Use SipHasher rather than SHA-512 for ISLE manifest. #3619
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bjorn3
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Dec 17, 2021
alexcrichton
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Dec 17, 2021
Fixes bytecodealliance#3609. It turns out that `sha2` is a nontrivial dependency for Cranelift in many contexts, partly because it pulls in a number of other crates as well. One option is to remove the hash check under certain circumstances, as implemented in bytecodealliance#3616. However, this is undesirable for other reasons: having different dependency options in Wasmtime in particular for crates.io vs. local builds is not really possible, and so either we still have the higher build cost in Wasmtime, or we turn off the checks by default, which goes against the original intent of ensuring developer safety (no mysterious stale-source bugs). This PR uses `SipHash` instead, which is built into the standard library. `SipHash` is deprecated, but it's fixed and deterministic (across runs and across Rust versions), which is what we need, unlike the suggested replacement `std::collections::hash_map::DefaultHasher`. The result is only 64 bits, and is not cryptographically secure, but we never needed that; we just need a simple check to indicate when we forget a `rebuild-isle`.
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Fixes #3609. It turns out that
sha2is a nontrivial dependency forCranelift in many contexts, partly because it pulls in a number of other
crates as well.
One option is to remove the hash check under certain circumstances, as
implemented in #3616. However, this is undesirable for other reasons:
having different dependency options in Wasmtime in particular for
crates.io vs. local builds is not really possible, and so either we
still have the higher build cost in Wasmtime, or we turn off the checks
by default, which goes against the original intent of ensuring developer
safety (no mysterious stale-source bugs).
This PR uses
SipHashinstead, which is built into the standardlibrary.
SipHashis deprecated, but it's fixed and deterministic(across runs and across Rust versions), which is what we need, unlike
the suggested replacement
std::collections::hash_map::DefaultHasher.The result is only 64 bits, and is not cryptographically secure, but we
never needed that; we just need a simple check to indicate when we
forget a
rebuild-isle.