From: Daniel Borkmann <daniel@iogearbox.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Thomas Gleixner" <tglx@linutronix.de>,
"Linux List Kernel Mailing" <linux-kernel@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
"David S . Miller" <davem@davemloft.net>,
"Björn Töpel" <bjorn.topel@intel.com>,
"Magnus Karlsson" <magnus.karlsson@intel.com>,
"Jesper Dangaard Brouer" <brouer@redhat.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Peter Zijlstra" <peterz@infradead.org>,
"David Woodhouse" <dwmw2@infradead.org>,
"Andy Lutomirski" <luto@kernel.org>,
"Borislav Petkov" <bp@alien8.de>
Subject: Re: [PATCH] x86, retpolines: raise limit for generating indirect calls from switch-case
Date: Thu, 21 Feb 2019 23:56:55 +0100 [thread overview]
Message-ID: <d58b52ae-c4d9-991a-b53b-4047abe2cb56@iogearbox.net> (raw)
In-Reply-To: <CAHk-=wgNfnC-oe7aJGgNWoTbssc0LPYK6FyR=6LO4_U_dsphbg@mail.gmail.com>
On 02/21/2019 11:27 PM, Linus Torvalds wrote:
> On Thu, Feb 21, 2019 at 2:20 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
>>
>> In case of gcc, this setting is controlled by case-values-threshold
>> which has an architecture global default that selects 4 or 5 (
>
> Ack. For retpoline, that's much too low.
>
> Patch looks sane, although it would be good to verify just which
> versions of gcc this works for. All versions with retpoline?
The feature was first added in gcc 4.7 [0], under "General Optimizer Improvements":
Support for a new parameter --param case-values-threshold=n was added to allow
users to control the cutoff between doing switch statements as a series of if
statements and using a jump table.
From what I can tell, original author (H.J. Lu) provided backports up to gcc 4.8
and distros seem to have pulled it from his github branch [1] as upstream gcc does
not handle backports for stable versions that old.
Thanks,
Daniel
[0] https://www.gnu.org/software/gcc/gcc-4.7/changes.html
[1] https://bugs.launchpad.net/ubuntu/+source/gcc-4.8/+bug/1749261
https://github.com/hjl-tools/gcc/tree/hjl/indirect/gcc-4_8-branch/master
next prev parent reply other threads:[~2019-02-21 22:57 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 22:19 [PATCH] x86, retpolines: raise limit for generating indirect calls from switch-case Daniel Borkmann
2019-02-21 22:27 ` Linus Torvalds
2019-02-21 22:56 ` Daniel Borkmann [this message]
2019-02-22 7:31 ` Jesper Dangaard Brouer
2019-02-26 18:20 ` Björn Töpel
2019-02-28 11:12 ` [tip:x86/build] x86, retpolines: Raise " tip-bot for Daniel Borkmann
2019-02-28 11:27 ` David Woodhouse
2019-02-28 12:53 ` H.J. Lu
2019-02-28 16:18 ` Daniel Borkmann
2019-02-28 16:25 ` H.J. Lu
2019-02-28 17:58 ` Daniel Borkmann
2019-02-28 18:09 ` H.J. Lu
2019-02-28 18:13 ` Daniel Borkmann
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=d58b52ae-c4d9-991a-b53b-4047abe2cb56@iogearbox.net \
--to=daniel@iogearbox.net \
--cc=ast@kernel.org \
--cc=bjorn.topel@intel.com \
--cc=bp@alien8.de \
--cc=brouer@redhat.com \
--cc=davem@davemloft.net \
--cc=dwmw2@infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=magnus.karlsson@intel.com \
--cc=netdev@vger.kernel.org \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.