62c5af68b5aa7c3b0995053679df82d202cdbf15
3 Commits
| Author | SHA1 | Message | Date | |
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Alex Crichton
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650979ae40 |
Implement strings in adapter modules (#4623)
* Implement strings in adapter modules This commit is a hefty addition to Wasmtime's support for the component model. This implements the final remaining type (in the current type hierarchy) unimplemented in adapter module trampolines: strings. Strings are the most complicated type to implement in adapter trampolines because they are highly structured chunks of data in memory (according to specific encodings). Additionally each lift/lower operation can choose its own encoding for strings meaning that Wasmtime, the host, may have to convert between any pairwise ordering of string encodings. The `CanonicalABI.md` in the component-model repo in general specifies all the fiddly bits of string encoding so there's not a ton of wiggle room for Wasmtime to get creative. This PR largely "just" implements that. The high-level architecture of this implementation is: * Fused adapters are first identified to determine src/dst string encodings. This statically fixes what transcoding operation is being performed. * The generated adapter will be responsible for managing calls to `realloc` and performing bounds checks. The adapter itself does not perform memory copies or validation of string contents, however. Instead each transcoding operation is modeled as an imported function into the adapter module. This means that the adapter module dynamically, during compile time, determines what string transcoders are needed. Note that an imported transcoder is not only parameterized over the transcoding operation but additionally which memory is the source and which is the destination. * The imported core wasm functions are modeled as a new `CoreDef::Transcoder` structure. These transcoders end up being small Cranelift-compiled trampolines. The Cranelift-compiled trampoline will load the actual base pointer of memory and add it to the relative pointers passed as function arguments. This trampoline then calls a transcoder "libcall" which enters Rust-defined functions for actual transcoding operations. * Each possible transcoding operation is implemented in Rust with a unique name and a unique signature depending on the needs of the transcoder. I've tried to document inline what each transcoder does. This means that the `Module::translate_string` in adapter modules is by far the largest translation method. The main reason for this is due to the management around calling the imported transcoder functions in the face of validating string pointer/lengths and performing the dance of `realloc`-vs-transcode at the right time. I've tried to ensure that each individual case in transcoding is documented well enough to understand what's going on as well. Additionally in this PR is a full implementation in the host for the `latin1+utf16` encoding which means that both lifting and lowering host strings now works with this encoding. Currently the implementation of each transcoder function is likely far from optimal. Where possible I've leaned on the standard library itself and for latin1-related things I'm leaning on the `encoding_rs` crate. I initially tried to implement everything with `encoding_rs` but was unable to uniformly do so easily. For now I settled on trying to get a known-correct (even in the face of endianness) implementation for all of these transcoders. If an when performance becomes an issue it should be possible to implement more optimized versions of each of these transcoding operations. Testing this commit has been somewhat difficult and my general plan, like with the `(list T)` type, is to rely heavily on fuzzing to cover the various cases here. In this PR though I've added a simple test that pushes some statically known strings through all the pairs of encodings between source and destination. I've attempted to pick "interesting" strings that one way or another stress the various paths in each transcoding operation to ideally get full branch coverage there. Additionally a suite of "negative" tests have also been added to ensure that validity of encoding is actually checked. * Fix a temporarily commented out case * Fix wasmtime-runtime tests * Update deny.toml configuration * Add `BSD-3-Clause` for the `encoding_rs` crate * Remove some unused licenses * Add an exemption for `encoding_rs` for now * Split up the `translate_string` method Move out all the closures and package up captured state into smaller lists of arguments. * Test out-of-bounds for zero-length strings |
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Alex Crichton
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1ce9e8aa5f |
Fix an issue in adapter module partitioning (#4622)
When an adapter module depends on a particular core wasm instance this means that it actually depends on not only that instance but all prior core wasm instances as well. This is because core wasm instances must be instantiated in the specified order within a component and that cannot change depending on the dataflow between adapters. This commit fixes a possible panic from linearizing the component dfg where an adapter module tried to depend on an instance that hadn't been instantiated yet because the ordering dependency between core wasm instances hadn't been modeled. |
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Alex Crichton
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b4d7ab36f9 |
Add a dataflow-based representation of components (#4597)
* Add a dataflow-based representation of components This commit updates the inlining phase of compiling a component to creating a dataflow-based representation of a component instead of creating a final `Component` with a linear list of initializers. This dataflow graph is then linearized in a final step to create the actual final `Component`. The motivation for this commit stems primarily from my work implementing strings in fused adapters. In doing this my plan is to defer most low-level transcoding to the host itself rather than implementing that in the core wasm adapter modules. This means that small cranelift-generated trampolines will be used for adapter modules to call which then call "transcoding libcalls". The cranelift-generated trampolines will get raw pointers into linear memory and pass those to the libcall which core wasm doesn't have access to when passing arguments to an import. Implementing this with the previous representation of a `Component` was becoming too tricky to bear. The initialization of a transcoder needed to happen at just the right time: before the adapter module which needed it was instantiated but after the linear memories referenced had been extracted into the `VMComponentContext`. The difficulty here is further compounded by the current adapter module injection pass already being quite complicated. Adapter modules are already renumbering the index space of runtime instances and shuffling items around in the `GlobalInitializer` list. Perhaps the worst part of this was that memories could already be referenced by host function imports or exports to the host, and if adapters referenced the same memory it shouldn't be referenced twice in the component. This meant that `ExtractMemory` initializers ideally needed to be shuffled around in the initializer list to happen as early as possible instead of wherever they happened to show up during translation. Overall I did my best to implement the transcoders but everything always came up short. I have decided to throw my hands up in the air and try a completely different approach to this, namely the dataflow-based representation in this commit. This makes it much easier to edit the component after initial translation for injection of adapters, injection of transcoders, adding dependencies on possibly-already-existing items, etc. The adapter module partitioning pass in this commit was greatly simplified to something which I believe is functionally equivalent but is probably an order of magnitude easier to understand. The biggest downside of this representation I believe is having a duplicate representation of a component. The `component::info` was largely duplicated into the `component::dfg` module in this commit. Personally though I think this is a more appropriate tradeoff than before because it's very easy to reason about "convert representation A to B" code whereas it was very difficult to reason about shuffling around `GlobalInitializer` items in optimal fashions. This may also have a cost at compile-time in terms of shuffling data around, but my hope is that we have lots of other low-hanging fruit to optimize if it ever comes to that which allows keeping this easier-to-understand representation. Finally, to reiterate, the final representation of components is not changed by this PR. To the runtime internals everything is still the same. * Fix compile of factc |