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

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Date:	Thu, 13 Aug 2015 20:51:29 +0300
From:	Stas Sergeev <stsp@...t.ru>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	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

13.08.2015 18:37, Linus Torvalds пишет:
> 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?
>
> Stas, can you verify that this actually fixes it? There's two
> different versions here: one that reverts *just* that one commit, and
> one that reverts the fs/gs changes too. Can you test them both?
Hello Linus, I verified that patch-minimal.diff is enough
to fix the problem, BUT! dosemu is in fact using the .fs and
.gs fields of sigcontext as a placeholders. Why the minimal
patch alone helps is simply because the kernel headers
installed in a system do not yet represent the newer kernel
developments and have the .fs and .gs fields in.
So, to allow the pre-compiled dosemu binary to run, patch-minimal
is enough. To allow re-compiling it, you'd need patch.diff.
Although I guess compilation is not the point, and the
fact that the pre-compiled binary works, is enough.

Now my PC is dying of overheat, I am struggling to even
boot it. I am not sure I'll test the "really-minimal" patch,
but it will unlikely to help because dosemu expects unmodified
ss in a sighandler, which "really-minimal" patch doesn't seem
to give.
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