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From: Andy Lutomirski <luto@amacapital.net>
Date: Thu, 23 Jul 2015 10:35:36 -0700
Message-ID: <CALCETrXvgxdQTAgxsnR5kGk=orHQ0PZWDjhM-qhQSYY+EssUSg@mail.gmail.com>
Subject: Re: Kernel broken on processors without performance counters
To: Peter Zijlstra <peterz@infradead.org>
Cc: "hillf. zj" <hillf.zj@alibaba-inc.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Jason Baron <jasonbaron0@gmail.com>, Paul Mackerras <paulus@samba.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kees Cook <keescook@chromium.org>, Vince Weaver <vince@deater.net>,
        Borislav Petkov <bp@alien8.de>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        Steven Rostedt <rostedt@goodmis.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mikulas Patocka <mpatocka@redhat.com>
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On Jul 23, 2015 10:08 AM, "Peter Zijlstra" <peterz@infradead.org> wrote:
>
> On Thu, Jul 23, 2015 at 11:34:50AM -0400, Steven Rostedt wrote:
> > On Thu, 23 Jul 2015 12:42:15 +0200
> > Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > > static __always_inline bool arch_static_branch_jump(struct static_key *key, bool inv)
> > > {
> > >     if (!inv) {
> > >             asm_volatile_goto("1:"
> > >                     "jmp %l[l_yes]\n\t"
> >
> > And what happens when this gets converted to a two byte jump?
> >
>
> That would be bad, how can we force it to emit 5 bytes?

jmp.d32 on newer toolchains IIRC.

--Andy
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