linux-kernel - Re: [PATCH v2 0/5] arm64: advertise availability of CRC and crypto instructions

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Date:	Mon, 20 Jan 2014 17:38:38 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"nico@...aro.org" <nico@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/5] arm64: advertise availability of CRC and crypto
 instructions

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
glibc.

-- 
Catalin
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