Re: [PATCH v2 0/5] arm64: advertise availability of CRC and cryptoinstructions

From: Catalin Marinas
Date: Mon Jan 20 2014 - 12:39:14 EST

On Mon, Dec 23, 2013 at 02:06:27PM +0000, Ard Biesheuvel wrote:
> This series is a followup to the patch that was recently merged by Catalin that
> allocates hwcaps bits for CRC and Crypto Extensions instructions so userland can
> discover whether the current CPU has any of those capabilities.
> Patch #1 enables ARM support for the ELF_HWCAP2/AT_HWCAP2 ELF auxv entry that
> was recently added to the kernel and glibc (2.18). It extends the feature bit
> space to 64 bits (on 32-bit architectures)
> Patch #2 adds generic support for ELF_HWCAP2/AT_HWCAP2 to the 32-bit ELF compat
> mode for 64-bit architectures.
> Patch #3 adds support for ELF_HWCAP2/AT_HWCAP2 to arm64's 32-bit ELF compat mode
> Patch #4 allocates the HWCAP2 bits in the arch/arm tree. This is necessary
> because 32-bit ARM binaries can execute both under ARM and under arm64 kernels,
> so there should be agreement about the meaning of feature bits, even if the ARM
> kernel has no support yet for ARMv8 32-bit only hardware (such as ARMv8-R).

It looks a bit strange to start filling HWCAP2 before HWCAP is full but
I guess we want to preserve some future extensions in HWCAP for older

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