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RustCrypto gates the aarch64 hardware SHA-2 backend behind the `asm` feature; enabling it pulls sha2-asm (cc-compiled) and, via cpufeatures, runtime-detects the HWCAP sha2 bit. One binary then uses on-core hardware SHA-256 where present and the software path elsewhere. Digest hashing is a hot path for the CAS. Co-Authored-By: Claude Fable 5 <[email protected]>
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What and why
sha2: enable
asm— hardware SHA-256 with runtime detectionRustCrypto gates the aarch64 hardware SHA-2 backend behind the
asmfeature; enabling it pulls sha2-asm (cc-compiled) and, via cpufeatures,
runtime-detects the HWCAP sha2 bit. One binary then uses on-core
hardware SHA-256 where present and the software path elsewhere.
Digest hashing is a hot path for the CAS.
How was this verified?
The branch's own tests, run with Bazel on railgun today after the rebase onto upstream
b01417643e; CI on this PR is the first automated run.Also part of the soak branch (#73): upstream HEAD plus every pending fix, run through the railgun fleet for an hour of continuous remote builds with no errors.
Risk
Adds
sha2-asm(cc-compiled) to the build; runtime detection viacpufeatureskeeps the software path on cores without SHA-2 extensions.MODULE.bazel.lockcarries the new crate.AI assistance
Written with Claude Code; b7r6 reviewed the change. Draft until the author has read the CI results.
🤖 Generated with Claude Code