wasmtime_environ/module.rs
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//! Data structures for representing decoded wasm modules.
use crate::prelude::*;
use crate::*;
use alloc::collections::BTreeMap;
use core::ops::Range;
use cranelift_entity::{packed_option::ReservedValue, EntityRef};
use serde_derive::{Deserialize, Serialize};
/// Implementation styles for WebAssembly linear memory.
#[derive(Debug, Clone, Hash, Serialize, Deserialize)]
pub enum MemoryStyle {
/// The actual memory can be resized and moved.
Dynamic {
/// Extra space to reserve when a memory must be moved due to growth.
reserve: u64,
},
/// Address space is allocated up front.
Static {
/// The number of bytes which are reserved for this linear memory. Only
/// the lower bytes which represent the actual linear memory need be
/// mapped, but other bytes must be guaranteed to be unmapped.
byte_reservation: u64,
},
}
impl MemoryStyle {
/// Decide on an implementation style for the given `Memory`.
pub fn for_memory(memory: Memory, tunables: &Tunables) -> (Self, u64) {
let is_static =
// Ideally we would compare against (an upper bound on) the target's
// page size, but unfortunately that is a little hard to plumb
// through here.
memory.page_size_log2 >= Memory::DEFAULT_PAGE_SIZE_LOG2
&& tunables.signals_based_traps
&& match memory.maximum_byte_size() {
Ok(mut maximum) => {
if !tunables.memory_may_move {
maximum = maximum.min(tunables.memory_reservation);
}
// Ensure the minimum is less than the maximum; the minimum
// might exceed the maximum when the memory is artificially
// bounded via `memory_may_move` above
memory.minimum_byte_size().unwrap() <= maximum
&& maximum <= tunables.memory_reservation
}
// If the maximum size of this memory is not representable with
// `u64` then use the `memory_may_move` to indicate whether
// it's a static memory or not. It should be ok to discard the
// linear memory's maximum size here as growth to the maximum
// is always fallible and never guaranteed.
Err(_) => !tunables.memory_may_move,
};
if is_static {
return (
Self::Static {
byte_reservation: tunables.memory_reservation,
},
tunables.memory_guard_size,
);
}
// Otherwise, make it dynamic.
(
Self::Dynamic {
reserve: tunables.memory_reservation_for_growth,
},
tunables.memory_guard_size,
)
}
}
/// A WebAssembly linear memory initializer.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct MemoryInitializer {
/// The index of a linear memory to initialize.
pub memory_index: MemoryIndex,
/// The base offset to start this segment at.
pub offset: ConstExpr,
/// The range of the data to write within the linear memory.
///
/// This range indexes into a separately stored data section which will be
/// provided with the compiled module's code as well.
pub data: Range<u32>,
}
/// Similar to the above `MemoryInitializer` but only used when memory
/// initializers are statically known to be valid.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct StaticMemoryInitializer {
/// The 64-bit offset, in bytes, of where this initializer starts.
pub offset: u64,
/// The range of data to write at `offset`, where these indices are indexes
/// into the compiled wasm module's data section.
pub data: Range<u32>,
}
/// The type of WebAssembly linear memory initialization to use for a module.
#[derive(Debug, Serialize, Deserialize)]
pub enum MemoryInitialization {
/// Memory initialization is segmented.
///
/// Segmented initialization can be used for any module, but it is required
/// if:
///
/// * A data segment referenced an imported memory.
/// * A data segment uses a global base.
///
/// Segmented initialization is performed by processing the complete set of
/// data segments when the module is instantiated.
///
/// This is the default memory initialization type.
Segmented(Vec<MemoryInitializer>),
/// Memory initialization is statically known and involves a single `memcpy`
/// or otherwise simply making the defined data visible.
///
/// To be statically initialized everything must reference a defined memory
/// and all data segments have a statically known in-bounds base (no
/// globals).
///
/// This form of memory initialization is a more optimized version of
/// `Segmented` where memory can be initialized with one of a few methods:
///
/// * First it could be initialized with a single `memcpy` of data from the
/// module to the linear memory.
/// * Otherwise techniques like `mmap` are also possible to make this data,
/// which might reside in a compiled module on disk, available immediately
/// in a linear memory's address space.
///
/// To facilitate the latter of these techniques the `try_static_init`
/// function below, which creates this variant, takes a host page size
/// argument which can page-align everything to make mmap-ing possible.
Static {
/// The initialization contents for each linear memory.
///
/// This array has, for each module's own linear memory, the contents
/// necessary to initialize it. If the memory has a `None` value then no
/// initialization is necessary (it's zero-filled). Otherwise with
/// `Some` the first element of the tuple is the offset in memory to
/// start the initialization and the `Range` is the range within the
/// final data section of the compiled module of bytes to copy into the
/// memory.
///
/// The offset, range base, and range end are all guaranteed to be page
/// aligned to the page size passed in to `try_static_init`.
map: PrimaryMap<MemoryIndex, Option<StaticMemoryInitializer>>,
},
}
impl Default for MemoryInitialization {
fn default() -> Self {
Self::Segmented(Vec::new())
}
}
impl MemoryInitialization {
/// Returns whether this initialization is of the form
/// `MemoryInitialization::Segmented`.
pub fn is_segmented(&self) -> bool {
match self {
MemoryInitialization::Segmented(_) => true,
_ => false,
}
}
/// Performs the memory initialization steps for this set of initializers.
///
/// This will perform wasm initialization in compliance with the wasm spec
/// and how data segments are processed. This doesn't need to necessarily
/// only be called as part of initialization, however, as it's structured to
/// allow learning about memory ahead-of-time at compile time possibly.
///
/// This function will return true if all memory initializers are processed
/// successfully. If any initializer hits an error or, for example, a
/// global value is needed but `None` is returned, then false will be
/// returned. At compile-time this typically means that the "error" in
/// question needs to be deferred to runtime, and at runtime this means
/// that an invalid initializer has been found and a trap should be
/// generated.
pub fn init_memory(&self, state: &mut dyn InitMemory) -> bool {
let initializers = match self {
// Fall through below to the segmented memory one-by-one
// initialization.
MemoryInitialization::Segmented(list) => list,
// If previously switched to static initialization then pass through
// all those parameters here to the `write` callback.
//
// Note that existence of `Static` already guarantees that all
// indices are in-bounds.
MemoryInitialization::Static { map } => {
for (index, init) in map {
if let Some(init) = init {
let result = state.write(index, init);
if !result {
return result;
}
}
}
return true;
}
};
for initializer in initializers {
let &MemoryInitializer {
memory_index,
ref offset,
ref data,
} = initializer;
// First up determine the start/end range and verify that they're
// in-bounds for the initial size of the memory at `memory_index`.
// Note that this can bail if we don't have access to globals yet
// (e.g. this is a task happening before instantiation at
// compile-time).
let start = match state.eval_offset(memory_index, offset) {
Some(start) => start,
None => return false,
};
let len = u64::try_from(data.len()).unwrap();
let end = match start.checked_add(len) {
Some(end) => end,
None => return false,
};
match state.memory_size_in_bytes(memory_index) {
Ok(max) => {
if end > max {
return false;
}
}
// Note that computing the minimum can overflow if the page size
// is the default 64KiB and the memory's minimum size in pages
// is `1 << 48`, the maximum number of minimum pages for 64-bit
// memories. We don't return `false` to signal an error here and
// instead defer the error to runtime, when it will be
// impossible to allocate that much memory anyways.
Err(_) => {}
}
// The limits of the data segment have been validated at this point
// so the `write` callback is called with the range of data being
// written. Any erroneous result is propagated upwards.
let init = StaticMemoryInitializer {
offset: start,
data: data.clone(),
};
let result = state.write(memory_index, &init);
if !result {
return result;
}
}
return true;
}
}
/// The various callbacks provided here are used to drive the smaller bits of
/// memory initialization.
pub trait InitMemory {
/// Returns the size, in bytes, of the memory specified. For compile-time
/// purposes this would be the memory type's minimum size.
fn memory_size_in_bytes(&mut self, memory_index: MemoryIndex) -> Result<u64, SizeOverflow>;
/// Returns the value of the constant expression, as a `u64`. Note that
/// this may involve zero-extending a 32-bit global to a 64-bit number. May
/// return `None` to indicate that the expression involves a value which is
/// not available yet.
fn eval_offset(&mut self, memory_index: MemoryIndex, expr: &ConstExpr) -> Option<u64>;
/// A callback used to actually write data. This indicates that the
/// specified memory must receive the specified range of data at the
/// specified offset. This can return false on failure.
fn write(&mut self, memory_index: MemoryIndex, init: &StaticMemoryInitializer) -> bool;
}
/// Table initialization data for all tables in the module.
#[derive(Debug, Default, Serialize, Deserialize)]
pub struct TableInitialization {
/// Initial values for tables defined within the module itself.
///
/// This contains the initial values and initializers for tables defined
/// within a wasm, so excluding imported tables. This initializer can
/// represent null-initialized tables, element-initialized tables (e.g. with
/// the function-references proposal), or precomputed images of table
/// initialization. For example table initializers to a table that are all
/// in-bounds will get removed from `segment` and moved into
/// `initial_values` here.
pub initial_values: PrimaryMap<DefinedTableIndex, TableInitialValue>,
/// Element segments present in the initial wasm module which are executed
/// at instantiation time.
///
/// These element segments are iterated over during instantiation to apply
/// any segments that weren't already moved into `initial_values` above.
pub segments: Vec<TableSegment>,
}
/// Initial value for all elements in a table.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub enum TableInitialValue {
/// Initialize each table element to null, optionally setting some elements
/// to non-null given the precomputed image.
Null {
/// A precomputed image of table initializers for this table.
///
/// This image is constructed during `try_func_table_init` and
/// null-initialized elements are represented with
/// `FuncIndex::reserved_value()`. Note that this image is empty by
/// default and may not encompass the entire span of the table in which
/// case the elements are initialized to null.
precomputed: Vec<FuncIndex>,
},
/// An arbitrary const expression.
Expr(ConstExpr),
}
/// A WebAssembly table initializer segment.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct TableSegment {
/// The index of a table to initialize.
pub table_index: TableIndex,
/// The base offset to start this segment at.
pub offset: ConstExpr,
/// The values to write into the table elements.
pub elements: TableSegmentElements,
}
/// Elements of a table segment, either a list of functions or list of arbitrary
/// expressions.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub enum TableSegmentElements {
/// A sequential list of functions where `FuncIndex::reserved_value()`
/// indicates a null function.
Functions(Box<[FuncIndex]>),
/// Arbitrary expressions, aka either functions, null or a load of a global.
Expressions(Box<[ConstExpr]>),
}
impl TableSegmentElements {
/// Returns the number of elements in this segment.
pub fn len(&self) -> u64 {
match self {
Self::Functions(s) => u64::try_from(s.len()).unwrap(),
Self::Expressions(s) => u64::try_from(s.len()).unwrap(),
}
}
}
/// A translated WebAssembly module, excluding the function bodies and
/// memory initializers.
#[derive(Default, Debug, Serialize, Deserialize)]
pub struct Module {
/// The name of this wasm module, often found in the wasm file.
pub name: Option<String>,
/// All import records, in the order they are declared in the module.
pub initializers: Vec<Initializer>,
/// Exported entities.
pub exports: IndexMap<String, EntityIndex>,
/// The module "start" function, if present.
pub start_func: Option<FuncIndex>,
/// WebAssembly table initialization data, per table.
pub table_initialization: TableInitialization,
/// WebAssembly linear memory initializer.
pub memory_initialization: MemoryInitialization,
/// WebAssembly passive elements.
pub passive_elements: Vec<TableSegmentElements>,
/// The map from passive element index (element segment index space) to index in `passive_elements`.
pub passive_elements_map: BTreeMap<ElemIndex, usize>,
/// The map from passive data index (data segment index space) to index in `passive_data`.
pub passive_data_map: BTreeMap<DataIndex, Range<u32>>,
/// Types declared in the wasm module.
pub types: PrimaryMap<TypeIndex, ModuleInternedTypeIndex>,
/// Number of imported or aliased functions in the module.
pub num_imported_funcs: usize,
/// Number of imported or aliased tables in the module.
pub num_imported_tables: usize,
/// Number of imported or aliased memories in the module.
pub num_imported_memories: usize,
/// Number of imported or aliased globals in the module.
pub num_imported_globals: usize,
/// Number of functions that "escape" from this module may need to have a
/// `VMFuncRef` constructed for them.
///
/// This is also the number of functions in the `functions` array below with
/// an `func_ref` index (and is the maximum func_ref index).
pub num_escaped_funcs: usize,
/// Number of call-indirect caches.
pub num_call_indirect_caches: usize,
/// Types of functions, imported and local.
pub functions: PrimaryMap<FuncIndex, FunctionType>,
/// WebAssembly tables.
pub tables: PrimaryMap<TableIndex, Table>,
/// WebAssembly linear memory plans.
pub memories: PrimaryMap<MemoryIndex, Memory>,
/// WebAssembly global variables.
pub globals: PrimaryMap<GlobalIndex, Global>,
/// WebAssembly global initializers for locally-defined globals.
pub global_initializers: PrimaryMap<DefinedGlobalIndex, ConstExpr>,
}
/// Initialization routines for creating an instance, encompassing imports,
/// modules, instances, aliases, etc.
#[derive(Debug, Serialize, Deserialize)]
pub enum Initializer {
/// An imported item is required to be provided.
Import {
/// Name of this import
name: String,
/// The field name projection of this import
field: String,
/// Where this import will be placed, which also has type information
/// about the import.
index: EntityIndex,
},
}
impl Module {
/// Allocates the module data structures.
pub fn new() -> Self {
Module::default()
}
/// Convert a `DefinedFuncIndex` into a `FuncIndex`.
#[inline]
pub fn func_index(&self, defined_func: DefinedFuncIndex) -> FuncIndex {
FuncIndex::new(self.num_imported_funcs + defined_func.index())
}
/// Convert a `FuncIndex` into a `DefinedFuncIndex`. Returns None if the
/// index is an imported function.
#[inline]
pub fn defined_func_index(&self, func: FuncIndex) -> Option<DefinedFuncIndex> {
if func.index() < self.num_imported_funcs {
None
} else {
Some(DefinedFuncIndex::new(
func.index() - self.num_imported_funcs,
))
}
}
/// Test whether the given function index is for an imported function.
#[inline]
pub fn is_imported_function(&self, index: FuncIndex) -> bool {
index.index() < self.num_imported_funcs
}
/// Convert a `DefinedTableIndex` into a `TableIndex`.
#[inline]
pub fn table_index(&self, defined_table: DefinedTableIndex) -> TableIndex {
TableIndex::new(self.num_imported_tables + defined_table.index())
}
/// Convert a `TableIndex` into a `DefinedTableIndex`. Returns None if the
/// index is an imported table.
#[inline]
pub fn defined_table_index(&self, table: TableIndex) -> Option<DefinedTableIndex> {
if table.index() < self.num_imported_tables {
None
} else {
Some(DefinedTableIndex::new(
table.index() - self.num_imported_tables,
))
}
}
/// Test whether the given table index is for an imported table.
#[inline]
pub fn is_imported_table(&self, index: TableIndex) -> bool {
index.index() < self.num_imported_tables
}
/// Convert a `DefinedMemoryIndex` into a `MemoryIndex`.
#[inline]
pub fn memory_index(&self, defined_memory: DefinedMemoryIndex) -> MemoryIndex {
MemoryIndex::new(self.num_imported_memories + defined_memory.index())
}
/// Convert a `MemoryIndex` into a `DefinedMemoryIndex`. Returns None if the
/// index is an imported memory.
#[inline]
pub fn defined_memory_index(&self, memory: MemoryIndex) -> Option<DefinedMemoryIndex> {
if memory.index() < self.num_imported_memories {
None
} else {
Some(DefinedMemoryIndex::new(
memory.index() - self.num_imported_memories,
))
}
}
/// Convert a `DefinedMemoryIndex` into an `OwnedMemoryIndex`. Returns None
/// if the index is an imported memory.
#[inline]
pub fn owned_memory_index(&self, memory: DefinedMemoryIndex) -> OwnedMemoryIndex {
assert!(
memory.index() < self.memories.len(),
"non-shared memory must have an owned index"
);
// Once we know that the memory index is not greater than the number of
// plans, we can iterate through the plans up to the memory index and
// count how many are not shared (i.e., owned).
let owned_memory_index = self
.memories
.iter()
.skip(self.num_imported_memories)
.take(memory.index())
.filter(|(_, mp)| !mp.shared)
.count();
OwnedMemoryIndex::new(owned_memory_index)
}
/// Test whether the given memory index is for an imported memory.
#[inline]
pub fn is_imported_memory(&self, index: MemoryIndex) -> bool {
index.index() < self.num_imported_memories
}
/// Convert a `DefinedGlobalIndex` into a `GlobalIndex`.
#[inline]
pub fn global_index(&self, defined_global: DefinedGlobalIndex) -> GlobalIndex {
GlobalIndex::new(self.num_imported_globals + defined_global.index())
}
/// Convert a `GlobalIndex` into a `DefinedGlobalIndex`. Returns None if the
/// index is an imported global.
#[inline]
pub fn defined_global_index(&self, global: GlobalIndex) -> Option<DefinedGlobalIndex> {
if global.index() < self.num_imported_globals {
None
} else {
Some(DefinedGlobalIndex::new(
global.index() - self.num_imported_globals,
))
}
}
/// Test whether the given global index is for an imported global.
#[inline]
pub fn is_imported_global(&self, index: GlobalIndex) -> bool {
index.index() < self.num_imported_globals
}
/// Returns an iterator of all the imports in this module, along with their
/// module name, field name, and type that's being imported.
pub fn imports(&self) -> impl ExactSizeIterator<Item = (&str, &str, EntityType)> {
self.initializers.iter().map(move |i| match i {
Initializer::Import { name, field, index } => {
(name.as_str(), field.as_str(), self.type_of(*index))
}
})
}
/// Returns the type of an item based on its index
pub fn type_of(&self, index: EntityIndex) -> EntityType {
match index {
EntityIndex::Global(i) => EntityType::Global(self.globals[i]),
EntityIndex::Table(i) => EntityType::Table(self.tables[i]),
EntityIndex::Memory(i) => EntityType::Memory(self.memories[i]),
EntityIndex::Function(i) => {
EntityType::Function(EngineOrModuleTypeIndex::Module(self.functions[i].signature))
}
}
}
/// Appends a new function to this module with the given type information,
/// used for functions that either don't escape or aren't certain whether
/// they escape yet.
pub fn push_function(&mut self, signature: ModuleInternedTypeIndex) -> FuncIndex {
self.functions.push(FunctionType {
signature,
func_ref: FuncRefIndex::reserved_value(),
})
}
/// Returns an iterator over all of the defined function indices in this
/// module.
pub fn defined_func_indices(&self) -> impl Iterator<Item = DefinedFuncIndex> {
(0..self.functions.len() - self.num_imported_funcs).map(|i| DefinedFuncIndex::new(i))
}
/// Returns the number of tables defined by this module itself: all tables
/// minus imported tables.
pub fn num_defined_tables(&self) -> usize {
self.tables.len() - self.num_imported_tables
}
/// Returns the number of memories defined by this module itself: all
/// memories minus imported memories.
pub fn num_defined_memories(&self) -> usize {
self.memories.len() - self.num_imported_memories
}
}
/// Type information about functions in a wasm module.
#[derive(Debug, Serialize, Deserialize)]
pub struct FunctionType {
/// The type of this function, indexed into the module-wide type tables for
/// a module compilation.
pub signature: ModuleInternedTypeIndex,
/// The index into the funcref table, if present. Note that this is
/// `reserved_value()` if the function does not escape from a module.
pub func_ref: FuncRefIndex,
}
impl FunctionType {
/// Returns whether this function's type is one that "escapes" the current
/// module, meaning that the function is exported, used in `ref.func`, used
/// in a table, etc.
pub fn is_escaping(&self) -> bool {
!self.func_ref.is_reserved_value()
}
}
/// Index into the funcref table within a VMContext for a function.
#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Debug, Serialize, Deserialize)]
pub struct FuncRefIndex(u32);
cranelift_entity::entity_impl!(FuncRefIndex);