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: <CALCETrV0SXVtxNLpOi6VK_U5Q8xD3CCec6aDNojwiYJ182dS0w@mail.gmail.com>
Date:	Thu, 13 Aug 2015 08:43:24 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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 8:37 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Tue, Aug 11, 2015 at 5:17 PM, Stas Sergeev <stsp@...t.ru> wrote:
>>
>> I realize this patch may be good to have in general, but
>> breaking userspace without a single warning is a bit
>> discouraging. Seems like the old "we don't break userspace"
>> rule have gone.
>
> 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.

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.

--Andy
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