strange Bug

ba_f ba_f at rbg.informatik.tu-darmstadt.de
Mon Nov 24 23:37:23 CET 2014


Hi Martin,

thank you, but i'm afraid, i haven't learnt the full lesson, yet.

> Hi ba_f,
> 
> blx r7 is a false alarm, it cannot cause this type of write page
> fault. Even the instruction itself makes no sense since r7 has a value
> of 1.
> 
> Could you do the following: Insert a known write page fault into your
> client (maybe something like *(volatile int *)0x0=0xaffedead; ) and
> search for the pc in "objdump -d" on myClient. You can do the same
> with myServer. This should match and you will see opcode causing the
> write page fault.
> 
> Now enter JDB and dump the instruction @pc. This does not match the
> opcode caused the write page fault. Check the last line of the dump
> screen and you will see the reason: "dump: d<010001fc> physical".
> 
> 
> Martin.


All right,
i inserted the faulty instruction, and the familiar Error Message 
occurs.

   myClient| L4Re[rm]: unhandled write page fault @0 pc=7cddc


Now, objdump does not show this PC in myClient or libClient. But as 
before, the PC is found in moe.

Lesson learnt, this PC is useless for me???


Ok back to myClient.
Since i don't know the PC of *(volatile int *)0x0=0xaffedead; i search 
for the opcode and found this.

   1fdd4:       e30d3ead        movw    r3, #57005      ; 0xdead
   1fdd8:       e34a3ffe        movt    r3, #45054      ; 0xaffe

Weird again, i can't find one of this instructions in bootstrap.elf.



So still, i have no clue, how the PC in the Error Message shall lead me 
to the faulty instruction.



thanks for patience,

ba_f



More information about the l4-hackers mailing list