1639f2c844e5c06de9d102d6298af192af99d11c
2 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
Benjamin Bouvier
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5fecdfa491 |
Mach ports continued + support aarch64-apple unwinding (#2723)
* Switch macOS to using mach ports for trap handling This commit moves macOS to using mach ports instead of signals for handling traps. The motivation for this is listed in #2456, namely that once mach ports are used in a process that means traditional UNIX signal handlers won't get used. This means that if Wasmtime is integrated with Breakpad, for example, then Wasmtime's trap handler never fires and traps don't work. The `traphandlers` module is refactored as part of this commit to split the platform-specific bits into their own files (it was growing quite a lot for one inline `cfg_if!`). The `unix.rs` and `windows.rs` files remain the same as they were before with a few minor tweaks for some refactored interfaces. The `macos.rs` file is brand new and lifts almost its entire implementation from SpiderMonkey, adapted for Wasmtime though. The main gotcha with mach ports is that a separate thread is what services the exception. Some unsafe magic allows this separate thread to read non-`Send` and temporary state from other threads, but is hoped to be safe in this context. The unfortunate downside is that calling wasm on macOS now involves taking a global lock and modifying a global hash map twice-per-call. I'm not entirely sure how to get out of this cost for now, but hopefully for any embeddings on macOS it's not the end of the world. Closes #2456 * Add a sketch of arm64 apple support * store: maintain CallThreadState mapping when switching fibers * cranelift/aarch64: generate unwind directives to disable pointer auth Aarch64 post ARMv8.3 has a feature called pointer authentication, designed to fight ROP/JOP attacks: some pointers may be signed using new instructions, adding payloads to the high (previously unused) bits of the pointers. More on this here: https://lwn.net/Articles/718888/ Unwinders on aarch64 need to know if some pointers contained on the call frame contain an authentication code or not, to be able to properly authenticate them or use them directly. Since native code may have enabled it by default (as is the case on the Mac M1), and the default is that this configuration value is inherited, we need to explicitly disable it, for the only kind of supported pointers (return addresses). To do so, we set the value of a non-existing dwarf pseudo register (34) to 0, as documented in https://github.com/ARM-software/abi-aa/blob/master/aadwarf64/aadwarf64.rst#note-8. This is done at the function granularity, in the spirit of Cranelift compilation model. Alternatively, a single directive could be generated in the CIE, generating less information per module. * Make exception handling work on Mac aarch64 too * fibers: use a breakpoint instruction after the final call in wasmtime_fiber_start Co-authored-by: Alex Crichton <alex@alexcrichton.com> |
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Alex Crichton
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7795a230f2 |
Implement support for async functions in Wasmtime (#2434)
* Implement support for `async` functions in Wasmtime This is an implementation of [RFC 2] in Wasmtime which is to support `async`-defined host functions. At a high level support is added by executing WebAssembly code that might invoke an asynchronous host function on a separate native stack. When the host function's future is not ready we switch back to the main native stack to continue execution. There's a whole bunch of details in this commit, and it's a bit much to go over them all here in this commit message. The most important changes here are: * A new `wasmtime-fiber` crate has been written to manage the low-level details of stack-switching. Unixes use `mmap` to allocate a stack and Windows uses the native fibers implementation. We'll surely want to refactor this to move stack allocation elsewhere in the future. Fibers are intended to be relatively general with a lot of type paremters to fling values back and forth across suspension points. The whole crate is a giant wad of `unsafe` unfortunately and involves handwritten assembly with custom dwarf CFI directives to boot. Definitely deserves a close eye in review! * The `Store` type has two new methods -- `block_on` and `on_fiber` which bridge between the async and non-async worlds. Lots of unsafe fiddly bits here as we're trying to communicate context pointers between disparate portions of the code. Extra eyes and care in review is greatly appreciated. * The APIs for binding `async` functions are unfortunately pretty ugly in `Func`. This is mostly due to language limitations and compiler bugs (I believe) in Rust. Instead of `Func::wrap` we have a `Func::wrapN_async` family of methods, and we've also got a whole bunch of `Func::getN_async` methods now too. It may be worth rethinking the API of `Func` to try to make the documentation page actually grok'able. This isn't super heavily tested but the various test should suffice for engaging hopefully nearly all the infrastructure in one form or another. This is just the start though! [RFC 2]: https://github.com/bytecodealliance/rfcs/pull/2 * Add wasmtime-fiber to publish script * Save vector/float registers on ARM too. * Fix a typo * Update lock file * Implement periodically yielding with fuel consumption This commit implements APIs on `Store` to periodically yield execution of futures through the consumption of fuel. When fuel runs out a future's execution is yielded back to the caller, and then upon resumption fuel is re-injected. The goal of this is to allow cooperative multi-tasking with futures. * Fix compile without async * Save/restore the frame pointer in fiber switching Turns out this is another caller-saved register! * Simplify x86_64 fiber asm Take a leaf out of aarch64's playbook and don't have extra memory to load/store these arguments, instead leverage how `wasmtime_fiber_switch` already loads a bunch of data into registers which we can then immediately start using on a fiber's start without any extra memory accesses. * Add x86 support to wasmtime-fiber * Add ARM32 support to fiber crate * Make fiber build file probing more flexible * Use CreateFiberEx on Windows * Remove a stray no-longer-used trait declaration * Don't reach into `Caller` internals * Tweak async fuel to eventually run out. With fuel it's probably best to not provide any way to inject infinite fuel. * Fix some typos * Cleanup asm a bit * Use a shared header file to deduplicate some directives * Guarantee hidden visibility for functions * Enable gc-sections on macOS x86_64 * Add `.type` annotations for ARM * Update lock file * Fix compile error * Review comments |