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Implement AOT compilation for components (#5160)

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* Pull `Module` out of `ModuleTextBuilder`

This commit is the first in what will likely be a number towards
preparing for serializing a compiled component to bytes, a precompiled
artifact. To that end my rough plan is to merge all of the compiled
artifacts for a component into one large object file instead of having
lots of separate object files and lots of separate mmaps to manage. To
that end I plan on eventually using `ModuleTextBuilder` to build one
large text section for all core wasm modules and trampolines, meaning
that `ModuleTextBuilder` is no longer specific to one module. I've
extracted out functionality such as function name calculation as well as
relocation resolving (now a closure passed in) in preparation for this.

For now this just keeps tests passing, and the trajectory for this
should become more clear over the following commits.

* Remove component-specific object emission

This commit removes the `ComponentCompiler::emit_obj` function in favor
of `Compiler::emit_obj`, now renamed `append_code`. This involved
significantly refactoring code emission to take a flat list of functions
into `append_code` and the caller is responsible for weaving together
various "families" of functions and un-weaving them afterwards.

* Consolidate ELF parsing in `CodeMemory`

This commit moves the ELF file parsing and section iteration from
`CompiledModule` into `CodeMemory` so one location keeps track of
section ranges and such. This is in preparation for sharing much of this
code with components which needs all the same sections to get tracked
but won't be using `CompiledModule`. A small side benefit from this is
that the section parsing done in `CodeMemory` and `CompiledModule` is no
longer duplicated.

* Remove separately tracked traps in components

Previously components would generate an "always trapping" function
and the metadata around which pc was allowed to trap was handled
manually for components. With recent refactorings the Wasmtime-standard
trap section in object files is now being generated for components as
well which means that can be reused instead of custom-tracking this
metadata. This commit removes the manual tracking for the `always_trap`
functions and plumbs the necessary bits around to make components look
more like modules.

* Remove a now-unnecessary `Arc` in `Module`

Not expected to have any measurable impact on performance, but
complexity-wise this should make it a bit easier to understand the
internals since there's no longer any need to store this somewhere else
than its owner's location.

* Merge compilation artifacts of components

This commit is a large refactoring of the component compilation process
to produce a single artifact instead of multiple binary artifacts. The
core wasm compilation process is refactored as well to share as much
code as necessary with the component compilation process.

This method of representing a compiled component necessitated a few
medium-sized changes internally within Wasmtime:

* A new data structure was created, `CodeObject`, which represents
  metadata about a single compiled artifact. This is then stored as an
  `Arc` within a component and a module. For `Module` this is always
  uniquely owned and represents a shuffling around of data from one
  owner to another. For a `Component`, however, this is shared amongst
  all loaded modules and the top-level component.

* The "module registry" which is used for symbolicating backtraces and
  for trap information has been updated to account for a single region
  of loaded code holding possibly multiple modules. This involved adding
  a second-level `BTreeMap` for now. This will likely slow down
  instantiation slightly but if it poses an issue in the future this
  should be able to be represented with a more clever data structure.

This commit additionally solves a number of longstanding issues with
components such as compiling only one host-to-wasm trampoline per
signature instead of possibly once-per-module. Additionally the
`SignatureCollection` registration now happens once-per-component
instead of once-per-module-within-a-component.

* Fix compile errors from prior commits

* Support AOT-compiling components

This commit adds support for AOT-compiled components in the same manner
as `Module`, specifically adding:

* `Engine::precompile_component`
* `Component::serialize`
* `Component::deserialize`
* `Component::deserialize_file`

Internally the support for components looks quite similar to `Module`.
All the prior commits to this made adding the support here
(unsurprisingly) easy. Components are represented as a single object
file as are modules, and the functions for each module are all piled
into the same object file next to each other (as are areas such as data
sections). Support was also added here to quickly differentiate compiled
components vs compiled modules via the `e_flags` field in the ELF
header.

* Prevent serializing exported modules on components

The current representation of a module within a component means that the
implementation of `Module::serialize` will not work if the module is
exported from a component. The reason for this is that `serialize`
doesn't actually do anything and simply returns the underlying mmap as a
list of bytes. The mmap, however, has `.wasmtime.info` describing
component metadata as opposed to this module's metadata. While rewriting
this section could be implemented it's not so easy to do so and is
otherwise seen as not super important of a feature right now anyway.

* Fix windows build

* Fix an unused function warning

* Update crates/environ/src/compilation.rs

Co-authored-by: Nick Fitzgerald <fitzgen@gmail.com>

Co-authored-by: Nick Fitzgerald <fitzgen@gmail.com>
This commit is contained in:
Alex Crichton
2022-11-02 10:26:26 -05:00
committed by GitHub
parent 033758daaf
commit cd53bed898
45 changed files with 1991 additions and 1763 deletions
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80
crates/cranelift/src/obj.rs
View File

@@ -26,8 +26,7 @@ use object::write::{Object, SectionId, StandardSegment, Symbol, SymbolId, Symbol
use object::{Architecture, SectionKind, SymbolFlags, SymbolKind, SymbolScope};
use std::convert::TryFrom;
use std::ops::Range;
use wasmtime_environ::obj;
use wasmtime_environ::{DefinedFuncIndex, Module, PrimaryMap, SignatureIndex, Trampoline};
use wasmtime_environ::FuncIndex;
const TEXT_SECTION_NAME: &[u8] = b".text";
@@ -46,24 +45,23 @@ pub struct ModuleTextBuilder<'a> {
obj: &'a mut Object<'static>,
/// The WebAssembly module we're generating code for.
module: &'a Module,
text_section: SectionId,
unwind_info: UnwindInfoBuilder<'a>,
/// The corresponding symbol for each function, inserted as they're defined.
///
/// If an index isn't here yet then it hasn't been defined yet.
func_symbols: PrimaryMap<DefinedFuncIndex, SymbolId>,
/// In-progress text section that we're using cranelift's `MachBuffer` to
/// build to resolve relocations (calls) between functions.
text: Box<dyn TextSectionBuilder>,
}
impl<'a> ModuleTextBuilder<'a> {
pub fn new(obj: &'a mut Object<'static>, module: &'a Module, isa: &'a dyn TargetIsa) -> Self {
/// Creates a new builder for the text section of an executable.
///
/// The `.text` section will be appended to the specified `obj` along with
/// any unwinding or such information as necessary. The `num_funcs`
/// parameter indicates the number of times the `append_func` function will
/// be called. The `finish` function will panic if this contract is not met.
pub fn new(obj: &'a mut Object<'static>, isa: &'a dyn TargetIsa, num_funcs: usize) -> Self {
// Entire code (functions and trampolines) will be placed
// in the ".text" section.
let text_section = obj.add_section(
@@ -72,37 +70,40 @@ impl<'a> ModuleTextBuilder<'a> {
SectionKind::Text,
);
let num_defined = module.functions.len() - module.num_imported_funcs;
Self {
isa,
obj,
module,
text_section,
func_symbols: PrimaryMap::with_capacity(num_defined),
unwind_info: Default::default(),
text: isa.text_section_builder(num_defined as u32),
text: isa.text_section_builder(num_funcs),
}
}
/// Appends the `func` specified named `name` to this object.
///
/// The `resolve_reloc_target` closure is used to resolve a relocation
/// target to an adjacent function which has already been added or will be
/// added to this object. The argument is the relocation target specified
/// within `CompiledFunction` and the return value must be an index where
/// the target will be defined by the `n`th call to `append_func`.
///
/// Returns the symbol associated with the function as well as the range
/// that the function resides within the text section.
pub fn append_func(
&mut self,
labeled: bool,
name: Vec<u8>,
name: &str,
func: &'a CompiledFunction,
resolve_reloc_target: impl Fn(FuncIndex) -> usize,
) -> (SymbolId, Range<u64>) {
let body_len = func.body.len() as u64;
let off = self.text.append(
labeled,
true,
&func.body,
self.isa.function_alignment().max(func.info.alignment),
self.isa.function_alignment().max(func.alignment),
);
let symbol_id = self.obj.add_symbol(Symbol {
name,
name: name.as_bytes().to_vec(),
value: off,
size: body_len,
kind: SymbolKind::Text,
@@ -125,13 +126,11 @@ impl<'a> ModuleTextBuilder<'a> {
// file, but if it can't handle it then we pass through the
// relocation.
RelocationTarget::UserFunc(index) => {
let defined_index = self.module.defined_func_index(index).unwrap();
if self.text.resolve_reloc(
off + u64::from(r.offset),
r.reloc,
r.addend,
defined_index.as_u32(),
) {
let target = resolve_reloc_target(index);
if self
.text
.resolve_reloc(off + u64::from(r.offset), r.reloc, r.addend, target)
{
continue;
}
@@ -160,31 +159,6 @@ impl<'a> ModuleTextBuilder<'a> {
(symbol_id, off..off + body_len)
}
/// Appends a function to this object file.
///
/// This is expected to be called in-order for ascending `index` values.
pub fn func(&mut self, index: DefinedFuncIndex, func: &'a CompiledFunction) -> Range<u64> {
let name = obj::func_symbol_name(self.module.func_index(index));
let (symbol_id, range) = self.append_func(true, name.into_bytes(), func);
assert_eq!(self.func_symbols.push(symbol_id), index);
range
}
pub fn trampoline(&mut self, sig: SignatureIndex, func: &'a CompiledFunction) -> Trampoline {
let name = obj::trampoline_symbol_name(sig);
let range = self.named_func(&name, func);
Trampoline {
signature: sig,
start: range.start,
length: u32::try_from(range.end - range.start).unwrap(),
}
}
pub fn named_func(&mut self, name: &str, func: &'a CompiledFunction) -> Range<u64> {
let (_, range) = self.append_func(false, name.as_bytes().to_vec(), func);
range
}
/// Forces "veneers" to be used for inter-function calls in the text
/// section which means that in-bounds optimized addresses are never used.
///
@@ -210,7 +184,7 @@ impl<'a> ModuleTextBuilder<'a> {
///
/// Note that this will also write out the unwind information sections if
/// necessary.
pub fn finish(mut self) -> Result<PrimaryMap<DefinedFuncIndex, SymbolId>> {
pub fn finish(mut self) {
// Finish up the text section now that we're done adding functions.
let text = self.text.finish();
self.obj
@@ -220,8 +194,6 @@ impl<'a> ModuleTextBuilder<'a> {
// Append the unwind information for all our functions, if necessary.
self.unwind_info
.append_section(self.isa, self.obj, self.text_section);
Ok(self.func_symbols)
}
}