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Re: [PATCH 2.5] clear USEDFPU in copy_thread

To: Jun Sun <>
Subject: Re: [PATCH 2.5] clear USEDFPU in copy_thread
From: Juan Quintela <>
Date: Fri, 07 Feb 2003 02:20:58 +0100
Cc: Vivien Chappelier <>, Ralf Baechle <>,
In-reply-to: <> (Jun Sun's message of "Thu, 6 Feb 2003 16:43:42 -0800")
Original-recipient: rfc822;
References: <Pine.LNX.4.21.0302042349200.31806-100000@melkor> <>
User-agent: Gnus/5.090012 (Oort Gnus v0.12) Emacs/21.2.92 (i386-mandrake-linux-gnu)
>>>>> "jun" == Jun Sun <> writes:


jun> Even if you don't have it cleared in start_thread(), things
jun> should be generally OK.  You will have some dirty FPU content
jun> instead of a all-zero one when you start a new program.  But then
jun> since all sane program should assign register values before they
jun> first time use them, so this bug should be well hidden.

I don't remind the exact details, but the problem appears to be the
security implications, you can see last values of previous process.

Yes, I still have to find a way where that is useful, but ...

Later, Juan.

In theory, practice and theory are the same, but in practice they 
are different -- Larry McVoy

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