CREATE EXCEPTION TEST_EXCEPTION 'Исключение';

CREATE OR ALTER PROCEDURE TEST_SP (
    TEXT VARCHAR(10))
AS
BEGIN
    EXCEPTION TEST_EXCEPTION :TEXT;
END

DECLARE EXTERNAL FUNCTION ib_floor
    DOUBLE PRECISION
    RETURNS DOUBLE PRECISION BY VALUE
    ENTRY_POINT 'IB_UDF_floor' MODULE_NAME 'ib_udf';

EXECUTE PROCEDURE TEST_SP((SELECT COUNT(*) FROM RDB$DATABASE)) || IB_FLOOR(1);

TEST_EXCEPTION.
11.000000000000000.
At procedure 'TEST_SP' line: 5, col: 5.