Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32)

[Andy Lutomirski]

On Mon, Jun 13, 2016 at 6:50 AM, Oleg Nesterov <oleg@xxxxxxxxxx> 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@xxxxxxxxxx> 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?