kernel NULL pointer dereference

[Nirmal Thacker]

Hello,

In a kernel related project which I am working on, after compilation I
face certain errors, which I am having difficulty in debugging. The
error is of the form:

Unable to handle kernel NULL pointer dereference at virtual address 00000006
current->tss.cr3=1ff88000, %cr3=1ff88000
*pde=00000000
Oops:0000
CPU:0
EIP:0010:[<c01386a9>]
EFLAGS:00010282
eax:ffffffe ebz:fffffff2 ..............
.............
Process init(pid:1, process nr:1 , stackpage=dffcb000)
Stack: ............ (stack listing here)
Call Trace:[<c013873e>][<c0107b70>]
Code: 8b 40 .............

I tried debugging this error by examining the EIP in the System.map
file and found it to be a function , part of my code. However that
function did not dereference any NULL pointer.
The call trace values too, when examined showed no NULL pointer dereference.

I are working on the 2.2.15 kernel and installed a KALLSYMS patch but
we there was no stack listing as well.

I am aware that the above information is not enough but if some one
could help me out i'd be glad to pass the code entirely .

Thanks,
nirmal

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[Randy Dunlap]

On Wed, 2 May 2007 15:50:19 +0530 Nirmal Thacker wrote:

> Hello,
>
> In a kernel related project which I am working on, after compilation I
> face certain errors, which I am having difficulty in debugging. The
> error is of the form:
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000006
> current->tss.cr3=1ff88000, %cr3=1ff88000
> *pde=00000000
> Oops:0000
> CPU:0
> EIP:0010:[<c01386a9>]
> EFLAGS:00010282
> eax:ffffffe ebz:fffffff2 ..............
> .............
> Process init(pid:1, process nr:1 , stackpage=dffcb000)
> Stack: ............ (stack listing here)
> Call Trace:[<c013873e>][<c0107b70>]
> Code: 8b 40 .............
>
> I tried debugging this error by examining the EIP in the System.map
> file and found it to be a function , part of my code. However that
> function did not dereference any NULL pointer.
> The call trace values too, when examined showed no NULL pointer dereference.

NULL pointer in this context actually means between 0 and PAGE_SIZE - 1,
i.e., somewhere in the 0-th page of the address space.
And the message tells us that it was at address 00000006 (hex).
So I would be suspecting something in your function.

> I are working on the 2.2.15 kernel and installed a KALLSYMS patch but
> we there was no stack listing as well.

Why? :(

> I am aware that the above information is not enough but if some one
> could help me out i'd be glad to pass the code entirely .

Yes, please post the source code to the mailing list.

---
~Randy
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