One of the very first things to do in a buildfile is to start a driver that you then redirect standard input, output, and error to. This allows all subsequent drivers and applications to output their startup messages and any diagnostics messages they may emit to a known place where you can examine the output.
Generally, you'd start either the console driver or a serial port driver. The console driver is used when you're developing on a fairly complete "desktop" type of environment; the serial driver is suitable for most "embedded" environments.
But you may not even have any such devices in your deeply embedded system, in which case you would omit this step. Or you may have other types of devices that you can use as your output device, in which case you may require a specialized driver (that you supply). If you don't specify a driver, output will go to the debug output driver provided by the startup code.