os: div_zero trace policy

This trace policy can be used as a fault-injection mechanism.
Once installed, the next time the traced thread passes a trace point
(e.g., RPC call, RPC request, ...), the policy produces a divide-by-zero
exception.

repos/os/src/lib/trace/policy/div_zero/policy.cc

@@ -0,0 +1,54 @@
+#include <util/string.h>
+#include <trace/policy.h>
+
+using namespace Genode;
+
+enum { MAX_EVENT_SIZE = 64 };
+
+static inline int div_zero()
+{
+	static int zero;
+
+	/* use variable to prevent compiler warning about division by zero */
+	return 1 / zero;
+}
+
+size_t max_event_size()
+{
+	return MAX_EVENT_SIZE;
+}
+
+size_t log_output(char *dst, char const *log_message, size_t len)
+{
+	return div_zero();
+}
+
+size_t rpc_call(char *dst, char const *rpc_name, Msgbuf_base const &)
+{
+	return div_zero();
+}
+
+size_t rpc_returned(char *dst, char const *rpc_name, Msgbuf_base const &)
+{
+	return div_zero();
+}
+
+size_t rpc_dispatch(char *dst, char const *rpc_name)
+{
+	return div_zero();
+}
+
+size_t rpc_reply(char *dst, char const *rpc_name)
+{
+	return div_zero();
+}
+
+size_t signal_submit(char *dst, unsigned const)
+{
+	return div_zero();
+}
+
+size_t signal_receive(char *dst, Signal_context const &, unsigned)
+{
+	return div_zero();
+}

repos/os/src/lib/trace/policy/div_zero/target.mk

@@ -0,0 +1,5 @@
+TARGET = div_zero_policy
+
+TARGET_POLICY = div_zero
+
+include $(PRG_DIR)/../policy.inc