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

[Nicolas Pitre]

On Mon, 20 Jan 2014, Catalin Marinas wrote:

> 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.

How could older glibc possibly care about future extensions?


Nicolas
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