linux-kernel - Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu

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Message-ID: <20150814081058.GB2129@uranus>
Date:	Fri, 14 Aug 2015 11:10:58 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stas Sergeev <stsp@...t.ru>,
	Linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: [regression] x86/signal/64: Fix SS handling for signals
 delivered to 64-bit programs breaks dosemu

On Thu, Aug 13, 2015 at 08:43:24AM -0700, Andy Lutomirski wrote:
...
> >
> > That rule hasn't gone anywhere.
> >
> > Does a plain revert just fix everything? Because if so, that's the
> > right thing to do, and we can just re-visit this later.
> >
> > I don't understand why Andy and Ingo are even discussing this. What
> > the f*ck, guys?
> >
> 
> I'm trying to fix it without reverting.  If that doesn't work, then we
> revert.  Yesterday, I thought I had a reasonably clean fix, but it
> turned out that it only solved half of the problem.
> 
> If we revert, I think I need to check what will break due to the
> revert.  I need to check at least Wine, and we'll have to do something
> about all the selftests that will start failing.  I also need to check
> CRIU, and IIRC CRIU has started using the new sigcontext SS in new
> versions.

Yes, we've tuned up our sigcontext structure and put ss into the place
where previously __pad0 were. After the revert the kernel simply ignores
this field again. But we never did any "weird" gaming over segment registers
for testing purposes, neither we note any application (in containers) which
does some weird things like dosemu.

> 
> And, damnit, those selftests are *useful*.  They've smoked out all
> kinds of problems.  That's part of the reason I'd prefer not to revert
> if there's a better option.
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