tests: kernel: common: added test on atomic_t overflow

Added test to verify that the value of atomic_t will be the same
in case of overflow if incremented in atomic and non-atomic manner

Signed-off-by: Alexander Razinkov <[email protected]>

tests/kernel/common/src/atomic.c

@@ -338,6 +338,51 @@ ZTEST(atomic, test_threads_access_atomic)
 		"atomic counting failure");
 }
 
+/**
+ * @brief Checks that the value of atomic_t will be the same in case of overflow
+ *		if incremented in atomic and non-atomic manner
+ *
+ * @details According to C standard the value of a signed variable
+ *	is undefined in case of overflow. This test checks that the the value
+ *	of atomic_t will be the same in case of overflow if incremented in atomic
+ *	and non-atomic manner. This allows us to increment an atomic variable
+ *	in a non-atomic manner (as long as it is logically safe)
+ *	and expect its value to match the result of the similar atomic increment.
+ *
+ * @ingroup kernel_common_tests
+ */
+ZTEST(atomic, test_atomic_overflow)
+{
+	/* Check overflow over max signed value */
+	uint64_t overflowed_value = (uint64_t)1 << (ATOMIC_BITS - 1);
+	atomic_val_t atomic_value = overflowed_value - 1;
+	atomic_t atomic_var = ATOMIC_INIT(atomic_value);
+
+	atomic_value++;
+	atomic_inc(&atomic_var);
+
+	zassert_true(atomic_value == atomic_get(&atomic_var),
+		"max signed overflow mismatch: %lx/%lx",
+		atomic_value, atomic_get(&atomic_var));
+	zassert_true(atomic_value == (atomic_val_t)overflowed_value,
+		"unexpected value after overflow: %lx, expected: %lx",
+		atomic_value, (atomic_val_t)overflowed_value);
+
+	/* Check overflow over max unsigned value */
+	atomic_value = -1;
+	atomic_var = ATOMIC_INIT(atomic_value);
+
+	atomic_value++;
+	atomic_inc(&atomic_var);
+
+	zassert_true(atomic_value == atomic_get(&atomic_var),
+		"max unsigned overflow mismatch: %lx/%lx",
+		atomic_value, atomic_get(&atomic_var));
+	zassert_true(atomic_value == 0,
+		"unexpected value after overflow: %lx, expected: 0",
+		atomic_value);
+}
+
 extern void *common_setup(void);
 ZTEST_SUITE(atomic, NULL, common_setup, NULL, NULL, NULL);
 /**