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Date: Mon, 26 Sep 2016 10:51:29 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Colin Percival <cperciva@tarsnap.com>
Cc: Bruce Evans <brde@optusnet.com.au>, src-committers@FreeBSD.org,
 svn-src-all@FreeBSD.org, svn-src-head@FreeBSD.org
Subject: Re: svn commit: r306319 - head/sys/i386/i386
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On Mon, Sep 26, 2016 at 07:09:17AM +0000, Colin Percival wrote:
> Traditionally x86 CPUs would generate an invalid-opcode fault if redundant
> instruction prefixes resulted in an instruction exceeding 15 bytes.  This
> behaviour might have changed in the past two decades, but I doubt it.

It did not, 15 bytes is the current limit.  In fact, the longest AVX
VEX-encoded instructions are 11 bytes without prefixes, AFAIR.