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Date:   Thu, 23 Feb 2017 15:36:44 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
        richard.weinberger@...il.com
Subject: Re: [PATCH] x86: Implement __WARN using UD0

On Thu, Feb 23, 2017 at 08:12:32AM -0600, Josh Poimboeuf wrote:
> On Thu, Feb 23, 2017 at 02:28:13PM +0100, Peter Zijlstra wrote:
> > +/*
> > + * Only UD2 is defined in the Intel SDM and AMD64 docs,
> > + * but the interweb provided UD0 and UD1:
> > + *
> > + *   https://groups.google.com/forum/#!topic/alt.os.assembly/_rS4L0fnqGE
> 
> FYI, the latest Intel SDM does have UD0 and UD1.

Ooh, shiny, a new one.

> > + * Since various instruction decoders disagree on the length of UD1,
> > + * we cannot use it either. So use UD0 for WARN.
> 
> It shows up as "(bad)" in objtool and gdb, though it still gets the
> length right:
> 
>   8b9:       0f ff                   (bad)  
> 
> It would be nice if the tools knew about it...

Now that the SDM lists them, I suppose that's going to be any day now
:-)

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