linux-kernel - Re: [PATCH v4 1/2] arm64: Define Documentation/arm64/tagged-address-abi.txt

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Date:   Thu, 13 Jun 2019 13:28:21 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kselftest@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/2] arm64: Define
 Documentation/arm64/tagged-address-abi.txt

On Thu, Jun 13, 2019 at 12:37:32PM +0100, Dave P Martin wrote:
> On Thu, Jun 13, 2019 at 11:15:34AM +0100, Vincenzo Frascino wrote:
> > On 12/06/2019 16:35, Catalin Marinas wrote:
> > > On Wed, Jun 12, 2019 at 03:21:10PM +0100, Vincenzo Frascino wrote:
> > >> +  - PR_GET_TAGGED_ADDR_CTRL: can be used to check the status of the Tagged
> > >> +                             Address ABI.
[...]
> Is there a canonical way to detect whether this whole API/ABI is
> available?  (i.e., try to call this prctl / check for an HWCAP bit,
> etc.)

The canonical way is a prctl() call. HWCAP doesn't make sense since it's
not a hardware feature. If you really want a different way of detecting
this (which I don't think it's worth), we can reinstate the AT_FLAGS
bit.

-- 
Catalin