# OS Assignment 6
# Rick van der Zwet - 0433373
# $Id: README.txt 619 2008-05-19 19:35:46Z rick $

# Please let me know if you are also interested in the actual diff of
# the files if those brief outputs are not sufficient

# WARNING: Using different system, Ubuntu Linux under Parallels, kernel
# version 2.6.24.3 on a x86 system
$ cd /usr/src/linux/kernel
$ vim sys.c

# Syscall lives in different location
$ vim arch/x86/kernel/syscall_table_32.S
code: .long sys_multiply              /* 325 *

# __NR_syscall_max has been replaced by NR_syscalls in file
$ vim include/asm/unistd_32.h

# include/linux/syscalls.h does not need to be altered anymore, as it
# directly links to include/asm/unistd_32.h

# Build new kernel

#Code used:
=== BEGIN CODE ===
#include <stdio.h>
#include <sysexits.h>
#include <unistd.h>
int main() {
    printf("6 * 7 = %li\n", syscall(325, 6, 7));
    return(EX_OK);
}
=== END CODE ===
$ gcc -Wall -o syscall-test syscall-test.c
$ ./syscall-test
# When calling it on original kernel the output is `6 * 7 = -1', the
# `-1' is in fact syscall error return code, due the fact the syscall
# does not exists yet

# Install new kernel and reboot
$ ./syscall-test
# After rebooting the output is set to be `6 * 7 = 42`
$ time ./syscall-test
# when using larger numbers and `time' to measure output it will become
# clear the program is spending almost all of his time in sys(tem) mode.