Added x86_64-unknown-hermit support

[sjmackenzie]

Later once hermit supports aarch64 rng I'll make a patch to support it.

For more context see #199

[newpavlov]

Hm, I would prefer a proper buffer-based API, but I guess this code should be a fine stop-gap solution.

I will leave this PR open for some time in the case if @josephlr has any concerns.

Meanwhile can you please add an [UNRELEASED] section to the changelog with an entry containing description of this PR? Also it would be nice to add a Hermit build test to the CI workflow.

[sjmackenzie]

Agreed on the buffer-based API, I suggest this is good feedback for @stlankes & @josephlr!

I believe getrandom CI already has hermit workflow support, correct me if I'm wrong please:

getrandom/.github/workflows/tests.yml

Line 312 in f5e3300

run: cargo build -Z build-std=core --features=rdrand --target=x86_64-unknown-hermit

Ideally I'd love to try get this stop-gap merged relatively soon as there are a number of transitive dependencies I need to lobby to bump to a hermit-supported-getrandom. I'm choosing hermit as the sole target platform for an existing project.

@josephlr I'd love your feedback on this stop-gap solution.

@newpavlov I pushed the requested changes, if you could be so kind and review them.

Thanks!

[sjmackenzie]

By buffer-based API do you mean you can pass in an arbitrary sized u8 buffer and it'd be filled accordingly? If so, this is what is happening in this PR.

[newpavlov]

By buffer-based API do you mean you can pass in an arbitrary sized u8 buffer and it'd be filled accordingly? If so, this is what is happening in this PR.

I meant a "syscall" on the Hermit side, like requested in hermit-os/kernel#143

I believe getrandom CI already has hermit workflow support, correct me if I'm wrong please:

Ah, I forgot about that. You can simply remove the --features=rdrand part then since it's not longer needed.

[sjmackenzie]

Thanks for removing the --features=rdrand, it fell on the wayside. Appreciate the merge!