arch-arm: Check if VectorCatch is nullptr

This is needed after [1].
Simulation starts with a call to the reset fault in the
initState stage and therefore checks for the vector catch
object. This happens before the SelfDebug object is properly
initialized.

[1]: https://gem5-review.googlesource.com/c/public/gem5/+/60730

Change-Id: Ic117413611aa30386327bbc13e5489fab32733de
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60769
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

src/arch/arm/faults.cc

@@ -734,7 +734,7 @@ ArmFault::vectorCatch(ThreadContext *tc, const StaticInstPtr &inst)
 {
     SelfDebug *sd = ArmISA::ISA::getSelfDebug(tc);
     VectorCatch* vc = sd->getVectorCatch(tc);
-    if (!vc->isVCMatch()) {
+    if (vc && !vc->isVCMatch()) {
         Fault fault = sd->testVectorCatch(tc, 0x0, this);
         if (fault != NoFault)
             fault->invoke(tc, inst);

src/arch/arm/self_debug.hh

@@ -294,7 +294,7 @@ class SelfDebug
 
   public:
     SelfDebug()
-      : enableTdeTge(false),
+      : softStep(nullptr), vcExcpt(nullptr), enableTdeTge(false),
         mde(false), sdd(false), kde(false), oslk(false)
     {
         softStep = new SoftwareStep(this);