[U-Boot-Users] PPC: problem with syscalls

Pierre AUBERT p.aubert at staubli.com
Fri Nov 29 13:04:03 CET 2002

Pierre AUBERT wrote:

> Hello everybody,
> I've a problem with examples/timer.c. I've tried to launch it on my
> mpc860t board, if I start the timer and if I
> press a key after one or more interrupts occured, the u-boot crashes.
> The problem is that an interrupt handler
> uses a system call (mon_printf) while the main loop is inside a system
> call (mon_getc). During a system call,
> the LR and SRRx are saved at a fixed location (0xcf4, 0xcf8 and 0xcfc)
> then the return address of the mon_printf
> in the main loop is overridden by the return address of the mon_getc in
> the interrupt handler. To avoid this problem,
> I think that we need to use a stack to store the return addresses (and
> the SRRx) of the system calls.

Dear Wolfgang,

Please find attached a patch fixing the problem described above. A little
stack (located between the end of the syscall exception handler and the
beginning of the following exception) is used to save the LR and SRRx.
With this patch, examples/timer is running fine.

Best regards.

* Patch by Pierre Aubert , 28 Nov 2002
  Fix nested syscalls bug in standalone applications.

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