2 Commits

Author	SHA1	Message	Date
Nick Fitzgerald	a2f846f124	Don't re-capture backtraces when propagating traps through host frames (#5049) ... * Add a benchmark for traps with many Wasm<-->host calls on the stack * Add a test for expected Wasm stack traces with Wasm<--host calls on the stack when we trap * Don't re-capture backtraces when propagating traps through host frames This fixes some accidentally quadratic code where we would re-capture a Wasm stack trace (takes `O(n)` time) every time we propagated a trap through a host frame back to Wasm (can happen `O(n)` times). And `O(n) * O(n) = O(n^2)`, of course. Whoops. After this commit, it trapping with a call stack that is `n` frames deep of Wasm-to-host-to-Wasm calls just captures a single backtrace and is therefore just a proper `O(n)` time operation, as it is intended to be. Now we explicitly track whether we need to capture a Wasm backtrace or not when raising a trap. This unfortunately isn't as straightforward as one might hope, however, because of the split between `wasmtime::Trap` and `wasmtime_runtime::Trap`. We need to decide whether or not to capture a Wasm backtrace inside `wasmtime_runtime` but in order to determine whether to do that or not we need to reflect on the `anyhow::Error` and see if it is a `wasmtime::Trap` that already has a backtrace or not. This can't be done the straightforward way because it would introduce a cyclic dependency between the `wasmtime` and `wasmtime-runtime` crates. We can't merge those two `Trap` types-- at least not without effectively merging the whole `wasmtime` and `wasmtime-runtime` crates together, which would be a good idea in a perfect world but would be a *ton* of ocean boiling from where we currently are -- because `wasmtime::Trap` does symbolication of stack traces which relies on module registration information data that resides inside the `wasmtime` crate and therefore can't be moved into `wasmtime-runtime`. We resolve this problem by adding a boolean to `wasmtime_runtime::raise_user_trap` that controls whether we should capture a Wasm backtrace or not, and then determine whether we need a backtrace or not at each of that function's call sites, which are in `wasmtime` and therefore can do the reflection to determine whether the user trap already has a backtrace or not. Phew! Fixes #5037 * debug assert that we don't record unnecessary backtraces for traps * Add assertions around `needs_backtrace` Unfortunately we can't do debug_assert_eq!(needs_backtrace, trap.inner.backtrace.get().is_some()); because `needs_backtrace` doesn't consider whether Wasm backtraces have been disabled via config. * Consolidate `needs_backtrace` calculation followed by calling `raise_user_trap` into one place	2022-10-13 07:22:46 -07:00
Alex Crichton	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	2022-08-08 16:01:57 +00:00