T0b1/wasmtime
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Fully support multiple returns in Wasmtime (#2806)

Browse Source 
* Fully support multiple returns in Wasmtime

For quite some time now Wasmtime has "supported" multiple return values,
but only in the mose bare bones ways. Up until recently you couldn't get
a typed version of functions with multiple return values, and never have
you been able to use `Func::wrap` with functions that return multiple
values. Even recently where `Func::typed` can call functions that return
multiple values it uses a double-indirection by calling a trampoline
which calls the real function.

The underlying reason for this lack of support is that cranelift's ABI
for returning multiple values is not possible to write in Rust. For
example if a wasm function returns two `i32` values there is no Rust (or
C!) function you can write to correspond to that. This commit, however
fixes that.

This commit adds two new ABIs to Cranelift: `WasmtimeSystemV` and
`WasmtimeFastcall`. The intention is that these Wasmtime-specific ABIs
match their corresponding ABI (e.g. `SystemV` or `WindowsFastcall`) for
everything *except* how multiple values are returned. For multiple
return values we simply define our own version of the ABI which Wasmtime
implements, which is that for N return values the first is returned as
if the function only returned that and the latter N-1 return values are
returned via an out-ptr that's the last parameter to the function.

These custom ABIs provides the ability for Wasmtime to bind these in
Rust meaning that `Func::wrap` can now wrap functions that return
multiple values and `Func::typed` no longer uses trampolines when
calling functions that return multiple values. Although there's lots of
internal changes there's no actual changes in the API surface area of
Wasmtime, just a few more impls of more public traits which means that
more types are supported in more places!

Another change made with this PR is a consolidation of how the ABI of
each function in a wasm module is selected. The native `SystemV` ABI,
for example, is more efficient at returning multiple values than the
wasmtime version of the ABI (since more things are in more registers).
To continue to take advantage of this Wasmtime will now classify some
functions in a wasm module with the "fast" ABI. Only functions that are
not reachable externally from the module are classified with the fast
ABI (e.g. those not exported, used in tables, or used with `ref.func`).
This should enable purely internal functions of modules to have a faster
calling convention than those which might be exposed to Wasmtime itself.

Closes #1178

* Tweak some names and add docs

* "fix" lightbeam compile

* Fix TODO with dummy environ

* Unwind info is a property of the target, not the ABI

* Remove lightbeam unused imports

* Attempt to fix arm64

* Document new ABIs aren't stable

* Fix filetests to use the right target

* Don't always do 64-bit stores with cranelift

This was overwriting upper bits when 32-bit registers were being stored
into return values, so fix the code inline to do a sized store instead
of one-size-fits-all store.

* At least get tests passing on the old backend

* Fix a typo

* Add some filetests with mixed abi calls

* Get `multi` example working

* Fix doctests on old x86 backend

* Add a mixture of wasmtime/system_v tests
This commit is contained in:
Alex Crichton
2021-04-07 12:34:26 -05:00
committed by GitHub
parent 7588565078
commit 195bf0e29a
37 changed files with 1116 additions and 459 deletions
Download Patch File Download Diff File Expand all files Collapse all files

48
crates/environ/src/module_environ.rs
View File

@@ -4,14 +4,14 @@ use crate::module::{
};
use crate::tunables::Tunables;
use cranelift_codegen::ir;
use cranelift_codegen::ir::{AbiParam, ArgumentPurpose};
use cranelift_codegen::isa::TargetFrontendConfig;
use cranelift_codegen::packed_option::ReservedValue;
use cranelift_entity::PrimaryMap;
use cranelift_wasm::{
self, translate_module, Alias, DataIndex, DefinedFuncIndex, ElemIndex, EntityIndex, EntityType,
FuncIndex, Global, GlobalIndex, InstanceIndex, InstanceTypeIndex, Memory, MemoryIndex,
ModuleIndex, ModuleTypeIndex, SignatureIndex, Table, TableIndex, TargetEnvironment, TypeIndex,
WasmError, WasmFuncType, WasmResult,
FuncIndex, Global, GlobalIndex, GlobalInit, InstanceIndex, InstanceTypeIndex, Memory,
MemoryIndex, ModuleIndex, ModuleTypeIndex, SignatureIndex, Table, TableIndex,
TargetEnvironment, TypeIndex, WasmError, WasmFuncType, WasmResult,
};
use std::collections::{hash_map::Entry, HashMap};
use std::convert::TryFrom;
@@ -357,6 +357,15 @@ impl<'data> ModuleEnvironment<'data> {
.module_signatures
.push(ModuleSignature { imports, exports })
}
fn flag_func_possibly_exported(&mut self, func: FuncIndex) {
if func.is_reserved_value() {
return;
}
if let Some(idx) = self.result.module.defined_func_index(func) {
self.result.module.possibly_exported_funcs.insert(idx);
}
}
}
impl<'data> TargetEnvironment for ModuleEnvironment<'data> {
@@ -375,21 +384,17 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
fn reserve_types(&mut self, num: u32) -> WasmResult<()> {
let num = usize::try_from(num).unwrap();
self.result.module.types.reserve(num);
self.types.native_signatures.reserve(num);
self.types.wasm_signatures.reserve(num);
Ok(())
}
fn declare_type_func(&mut self, wasm: WasmFuncType, sig: ir::Signature) -> WasmResult<()> {
fn declare_type_func(&mut self, wasm: WasmFuncType) -> WasmResult<()> {
// Deduplicate wasm function signatures through `interned_func_types`,
// which also deduplicates across wasm modules with module linking.
let sig_index = match self.interned_func_types.get(&wasm) {
Some(idx) => *idx,
None => {
let sig = translate_signature(sig, self.pointer_type());
let sig_index = self.types.native_signatures.push(sig);
let sig_index2 = self.types.wasm_signatures.push(wasm.clone());
debug_assert_eq!(sig_index, sig_index2);
let sig_index = self.types.wasm_signatures.push(wasm.clone());
self.interned_func_types.insert(wasm, sig_index);
sig_index
}
@@ -641,6 +646,9 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
}
fn declare_global(&mut self, global: Global) -> WasmResult<()> {
if let GlobalInit::RefFunc(index) = global.initializer {
self.flag_func_possibly_exported(index);
}
self.result.module.globals.push(global);
Ok(())
}
@@ -654,6 +662,7 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
}
fn declare_func_export(&mut self, func_index: FuncIndex, name: &str) -> WasmResult<()> {
self.flag_func_possibly_exported(func_index);
self.declare_export(EntityIndex::Function(func_index), name)
}
@@ -678,6 +687,7 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
}
fn declare_start_func(&mut self, func_index: FuncIndex) -> WasmResult<()> {
self.flag_func_possibly_exported(func_index);
debug_assert!(self.result.module.start_func.is_none());
self.result.module.start_func = Some(func_index);
Ok(())
@@ -698,6 +708,9 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
offset: usize,
elements: Box<[FuncIndex]>,
) -> WasmResult<()> {
for element in elements.iter() {
self.flag_func_possibly_exported(*element);
}
self.result
.module
.table_initializers
@@ -715,6 +728,9 @@ impl<'data> cranelift_wasm::ModuleEnvironment<'data> for ModuleEnvironment<'data
elem_index: ElemIndex,
segments: Box<[FuncIndex]>,
) -> WasmResult<()> {
for element in segments.iter() {
self.flag_func_possibly_exported(*element);
}
let index = self.result.module.passive_elements.len();
self.result.module.passive_elements.push(segments);
let old = self
@@ -1070,15 +1086,3 @@ and for re-adding support for interface types you can see this issue:
Ok(())
}
}
/// Add environment-specific function parameters.
pub fn translate_signature(mut sig: ir::Signature, pointer_type: ir::Type) -> ir::Signature {
// Prepend the vmctx argument.
sig.params.insert(
0,
AbiParam::special(pointer_type, ArgumentPurpose::VMContext),
);
// Prepend the caller vmctx argument.
sig.params.insert(1, AbiParam::new(pointer_type));
sig
}