From: David Woodhouse <dwmw2@infradead.org>
To: "H.J. Lu" <hjl.tools@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [PATCH] x86: Don't build vDSO with $(RETPOLINE_CFLAGS) -DRETPOLINE
Date: Tue, 20 Mar 2018 08:21:11 +0000 [thread overview]
Message-ID: <1521534071.20126.218.camel@infradead.org> (raw)
In-Reply-To: <CAMe9rOoa81MC=oFW3coLuxha0pp6qdZowYR_o_my=n7ZXjVu=g@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 758 bytes --]
On Mon, 2018-03-19 at 14:11 -0700, H.J. Lu wrote:
> vDSO code runs in userspace. Don't compile it with retpoline.
>
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
There are cases where we might actually want userspace to be using
retpoline though. We still only do IBPB for *some* processes, and
haven't really even finished the argument about the heuristics we use
for that.
If this is only for the switch in __vdso_clock_gettime() then maybe we
turn that into a series of if/else instead of a switch. Or just write
it in asm.
Or better still, teach GCC that when it's using retpoline, a jump table
is *NOT* faster than a series of that many conditional branches. The
costs are higher, and I don't think we taught GCC that yet, did we?
[-- Attachment #2: smime.p7s --]
[-- Type: application/x-pkcs7-signature, Size: 5213 bytes --]
next prev parent reply other threads:[~2018-03-20 8:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-19 21:11 H.J. Lu
2018-03-20 8:21 ` David Woodhouse [this message]
2018-03-20 8:32 ` Thomas Gleixner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1521534071.20126.218.camel@infradead.org \
--to=dwmw2@infradead.org \
--cc=hjl.tools@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox
all inboxes | Powered by JetHome®