[otbn] Don't overflow the call stack in RIG programs
Signed-off-by: Rupert Swarbrick <rswarbrick@lowrisc.org>
diff --git a/hw/ip/otbn/util/rig/model.py b/hw/ip/otbn/util/rig/model.py
index e627427..32a715b 100644
--- a/hw/ip/otbn/util/rig/model.py
+++ b/hw/ip/otbn/util/rig/model.py
@@ -470,9 +470,16 @@
return random.choice(known_list)
- # This operand isn't treated as a source. Pick any register!
+ # This operand isn't treated as a source. Pick any register, but "roll
+ # again" if we pick x1 and the call stack is full.
assert op_type.width is not None
- return random.getrandbits(op_type.width)
+ while True:
+ idx = random.getrandbits(op_type.width)
+ if ((idx == 1 and
+ op_type.reg_type == 'gpr' and
+ len(self._call_stack) >= 8)):
+ continue
+ return idx
def regs_with_known_vals(self, reg_type: str) -> List[Tuple[int, int]]:
'''Find registers whose values are known
