From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Matthias Kaehlcke <mka@chromium.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [GIT PULL] x86/build changes for v4.17
Date: Tue, 3 Apr 2018 10:59:04 +0200 [thread overview]
Message-ID: <20180403085904.GY4082@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CA+55aFzV8L-uv9706ryJ2mP9VGBuzqFVPu1cgYY+sZAtDAroqg@mail.gmail.com>
On Mon, Apr 02, 2018 at 02:44:48PM -0700, Linus Torvalds wrote:
> On Mon, Apr 2, 2018 at 2:50 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > The biggest change is the forcing of asm-goto support on x86, which effectively
> > increases the GCC minimum supported version to gcc-4.5 (on x86).
>
> So my biggest worry isn't gcc-4.5 (anybody who hasn't updated deserves
> to be forced, or can stay with old kernels).
>
> No, my biggest worry is clang. What's the status there?
>
> I've pulled this, and honestly, the disaster with
> -fmerge-all-constants makes me think that clang isn't that good a
> compiler choice anyway, but it's sad if this undoes a lot of clang
> work just because of the worries about Spectre and mis-speculated
> branches.
It's not just spectre, I believe you yourself wanted to use asm-goto
somewhere in the x86 code:
http://lkml.kernel.org/r/CA+55aFyCp-9Qqjcn9wp=VDp2KO7tfYuUMJxVKC75Xxu0wEB5Cw@mail.gmail.com
There was some KVM talk of relying on it here:
http://lkml.kernel.org/r/6a5f2453-cf51-d491-db54-5f239caa29bc@redhat.com
And there's the comment here:
https://elixir.bootlin.com/linux/v4.16-rc7/source/arch/x86/kvm/emulate.c#L457
As to the suitablility of using clang, there's also this unresolved
issue:
http://lkml.kernel.org/r/20180321211931.GA111711@google.com
The fact that even without asm-goto they cannot correctly compile a
kernel and have sat on their hands regarding asm-goto for the past 7 odd
years makes me care very little.
And since they need to spin a new version of the compiler with all the
various bugs fixed, they might as well include asm-goto in that and be
done with it.
next prev parent reply other threads:[~2018-04-03 8:59 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-02 9:50 [GIT PULL] x86/build changes for v4.17 Ingo Molnar
2018-04-02 21:44 ` Linus Torvalds
2018-04-02 22:38 ` Matthias Kaehlcke
2018-04-03 1:26 ` Matthias Kaehlcke
2018-04-03 8:59 ` Peter Zijlstra [this message]
2018-04-03 9:51 ` Ingo Molnar
2018-04-03 12:09 ` Peter Zijlstra
2018-04-03 18:06 ` Matthias Kaehlcke
2018-04-03 21:58 ` Nick Desaulniers
2018-04-04 9:19 ` Peter Zijlstra
2018-04-04 9:38 ` Greg KH
2018-04-04 16:49 ` Nick Desaulniers
2018-04-04 17:13 ` Linus Torvalds
2018-04-04 17:46 ` Nick Desaulniers
2018-04-04 23:10 ` Nick Desaulniers
2018-04-04 16:53 ` Nick Desaulniers
2018-04-04 16:59 ` Greg KH
2018-04-04 19:26 ` James Y Knight
2018-04-04 19:42 ` Linus Torvalds
2018-04-04 22:21 ` James Y Knight
2018-04-04 22:29 ` Linus Torvalds
2018-04-05 7:08 ` Peter Zijlstra
2018-04-05 16:21 ` James Y Knight
2018-04-04 19:32 ` Josh Poimboeuf
2018-06-07 19:23 ` Nick Desaulniers
2018-06-07 20:11 ` Greg KH
2018-04-04 9:30 ` Peter Zijlstra
2018-04-04 19:17 ` Matthias Kaehlcke
2018-04-04 20:33 ` Arnd Bergmann
2018-04-04 20:58 ` Matthias Kaehlcke
2018-04-04 21:11 ` Arnd Bergmann
2018-04-04 21:46 ` Matthias Kaehlcke
2018-04-04 21:59 ` Linus Torvalds
2018-04-04 22:17 ` Matthias Kaehlcke
2018-04-04 22:39 ` Linus Torvalds
2018-04-04 23:31 ` Matthias Kaehlcke
2018-04-05 0:05 ` Linus Torvalds
2018-04-05 0:20 ` Kees Cook
2018-04-05 7:24 ` Peter Zijlstra
2018-04-05 8:04 ` Ingo Molnar
2018-04-05 8:24 ` Peter Zijlstra
2018-04-05 16:43 ` Linus Torvalds
2018-04-05 7:20 ` Peter Zijlstra
2018-04-05 17:46 ` James Y Knight
2018-04-05 18:06 ` Linus Torvalds
2018-04-05 20:51 ` James Y Knight
2018-04-05 21:13 ` Linus Torvalds
2018-04-05 22:51 ` James Y Knight
2018-04-06 2:02 ` Linus Torvalds
2018-04-05 17:47 ` James Y Knight
2018-04-04 23:04 ` Nick Desaulniers
2018-04-03 17:36 ` Linus Torvalds
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