Hello all,
I just joined this list and I look forward to learning a lot of introductory
information about linux kernel programming. If my post does not follow
proper posting form please inform me of the way things should be done. I was
not
able to locate anything on the website under mailing lists to explain it. :)
A little bit about myself: I am a first year graduate student taking an
Operating System class and we are focusing on the linux kernel for our lab
assignments. This is a new area for me so I require some extra assistance in
answering some questions, and fixing some problems :) I do not expect anyone to
do
my work for me.
I am using Fedora Core 6 with the kernel version of 2.6.22 on an i386
machine.
I am to implement a simple system call that will use printk to display some
text (the time, in nanoseconds) to the screen.
Here are the steps that I am performing in order to implement this system
call:
1.) I went into /linux/arch/i386/kernel/syscall_table.S and I added an
entry at the very end with the value of: ".long sys_my_xtime"
2.) I went into /linux/include/asm-i386/unistd.h and I added #define
__NR_my_xtime 324 after 323.
3.) I incremented #define NR_syscalls 324 to #define NR_syscalls 325
4.) I went into /linux/include/linux/syscalls.h and added asmlinkage long
sys_my_xtime(struct timespec __user *current_time)
5.) I then placed the following function into /linux/kernel/time.c:
asmlinkage long sys_my_xtime(struct timespec __user *current_time)
{
//code here to check writable
//TEST! display to console - send the worst type so it is easier
printfk(KERN_EMERG "This is a test\n");
return 0;
}
6.) I then go to the shell and type the following commands:
make bzImage
make modules_install [I do not do make modules anymore since I've already
made them]
make install
7.) I reboot.
8.) I select my kernel to boot up.
9.) I wrote my test program, with the macro:
#define __NR_my_xtime 324
#define _syscall1(type,name,type1,arg1) \
long my_xtime(struct timespec * current_time) \
{ \
long __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_my_xtime),"b" ((long)(current_time))); \
if (__res >= 0) \
return (type) __res; \
errno = -__res; \
return -1; \
}
Then in my main function:
_syscall1(long, my_xtime, struct timespec *, mytimespec);
When I run my program, I do not receive any messages and it does not appear
to work. I also cannot use the macro I have defined in such a way to return a
value, as it gives compile errors. I have also tried to set __res to a global
value in my user program, to see if the macro is working properly. That does
not work. Additionally, I can put the incorrect function name in the marco
call and it will compile and 'run just fine'.
I'm not sure what I am missing here, I used the guide
_http://tldp.org/HOWTO/html_single/Implement-Sys-Call-Linux-2.6-i386/#AEN89_
(http://tldp.org/HOWTO/html_single/Implement-Sys-Call-Linux-2.6-i386/#AEN89)
and that does not work either (I get compile errors for the header file and
thus cannot complete it). It says you can place the new function anywhere, so
the steps are the same for placing the information for the new call.
I am doing this on another machine so let me know if you need any more
information regarding this (as I suspect you will).
Thanks
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