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

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Date:	Wed, 27 Feb 2013 21:40:10 +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

>>>>
>>>> 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.

It really does look like gcc is screwing up here, after a debug
session on irc with dhowells and rmk.

I'm going to sleep, its too much for my brain at the moment.

Dave.
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