[Qemu-devel] PPC Bug Report - Trap Exception setting SRR0 incorrectly

[Ely Soto]

PPC Bug Only

Call Stack

op_helper.c : do_tw()
op_helper.c : do_raise_exception_err()
op_helper.c : cpu_loop_exit()
op_helper.c : longjmp()
???
helper.c : do_interrupt()

Normally when an exception gets to
do_interrupt(), env->nip is set to the instruction after the one causing
the exception.
However, a trap instruction arrives
at the do_interrupt() with the env->nip set at the instruction that
caused the exception.
This causes an the SRR0 to get set
incorrectly to one instruction back when calling the exception handler.

I'm still learning the code so I'm
still trying to figure out the right fix since
its possible that more exceptions are
affected. I've already verified that forcing the env->nip forward for
just the trap case
fixes the execution.

From the middle of helper.c : do_interrupt()
...
case
EXCP_TRAP:
...
goto
store_current;
...

From the bottom of helper.c : do_interrupt()
...
    store_current:
        /*
save current instruction location */
        *srr_0
= (env->nip - 4) & 0xFFFFFFFFULL;
        break;
    store_next:
        /*
save next instruction location */
        *srr_0
= env->nip & 0xFFFFFFFFULL;
        break;
...


I discovered this because I'm trying
to get a vxworks debugger working when the os is running.
Ohh ya, I've got a VxWorks 6.3 kernel
up and running on PPC QEMU. 8-) Custom BSP and all.

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