Wasmtime: Implement the custom-page-sizes proposal #8763
Merged
Commits on Jun 12, 2024
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Wasmtime: Implement the custom-page-sizes proposal
This commit adds support for the custom-page-sizes proposal to Wasmtime: https://github.com/WebAssembly/custom-page-sizes I've migrated, fixed some bugs within, and extended the `*.wast` tests for this proposal from the `wasm-tools` repository. I intend to upstream them into the proposal shortly. There is a new `wasmtime::Config::wasm_custom_page_sizes_proposal` method to enable or disable the proposal. It is disabled by default. Our fuzzing config has been updated to turn this feature on/off as dictated by the arbitrary input given to us from the fuzzer. Additionally, there were getting to be so many constructors for `wasmtime::MemoryType` that I added a builder rather than add yet another constructor. In general, we store the `log2(page_size)` rather than the page size directly. This helps cut down on invalid states and properties we need to assert. I've also intentionally written this code such that supporting any power of two page size (rather than just the exact values `1` and `65536` that are currently valid) will essentially just involve updating `wasmparser`'s validation and removing some debug asserts in Wasmtime.
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Better handle overflows when rounding up to the host page size
Propagate errors instead of returning a value that is not actually a rounded up version of the input. Delay rounding up various config sizes until runtime instead of eagerly doing it at config time (which isn't even guaranteed to work, so we already had to have a backup plan to round up at runtime, since we might be cross-compiling wasm or not have the runtime feature enabled).
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Avoid actually trying to allocate the whole address space in the `mas…
…sive_64_bit_still_limited` test The point of the test is to ensure that we hit the limiter, so just cancel the allocation from the limiter, and otherwise avoid MIRI attempting to allocate a bunch of memory after we hit the limiter.
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Revert "Avoid actually trying to allocate the whole address space in …
…the `massive_64_bit_still_limited` test" This reverts commit ccfa34a.
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miri: don't attempt to allocate more than 4GiB of memory
It seems that rather than returning a null pointer from `std::alloc::alloc`, miri will sometimes choose to simply crash the whole program.
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