linux-kernel - Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add SA_{X32,IA32}_ABI sa

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Date:   Wed, 19 Oct 2016 20:45:29 +0300
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Mikulas Patocka <mpatocka@...hat.com>
Cc:     Dmitry Safonov <dsafonov@...tuozzo.com>,
        Oleg Nesterov <oleg@...hat.com>, linux-mm@...ck.org,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: x32 is broken in 4.9-rc1 due to "x86/signal: Add
 SA_{X32,IA32}_ABI sa_flags"

2016-10-19 20:33 GMT+03:00 Mikulas Patocka <mpatocka@...hat.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".

Thanks for catching, will check it today.

-- 
             Dmitry