RE: [ECOS] eCos Code at address 0x000? (MPC8270)

[Gary Thomas <gary at mlbassoc dot com>]

On Tue, 2004-05-18 at 12:47, Tim Sohacki wrote:
> Gary Thomas wrote:
> >
> > On Tue, 2004-05-18 at 11:44, Tim Sohacki wrote:
> > > Hello,
> > >  
> > > On the MPC8270, it appears that eCos has some code running at (or 
> > > near) address 0. I suspect this is eCos specific because the first
> PPC 
> > > interrupt vector stub is at 0x100.
> > >  
> > > What is this code?  It appears to be executed at runtime, because if
> 
> > > it is trampled, the target will crash. Is it a NULL pointer write 
> > > detector?
> >
> > It's just a place holder - in this case, your code will just hang
> there 
> > if you did a jump (or function call) to 0x0.
> > 
> > What do you mean "trampled" and how does the problem show up?  That
> code 
> > should never be executed - if it does, your program would just stop.
> 
> 
> 
> Interesting.  Does that suggest that someone may be calling 
> a NULL function pointer?  Where is the code for this stub? 
> 

Look at "hal_reserved_vector_0000" in 
  hal/powerpc/mpc8xxx/current/include/variant.inc

> We've seen some crashes at address 0x4.  Dumping that area, 
> it appeared that the values around 0 had been written to 
> (trampled), because they no longer matched the power up 
> values.
> 
> Later, I manually "trampled" the area around 0 with a debug 
> command, and the target crashed shortly afterwards. 

Then there's probably something else wrong with your code - eCos neither
uses nor relies on anything in this chunk of memory (0x0..0x100)

-- 
Gary Thomas <gary@mlbassoc.com>
MLB Associates


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