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Date: Wed, 13 Jan 2016 11:55:03 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
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        live-patching@vger.kernel.org, Michal Marek <mmarek@suse.cz>,
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        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>, Pedro Alves <palves@redhat.com>,
        Namhyung Kim <namhyung@gmail.com>,
        Bernd Petrovitsch <bernd@petrovitsch.priv.at>,
        Chris J Arges <chris.j.arges@canonical.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jiri Slaby <jslaby@suse.cz>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [PATCH v15 13/25] x86/reboot: Add ljmp instructions to stacktool
 whitelist
Message-ID: <20160113105503.GB11575@gmail.com>
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* Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> > Well, I can't say that I'm crazy about all those new tools adding markers to 
> > unrelated kernel code.
> > 
> > Can't you teach stacktool to ignore the whole machine_real_restart() function 
> > simply?
> 
> Well, these STACKTOOL_IGNORE whitelist markers are only needed in a handful of 
> places, and only for code that does very weird things.  Yes, they're a bit ugly, 
> but IMO they also communicate valuable information: "be careful, this code does 
> something very weird."

How common are these markers? Like with lockdep, it all depends on magnitude:

 - If it's less than 10 I'd say it's OK.

 - If it's dozens then it's ho-hum.

 - If certain types of annotations can go over 100, then they are unacceptable.

all such in-code overhead has to be balanced against the utility of the tooling.

> As for whether to put the whitelist info in the code vs hard-coding it in 
> stacktool, I think it's clearer and less "magical" to put them directly in the 
> code.

That's true - but I think Boris tried to ask something slightly different: can 
stacktool be taught to detect weird signatures automatically, and to ignore them 
automatically?

Stuff like 16-bit code sure wounds 'weird' and the tool could detect that?

Thanks,

	Ingo