wasmtime_environ/fact.rs
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//! Wasmtime's Fused Adapter Compiler of Trampolines (FACT)
//!
//! This module contains a compiler which emits trampolines to implement fused
//! adapters for the component model. A fused adapter is when a core wasm
//! function is lifted from one component instance and then lowered into another
//! component instance. This communication between components is well-defined by
//! the spec and ends up creating what's called a "fused adapter".
//!
//! Adapters are currently implemented with WebAssembly modules. This submodule
//! will generate a core wasm binary which contains the adapters specified
//! during compilation. The actual wasm is then later processed by standard
//! paths in Wasmtime to create native machine code and runtime representations
//! of modules.
//!
//! Note that identification of precisely what goes into an adapter module is
//! not handled in this file, instead that's all done in `translate/adapt.rs`.
//! Otherwise this module is only responsible for taking a set of adapters and
//! their imports and then generating a core wasm module to implement all of
//! that.
use crate::component::dfg::CoreDef;
use crate::component::{
Adapter, AdapterOptions as AdapterOptionsDfg, ComponentTypesBuilder, FlatType, InterfaceType,
StringEncoding, Transcode, TypeFuncIndex,
};
use crate::fact::transcode::Transcoder;
use crate::prelude::*;
use crate::{EntityRef, FuncIndex, GlobalIndex, MemoryIndex, PrimaryMap};
use std::borrow::Cow;
use std::collections::HashMap;
use wasm_encoder::*;
mod core_types;
mod signature;
mod trampoline;
mod transcode;
mod traps;
/// Representation of an adapter module.
pub struct Module<'a> {
/// Whether or not debug code is inserted into the adapters themselves.
debug: bool,
/// Type information from the creator of this `Module`
types: &'a ComponentTypesBuilder,
/// Core wasm type section that's incrementally built
core_types: core_types::CoreTypes,
/// Core wasm import section which is built as adapters are inserted. Note
/// that imports here are intern'd to avoid duplicate imports of the same
/// item.
core_imports: ImportSection,
/// Final list of imports that this module ended up using, in the same order
/// as the imports in the import section.
imports: Vec<Import>,
/// Intern'd imports and what index they were assigned. Note that this map
/// covers all the index spaces for imports, not just one.
imported: HashMap<CoreDef, usize>,
/// Intern'd transcoders and what index they were assigned.
imported_transcoders: HashMap<Transcoder, FuncIndex>,
/// Cached versions of imported trampolines for working with resources.
imported_resource_transfer_own: Option<FuncIndex>,
imported_resource_transfer_borrow: Option<FuncIndex>,
imported_resource_enter_call: Option<FuncIndex>,
imported_resource_exit_call: Option<FuncIndex>,
// Current status of index spaces from the imports generated so far.
imported_funcs: PrimaryMap<FuncIndex, Option<CoreDef>>,
imported_memories: PrimaryMap<MemoryIndex, CoreDef>,
imported_globals: PrimaryMap<GlobalIndex, CoreDef>,
funcs: PrimaryMap<FunctionId, Function>,
helper_funcs: HashMap<Helper, FunctionId>,
helper_worklist: Vec<(FunctionId, Helper)>,
}
struct AdapterData {
/// Export name of this adapter
name: String,
/// Options specified during the `canon lift` operation
lift: AdapterOptions,
/// Options specified during the `canon lower` operation
lower: AdapterOptions,
/// The core wasm function that this adapter will be calling (the original
/// function that was `canon lift`'d)
callee: FuncIndex,
/// FIXME(#4185) should be plumbed and handled as part of the new reentrance
/// rules not yet implemented here.
called_as_export: bool,
}
/// Configuration options which apply at the "global adapter" level.
///
/// These options are typically unique per-adapter and generally aren't needed
/// when translating recursive types within an adapter.
struct AdapterOptions {
/// The ascribed type of this adapter.
ty: TypeFuncIndex,
/// The global that represents the instance flags for where this adapter
/// came from.
flags: GlobalIndex,
/// The configured post-return function, if any.
post_return: Option<FuncIndex>,
/// Other, more general, options configured.
options: Options,
}
/// This type is split out of `AdapterOptions` and is specifically used to
/// deduplicate translation functions within a module. Consequently this has
/// as few fields as possible to minimize the number of functions generated
/// within an adapter module.
#[derive(PartialEq, Eq, Hash, Copy, Clone)]
struct Options {
/// The encoding that strings use from this adapter.
string_encoding: StringEncoding,
/// Whether or not the `memory` field, if present, is a 64-bit memory.
memory64: bool,
/// An optionally-specified memory where values may travel through for
/// types like lists.
memory: Option<MemoryIndex>,
/// An optionally-specified function to be used to allocate space for
/// types such as strings as they go into a module.
realloc: Option<FuncIndex>,
}
enum Context {
Lift,
Lower,
}
/// Representation of a "helper function" which may be generated as part of
/// generating an adapter trampoline.
///
/// Helper functions are created when inlining the translation for a type in its
/// entirety would make a function excessively large. This is currently done via
/// a simple fuel/cost heuristic based on the type being translated but may get
/// fancier over time.
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
struct Helper {
/// Metadata about the source type of what's being translated.
src: HelperType,
/// Metadata about the destination type which is being translated to.
dst: HelperType,
}
/// Information about a source or destination type in a `Helper` which is
/// generated.
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
struct HelperType {
/// The concrete type being translated.
ty: InterfaceType,
/// The configuration options (memory, etc) for the adapter.
opts: Options,
/// Where the type is located (either the stack or in memory)
loc: HelperLocation,
}
/// Where a `HelperType` is located, dictating the signature of the helper
/// function.
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
enum HelperLocation {
/// Located on the stack in wasm locals.
Stack,
/// Located in linear memory as configured by `opts`.
Memory,
}
impl<'a> Module<'a> {
/// Creates an empty module.
pub fn new(types: &'a ComponentTypesBuilder, debug: bool) -> Module<'a> {
Module {
debug,
types,
core_types: Default::default(),
core_imports: Default::default(),
imported: Default::default(),
imports: Default::default(),
imported_transcoders: Default::default(),
imported_funcs: PrimaryMap::new(),
imported_memories: PrimaryMap::new(),
imported_globals: PrimaryMap::new(),
funcs: PrimaryMap::new(),
helper_funcs: HashMap::new(),
helper_worklist: Vec::new(),
imported_resource_transfer_own: None,
imported_resource_transfer_borrow: None,
imported_resource_enter_call: None,
imported_resource_exit_call: None,
}
}
/// Registers a new adapter within this adapter module.
///
/// The `name` provided is the export name of the adapter from the final
/// module, and `adapter` contains all metadata necessary for compilation.
pub fn adapt(&mut self, name: &str, adapter: &Adapter) {
// Import any items required by the various canonical options
// (memories, reallocs, etc)
let mut lift = self.import_options(adapter.lift_ty, &adapter.lift_options);
let lower = self.import_options(adapter.lower_ty, &adapter.lower_options);
// Lowering options are not allowed to specify post-return as per the
// current canonical abi specification.
assert!(adapter.lower_options.post_return.is_none());
// Import the core wasm function which was lifted using its appropriate
// signature since the exported function this adapter generates will
// call the lifted function.
let signature = self.types.signature(&lift, Context::Lift);
let ty = self
.core_types
.function(&signature.params, &signature.results);
let callee = self.import_func("callee", name, ty, adapter.func.clone());
// Handle post-return specifically here where we have `core_ty` and the
// results of `core_ty` are the parameters to the post-return function.
lift.post_return = adapter.lift_options.post_return.as_ref().map(|func| {
let ty = self.core_types.function(&signature.results, &[]);
self.import_func("post_return", name, ty, func.clone())
});
// This will internally create the adapter as specified and append
// anything necessary to `self.funcs`.
trampoline::compile(
self,
&AdapterData {
name: name.to_string(),
lift,
lower,
callee,
// FIXME(#4185) should be plumbed and handled as part of the new
// reentrance rules not yet implemented here.
called_as_export: true,
},
);
while let Some((result, helper)) = self.helper_worklist.pop() {
trampoline::compile_helper(self, result, helper);
}
}
fn import_options(&mut self, ty: TypeFuncIndex, options: &AdapterOptionsDfg) -> AdapterOptions {
let AdapterOptionsDfg {
instance,
string_encoding,
memory,
memory64,
realloc,
post_return: _, // handled above
} = options;
let flags = self.import_global(
"flags",
&format!("instance{}", instance.as_u32()),
GlobalType {
val_type: ValType::I32,
mutable: true,
shared: false,
},
CoreDef::InstanceFlags(*instance),
);
let memory = memory.as_ref().map(|memory| {
self.import_memory(
"memory",
&format!("m{}", self.imported_memories.len()),
MemoryType {
minimum: 0,
maximum: None,
shared: false,
memory64: *memory64,
page_size_log2: None,
},
memory.clone().into(),
)
});
let realloc = realloc.as_ref().map(|func| {
let ptr = if *memory64 {
ValType::I64
} else {
ValType::I32
};
let ty = self.core_types.function(&[ptr, ptr, ptr, ptr], &[ptr]);
self.import_func(
"realloc",
&format!("f{}", self.imported_funcs.len()),
ty,
func.clone(),
)
});
AdapterOptions {
ty,
flags,
post_return: None,
options: Options {
string_encoding: *string_encoding,
memory64: *memory64,
memory,
realloc,
},
}
}
fn import_func(&mut self, module: &str, name: &str, ty: u32, def: CoreDef) -> FuncIndex {
self.import(module, name, EntityType::Function(ty), def, |m| {
&mut m.imported_funcs
})
}
fn import_global(
&mut self,
module: &str,
name: &str,
ty: GlobalType,
def: CoreDef,
) -> GlobalIndex {
self.import(module, name, EntityType::Global(ty), def, |m| {
&mut m.imported_globals
})
}
fn import_memory(
&mut self,
module: &str,
name: &str,
ty: MemoryType,
def: CoreDef,
) -> MemoryIndex {
self.import(module, name, EntityType::Memory(ty), def, |m| {
&mut m.imported_memories
})
}
fn import<K: EntityRef, V: From<CoreDef>>(
&mut self,
module: &str,
name: &str,
ty: EntityType,
def: CoreDef,
map: impl FnOnce(&mut Self) -> &mut PrimaryMap<K, V>,
) -> K {
if let Some(prev) = self.imported.get(&def) {
return K::new(*prev);
}
let idx = map(self).push(def.clone().into());
self.core_imports.import(module, name, ty);
self.imported.insert(def.clone(), idx.index());
self.imports.push(Import::CoreDef(def));
idx
}
fn import_transcoder(&mut self, transcoder: transcode::Transcoder) -> FuncIndex {
*self
.imported_transcoders
.entry(transcoder)
.or_insert_with(|| {
// Add the import to the core wasm import section...
let name = transcoder.name();
let ty = transcoder.ty(&mut self.core_types);
self.core_imports.import("transcode", &name, ty);
// ... and also record the metadata for what this import
// corresponds to.
let from = self.imported_memories[transcoder.from_memory].clone();
let to = self.imported_memories[transcoder.to_memory].clone();
self.imports.push(Import::Transcode {
op: transcoder.op,
from,
from64: transcoder.from_memory64,
to,
to64: transcoder.to_memory64,
});
self.imported_funcs.push(None)
})
}
fn import_simple(
&mut self,
module: &str,
name: &str,
params: &[ValType],
results: &[ValType],
import: Import,
get: impl Fn(&mut Self) -> &mut Option<FuncIndex>,
) -> FuncIndex {
if let Some(idx) = get(self) {
return *idx;
}
let ty = self.core_types.function(params, results);
let ty = EntityType::Function(ty);
self.core_imports.import(module, name, ty);
self.imports.push(import);
let idx = self.imported_funcs.push(None);
*get(self) = Some(idx);
idx
}
fn import_resource_transfer_own(&mut self) -> FuncIndex {
self.import_simple(
"resource",
"transfer-own",
&[ValType::I32, ValType::I32, ValType::I32],
&[ValType::I32],
Import::ResourceTransferOwn,
|me| &mut me.imported_resource_transfer_own,
)
}
fn import_resource_transfer_borrow(&mut self) -> FuncIndex {
self.import_simple(
"resource",
"transfer-borrow",
&[ValType::I32, ValType::I32, ValType::I32],
&[ValType::I32],
Import::ResourceTransferBorrow,
|me| &mut me.imported_resource_transfer_borrow,
)
}
fn import_resource_enter_call(&mut self) -> FuncIndex {
self.import_simple(
"resource",
"enter-call",
&[],
&[],
Import::ResourceEnterCall,
|me| &mut me.imported_resource_enter_call,
)
}
fn import_resource_exit_call(&mut self) -> FuncIndex {
self.import_simple(
"resource",
"exit-call",
&[],
&[],
Import::ResourceExitCall,
|me| &mut me.imported_resource_exit_call,
)
}
fn translate_helper(&mut self, helper: Helper) -> FunctionId {
*self.helper_funcs.entry(helper).or_insert_with(|| {
// Generate a fresh `Function` with a unique id for what we're about to
// generate.
let ty = helper.core_type(self.types, &mut self.core_types);
let id = self.funcs.push(Function::new(None, ty));
self.helper_worklist.push((id, helper));
id
})
}
/// Encodes this module into a WebAssembly binary.
pub fn encode(&mut self) -> Vec<u8> {
// Build the function/export sections of the wasm module in a first pass
// which will assign a final `FuncIndex` to all functions defined in
// `self.funcs`.
let mut funcs = FunctionSection::new();
let mut exports = ExportSection::new();
let mut id_to_index = PrimaryMap::<FunctionId, FuncIndex>::new();
for (id, func) in self.funcs.iter() {
assert!(func.filled_in);
let idx = FuncIndex::from_u32(self.imported_funcs.next_key().as_u32() + id.as_u32());
let id2 = id_to_index.push(idx);
assert_eq!(id2, id);
funcs.function(func.ty);
if let Some(name) = &func.export {
exports.export(name, ExportKind::Func, idx.as_u32());
}
}
// With all functions numbered the fragments of the body of each
// function can be assigned into one final adapter function.
let mut code = CodeSection::new();
let mut traps = traps::TrapSection::default();
for (id, func) in self.funcs.iter() {
let mut func_traps = Vec::new();
let mut body = Vec::new();
// Encode all locals used for this function
func.locals.len().encode(&mut body);
for (count, ty) in func.locals.iter() {
count.encode(&mut body);
ty.encode(&mut body);
}
// Then encode each "chunk" of a body which may have optional traps
// specified within it. Traps get offset by the current length of
// the body and otherwise our `Call` instructions are "relocated"
// here to the final function index.
for chunk in func.body.iter() {
match chunk {
Body::Raw(code, traps) => {
let start = body.len();
body.extend_from_slice(code);
for (offset, trap) in traps {
func_traps.push((start + offset, *trap));
}
}
Body::Call(id) => {
Instruction::Call(id_to_index[*id].as_u32()).encode(&mut body);
}
}
}
code.raw(&body);
traps.append(id_to_index[id].as_u32(), func_traps);
}
let traps = traps.finish();
let mut result = wasm_encoder::Module::new();
result.section(&self.core_types.section);
result.section(&self.core_imports);
result.section(&funcs);
result.section(&exports);
result.section(&code);
if self.debug {
result.section(&CustomSection {
name: "wasmtime-trampoline-traps".into(),
data: Cow::Borrowed(&traps),
});
}
result.finish()
}
/// Returns the imports that were used, in order, to create this adapter
/// module.
pub fn imports(&self) -> &[Import] {
&self.imports
}
}
/// Possible imports into an adapter module.
#[derive(Clone)]
pub enum Import {
/// A definition required in the configuration of an `Adapter`.
CoreDef(CoreDef),
/// A transcoding function from the host to convert between string encodings.
Transcode {
/// The transcoding operation this performs.
op: Transcode,
/// The memory being read
from: CoreDef,
/// Whether or not `from` is a 64-bit memory
from64: bool,
/// The memory being written
to: CoreDef,
/// Whether or not `to` is a 64-bit memory
to64: bool,
},
/// Transfers an owned resource from one table to another.
ResourceTransferOwn,
/// Transfers a borrowed resource from one table to another.
ResourceTransferBorrow,
/// Sets up entry metadata for a borrow resources when a call starts.
ResourceEnterCall,
/// Tears down a previous entry and handles checking borrow-related
/// metadata.
ResourceExitCall,
}
impl Options {
fn ptr(&self) -> ValType {
if self.memory64 {
ValType::I64
} else {
ValType::I32
}
}
fn ptr_size(&self) -> u8 {
if self.memory64 {
8
} else {
4
}
}
fn flat_types<'a>(
&self,
ty: &InterfaceType,
types: &'a ComponentTypesBuilder,
) -> Option<&'a [FlatType]> {
let flat = types.flat_types(ty)?;
Some(if self.memory64 {
flat.memory64
} else {
flat.memory32
})
}
}
/// Temporary index which is not the same as `FuncIndex`.
///
/// This represents the nth generated function in the adapter module where the
/// final index of the function is not known at the time of generation since
/// more imports may be discovered (specifically string transcoders).
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
struct FunctionId(u32);
cranelift_entity::entity_impl!(FunctionId);
/// A generated function to be added to an adapter module.
///
/// At least one function is created per-adapter and depending on the type
/// hierarchy multiple functions may be generated per-adapter.
struct Function {
/// Whether or not the `body` has been finished.
///
/// Functions are added to a `Module` before they're defined so this is used
/// to assert that the function was in fact actually filled in by the
/// time we reach `Module::encode`.
filled_in: bool,
/// The type signature that this function has, as an index into the core
/// wasm type index space of the generated adapter module.
ty: u32,
/// The locals that are used by this function, organized by the number of
/// types of each local.
locals: Vec<(u32, ValType)>,
/// If specified, the export name of this function.
export: Option<String>,
/// The contents of the function.
///
/// See `Body` for more information, and the `Vec` here represents the
/// concatenation of all the `Body` fragments.
body: Vec<Body>,
}
/// Representation of a fragment of the body of a core wasm function generated
/// for adapters.
///
/// This variant comes in one of two flavors:
///
/// 1. First a `Raw` variant is used to contain general instructions for the
/// wasm function. This is populated by `Compiler::instruction` primarily.
/// This also comes with a list of traps. and the byte offset within the
/// first vector of where the trap information applies to.
///
/// 2. A `Call` instruction variant for a `FunctionId` where the final
/// `FuncIndex` isn't known until emission time.
///
/// The purpose of this representation is the `Body::Call` variant. This can't
/// be encoded as an instruction when it's generated due to not knowing the
/// final index of the function being called. During `Module::encode`, however,
/// all indices are known and `Body::Call` is turned into a final
/// `Instruction::Call`.
///
/// One other possible representation in the future would be to encode a `Call`
/// instruction with a 5-byte leb to fill in later, but for now this felt
/// easier to represent. A 5-byte leb may be more efficient at compile-time if
/// necessary, however.
enum Body {
Raw(Vec<u8>, Vec<(usize, traps::Trap)>),
Call(FunctionId),
}
impl Function {
fn new(export: Option<String>, ty: u32) -> Function {
Function {
filled_in: false,
ty,
locals: Vec::new(),
export,
body: Vec::new(),
}
}
}
impl Helper {
fn core_type(
&self,
types: &ComponentTypesBuilder,
core_types: &mut core_types::CoreTypes,
) -> u32 {
let mut params = Vec::new();
let mut results = Vec::new();
// The source type being translated is always pushed onto the
// parameters first, either a pointer for memory or its flat
// representation.
self.src.push_flat(&mut params, types);
// The destination type goes into the parameter list if it's from
// memory or otherwise is the result of the function itself for a
// stack-based representation.
match self.dst.loc {
HelperLocation::Stack => self.dst.push_flat(&mut results, types),
HelperLocation::Memory => params.push(self.dst.opts.ptr()),
}
core_types.function(¶ms, &results)
}
}
impl HelperType {
fn push_flat(&self, dst: &mut Vec<ValType>, types: &ComponentTypesBuilder) {
match self.loc {
HelperLocation::Stack => {
for ty in self.opts.flat_types(&self.ty, types).unwrap() {
dst.push((*ty).into());
}
}
HelperLocation::Memory => {
dst.push(self.opts.ptr());
}
}
}
}