linux-kernel - Re: What exactly do 32-bit x86 exceptions push on the stack in the CS slot?

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Message-ID: <6e5a0f8b-31e3-8ed7-62f7-f9f28f73f503@zytor.com>
Date:   Mon, 21 Nov 2016 07:58:28 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Andy Lutomirski <luto@...nel.org>, tedheadster@...il.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        George Spelvin <linux@...izon.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: What exactly do 32-bit x86 exceptions push on the stack in the CS
 slot?

On 11/20/16 20:54, hpa@...or.com wrote:
> 
> I believe i686+ writes zero, older CPUs leave unchanged.
> 

I should point out that, at least from my memory, the same applies to
instructions like "movl <seg>".  I can't even remember for sure how the
behavior differs between "movl <seg>,<reg32>" and "movl <seg>,<mem>";
I'd have to do some digging.

	-hpa