linux-kernel - Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF

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Message-ID: <CALCETrUAZiKNJtY98wBqOxn3sjFYV4kssiMnNwV=z1px8tC9mw@mail.gmail.com>
Date:	Mon, 13 Jun 2016 13:40:55 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Dmitry Safonov <dsafonov@...tuozzo.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Dmitry Safonov <0x7f454c46@...il.com>, khorenko@...tuozzo.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Cyrill Gorcunov <gorcunov@...nvz.org>, xemul@...tuozzo.com,
	X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32)

On Mon, Jun 13, 2016 at 6:50 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> To avoid the confusion, let me first say that I am not going to argue
> with these changes, I simply do not understand the problem space enough.
>
> On 06/10, Andy Lutomirski wrote:
>>
>> On Fri, Jun 10, 2016 at 1:07 PM, Oleg Nesterov <oleg@...hat.com> wrote:
>> >
>> > IIRC, CRIU can't c/r the 32-bit applications, or this is no longer true?
>> >
>>
>> CRIU has a horrible, nasty, brilliant idea: it will start restoring
>> 32-bit processes by treating them mostly like 64-bit processes.  The
>> restorer will start out 64-bit, set everything up, and long
>> jump/return/sigreturn/whatever back to 32-bit mode.
>
> OK, I see,
>
>> My proposal was
>> that, rather than coming up with nasty hacks to switch the kernel's
>> idea of the task bitness,
>
> Well, I can't resist but to me SA_IA32_ABI/SA_X32_ABI looks like a hack
> too.  We actually shift TIF_*32 into k_sigaction->flags, and the fact
> that we do this per-signal looks, well, interesting ;)

Is anything actually wrong with this, though?