AM62A7-Q1: Where does define the function named putc in u-boot-spl

Tool/software:

Hi, TI experts

        Now, We should disable the log out for cyber security in u-boot-spl.

        We have tracked the printf function will call putc function to log out in the console.

        We use the source code of u-boot-spl is ti-u-boot-2024.04/ based on SDK 10.01.

       We have found printf fuction is defined in lib/tiny-printf.c.

       But we cannot find where the putc fuction is defined.

      So I am confused how we can build image successfully.

      How can we disable the log output in u-boot-spl ?

Thanks