MIME-Version: 1.0
In-Reply-To: <5808.1437505205@turing-police.cc.vt.edu>
References: <20150708160750.GQ19282@twins.programming.kicks-ass.net>
 <CALCETrVqeG=3sKJv=pe9ZfaeRmx9uz+jNmXGmPu-7Hah4NvYDQ@mail.gmail.com>
 <559D8250.8000707@gmail.com> <CALCETrUb8tjDLQHF3q=_F7JRXhC8iEHW9o2xFsUbqsmyEOAiCQ@mail.gmail.com>
 <20150710141359.GJ19282@twins.programming.kicks-ass.net> <20150721082107.GE18673@twins.programming.kicks-ass.net>
 <alpine.DEB.2.11.1507211726040.18576@nanos> <20150721154959.GS19282@twins.programming.kicks-ass.net>
 <CALCETrWwy777nYTVpOn8Hs1JRG5nDyvky9B11otDRAid1L19vg@mail.gmail.com>
 <20150721161215.GU19282@twins.programming.kicks-ass.net> <20150721181553.GA3378@nazgul.tnic>
 <55AE9471.1000601@gmail.com> <CALCETrUYnddMbS3Yx=MV+_98tQ7ibKDBw1trpssJGo6D4W_VFw@mail.gmail.com>
 <5808.1437505205@turing-police.cc.vt.edu>
From: Andy Lutomirski <luto@amacapital.net>
Date: Tue, 21 Jul 2015 12:29:21 -0700
Message-ID: <CALCETrVU4HX=AL4oqajfMCJmWbV2C6xYLFtMnFy2guWBQLuYVw@mail.gmail.com>
Subject: Re: Kernel broken on processors without performance counters
To: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Jason Baron <jasonbaron0@gmail.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Vince Weaver <vince@deater.net>, "hillf.zj" <hillf.zj@alibaba-inc.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1020
Lines: 24

On Tue, Jul 21, 2015 at 12:00 PM,  <Valdis.Kletnieks@vt.edu> wrote:
> On Tue, 21 Jul 2015 11:54:30 -0700, Andy Lutomirski said:
>
>> Could this be done at link time, or perhaps when compressing the
>> kernel image, instead of at boot time?
>
> That's only safe to do if the kernel is built for one specific CPU - if it's
> a generic kernel that boots on multiple hardware designs, it will be wrong
> for some systems.
>
> In other words - safe to do if you're building it for *your* hardware. Totally
> unsafe for a distro.

That's not what I meant.  We do something in the C code that tells the
build step which way the initial state goes.  At link time, we make
the initial state actually work like that.  Then, at run time, we can
still switch it again if needed.

--Andy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/