hi, I found that I must modify the files under libgloss\arm. And also I noticed that there are syscall.c and redboot-syscall.c. So, what should I do. Modify the syscall.c or create another file named xxxx-syscall.c? >Something like that. See this: >http://wiki.osdev.org/Porting_Newlib the document you give is not mentioned this point. thank you very much