cpuoverlay

Overview ¶

Package cpuoverlay is a logic overlay on top of x/sys/cpu that attempts to avoid cases in which x/sys/cpu is wrong.

android/arm64

The main problem that we want to solve is that on Android there are cases where reading /proc/self/auxv is not possible.

This causes crypto/tls to not choose AES where it would otherwise be possible, in turn causing censorship. See also the https://github.com/ooni/probe/issues/1444 issue for more details.

Ideally we would like to call getauxval(3) when initializing the runtime package. However, runtime cannot use CGO. Doing that leads to an import loop, so we cannot build.

Until this is fixed in src/runtime, we call getauxval(3) here.

darwin/arm64

Additionally, we may use this package to solve other CPU issues. For example, x/sys/cpu does not currently know about darwin/arm64 features.

Design ¶

This package contains GOOS/GOARCH-specific files with predicate functions returning the correct value in cases in which x/sys/cpu is wrong. You are expected to replace the code that normally lives inside src/crypto/tls and src/cryto/aes and that we have forked in this repository such that you call the predicates of this package as opposed to using directly x/sys/cpu values.