Russell King wrote:
> On Mon, Feb 19, 2007 at 04:29:39PM +0000, Jose Goncalves wrote:
>
>> Russell King wrote:
>>
>>> On Tue, Feb 20, 2007 at 02:48:14PM +0000, Frederik Deweerdt wrote:
>>>
>>>
>>>> (trimmed tie-fei.zang from the CC, added by mistake)
>>>> On Mon, Feb 19, 2007 at 02:35:20PM +0000, Russell King wrote:
>>>>
>>>>
>>>>>> Neither did I, but introducing printk's through the function, we narrowed
>>>>>> the problem to this part of the code. And removing it makes the problem
>>>>>> go away. We inserted 37 printk's in the function body, and Jose bisected
>>>>>> those until the problem went away.
>>>>>>
>>>>>>
>>>>> Well, there's still little clue about why this is causing a NULL pointer
>>>>> dereference. The only thing I can think is that somehow performing
>>>>> this test is causing a power glitch to your CPU, causing its registers
>>>>> to get corrupted, and which results in it doing a NULL pointer deref.
>>>>>
>>>>>
>>>> That may be the case, indeed.
>>>>
>>>>
>> But if the problem was a power glitch I should get Oops with or without
>> printk() inserted, shouldn't I?
>>
>
> That depends if the printk() changes the timing such that it doesn't occur.
> Don't know, I'm only grasping at straws due to the lack of any concrete
> information.
>
>
>>>> If you see other tests to be performed...
>>>>
>>> Maybe adding some delays in that bit of code? I'm sure you've already
>>> thought of that though. Since no one has a proper understanding of the
>>> problem, the only suggestions possible are mere shots in the dark.
>>>
>> I'm no kernel expert, but it's not possible to trace what is the
>> instruction that is causing the NULL pointer dereference?
>>
>
> The reported dump shows that the kernel tried to access virtual address 0,
> and the instruction pointer seems to be the cause of that - it has a value
> of zero in that dump.
>
> The call trace indicates that the last function was called from around
> "uart_startup+0x63/0xf4" which is probably the indirect function call
> to serial8250_startup(). That's unconfirmed - the only way to get it
> confirmed is if you could dump the entire uart_startup() function.
>
> $ grep uart_startup System.map
> (address) T uart_startup
> $ objdump -r -d vmlinux --start-addr=0x<address> --stop-addr=0x<address+256>
>
> The grep should get you the address of uart_startup. Replace <address>
> with that value and <address+256> with the value plus 256 (0x100) and
> mail the result.
>
Result is attached.
José Gonçalves
vmlinux-2.6.16.38-mtm4-debug: file format elf32-i386
Disassembly of section .text:
c01ba437 <uart_startup>:
c01ba437: 55 push %ebp
c01ba438: 57 push %edi
c01ba439: 56 push %esi
c01ba43a: 53 push %ebx
c01ba43b: 8b 7c 24 14 mov 0x14(%esp),%edi
c01ba43f: 31 d2 xor %edx,%edx
c01ba441: 8b 5f 10 mov 0x10(%edi),%ebx
c01ba444: 8b 77 14 mov 0x14(%edi),%esi
c01ba447: 83 7b 10 00 cmpl $0x0,0x10(%ebx)
c01ba44b: 0f 88 d3 00 00 00 js c01ba524 <uart_startup+0xed>
c01ba451: 8b 03 mov (%ebx),%eax
c01ba453: 0f ba a8 b4 00 00 00 btsl $0x1,0xb4(%eax)
c01ba45a: 01
c01ba45b: 83 7e 60 00 cmpl $0x0,0x60(%esi)
c01ba45f: 0f 84 bf 00 00 00 je c01ba524 <uart_startup+0xed>
c01ba465: 83 7b 04 00 cmpl $0x0,0x4(%ebx)
c01ba469: 75 28 jne c01ba493 <uart_startup+0x5c>
c01ba46b: b8 d0 00 00 00 mov $0xd0,%eax
c01ba470: e8 36 c7 f6 ff call c0126bab <get_zeroed_page>
c01ba475: ba f4 ff ff ff mov $0xfffffff4,%edx
c01ba47a: 85 c0 test %eax,%eax
c01ba47c: 0f 84 a2 00 00 00 je c01ba524 <uart_startup+0xed>
c01ba482: 89 43 04 mov %eax,0x4(%ebx)
c01ba485: c7 43 0c 00 00 00 00 movl $0x0,0xc(%ebx)
c01ba48c: c7 43 08 00 00 00 00 movl $0x0,0x8(%ebx)
c01ba493: 8b 46 64 mov 0x64(%esi),%eax
c01ba496: 56 push %esi
c01ba497: ff 50 24 call *0x24(%eax)
c01ba49a: 89 c5 mov %eax,%ebp
c01ba49c: 58 pop %eax
c01ba49d: 85 ed test %ebp,%ebp
c01ba49f: 75 6d jne c01ba50e <uart_startup+0xd7>
c01ba4a1: 83 7c 24 18 00 cmpl $0x0,0x18(%esp)
c01ba4a6: 74 36 je c01ba4de <uart_startup+0xa7>
c01ba4a8: 6a 00 push $0x0
c01ba4aa: 57 push %edi
c01ba4ab: e8 5f 02 00 00 call c01ba70f <uart_change_speed>
c01ba4b0: 8b 03 mov (%ebx),%eax
c01ba4b2: 8b 40 64 mov 0x64(%eax),%eax
c01ba4b5: 59 pop %ecx
c01ba4b6: 5f pop %edi
c01ba4b7: f7 40 08 0f 10 00 00 testl $0x100f,0x8(%eax)
c01ba4be: 74 1e je c01ba4de <uart_startup+0xa7>
c01ba4c0: 9c pushf
c01ba4c1: 5f pop %edi
c01ba4c2: fa cli
c01ba4c3: 8b 46 58 mov 0x58(%esi),%eax
c01ba4c6: 89 c2 mov %eax,%edx
c01ba4c8: 83 ca 06 or $0x6,%edx
c01ba4cb: 89 56 58 mov %edx,0x58(%esi)
c01ba4ce: 39 d0 cmp %edx,%eax
c01ba4d0: 74 0a je c01ba4dc <uart_startup+0xa5>
c01ba4d2: 8b 46 64 mov 0x64(%esi),%eax
c01ba4d5: 52 push %edx
c01ba4d6: 56 push %esi
c01ba4d7: ff 50 04 call *0x4(%eax)
c01ba4da: 58 pop %eax
c01ba4db: 5a pop %edx
c01ba4dc: 57 push %edi
c01ba4dd: 9d popf
c01ba4de: f6 43 13 04 testb $0x4,0x13(%ebx)
c01ba4e2: 74 17 je c01ba4fb <uart_startup+0xc4>
c01ba4e4: fa cli
c01ba4e5: 8b 46 64 mov 0x64(%esi),%eax
c01ba4e8: 56 push %esi
c01ba4e9: ff 50 08 call *0x8(%eax)
c01ba4ec: 5e pop %esi
c01ba4ed: a8 20 test $0x20,%al
c01ba4ef: 75 09 jne c01ba4fa <uart_startup+0xc3>
c01ba4f1: 8b 03 mov (%ebx),%eax
c01ba4f3: 80 88 c4 00 00 00 02 orb $0x2,0xc4(%eax)
c01ba4fa: fb sti
c01ba4fb: 81 4b 10 00 00 00 80 orl $0x80000000,0x10(%ebx)
c01ba502: 8b 03 mov (%ebx),%eax
c01ba504: 0f ba b0 b4 00 00 00 btrl $0x1,0xb4(%eax)
c01ba50b: 01
c01ba50c: eb 14 jmp c01ba522 <uart_startup+0xeb>
c01ba50e: 6a 15 push $0x15
c01ba510: e8 b0 c3 f5 ff call c01168c5 <capable>
c01ba515: 85 c0 test %eax,%eax
c01ba517: 59 pop %ecx
c01ba518: 0f 94 c0 sete %al
c01ba51b: 0f b6 c0 movzbl %al,%eax
c01ba51e: f7 d8 neg %eax
c01ba520: 21 c5 and %eax,%ebp
c01ba522: 89 ea mov %ebp,%edx
c01ba524: 89 d0 mov %edx,%eax
c01ba526: 5b pop %ebx
c01ba527: 5e pop %esi
c01ba528: 5f pop %edi
c01ba529: 5d pop %ebp
c01ba52a: c3 ret
c01ba52b <uart_shutdown>:
c01ba52b: 57 push %edi
c01ba52c: 56 push %esi
c01ba52d: 53 push %ebx
c01ba52e: 8b 44 24 10 mov 0x10(%esp),%eax
c01ba532: 8b 58 10 mov 0x10(%eax),%ebx
c01ba535: 8b 70 14 mov 0x14(%eax),%esi
Disassembly of section .init.text:
Disassembly of section .altinstr_replacement:
Disassembly of section .exit.text:
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