[PATCH v19 02/15] arm64: Introduce prctl() options to control the tagged user addresses ABI

[Dave Hansen]

On 8/1/19 5:38 AM, Kevin Brodsky wrote:
> This patch series only changes what is allowed or not at the syscall
> interface. It does not change the address space size. On arm64, TBI (Top
> Byte Ignore) has always been enabled for userspace, so it has never been
> possible to use the upper 8 bits of user pointers for addressing.

Oh, so does the address space that's available already chop that out?

> If other architectures were to support a similar functionality, then I
> agree that a common and more generic interface (if needed) would be
> helpful, but as it stands this is an arm64-specific prctl, and on arm64
> the address tag is defined by the architecture as bits [63:56].

It should then be an arch_prctl(), no?