linux-kernel - Re: [PATCH v4] drivers/tty: Folding Android's keyreset driver in sysRQ

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Date:	Wed, 27 Feb 2013 21:10:49 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	mathieu.poirier@...aro.org, linux-kernel@...r.kernel.org,
	arve@...roid.com, kernel-team@...roid.com, john.stultz@...aro.org,
	alan@...rguk.ukuu.org.uk,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v4] drivers/tty: Folding Android's keyreset driver in sysRQ

On Wed, Feb 27, 2013 at 9:06 PM, Dave Airlie <airlied@...il.com> wrote:
> On Wed, Feb 27, 2013 at 6:26 PM, Dave Airlie <airlied@...il.com> wrote:
>>>
>>> this patch seems to be oopsing on my x86 32-bit machine on bootup, pic attached.
>>>
>>> .config attached.
>>>
>>> It looks to me like the weak bit isn't working so well
>>>
>>>         if (platform_sysrq_reset_seq) {
>>>                 for (i = 0; i < ARRAY_SIZE(sysrq_reset_seq); i++) {
>>>                         key = platform_sysrq_reset_seq[i];
>>>   6d:   66 8b 8c 00 00 00 00    mov    0x0(%eax,%eax,1),%cx
>>>   74:   00
>>>
>>> is around where it craps out.
>>> gcc version 4.7.2 20121109 (Red Hat 4.7.2-8) (GCC)
>>> Fedora 18 machine.
>>
>> And just to confirm reverting
>> 154b7a489a5b1d808323b933b04864958c2f1056.in Linus' tree allows boot to
>> proceed.
>
>
> Looks like my first picture bounced,
>
> here's a link
> http://www.skynet.ie/~airlied/sysrq_oops.jpg

Just some more disasm:

       if (platform_sysrq_reset_seq) {
  4c:   ba 00 00 00 00          mov    $0x0,%edx
  51:   31 c0                   xor    %eax,%eax
  53:   8b 1d 04 00 00 00       mov    0x4,%ebx
  59:   85 d2                   test   %edx,%edx
  5b:   75 2d                   jne    8a <sysrq_init+0x72>

                        sysrq_reset_seq[sysrq_reset_seq_len++] = key;
                }
        }

        error = input_register_handler(&sysrq_handler);
  5d:   b8 b4 00 00 00          mov    $0xb4,%eax
  62:   e8 fc ff ff ff          call   63 <sysrq_init+0x4b>
        if (error)
  67:   85 c0                   test   %eax,%eax
  69:   74 3e                   je     a9 <sysrq_init+0x91>
  6b:   eb 2d                   jmp    9a <sysrq_init+0x82>
        int error;
        int i;
  6d:   66 8b 8c 00 00 00 00    mov    0x0(%eax,%eax,1),%cx
  74:   00
                        if (key == KEY_RESERVED || key > KEY_MAX)
  75:   8d 71 ff                lea    -0x1(%ecx),%esi
  78:   66 81 fe fe 02          cmp    $0x2fe,%si
  7d:   76 02                   jbe    81 <sysrq_init+0x69>
  7f:   eb 11                   jmp    92 <sysrq_init+0x7a>
                                break;

                        sysrq_reset_seq[sysrq_reset_seq_len++] = key;
  81:   66 89 8c 12 08 00 00    mov    %cx,0x8(%edx,%edx,1)
  88:   00

Dave.
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