Re: FTrace on MPC8xx

[Stefan Roese <ml@stefan-roese.de>]

Hi Joakim,

On Wednesday 13 April 2011 17:38:03 Joakim Tjernlund wrote:
> > > How big was the size to copy_tofrom_user()? Did it mange to copy
> > > any bytes?
> > 
> > The size in __copy_tofrom_user is 4. And its the first call in
> > ftrace_modify_code() that fails directly. This works just fine on a
> > PPC440EPx board.
> 
> Since the size is only 4 it would not use dcbX anyway(I think).
> Then is is probably called with the wrong addresses?

No, addresses seem to be correct. I checked a bit further (I'm quite new to 
the MPC8xx MMU) and it seems that trying to modify the code (that's the 
destination address) via __copy_tofrom_user() fails on MPC8xx. Still not sure 
why this is the case. Perhaps an 8xx guru might chime in here. ;)

BTW: I just noticed that enabling CONFIG_PIN_TLB seems to resolve this issue. 
With this option enabled, the dynamic code modification works just fine.

Joakim, Scott? Any ideas on this?

Thanks,
Stefan