Wow, that was it. I'm happy to hear that because I thought it should end up with a system call anyway. Then isn't there some codes making the system call? Or is it that the compiler understands that 'write' is a system call and inserts the assembly code for calling it by itself? Thanks in adv. Chan ________________________________ From : "Mohan L" <l.mohanphy@gmail.com> Sent : 2014-03-12 15:31:24 ( +09:00 ) To : Kim Chan <ckim@etri.re.kr> Cc : Dave Hylands <dhylands@gmail.com>, kernelnewbies@kernelnewbies.org <kernelnewbies@kernelnewbies.org> Subject : Re: where is the printf source for busybox? ssize_t attribute_hidden _cs_write(void *cookie, const char *buf, size_t bufsize) { return write(*((int *) cookie), (char *) buf, bufsize); } what does cs stand for here? (Hm.. seems like custom streams..in the code) and I couldn't follow past write above. Where is the function write defined? Hi Chan, write is a system call. $ man 2 write syscall table for x86 architecture can be found in : <path>/arch/x86/syscalls/syscall_32.tbl # cat <path>/arch/x86/syscalls/syscall_32.tbl | grep 'write' 4 i386 write sys_write The format is: <number> <abi> <name> <entry point> <compat entry point> search sys_write definition in kernel source. Thanks Mohan L