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `base` field in `VMMemoryDefinition` index `index`.
|
|
pub fn vmctx_vmmemory_definition_base(&self, index: DefinedMemoryIndex) -> u32 {
|
|
self.vmctx_vmmemory_definition(index)
|
|
.checked_add(u32::from(self.vmmemory_definition_base()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `current_length` field in `VMMemoryDefinition` index `index`.
|
|
pub fn vmctx_vmmemory_definition_current_length(&self, index: DefinedMemoryIndex) -> u32 {
|
|
self.vmctx_vmmemory_definition(index)
|
|
.checked_add(u32::from(self.vmmemory_definition_current_length()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to the `from` field in `VMGlobalImport` index `index`.
|
|
pub fn vmctx_vmglobal_import_from(&self, index: GlobalIndex) -> u32 {
|
|
self.vmctx_vmglobal_import(index)
|
|
.checked_add(u32::from(self.vmglobal_import_from()))
|
|
.unwrap()
|
|
}
|
|
|
|
/// Return the offset to builtin function in `VMBuiltinFunctionsArray` index `index`.
|
|
pub fn vmctx_builtin_function(&self, index: BuiltinFunctionIndex) -> u32 {
|
|
self.vmctx_builtin_functions_begin()
|
|
.checked_add(
|
|
index
|
|
.index()
|
|
.checked_mul(u32::from(self.pointer_size))
|
|
.unwrap(),
|
|
)
|
|
.unwrap()
|
|
}
|
|
}
|
|
|
|
/// Offsets for `VMExternData`.
|
|
impl VMOffsets {
|
|
/// Return the offset for `VMExternData::ref_count`.
|
|
pub fn vm_extern_data_ref_count() -> u32 {
|
|
0
|
|
}
|
|
}
|
|
|
|
/// Target specific type for shared signature index.
|
|
#[derive(Debug, Copy, Clone)]
|
|
pub struct TargetSharedSignatureIndex(u32);
|
|
|
|
impl TargetSharedSignatureIndex {
|
|
/// Constructs `TargetSharedSignatureIndex`.
|
|
pub fn new(value: u32) -> Self {
|
|
Self(value)
|
|
}
|
|
|
|
/// Returns index value.
|
|
pub fn index(self) -> u32 {
|
|
self.0
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod tests {
|
|
use crate::vmoffsets::align;
|
|
|
|
#[test]
|
|
fn alignment() {
|
|
fn is_aligned(x: u32) -> bool {
|
|
x % 16 == 0
|
|
}
|
|
assert!(is_aligned(align(0, 16)));
|
|
assert!(is_aligned(align(32, 16)));
|
|
assert!(is_aligned(align(33, 16)));
|
|
assert!(is_aligned(align(31, 16)));
|
|
}
|
|
}
|