[root@zymurgy jrb]# cat boom2.c

1. boom2.c
#define MODULE
#include <linux/module.h>

boom()
{
	char *f;
	f = 0;
	*f = 1;
}

int 
init_module(void) 
{

	printk("<1> init_module: Hello, world \n");
	boom();
	return (0);
}

void 
cleanup_module(void)
{
	printk("<1> cleanup_module: Goodbye, world\n");
	while(1) {
		schedule();
	}
}

2. inserting it
# insmod boom2.o
Segmentation Violation

3. noting that what is in the syslog is not helpful
klogd couldn't have caught it.  why?

Oct 22 10:12:08 zymurgy kernel:  init_module: Hello, world 
Oct 22 10:12:08 zymurgy kernel: Unable to handle kernel NULL pointer dereference at virtual address 00000000
Oct 22 10:12:08 zymurgy kernel:  printing eip:
Oct 22 10:12:08 zymurgy kernel: d2d23070
Oct 22 10:12:08 zymurgy kernel: *pde = 00000000
Oct 22 10:12:08 zymurgy kernel: Oops: 0002
Oct 22 10:12:08 zymurgy kernel: CPU:    0
Oct 22 10:12:08 zymurgy kernel: EIP:    0010:[scsi_mod:scsi_hosts_R80308476+38247092/78506563]
Oct 22 10:12:08 zymurgy kernel: EIP:    0010:[<d2d23070>]
Oct 22 10:12:08 zymurgy kernel: EFLAGS: 00010286
Oct 22 10:12:08 zymurgy kernel: eax: 00000000   ebx: d2d23000   ecx: 00000007   edx: 00000000
Oct 22 10:12:08 zymurgy kernel: esi: 00000000   edi: 00000000   ebp: c9167f18   esp: c9167f14
Oct 22 10:12:08 zymurgy kernel: ds: 0018   es: 0018   ss: 0018
Oct 22 10:12:08 zymurgy kernel: Process insmod (pid: 1650, stackpage=c9167000)
Oct 22 10:12:08 zymurgy kernel: Stack: 00000000 c9167f28 d2d23093 00000000 00000000 00000060 c01182e5 00000000 
Oct 22 10:12:08 zymurgy kernel:        c91fd000 00000120 c9387000 00000060 ffffffea 00000005 c957a5a0 00000060 
Oct 22 10:12:08 zymurgy kernel:        d096f000 d2d23060 000001c0 00000000 00000000 00000000 00000000 00000000 
Oct 22 10:12:08 zymurgy kernel: Call Trace: [scsi_mod:scsi_hosts_R80308476+38247127/78506528] [sys_init_module+1333/1520] [scsi_mod:scsi_hosts_R80308476+809540/115944115] [scsi_mod:scsi_hosts_R80308476+38247076/78506579] [system_call+51/56] 
Oct 22 10:12:08 zymurgy kernel: Call Trace: [<d2d23093>] [<c01182e5>] [<d096f000>] [<d2d23060>] [<c0106f0b>] 
Oct 22 10:12:08 zymurgy kernel: 
Oct 22 10:12:08 zymurgy kernel: Code: c6 00 01 c9 c3 8d 76 00 55 89 e5 83 ec 08 83 ec 0c 68 c0 30 


4. running ksymoops

[root@zymurgy jrb]# ksymoops -o boom2.o oops.txt
ksymoops 2.4.1 on i686 2.4.7-10.  Options used
     -V (default)
     -k /proc/ksyms (default)
     -l /proc/modules (default)
     -o boom2.o (specified)
     -m /boot/System.map-2.4.7-10 (default)

Error (expand_objects): cannot stat(/lib/ext3.o) for ext3
ksymoops: No such file or directory
Error (expand_objects): cannot stat(/lib/jbd.o) for jbd
ksymoops: No such file or directory
Warning (compare_maps): mismatch on symbol partition_name  , ksyms_base says c01b3570, System.map says c0155720.  Ignoring ksyms_base entry
Warning (compare_maps): mismatch on symbol proc_scsi  , scsi_mod says d08a958c, /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o says d08a7e14.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o entry
Warning (compare_maps): mismatch on symbol scsi_devicelist  , scsi_mod says d08a95b8, /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o says d08a7e40.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o entry
Warning (compare_maps): mismatch on symbol scsi_hostlist  , scsi_mod says d08a95b4, /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o says d08a7e3c.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o entry
Warning (compare_maps): mismatch on symbol scsi_hosts  , scsi_mod says d08a95bc, /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o says d08a7e44.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o entry
Warning (compare_maps): mismatch on symbol scsi_logging_level  , scsi_mod says d08a9588, /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o says d08a7e10.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/scsi/scsi_mod.o entry
Warning (compare_maps): mismatch on symbol output_offset  , ov511 says d0890718, /lib/modules/2.4.7-10/kernel/drivers/usb/ov511.o says d088ffa0.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/usb/ov511.o entry
Warning (compare_maps): mismatch on symbol usb_devfs_handle  , usbcore says d086a9a0, /lib/modules/2.4.7-10/kernel/drivers/usb/usbcore.o says d086a4c0.  Ignoring /lib/modules/2.4.7-10/kernel/drivers/usb/usbcore.o entry
Warning (map_ksym_to_module): cannot match loaded module ext3 to a unique module object.  Trace may not be reliable.
Warning (map_ksym_to_module): cannot match loaded module jbd to a unique module object.  Trace may not be reliable.
Unable to handle kernel NULL pointer dereference at virtual address 00000000
d2d23070
*pde = 00000000
Oops: 0002
CPU:    0
EIP:    0010:[<d2d23070>]
Using defaults from ksymoops -t elf32-i386 -a i386
EFLAGS: 00010286
eax: 00000000   ebx: d2d23000   ecx: 00000007   edx: 00000000
esi: 00000000   edi: 00000000   ebp: c9167f18   esp: c9167f14
ds: 0018   es: 0018   ss: 0018
Process insmod (pid: 1650, stackpage=c9167000)
Stack: 00000000 c9167f28 d2d23093 00000000 00000000 00000060 c01182e5 00000000 
       c91fd000 00000120 c9387000 00000060 ffffffea 00000005 c957a5a0 00000060 
       d096f000 d2d23060 000001c0 00000000 00000000 00000000 00000000 00000000 
Call Trace: [<d2d23093>] [<c01182e5>] [<d096f000>] [<d2d23060>] [<c0106f0b>] 
Code: c6 00 01 c9 c3 8d 76 00 55 89 e5 83 ec 08 83 ec 0c 68 c0 30 

>>EIP; d2d23070 <[boom2].text.start+10/18>   <=====
Trace; d2d23093 <[boom2]init_module+1b/24>
Trace; c01182e5 <sys_init_module+535/5f0>
Trace; d096f000 <[agpgart].bss.end+17441/174a1>
Trace; d2d23060 <[boom2]boom+0/0>
Trace; c0106f0b <system_call+33/38>
Code;  d2d23070 <[boom2].text.start+10/18>
00000000 <_EIP>:
Code;  d2d23070 <[boom2].text.start+10/18>   <=====
   0:   c6 00 01                  movb   $0x1,(%eax)   <=====
Code;  d2d23073 <[boom2].text.start+13/18>
   3:   c9                        leave  
Code;  d2d23074 <[boom2].text.start+14/18>
   4:   c3                        ret    
Code;  d2d23075 <[boom2].text.start+15/18>
   5:   8d 76 00                  lea    0x0(%esi),%esi
Code;  d2d23078 <[boom2]init_module+0/24>
   8:   55                        push   %ebp
Code;  d2d23079 <[boom2]init_module+1/24>
   9:   89 e5                     mov    %esp,%ebp
Code;  d2d2307b <[boom2]init_module+3/24>
   b:   83 ec 08                  sub    $0x8,%esp
Code;  d2d2307e <[boom2]init_module+6/24>
   e:   83 ec 0c                  sub    $0xc,%esp
Code;  d2d23081 <[boom2]init_module+9/24>
  11:   68 c0 30 00 00            push   $0x30c0

ksymoops nailed it.

5. note gdb output:

[root@zymurgy jrb]# gdb boom2.o
GNU gdb Red Hat Linux 7.x (5.0rh-15) (MI_OUT)
Copyright 2001 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i386-redhat-linux"...(no debugging symbols found)...
(gdb) x/20i 
0x0 <boom>:	push   %ebp
0x1 <boom+1>:	mov    %esp,%ebp
0x3 <boom+3>:	sub    $0x4,%esp
0x6 <boom+6>:	movl   $0x0,0xfffffffc(%ebp)
0xd <boom+13>:	mov    0xfffffffc(%ebp),%eax
0x10 <boom+16>:	movb   $0x1,(%eax)
0x13 <boom+19>:	leave  
0x14 <boom+20>:	ret    
0x15 <boom+21>:	lea    0x0(%esi),%esi
0x18 <init_module>:	push   %ebp
0x19 <init_module+1>:	mov    %esp,%ebp
0x1b <init_module+3>:	sub    $0x8,%esp
0x1e <init_module+6>:	sub    $0xc,%esp
0x21 <init_module+9>:	push   $0x0
0x26 <init_module+14>:	call   0x27 <init_module+15>
0x2b <init_module+19>:	add    $0x10,%esp
0x2e <init_module+22>:	call   0x2f <init_module+23>
0x33 <init_module+27>:	mov    $0x0,%eax
0x38 <init_module+32>:	leave  
0x39 <init_module+33>:	ret    
(gdb) q