["omit_ECE" <omit@rice.edu>]

Hi,

I want to know the one-way trip time in TCP header.
In tcp_input.c , I found many functions under which include
rcv_tsval and  rcv_tsecr . I don't know which two are right.
So, I put many "printf" and fprintf in functions and compile the kernel.
But when compiling it, some errors happen,

net/network.o: In function `tcp_parse_options':
net/network.o: In function `tcp_rcv_established':
net/network.o: In function `tcp_rcv_synsent_state_process':
net/network.o: In function `tcp_rcv_state_process':
net/network.o(.text+0x2807b): undefined reference to `printf'
net/network.o(.text+0x2808c): undefined reference to `printf'
net/network.o(.text+0x2631d): undefined reference to `fopen'
net/network.o(.text+0x26334): undefined reference to `fprintf'
net/network.o(.text+0x2634e): undefined reference to `fprintf'
net/network.o(.text+0x2635a): undefined reference to `fclose'

Aren't "printf" and "fprintf"  standard outputs? I also put #include <stdio.h>
and "FILE *in_file", but they didn't work. Please give me suggestions.
Thank you.