Date: Thu, 20 Oct 2016 11:22:42 -0400 (EDT)
From: Mikulas Patocka <mpatocka@redhat.com>
To: Dmitry Safonov <0x7f454c46@gmail.com>
cc: Dmitry Safonov <dsafonov@virtuozzo.com>,
        Oleg Nesterov <oleg@redhat.com>, linux-mm@kvack.org,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI
 sa_flags"
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On Thu, 20 Oct 2016, Dmitry Safonov wrote:

> 2016-10-19 20:33 GMT+03:00 Mikulas Patocka <mpatocka@redhat.com>:
> >
> >
> > On Wed, 19 Oct 2016, Mikulas Patocka wrote:
> >
> >> Hi
> >>
> >> In the kernel 4.9-rc1, the x32 support is seriously broken, a x32 process
> >> is killed with SIGKILL after returning from any signal handler.
> >
> > I should have said they are killed with SIGSEGV, not SIGKILL.
> >
> >> I use Debian sid x64-64 distribution with x32 architecture added from
> >> debian-ports.
> >>
> >> I bisected the bug and found out that it is caused by the patch
> >> 6846351052e685c2d1428e80ead2d7ca3d7ed913 ("x86/signal: Add
> >> SA_{X32,IA32}_ABI sa_flags").
> >>
> >> example (strace of a process after receiving the SIGWINCH signal):
> >>
> >> epoll_wait(10, 0xef6890, 32, -1)        = -1 EINTR (Interrupted system call)
> >> --- SIGWINCH {si_signo=SIGWINCH, si_code=SI_USER, si_pid=1772, si_uid=0} ---
> >> poll([{fd=4, events=POLLOUT}], 1, 0)    = 1 ([{fd=4, revents=POLLOUT}])
> >> write(4, "\0", 1)                       = 1
> >> rt_sigreturn({mask=[INT QUIT ILL TRAP BUS KILL SEGV USR2 PIPE ALRM STKFLT TSTP TTOU URG XCPU XFSZ VTALRM IO PWR SYS RTMIN]}) = 0
> >> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} ---
> >> +++ killed by SIGSEGV +++
> >> Neoprávnìný pøístup do pamìti (SIGSEGV)
> >>
> >> Mikulas
> >
> > BTW. when I take core dump of the killed x32 process, it shows:
> >
> > ELF Header:
> >   Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
> >   Class:                             ELF32
> >   Data:                              2's complement, little endian
> >   Version:                           1 (current)
> >   OS/ABI:                            UNIX - System V
> >   ABI Version:                       0
> >   Type:                              CORE (Core file)
> >   Machine:                           Intel 80386
> >                                 ^^^^^^^^^^^^^^^^^^^
> >
> > So, the kernel somehow thinks that it is i386 process, not x32 process. A
> > core dump of a real x32 process shows "Class: ELF32, Machine: Advanced
> > Micro Devices X86-64".
> 
> Hi Mikulas,
> 
> could you give attached patch a shot?
> In about 10 hours I'll be at work and will have debian-x32 install,
> but for now, I can't test it.
> Thanks again on catching that.
> 
> -- 
>              Dmitry

Yes, it fixes the bug.

Mikulas
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