Memo: How to build OpenBSD from source code and add system call on QEMU
Introduction
Memorandum for myself. I just follow these three articles. Thanks dude.
- http://undeadly.org/cgi?action=article&sid=20130109210346
- http://www.onlamp.com/pub/a/bsd/2003/10/09/adding_system_calls.html
- http://www.openbsd.org/faq/faq5.html#BldGetSrc
Prolly This's the easiest way to try kernel hack.
I tried with OpenBSD 5.6
How to install OpenBSD on QEMU
# on host $ cd work $ qemu-img create -f qcow2 ./obsd56.qcow2 20G $ wget http://ftp5.usa.openbsd.org/pub/OpenBSD/5.6/i386/install56.iso $ qemu-system-i386 -m 256M -net nic -net user -cdrom ./install56.iso ./obsd56.qcow2 # install OpenBSD on QEMU # Then quit qemu once with the following commands # $ Ctrl-Alt-2 # (qemu) quit
How to boot OpenBSD on QEMU
$ qemu-system-i386 -m 256M -net nic -net user ./obsd56.qcow2 # boot OpenBSD on QEMU
How to get OpenBSD source code via ftp
# on QEMU $ cd /tmp $ ftp ftp://ftp5.usa.openbsd.org/pub/OpenBSD/5.6/sys.tar.gz $ cd /usr/src $ tar xzf /tmp/sys.tar.gz
How to add a new system call
# on QEMU $ cd /usr/src/sys/kern $ vi syscalls.master # modify "260" to the following line # 260 STD { int sys_hello(void); } $ make init_sysent.c $ vi sys_hello.c # edit sys_hello.c as written below $ cd ../conf $ vi files # add the following line # file kern/sys_hello.c
/* /usr/src/sys/kern/sys_hello.c */ #include <sys/types.h> #include <sys/param.h> #include <sys/systm.h> #include <sys/kernel.h> #include <sys/proc.h> #include <sys/mount.h> #include <sys/syscallargs.h> int sys_hello(struct proc *p, void *v, register_t *retval) { printf("Hello World\n"); return (0); }
How to build OpenBSD from source code for debug
# on QEMU $ cd /usr/src/sys/arch/i386/conf $ cp GENERIC DEBUG $ vi DEBUG # add the following line # makeoptions DEBUG="-g" $ config DEBUG $ cd ../compile/DEBUG $ make depend $ COPTS="-O0" make $ make install $ reboot
make user program using the new system call
# on QEMU $ cd /tmp $ vi main.c # edit main.c as written below $ gcc main.c $ ./a.out Hello World
/* /tmp/main.c */ int main(int argc, char **argv) { syscall(260); }
