linux-kernel - Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals delivered to 64-bit programs

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Message-ID: <20150320115622.GR27066@moon>
Date:	Fri, 20 Mar 2015 14:56:22 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrey Wagin <avagin@...il.com>,
	Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Al Viro <viro@...iv.linux.org.uk>, X86 ML <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Pavel Emelyanov <xemul@...nvz.org>
Subject: Re: [PATCH v3 1/2] x86_64,signal: Fix SS handling for signals
 delivered to 64-bit programs

On Fri, Mar 20, 2015 at 12:43:14PM +0100, Denys Vlasenko wrote:
> On Thu, Mar 19, 2015 at 8:35 AM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> > On Wed, Mar 18, 2015 at 03:03:27PM -0700, Andy Lutomirski wrote:
> >> I don't have a great idea for how to work around this, unfortunately.
> >> Ideally we'd increment some kind of version counter or use an
> >> extension mechanism rather than shoving ss into a field that used to
> >> be padding.
> >
> > fwiw currently we're passing zero in this __pad0 (replying to your
> > previous email, so we can workaround in the kernel assuming zero
> > as a special case, not that good but better than nothing).
> 
> Special-casing zero sounds not that bad to me.
> It can be removed after a few years - just don't forget
> to document it in a good comment: why we have special
> case? What software required it?
> In which version of that software the need to have this hack
> was eliminated?

To be fair, such special case would be ideal for us, so that
if noone object against such hack, i would cook a patch.
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