linux-kernel - Re: [PATCH v5 1/4] x86/signal/64: Add a comment about sigcontext->fs and gs

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Message-ID: <20160217072122.GA19718@gmail.com>
Date:	Wed, 17 Feb 2016 08:21:23 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, Denys Vlasenko <dvlasenk@...hat.com>,
	Stas Sergeev <stsp@...t.ru>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v5 1/4] x86/signal/64: Add a comment about sigcontext->fs
 and gs


* Andy Lutomirski <luto@...nel.org> wrote:

> +	 * If the kernel ever adds explicit fs, gs, fsbase, and gsbase
> +	 * save/restore, it will most likely need to be opt-in and use
> +	 * different context slots.

Btw., that's not necessarily true: it could also be made opt-out, and a 
modify_ldt() or any other cleanly identifiable legacy usage/signature that is 
associated with DOSEMU might trigger the opt-out automatically as well.

I.e. behaviorally it would still keep the ABI and modern default behavior could 
still be whatever we want to make it.

Thanks,

	Ingo