hi
i have a simple module like this:


#include <linux/module.h> // Needed by all modules
#include <linux/kernel.h> // Needed for KERN_ALERT
#include <linux/init.h> // Needed for the macros


static int hello_init(void)
{
printk(KERN_ALERT "Hello, world 2\n");
return 0;
}


static void hello_exit(void)
{
printk(KERN_ALERT "Goodbye, world 2\n");
}


module_init(hello_init);
module_exit(hello_exit);


i tried to compile it like this:

gcc hello.c

but i recived error messages as fallows:

[root@localhost modules]# gcc hello.c
hello.c: In function `hello_init':
hello.c:11: error: `KERN_ALERT' undeclared (first use in this function)
hello.c:11: error: (Each undeclared identifier is reported only once
hello.c:11: error: for each function it appears in.)
hello.c:11: error: syntax error before string constant
hello.c: In function `hello_exit':
hello.c:18: error: `KERN_ALERT' undeclared (first use in this function)
hello.c:18: error: syntax error before string constant
[root@localhost modules]#



plz guide me........

venki

hi,

This is kernel module compilation not a user program you need Makefile to compile your program.the header file u r using u need to provide a path of kernel source to gcc command so that you will not get any error of KERN_ALERT

hi,
Forgot to post Makefile
create this Makefile file in current directory where your hello.c located and then simply type make

sorry actually i forgot to give u the Makefile
i had written makefile which was like this

TARGET := hello
WARN := -W -Wall -Wstrict-prototypes -Wmissing-prototypes
INCLUDE := -isystem /lib/modules/`uname -r`/build/include
CFLAGS := -O2 -DMODULE -D__KERNEL__ ${WARN} ${INCLUDE}
CC := gcc33

${TARGET}.o: ${TARGET}.c

.PHONY: clean

clean:
rm -rf {TARGET}.o

i issued make command in the current directory wr my makefile n modules r present but error was reported as fallows:


[root@localhost modules]# make
gcc-3.3.2 -O2 -DMODULE -D__KERNEL__ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -isystem /lib/modules/`uname -r`/build/include -c -o hello.o hello.c
/bin/sh: line 1: gcc-3.3.2: command not found
make: *** [hello.o] Error 127


n plz give me a compleate command what should be my gcc command to compile my module..........

hi,
which kernel version r u using?

hi,
change CC=gcc33 to CC=gcc in your Makefile and then try compiling again

venki, you cannot just compile program using gcc command line (ok you can but you need to type long set of commands) insted you need to create a makefile. Then compile program; your program is fine and it can be compiled without problem. The procedure to create makefile and commands are outlined here http://www.cyberciti.biz/nixcraft/vi...nel-module.php

my kernel version is: 2.4.22

[root@localhost modules]# make
make: `hello.o' is up to date.
[root@localhost modules]#

thanks thats fine.......

now can i insert my module into kernel using insmod or is it required to
recompile my kernel before i insert my module...

hi,
No need to recompile kernel code. Just use insmod hello.o as root

i issued the command
insmod hello.o
the result was:
[root@localhost modules]# insmod hello.o
Warning: loading hello.o will taint the kernel: no license
See http://www.tux.org/lkml/#export-tainted for information about tainted modules
Module hello loaded, with warnings


then changed my hello.c to include the fallowing at the end of my c file

MODULE_LICENSE("GPL");
MODULE_AUTHOR("VENKATESH");

then it was fallowed by this:

[root@localhost modules]# gcc hello.c

errors reported were:

hello.c: In function `hello_init':
hello.c:11: error: `KERN_ALERT' undeclared (first use in this function)
hello.c:11: error: (Each undeclared identifier is reported only once
hello.c:11: error: for each function it appears in.)
hello.c:11: error: syntax error before string constant
hello.c: In function `hello_exit':
hello.c:18: error: `KERN_ALERT' undeclared (first use in this function)
hello.c:18: error: syntax error before string constant


wt is the gcc command to include source to kernel dir...
my hello.c file is in /venki/modules/ and kernel path is /usr/src/linux-2.4.22

my friend was suggesting me to use -c option to compile is it ok to use -c option that is gcc -c hello.c can i use this command

hi,
Whats output of following command
gcc -O2 -DMODULE -D__KERNEL__ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -I/usr/src/linux-2.4.22/include -c -o hello.o hello.c

hi,
USe following Makefile as you r using 2.4 kernel
The one that i was posted before was for kernel 2.6

i used the gcc command with makefile u wrote
it goes as fallows:

[root@localhost modules]# gcc -O2 -DMODULE -D__KERNEL__ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -I/usr/src/linux-2.4/include -c -o hello.o hello.c
In file included from /usr/src/linux-2.4/include/linux/prefetch.h:13,
from /usr/src/linux-2.4/include/linux/list.h:6,
from /usr/src/linux-2.4/include/linux/module.h:12,
from hello.c:4:
/usr/src/linux-2.4/include/asm/processor.h:503: warning: no previous prototype for `prefetch'
In file included from /usr/src/linux-2.4/include/linux/kernel.h:15,
from hello.c:5:
/usr/src/linux-2.4/include/asm/byteorder.h:14: warning: type qualifiers ignored on function return type
/usr/src/linux-2.4/include/asm/byteorder.h:30: warning: type qualifiers ignored on function return type
In file included from /usr/src/linux-2.4/include/linux/byteorder/little_endian.h:11,
from /usr/src/linux-2.4/include/asm/byteorder.h:65,
from /usr/src/linux-2.4/include/linux/kernel.h:15,
from hello.c:5:
/usr/src/linux-2.4/include/linux/byteorder/swab.h:160: warning: type qualifiers ignored on function return type
/usr/src/linux-2.4/include/linux/byteorder/swab.h:173: warning: type qualifiers ignored on function return type
/usr/src/linux-2.4/include/linux/byteorder/swab.h:186: warning: type qualifiers ignored on function return type
/usr/src/linux-2.4/include/linux/byteorder/swab.h:200: warning: type qualifiers ignored on function return type
/usr/src/linux-2.4/include/asm/processor.h: In function `copy_segments':
/usr/src/linux-2.4/include/asm/processor.h:453: warning: unused parameter `p'
/usr/src/linux-2.4/include/asm/processor.h:453: warning: unused parameter `mm'
/usr/src/linux-2.4/include/asm/processor.h: In function `release_segments':
/usr/src/linux-2.4/include/asm/processor.h:454: warning: unused parameter `mm'
/usr/src/linux-2.4/include/linux/prefetch.h: In function `prefetchw':
/usr/src/linux-2.4/include/linux/prefetch.h:48: warning: unused parameter `x'
[root@localhost modules]#

hi,
just insert a tab at line 7 in your Makefile and try again with make command
arghhh i forgot 2.4 kernel module compilation using gcc
now try simple command
gcc -I/lib/modules/`uname -r`/build/include -D__KERNEL__ -DMODULE -DLINUX -O2 -Wall -Wstrict-prototypes -c -o hello.o hello.c

hey it worked man thanks..........