strange Bug

Björn Döbel doebel at os.inf.tu-dresden.de
Wed Nov 12 09:28:38 CET 2014


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On 12.11.2014 00:11, ba_f wrote:
> 
> Hello Hackers,
> 
> 
> this is a following to the thread below, but i didnt wanna occupy
> it so i start a new one. 
> http://os.inf.tu-dresden.de/pipermail/l4-hackers/2014/007049.html 
> http://os.inf.tu-dresden.de/pipermail/l4-hackers/2014/007050.html
> 
> 
>> This usually happens when you try to access an address with no
>> memory mapped. From the address it looks like you are accessing
>> an address right below your stack, i.e., you are exceeding L4Re's
>> default stack size. Most likely you have a function with a large
>> buffer on the stack or you are recursing very deeply?
> 
> Actually not. There is a tiny buffer (4096 Bytes), and one function
> calles itself recursively one time.

Ok, so my guess was wrong.

> before:
>>> L4Re[rm]: unhandled write page fault @7ffff300 pc=15c7a8
> now:
>>> L4Re[rm]: unhandled write page fault @7ffff2e0 pc=15c7a8
> 
>> you might want to use standard binutils (e.g., objdump) on your
>> binary to find out what instruction is at the respective PC and
>> map this to whatever function it belongs to in your code.
> 
> I only have a pc=115c7a8, but since i start from 0x01000000, i
> guess that right?
>>> 115c7a8:       e28cca13        add     ip, ip, #77824  ;
>>> 0x13000

No way. This instruction adds a constant to a register and does not
touch memory at all. Hence it won't raise a page fault. Did you
objdump your program for that?

> I couldn't find an image with debug information, so i dont know
> what C-code this belongs to.

objdump's '-d' option did not help? Are you specifying your own
compiler flags for this program? Otherwise, L4Re's build system by
default compiles with debug info.

Bjoern
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