Hello all,
I am writing a simple char driver on Linux (Suse 9.1, kernel 2.6.4.52,
gcc 3.3.3) and having the following problems (code is cut-pasted at
the end):
1) MODULE_LICENSE gives the following on make -
error: parse error before string constant
warning: type defaults to `int' in declaration of `MODULE_LICENCE'
warning: data definition has no type or storage class
Btw, it works fine in another program which simply does module_init()
and module_exit().
2) insmod faults (SIGSEGV) with strace ending at the line:
init_module("^?ELF^A^A^A", 0xc529 <unfinished ...>
4299 +++ killed by SIGSEGV +++
dmesg output:
MAJOR(dev)=253
Before cdev_init
Unable to handle kernel NULL pointer dereference at virtual address 00000018
printing eip:
c01da533
*pde = 00000000
Oops: 0002 [#2]
CPU: 0
EIP: 0060:[<c01da533>] Tainted: PF
EFLAGS: 00010292 (2.6.4-52-default)
EIP is at kobject_init+0x3/0x40
eax: 00000000 ebx: 00000000 ecx: 00000000 edx: 00000000
esi: d9126880 edi: d912684c ebp: d059de48 esp: d059de28
ds: 007b es: 007b ss: 0068
Process insmod (pid: 3877, threadinfo=d059c000 task=d6494d70)
Stack: c0341da8 d91280cc d9126800 000000fd 00000001 d9126232 0fd00000 c0341d98
c0341d98 c0132305 00000000 d9142e54 d9142e54 00000500 00000500 d05dc9a0
d059de8c c0138db0 0000304c 00000282 00000000 d05dc980 00000001 d059deb4
Call Trace:
[<d91280cc>] scull_init+0xcc/0x15f [cd]
[<c0132305>] sys_init_module+0x105/0x15b0
[<c0138db0>] file_read_actor+0x0/0xe0
[<c01da3e0>] kobject_put+0x0/0x20
[<d9128000>] scull_init+0x0/0x15f [cd]
[<c01c8d96>] selinux_file_alloc_security+0x26/0x80
[<c01ca1e0>] selinux_file_permission+0x160/0x170
[<c0155b5e>] __fput+0x9e/0xf0
[<c0107dc9>] sysenter_past_esp+0x52/0x79
Code: c7 40 18 01 00 00 00 8d 40 1c 89 43 1c 89 43 20 8b 43 28 31
Analysis done:
I was getting the same erorr on cdev_init() so to find out where
exactly the inmod was crashing, I manually did whatever was being done
inside cdev_init and figured out that it was crashing at
kobject_init().
I have gone through /proc/ksyms to figure out exactly which
instruction causes the fault but have not been successful.
relevant ksymoops info:
Code; c01da533 <kobject_init+3/40>
00000000 <_EIP>:
Code; c01da533 <kobject_init+3/40> <=====
0: c7 40 18 01 00 00 00 movl $0x1,0x18(%eax) <=====
Code; c01da53a <kobject_init+a/40>
7: 8d 40 1c lea 0x1c(%eax),%eax
Code; c01da53d <kobject_init+d/40>
a: 89 43 1c mov %eax,0x1c(%ebx)
Code; c01da540 <kobject_init+10/40>
d: 89 43 20 mov %eax,0x20(%ebx)
Code; c01da543 <kobject_init+13/40>
10: 8b 43 28 mov 0x28(%ebx),%eax
Code; c01da546 <kobject_init+16/40>
13: 31 00 xor %eax,(%eax)
Any help extended would be highly appreciated.
Thanks,
Hemant R Mohapatra
------------------------------------------------------------------------
Code:
#if defined( CONFIG_MODVERSIONS ) && ! defined( MODVERSIONS )
#define MODVERSIONS
#endif
#include <linux/module.h>
#include <linux/init.h>
#include <asm/current.h>
#include <asm/uaccess.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/kobj_map.h>
#include <linux/cdev.h>
#ifdef CONFIG_KMOD
#include <linux/kmod.h>
#endif
#include <linux/cdev.h>
#define DEVICE_NAME "scull"
#define SUCCESS 0
#define FAIL -1
#define SIZE 10
#define TYPE(dev) (MINOR(dev) >> 4) //highers 4 bits refer to type
of device (char, in this case)
//lower 4 bits refer to NUM for the device
#define NUM(dev) (MINOR(dev) & 0xf)
static int Major, Minor;
static int device_opened = 0;
static char MSGBUF[SIZE];
static char *msg_ptr;
static int device_open (struct inode *in, struct file *filp);
static int device_release (struct inode *in, struct file *filp);
/* static ssize_t device_read (struct file *, char *, size_t, loff_t *);
static ssize_t device_write (struct file *, char *, size_t, loff_t *);
* */
static int
device_open (struct inode *in, struct file *filp)
{
/* int type=TYPE(in->i_rdev); */// Old way of getting the driver's
// major/minor number.
/* int num=NUM(in->i_rdev); */
int counter = 0;
int type = TYPE (iminor (in));
int num = NUM (iminor (in));
if (device_opened)
{
return -EBUSY;
}
device_opened++;
msg_ptr = MSGBUF; //this is the pointer used in reading from
the device in the device_read func
sprintf (MSGBUF, "This is call to open() device number: %d\n", ++counter);
//return some info about the driver
printk ("<1> TYPE of device = %d\n and NUM of device = %d\n", type, num);
MOD_INC_USE_COUNT;
return SUCCESS;
}
static int
device_release (struct inode *in, struct file *filp)
{
device_opened--;
MOD_DEC_USE_COUNT;
return SUCCESS;
}
static struct file_operations scull_fops = {
.open = device_open,
.release = device_release,
.owner = THIS_MODULE,
// .read = device_read,
// .write = device_write,
};
static struct cdev scull_cdev = {
.kobj = {.name = "scull", },
.owner = THIS_MODULE,
};
static int __init scull_init (void)
{
/* dev_t dev=MKDEV(63,0); */
dev_t dev;
int retval;
retval=alloc_chrdev_region(&dev, 0, 1, DEVICE_NAME);
if(!retval)
{
Major=MAJOR(dev);
Minor=MINOR(dev);
}
else {
return FAIL;
}
printk("MAJOR(dev)=%d\n", MAJOR(dev));
printk("<1> Before cdev_init\n");
memset(&scull_cdev, 0, sizeof(scull_cdev));
INIT_LIST_HEAD(&scull_cdev.list);
//scull_cdev.kobj.ktype = &ktype_cdev_default; -- not working, why?
kobject_init(&scull_cdev.kobj);
scull_cdev.ops = &scull_fops;
//kobject_set_name(&scull_cdev.kobj,"scull");
//cdev_init(&scull_cdev, &scull_fops); -- was not working, so the above
//simplification
printk("<1> after cdev_init:\n");
retval=cdev_add(&scull_cdev, dev, 1);
if(retval)
{
cdev_del(&scull_cdev);
kobject_put(&scull_cdev.kobj);
unregister_chrdev_region(dev, 1);
printk("<1> Error in cdev_add:");
goto error;
}
printk ("<1> scull_init was a Success and the major device number is
%d \n", Major);
return 0;
error:
printk(KERN_ERR "error register raw device\n");
return FAIL;
}
static void scull_exit (void)
{
printk ("<1> Removing scull drivers from /proc/devices\n");
unregister_chrdev_region (MKDEV(Major,0), 1);
}
module_init (scull_init);
module_exit (scull_exit);
//MODULE_LICENCE("GPL"); - doesn't work.
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