From: "Maciej W. Rozycki" <macro@linux-mips.org>
To: Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Paul Burton <paul.burton@mips.com>,
"linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
Meng Zhuo <mengzhuo1203@gmail.com>,
Paul Burton <pburton@wavecomp.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v1] MIPS: elf_hwcap: Export userspace ASEs
Date: Wed, 16 Oct 2019 10:46:16 +0100 (BST) [thread overview]
Message-ID: <alpine.LFD.2.21.1910161030560.25496@eddie.linux-mips.org> (raw)
In-Reply-To: <d1d4cff7-ac3e-a9ab-ecee-cc941b0895e7@flygoat.com>
On Wed, 16 Oct 2019, Jiaxun Yang wrote:
> > This makes a part of the user ABI, so I would advise discussing this with
> > libc folks. Also you probably want to report microMIPS support too.
>
> How can hwcap advance libc? I know that Arm world is using it to probe SIMD
> extensions in high-level programs like ffmpeg.
Auxiliary vector entries do get used by libc, including HWCAP, so if you
introduce new stuff, then you want to consult its potential users. And
this is a part of the ABI, so once there it's cast in stone forever.
> microMIPS binary can't be applied at runtime, so userspace programs shouldn't
> aware that.
Mixing regular MIPS and microMIPS software is fully supported at load
time as indirect calls made through the GOT (or PLTGOT) are ISA-agnostic,
i.e. you can use a microMIPS DSO with a regular MIPS executable and vice
versa. This is something the dynamic loader can take advantage of, e.g.
choosing a smaller microMIPS DSO where supported by hardware over a
corresponding regular MIPS one will usually have a performance advantage
due to a smaller cache footprint.
Actually regular MIPS ISA support should be reported these days too, as
you can have a pure microMIPS CPU with no regular MIPS ISA implemented.
> Should I Cc this discussion to libc-alpha or other lists?
For the GNU C Library <libc-alpha@sourceware.org> is indeed the right
place; I can't speak for other libc implementations (uClibc, musl, etc.).
Maciej
prev parent reply other threads:[~2019-10-16 9:46 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-10 14:39 [PATCH] MIPS: elf_hwcap: Export userspace ASEs Jiaxun Yang
2019-10-10 15:01 ` [PATCH v1] " Jiaxun Yang
2019-10-10 21:04 ` Paul Burton
2019-10-15 23:27 ` Maciej W. Rozycki
2019-10-16 3:02 ` Jiaxun Yang
2019-10-16 9:46 ` Maciej W. Rozycki [this message]
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