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Date: Wed, 30 Jun 2010 15:40:51 +0100 (BST)
From: "Maciej W. Rozycki" <macro@linux-mips.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
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       Prasad <prasad@linux.vnet.ibm.com>,
       "2 . 6 . 33 . x 2 . 6 . 34 . x" <stable@kernel.org>
Subject: Re: [GIT PULL] x86 breakpoint regression fix
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On Wed, 30 Jun 2010, Frederic Weisbecker wrote:

>     - icebp/int01 trap. This instruction (0xf1) is undocumented and
>       generates an int 1 exception. Unlike single step through TF
>       flag, it doesn't set the single step origin of the exception
>       in dr6.

 Not quite completely undocumented, but a bit obscure indeed.  GDB calls 
this instruction ICEBP and some Intel sources -- INT1.  It's been around 
for a while (at least since 80286) and is mostly used by in-circuit 
emulators (hence the name GDB uses).

  Maciej