From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: linuxppc-dev@lists.ozlabs.org, libc-alpha@sourceware.org,
gcc@gcc.gnu.org, Paul E Murphy <murphyp@linux.ibm.com>,
Peter Bergner <bergner@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH Linux] powerpc: add documentation for HWCAPs
Date: Tue, 24 May 2022 12:38:14 -0500 [thread overview]
Message-ID: <20220524173814.GH25951@gate.crashing.org> (raw)
In-Reply-To: <20220524093828.505575-1-npiggin@gmail.com>
Hi!
On Tue, May 24, 2022 at 07:38:28PM +1000, Nicholas Piggin wrote:
> Thanks for all the comments and corrections. It should be nearing the
> point where it is useful now. Yes I do think it would be useful to align
> this more with OpenPOWER docs (and possibly eventually move it into the
> ABI, given that's the allocator of these numbers) but that's not
> done yet.
The auxiliary vector is a Linux/glibc thing, it should not be described
in more generic ABI documents. It is fine where you have it now afaics.
> +Where software relies on a feature described by a HWCAP, it should check the
> +relevant HWCAP flag to verify that the feature is present before attempting to
> +make use of the feature.
> +
> +Features should not be probed through other means. When a feature is not
> +available, attempting to use it may result in unpredictable behaviour, and
> +may not be guaranteed to result in any reliable indication that the feature
> +is unavailable.
Traditionally VMX was tested for by simply executing an instruction and
catching SIGILL. This is portable even. This has worked fine for over
two decades, it's a bit weird to declare this a forbidden practice
now :-)
It certainly isn't recommended for more complex and/or newer things.
> +verstions.
(typo. spellcheck maybe?)
Segher
next prev parent reply other threads:[~2022-05-24 17:40 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-24 9:38 Nicholas Piggin
2022-05-24 9:52 ` Florian Weimer
2022-05-24 18:32 ` Segher Boessenkool
2022-07-15 1:17 ` Nicholas Piggin
2022-07-15 14:35 ` Segher Boessenkool
2022-05-24 17:38 ` Segher Boessenkool [this message]
2022-07-15 1:00 ` Nicholas Piggin
2023-06-06 14:49 ` Passing the complex args in the GPR's Umesh Kalappa
2023-06-06 14:58 ` Andrew Pinski
2023-06-06 15:05 ` Umesh Kalappa
2023-06-06 15:16 ` Andrew Pinski
2023-06-06 16:42 ` Segher Boessenkool
2023-06-06 17:07 ` Umesh Kalappa
2023-06-06 17:33 ` David Edelsohn
2023-06-07 13:17 ` Michael Matz
2023-06-06 17:18 ` Joseph Myers
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