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 13:33:25 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Dmitry Safonov <dsafonov@...tuozzo.com>
cc:     0x7f454c46@...il.com, oleg@...hat.com, linux-mm@...ck.org,
        gorcunov@...nvz.org, xemul@...tuozzo.com,
        Thomas Gleixner <tglx@...utronix.de>,
        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"



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".

Mikulas