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rndr: Add support for aarch64 RNDR register backend #494

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rndr: Add support for aarch64 RNDR register backend #494

wants to merge 2 commits into from

Commits on Jul 30, 2024

  1. rndr: Add support for aarch64 RNDR register backend 

    AArch64 platforms from version Armv8.4 onwards may implement FEAT_RNG.
FEAT_RNG introduces the RNDR (and RNDRRS) register, reading from which
returns a random number.

Add support for using the RNDR register as a backend for getrandom.
The implementation is hidden behind a new "rndr" crate feature.
For the backend to work, users must ensure that the target platform
supports FEAT_RNG because it is not possible to reliably detect the
feature at runtime across platforms.
    @mrkajetanp
    mrkajetanp committed Jul 30, 2024
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  2. rndr_with_fallback: Add a RNDR backend with a Linux fallback 

    Currently, detecting whether FEAT_RNG is available without std relies
on the Linux Kernel's MRS emulation.

This commit adds a safe rndr_with_fallback backend for Linux systems.
With this backend, getrandom will use the RNDR register on Linux systems
where it is available and automatically fallback onto using Linux's
getrandom syscall on systems where it is not.
This implementation allows the crate to be build for Linux with this
feature in advance and then run without having to know whether
FEAT_RNG is implemented or not.

For the time being, this backend is not used by default on any platform
configuration. The intention is for it to be usable as an opt-in when an
opt-in mechanism is available in the crate.
    @mrkajetanp
    mrkajetanp committed Jul 30, 2024
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