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Remove the module linking implementation in Wasmtime (bytecodeallianc…
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…e#3958)

* Remove the module linking implementation in Wasmtime

This commit removes the experimental implementation of the module
linking WebAssembly proposal from Wasmtime. The module linking is no
longer intended for core WebAssembly but is instead incorporated into
the component model now at this point. This means that very large parts
of Wasmtime's implementation of module linking are no longer applicable
and would change greatly with an implementation of the component model.

The main purpose of this is to remove Wasmtime's reliance on the support
for module-linking in `wasmparser` and tooling crates. With this
reliance removed we can move over to the `component-model` branch of
`wasmparser` and use the updated support for the component model.
Additionally given the trajectory of the component model proposal the
embedding API of Wasmtime will not look like what it looks like today
for WebAssembly. For example the core wasm `Instance` will not change
and instead a `Component` is likely to be added instead.

Some more rationale for this is in bytecodealliance#3941, but the basic idea is that I
feel that it's not going to be viable to develop support for the
component model on a non-`main` branch of Wasmtime. Additionaly I don't
think it's viable, for the same reasons as `wasm-tools`, to support the
old module linking proposal and the new component model at the same
time.

This commit takes a moment to not only delete the existing module
linking implementation but some abstractions are also simplified. For
example module serialization is a bit simpler that there's only one
module. Additionally instantiation is much simpler since the only
initializer we have to deal with are imports and nothing else.

Closes bytecodealliance#3941

* Fix doc link

* Update comments
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@alexcrichton
alexcrichton authored Mar 23, 2022
1 parent 6a60e83 commit 76b8291
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Showing 51 changed files with 403 additions and 4,558 deletions.
1 change: 0 additions & 1 deletion build.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,6 @@ fn main() -> anyhow::Result<()> {
with_test_module(&mut out, "misc", |out| {
test_directory(out, "tests/misc_testsuite", strategy)?;
test_directory_module(out, "tests/misc_testsuite/multi-memory", strategy)?;
test_directory_module(out, "tests/misc_testsuite/module-linking", strategy)?;
test_directory_module(out, "tests/misc_testsuite/simd", strategy)?;
test_directory_module(out, "tests/misc_testsuite/threads", strategy)?;
test_directory_module(out, "tests/misc_testsuite/memory64", strategy)?;
Expand Down
2 changes: 1 addition & 1 deletion cranelift/wasm/src/environ/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,5 +6,5 @@ mod spec;

pub use crate::environ::dummy::DummyEnvironment;
pub use crate::environ::spec::{
Alias, FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode, TargetEnvironment,
FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode, TargetEnvironment,
};
125 changes: 3 additions & 122 deletions cranelift/wasm/src/environ/spec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,9 +8,9 @@
use crate::state::FuncTranslationState;
use crate::{
DataIndex, ElemIndex, EntityIndex, EntityType, FuncIndex, Global, GlobalIndex, InstanceIndex,
InstanceTypeIndex, Memory, MemoryIndex, ModuleIndex, ModuleTypeIndex, SignatureIndex, Table,
TableIndex, Tag, TagIndex, TypeIndex, WasmError, WasmFuncType, WasmResult, WasmType,
DataIndex, ElemIndex, EntityType, FuncIndex, Global, GlobalIndex, Memory, MemoryIndex,
SignatureIndex, Table, TableIndex, Tag, TagIndex, TypeIndex, WasmError, WasmFuncType,
WasmResult, WasmType,
};
use core::convert::From;
use cranelift_codegen::cursor::FuncCursor;
Expand All @@ -20,7 +20,6 @@ use cranelift_codegen::isa::TargetFrontendConfig;
use cranelift_frontend::FunctionBuilder;
use std::boxed::Box;
use std::string::ToString;
use std::vec::Vec;
use wasmparser::{FuncValidator, FunctionBody, Operator, ValidatorResources, WasmFeatures};

/// The value of a WebAssembly global variable.
Expand Down Expand Up @@ -52,39 +51,6 @@ pub enum ReturnMode {
FallthroughReturn,
}

/// An entry in the alias section of a wasm module (from the module linking
/// proposal)
pub enum Alias<'a> {
/// An outer module's module is being aliased into our own index space.
OuterModule {
/// The number of modules above us that we're referencing.
relative_depth: u32,
/// The module index in the outer module's index space we're referencing.
index: ModuleIndex,
},

/// An outer module's type is being aliased into our own index space
///
/// Note that the index here is in the outer module's index space, not our
/// own.
OuterType {
/// The number of modules above us that we're referencing.
relative_depth: u32,
/// The type index in the outer module's index space we're referencing.
index: TypeIndex,
},

/// A previously created instance is having one of its exports aliased into
/// our index space.
InstanceExport {
/// The index we're aliasing.
instance: InstanceIndex,
/// The nth export that we're inserting into our own index space
/// locally.
export: &'a str,
},
}

/// Environment affecting the translation of a WebAssembly.
pub trait TargetEnvironment {
/// Get the information needed to produce Cranelift IR for the given target.
Expand Down Expand Up @@ -588,20 +554,6 @@ pub trait ModuleEnvironment<'data> {
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Translates a type index to its module type index, only called for type
/// indices which point to modules.
fn type_to_module_type(&self, index: TypeIndex) -> WasmResult<ModuleTypeIndex> {
drop(index);
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Translates a type index to its instance type index, only called for type
/// indices which point to instances.
fn type_to_instance_type(&self, index: TypeIndex) -> WasmResult<InstanceTypeIndex> {
drop(index);
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Provides the number of imports up front. By default this does nothing, but
/// implementations can use this to preallocate memory if desired.
fn reserve_imports(&mut self, _num: u32) -> WasmResult<()> {
Expand Down Expand Up @@ -662,17 +614,6 @@ pub trait ModuleEnvironment<'data> {
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Declares an instance import to the environment.
fn declare_instance_import(
&mut self,
ty_index: TypeIndex,
module: &'data str,
field: Option<&'data str>,
) -> WasmResult<()> {
drop((ty_index, module, field));
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Notifies the implementation that all imports have been declared.
fn finish_imports(&mut self) -> WasmResult<()> {
Ok(())
Expand Down Expand Up @@ -759,22 +700,6 @@ pub trait ModuleEnvironment<'data> {
name: &'data str,
) -> WasmResult<()>;

/// Declares an instance export to the environment.
fn declare_instance_export(
&mut self,
index: InstanceIndex,
name: &'data str,
) -> WasmResult<()> {
drop((index, name));
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Declares an instance export to the environment.
fn declare_module_export(&mut self, index: ModuleIndex, name: &'data str) -> WasmResult<()> {
drop((index, name));
Err(WasmError::Unsupported("module linking".to_string()))
}

/// Notifies the implementation that all exports have been declared.
fn finish_exports(&mut self) -> WasmResult<()> {
Ok(())
Expand Down Expand Up @@ -880,48 +805,4 @@ pub trait ModuleEnvironment<'data> {
fn wasm_features(&self) -> WasmFeatures {
WasmFeatures::default()
}

/// Indicates that this module will have `amount` submodules.
///
/// Note that this is just child modules of this module, and each child
/// module may have yet more submodules.
fn reserve_modules(&mut self, amount: u32) {
drop(amount);
}

/// Called at the beginning of translating a module.
///
/// Note that for nested modules this may be called multiple times.
fn module_start(&mut self) {}

/// Called at the end of translating a module.
///
/// Note that for nested modules this may be called multiple times.
fn module_end(&mut self) {}

/// Indicates that this module will have `amount` instances.
fn reserve_instances(&mut self, amount: u32) {
drop(amount);
}

/// Declares a new instance which this module will instantiate before it's
/// instantiated.
fn declare_instance(
&mut self,
module: ModuleIndex,
args: Vec<(&'data str, EntityIndex)>,
) -> WasmResult<()> {
drop((module, args));
Err(WasmError::Unsupported("wasm instance".to_string()))
}

/// Declares a new alias being added to this module.
///
/// The alias comes from the `instance` specified (or the parent if `None`
/// is supplied) and the index is either in the module's own index spaces
/// for the parent or an index into the exports for nested instances.
fn declare_alias(&mut self, alias: Alias<'data>) -> WasmResult<()> {
drop(alias);
Err(WasmError::Unsupported("wasm alias".to_string()))
}
}
2 changes: 1 addition & 1 deletion cranelift/wasm/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,7 @@ mod state;
mod translation_utils;

pub use crate::environ::{
Alias, DummyEnvironment, FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode,
DummyEnvironment, FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode,
TargetEnvironment,
};
pub use crate::func_translator::FuncTranslator;
Expand Down
16 changes: 7 additions & 9 deletions cranelift/wasm/src/module_translator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,9 @@
//! to deal with each part of it.
use crate::environ::ModuleEnvironment;
use crate::sections_translator::{
parse_alias_section, parse_data_section, parse_element_section, parse_export_section,
parse_function_section, parse_global_section, parse_import_section, parse_instance_section,
parse_memory_section, parse_name_section, parse_start_section, parse_table_section,
parse_tag_section, parse_type_section,
parse_data_section, parse_element_section, parse_export_section, parse_function_section,
parse_global_section, parse_import_section, parse_memory_section, parse_name_section,
parse_start_section, parse_table_section, parse_tag_section, parse_type_section,
};
use crate::state::ModuleTranslationState;
use crate::WasmResult;
Expand All @@ -28,11 +27,9 @@ pub fn translate_module<'data>(
match payload? {
Payload::Version { num, range } => {
validator.version(num, &range)?;
environ.module_start();
}
Payload::End => {
validator.end()?;
environ.module_end();
}

Payload::TypeSection(types) => {
Expand Down Expand Up @@ -109,23 +106,24 @@ pub fn translate_module<'data>(

Payload::InstanceSection(s) => {
validator.instance_section(&s)?;
parse_instance_section(s, environ)?;
unimplemented!();
}
Payload::AliasSection(s) => {
validator.alias_section(&s)?;
parse_alias_section(s, environ)?;
unimplemented!();
}
Payload::ModuleSectionStart {
count,
range,
size: _,
} => {
validator.module_section_start(count, &range)?;
environ.reserve_modules(count);
unimplemented!();
}

Payload::ModuleSectionEntry { .. } => {
validator.module_section_entry();
unimplemented!();
}

Payload::CustomSection {
Expand Down
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