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Date:   Mon, 25 May 2020 12:40:38 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>
Subject: Re: [RFC][PATCH 0/4] x86/entry: disallow #DB more
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On Mon, May 25, 2020 at 12:02:48PM +0200, Rasmus Villemoes wrote:

> Naive question: did you check disassembly to see whether gcc threw your
> native_get_debugreg() away, given that the asm isn't volatile and the
> result is not used for anything? Testing here only shows a "mov
> %r9,%db7", but the read did seem to get thrown away.

Argh.. no I did not. Writing it all in asm gets me:

[    1.627405] XXX: 3900 8304 22632

which is a lot worse...