Any known compiler issues for CPU32? (stack corruption problem)

Mike Panetta ahuitzot at
Thu Feb 28 13:21:53 UTC 2002

On Wed, 2002-02-27 at 15:52, Matthew J Fletcher wrote:

> i might be stupid here, but your not trying to run 68332 (i.e cpu32), code
> on the not-totaly-cpu32, 68030 are you ?,.. i doubt it but what the hell,..

Nope.  Unless the RTEMS build process is flawed in that kind of way

> ok, when i was developing on 68331's we never had these problems but
> we did patch gcc 2.95.3 with a special inturrupt patch that fixed problems,
> with restoring regiesters (like stack pointers), after a context switch,.

That sounds intresting.  Ill have a look.  I am not sure if RTEMS
already has patches for this or not in their distributed compiler.

> here is the link,..
> > So far, all I know, is somewhere before the code gets to Init() (in
> > hello sample) the stack gets messed so bad that the stack pointer is
> > pointing to an address over 5000 bytes above the top of the stack!  
> ok, so thats before inturrupts have even been enabled (i think), so its
> probably not the above.

Well maybe,  I donno yet.  I do know that I was confused about where the
stack should have been after the process starts.  Its intresting what
you can learn after stepping through a context switch in a debugger :). 
Apparently the stack for processes is allocated in an area at the end of
memory called the workspace.  So the SP being above the stack top is
normal if your in a process.

The strange thing is, after disabling interrupt mode IO, I got the hello
sample to work, but after that I tried to run base_sp, and it failed. 
Something really wacky is going on here.  I stepped all the way through
the code  in the Init part of base_sp, from task creation, to starting
the second task, to the destruction of the init task, it all seemed
fine, untill it tried to do a context switch to the new task, then it
died.  The context switch from the OS to the Init task went smoothly
though.  Also, running in GDB does not seem to act the same as just
running on the board with a breakpoint set in CPU32BUG.  The code will
not get as far in CPU32BUG.  Say if I put a breakpoint right at Init in
the code running in GDB, it may get to it.  If I put a breakpoint in the
exact same place in CPU32BUG, it dies before it gets to it with an
illegal instruction exception at 0xFFFE (or somthing like that).  

> >In
> > addition the frame pointer has been set to 0 (is that ok?). Its fine at
> > boot_card(), and its fine at console_initialize() (a bsp specific
> > routine in this case), but between console_initialize() and Init() it
> > goes south.  I have stepped through all the code in console_initialize,
> > and the stack seems fine in there too. Maybe this is just me not quite
> > understanding how RTEMS initializes the stack for a process...  I do
> > know, that if I let the program run without any breakpoints, it goes
> > wild and overwrites itself...  Isn't that generally an indication of
> > stack corruption?
> is something just blowing the stack ?, do you have enough configured
> is trickey to really work out how much you need, but doubleing it is
> a good idea. 

I have doubled, and even quadrupled the stack, it does not help.

> i also seem to remember (but cant be sure), that rtems is running in 
> priverlaged mode at this point, is it possible that come code is stomping
> the stack pointer ? - ive seen stranger.

I donno.  I cant figure it out in GDB, because the code acts different
in the debugger :(

> regards
> ---
> Matthew J Fletcher		amimjf at
> Software Engineering		Matthew.Fletcher at
>			ICQ amimjf 44193496
> ---
> 2.4.17-20mdk #1 Wed Feb 20 20:45:19 CET 2002
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