A monolithic kernel, though faster than a microkernel, has the disadvantage of lack of modularity and extensibility. On modern monolithic kernels, this has been solved by using kernel modules. A kernel module (or loadable kernel mode) is an object file that contains code that can extend the kernel functionality at runtime (it is loaded as needed); When a kernel module is no longer needed, it can be unloaded. Most of the device drivers are used in the form of kernel modules.
For the development of Linux device drivers, it is recommended to download the kernel sources, configure and compile them and then install the compiled version on the test /development tool machine.
Below is a very simple example of a kernel module. When loading into the kernel, it will generate the message "Hi" . When unloading the kernel module, the "Bye" message will be generated.
#include #include #include MODULE_DESCRIPTION("My kernel module"); MODULE_AUTHOR("Me"); MODULE_LICENSE("GPL"); static int dummy_init(void) pr_debug("Hi\n"); return 0; > static void dummy_exit(void) pr_debug("Bye\n"); > module_init(dummy_init); module_exit(dummy_exit);
The generated messages will not be displayed on the console but will be saved in a specially reserved memory area for this, from where they will be extracted by the logging daemon (syslog). To display kernel messages, you can use the dmesg command or inspect the logs:
# cat /var/log/syslog | tail -2 Feb 20 13:57:38 asgard kernel: Hi Feb 20 13:57:43 asgard kernel: Bye # dmesg | tail -2 Hi Bye
Compiling a kernel module differs from compiling an user program. First, other headers should be used. Also, the module should not be linked to libraries. And, last but not least, the module must be compiled with the same options as the kernel in which we load the module. For these reasons, there is a standard compilation method ( kbuild ). This method requires the use of two files: a Makefile and a Kbuild file.
Below is an example of a Makefile :
KDIR = /lib/modules/`uname -r`/build kbuild: make -C $(KDIR) M=`pwd` clean: make -C $(KDIR) M=`pwd` clean
And the example of a Kbuild file used to compile a module:
EXTRA_CFLAGS = -Wall -g obj-m = modul.o
As you can see, calling make on the Makefile file in the example shown will result in the make invocation in the kernel source directory ( /lib/modules/`uname -r`/build ) and referring to the current directory ( M = `pwd` ). This process ultimately leads to reading the Kbuild file from the current directory and compiling the module as instructed in this file.
For labs we will configure different KDIR, according to the virtual machine specifications:
KDIR = /home/student/src/linux [. ]
A Kbuild file contains one or more directives for compiling a kernel module. The easiest example of such a directive is obj-m = module.o . Following this directive, a kernel module ( ko - kernel object) will be created, starting from the module.o file. module.o will be created starting from module.c or module.S . All of these files can be found in the Kbuild 's directory.
An example of a Kbuild file that uses several sub-modules is shown below:
EXTRA_CFLAGS = -Wall -g obj-m = supermodule.o supermodule-y = module-a.o module-b.o
For the example above, the steps to compile are:
The suffix of targets in Kbuild determines how they are used, as follows:
These suffixes are used to easily configure the kernel by running the make menuconfig command or directly editing the .config file. This file sets a series of variables that are used to determine which features are added to the kernel at build time. For example, when adding BTRFS support with make menuconfig, add the line CONFIG_BTRFS_FS = y to the .config file. The BTRFS kbuild contains the line obj-$(CONFIG_BTRFS_FS):= btrfs.o , which becomes obj-y:= btrfs.o . This will compile the btrfs.o object and will be linked to the kernel. Before the variable was set, the line became obj:=btrfs.o and so it was ignored, and the kernel was build without BTRFS support.
For more details, see the Documentation/kbuild/makefiles.txt and Documentation/kbuild/modules.txt files within the kernel sources.
To load a kernel module, use the insmod utility. This utility receives as a parameter the path to the *.ko file in which the module was compiled and linked. Unloading the module from the kernel is done using the rmmod command, which receives the module name as a parameter.
$ insmod module.ko $ rmmod module.ko
When loading the kernel module, the routine specified as a parameter of the module_init macro will be executed. Similarly, when the module is unloaded the routine specified as a parameter of the module_exit will be executed.
A complete example of compiling and loading/unloading a kernel module is presented below:
faust:~/lab-01/modul-lin# ls Kbuild Makefile modul.c faust:~/lab-01/modul-lin# make make -C /lib/modules/`uname -r`/build M=`pwd` make[1]: Entering directory `/usr/src/linux-2.6.28.4' LD /root/lab-01/modul-lin/built-in.o CC [M] /root/lab-01/modul-lin/modul.o Building modules, stage 2. MODPOST 1 modules CC /root/lab-01/modul-lin/modul.mod.o LD [M] /root/lab-01/modul-lin/modul.ko make[1]: Leaving directory `/usr/src/linux-2.6.28.4' faust:~/lab-01/modul-lin# ls built-in.o Kbuild Makefile modul.c Module.markers modules.order Module.symvers modul.ko modul.mod.c modul.mod.o modul.o faust:~/lab-01/modul-lin# insmod modul.ko faust:~/lab-01/modul-lin# dmesg | tail -1 Hi faust:~/lab-01/modul-lin# rmmod modul faust:~/lab-01/modul-lin# dmesg | tail -2 Hi Bye
Information about modules loaded into the kernel can be found using the lsmod command or by inspecting the /proc/modules , /sys/module directories.
Troubleshooting a kernel module is much more complicated than debugging a regular program. First, a mistake in a kernel module can lead to blocking the entire system. Troubleshooting is therefore much slowed down. To avoid reboot, it is recommended to use a virtual machine (qemu, virtualbox, vmware).
When a module containing bugs is inserted into the kernel, it will eventually generate a kernel oops. A kernel oops is an invalid operation detected by the kernel and can only be generated by the kernel. For a stable kernel version, it almost certainly means that the module contains a bug. After the oops appears, the kernel will continue to work.
Very important to the appearance of a kernel oops is saving the generated message. As noted above, messages generated by the kernel are saved in logs and can be displayed with the dmesg command. To make sure that no kernel message is lost, it is recommended to insert/test the kernel directly from the console, or periodically check the kernel messages. Noteworthy is that an oops can occur because of a programming error, but also a because of hardware error.
If a fatal error occurs, after which the system can not return to a stable state, a kernel panic is generated.
Look at the kernel module below that contains a bug that generates an oops:
/* * Oops generating kernel module */ #include #include #include MODULE_DESCRIPTION ("Oops"); MODULE_LICENSE ("GPL"); MODULE_AUTHOR ("PSO"); #define OP_READ 0 #define OP_WRITE 1 #define OP_OOPS OP_WRITE static int my_oops_init (void) int *a; a = (int *) 0x00001234; #if OP_OOPS == OP_WRITE *a = 3; #elif OP_OOPS == OP_READ printk (KERN_ALERT "value = %d\n", *a); #else #error "Unknown op for oops!" #endif return 0; > static void my_oops_exit (void) > module_init (my_oops_init); module_exit (my_oops_exit);
Inserting this module into the kernel will generate an oops:
faust:~/lab-01/modul-oops# insmod oops.ko [. ] faust:~/lab-01/modul-oops# dmesg | tail -32 BUG: unable to handle kernel paging request at 00001234 IP: [] my_oops_init+0x5/0x20 [oops] *de = 00000000 Oops: 0002 [#1] PREEMPT DEBUG_PAGEALLOC last sysfs file: /sys/devices/virtual/net/lo/operstate Modules linked in: oops(+) netconsole ide_cd_mod pcnet32 crc32 cdrom [last unloaded: modul] Pid: 4157, comm: insmod Not tainted (2.6.28.4 #2) VMware Virtual Platform EIP: 0060:[] EFLAGS: 00010246 CPU: 0 EIP is at my_oops_init+0x5/0x20 [oops] EAX: 00000000 EBX: fffffffc ECX: c89d4300 EDX: 00000001 ESI: c89d4000 EDI: 00000000 EBP: c5799e24 ESP: c5799e24 DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068 Process insmod (pid: 4157, ti=c5799000 task=c665c780 task.ti=c5799000) Stack: c5799f8c c010102d c72b51d8 0000000c c5799e58 c01708e4 00000124 00000000 c89d4300 c5799e58 c724f448 00000001 c89d4300 c5799e60 c0170981 c5799f8c c014b698 00000000 00000000 c5799f78 c5799f20 00000500 c665cb00 c89d4300 Call Trace: [] ? _stext+0x2d/0x170 [] ? __vunmap+0xa4/0xf0 [] ? vfree+0x21/0x30 [] ? load_module+0x19b8/0x1a40 [] ? __mutex_unlock_slowpath+0xd5/0x140 [] ? trace_hardirqs_on_caller+0x106/0x150 [] ? sys_init_module+0x8a/0x1b0 [] ? trace_hardirqs_on_caller+0x106/0x150 [] ? trace_hardirqs_on_thunk+0xc/0x10 [] ? sysenter_do_call+0x12/0x43 Code: 05 34 12 00 00 03 00 00 00 5d c3 eb 0d 90 90 90 90 90 90 90 90 EIP: [] my_oops_init+0x5/0x20 [oops] SS:ESP 0068:c5799e24 ---[ end trace 2981ce73ae801363 ]---
Although relatively cryptic, the message provided by the kernel to the appearance of an oops provides valuable information about the error. First line:
BUG: unable to handle kernel paging request at 00001234 EIP: [] my_oops_init + 0x5 / 0x20 [oops]
Tells us the cause and the address of the instruction that generated the error. In our case this is an invalid access to memory.
Oops: 0002 [# 1] PREEMPT DEBUG_PAGEALLOCTells us that it's the first oops (#1). This is important in the context that an oops can lead to other oopses. Usually only the first oops is relevant. Furthermore, the oops code ( 0002 ) provides information about the error type (see arch/x86/include/asm/trap_pf.h ):
In this case, we have a write access that generated the oops (bit 1 is 1).
Below is a dump of the registers. It decodes the instruction pointer ( EIP ) value and notes that the bug appeared in the my_oops_init function with a 5-byte offset ( EIP: [] my_oops_init+0x5 ). The message also shows the stack content and a backtrace of calls until then.
If an invalid read call is generated ( #define OP_OOPS OP_READ ), the message will be the same, but the oops code will differ, which would now be 0000 :
faust:~/lab-01/modul-oops# dmesg | tail -33 BUG: unable to handle kernel paging request at 00001234 IP: [] my_oops_init+0x6/0x20 [oops] *de = 00000000 Oops: 0000 [#1] PREEMPT DEBUG_PAGEALLOC last sysfs file: /sys/devices/virtual/net/lo/operstate Modules linked in: oops(+) netconsole pcnet32 crc32 ide_cd_mod cdrom Pid: 2754, comm: insmod Not tainted (2.6.28.4 #2) VMware Virtual Platform EIP: 0060:[] EFLAGS: 00010292 CPU: 0 EIP is at my_oops_init+0x6/0x20 [oops] EAX: 00000000 EBX: fffffffc ECX: c89c3380 EDX: 00000001 ESI: c89c3010 EDI: 00000000 EBP: c57cbe24 ESP: c57cbe1c DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068 Process insmod (pid: 2754, ti=c57cb000 task=c66ec780 task.ti=c57cb000) Stack: c57cbe34 00000282 c57cbf8c c010102d c57b9280 0000000c c57cbe58 c01708e4 00000124 00000000 c89c3380 c57cbe58 c5db1d38 00000001 c89c3380 c57cbe60 c0170981 c57cbf8c c014b698 00000000 00000000 c57cbf78 c57cbf20 00000580 Call Trace: [] ? _stext+0x2d/0x170 [] ? __vunmap+0xa4/0xf0 [] ? vfree+0x21/0x30 [] ? load_module+0x19b8/0x1a40 [] ? printk+0x0/0x1a [] ? __mutex_unlock_slowpath+0xd5/0x140 [] ? trace_hardirqs_on_caller+0x106/0x150 [] ? sys_init_module+0x8a/0x1b0 [] ? trace_hardirqs_on_caller+0x106/0x150 [] ? trace_hardirqs_on_thunk+0xc/0x10 [] ? sysenter_do_call+0x12/0x43 Code: 34 12 00 00 c7 04 24 54 30 9c c8 89 44 24 04 e8 58 a0 99 f7 31 EIP: [] my_oops_init+0x6/0x20 [oops] SS:ESP 0068:c57cbe1c ---[ end trace 45eeb3d6ea8ff1ed ]---
Detailed information about the instruction that generated the oops can be found using the objdump utility. Useful options to use are -d to disassemble the code and -S for interleaving C code in assembly language code. For efficient decoding, however, we need the address where the kernel module was loaded. This can be found in /proc/modules .
Here's an example of using objdump on the above module to identify the instruction that generated the oops:
faust:~/lab-01/modul-oops# cat /proc/modules oops 1280 1 - Loading 0xc89d4000 netconsole 8352 0 - Live 0xc89ad000 pcnet32 33412 0 - Live 0xc895a000 ide_cd_mod 34952 0 - Live 0xc8903000 crc32 4224 1 pcnet32, Live 0xc888a000 cdrom 34848 1 ide_cd_mod, Live 0xc886d000 faust:~/lab-01/modul-oops# objdump -dS --adjust-vma=0xc89d4000 oops.ko oops.ko: file format elf32-i386 Disassembly of section .text: c89d4000 : #define OP_READ 0 #define OP_WRITE 1 #define OP_OOPS OP_WRITE static int my_oops_init (void) c89d4000: 55 push %ebp #else #error "Unknown op for oops!" #endif return 0; > c89d4001: 31 c0 xor %eax,%eax #define OP_READ 0 #define OP_WRITE 1 #define OP_OOPS OP_WRITE static int my_oops_init (void) c89d4003: 89 e5 mov %esp,%ebp int *a; a = (int *) 0x00001234; #if OP_OOPS == OP_WRITE *a = 3; c89d4005: c7 05 34 12 00 00 03 movl $0x3,0x1234 c89d400c: 00 00 00 #else #error "Unknown op for oops!" #endif return 0; > c89d400f: 5d pop %ebp c89d4010: c3 ret c89d4011: eb 0d jmp c89c3020 c89d4013: 90 nop c89d4014: 90 nop c89d4015: 90 nop c89d4016: 90 nop c89d4017: 90 nop c89d4018: 90 nop c89d4019: 90 nop c89d401a: 90 nop c89d401b: 90 nop c89d401c: 90 nop c89d401d: 90 nop c89d401e: 90 nop c89d401f: 90 nop c89d4020 : static void my_oops_exit (void) c89d4020: 55 push %ebp c89d4021: 89 e5 mov %esp,%ebp > c89d4023: 5d pop %ebp c89d4024: c3 ret c89d4025: 90 nop c89d4026: 90 nop c89d4027: 90 nop
Note that the instruction that generated the oops ( c89d4005 identified earlier) is:
C89d4005: c7 05 34 12 00 00 03 movl $ 0x3,0x1234That is exactly what was expected - storing value 3 at 0x0001234.
The /proc/modules is used to find the address where a kernel module is loaded. The --adjust-vma option allows you to display instructions relative to 0xc89d4000 . The -l option displays the number of each line in the source code interleaved with the assembly language code.
A more simplistic way to find the code that generated an oops is to use the addr2line utility:
faust:~/lab-01/modul-oops# addr2line -e oops.o 0x5 /root/lab-01/modul-oops/oops.c:23
Where 0x5 is the value of the program counter ( EIP = c89d4005 ) that generated the oops, minus the base address of the module ( 0xc89d4000 ) according to /proc/modules
Minicom (or other equivalent utilities, eg picocom, screen) is a utility that can be used to connect and interact with a serial port. The serial port is the basic method for analyzing kernel messages or interacting with an embedded system in the development phase. There are two more common ways to connect:
For the virtual machine used in the lab, the device that we need to use is displayed after the virtual machine starts:
char device redirected to /dev/pts/20 (label virtiocon0)
#for connecting via COM1 and using a speed of 115,200 characters per second minicom -b 115200 -D /dev/ttyS0 #For USB serial port connection minicom -D /dev/ttyUSB0 #To connect to the serial port of the virtual machine minicom -D /dev/pts/20
Netconsole is a utility that allows logging of kernel debugging messages over the network. This is useful when the disk logging system does not work or when serial ports are not available or when the terminal does not respond to commands. Netconsole comes in the form of a kernel module.
To work, it needs the following parameters:
These parameters can be configured when the module is inserted into the kernel, or even while the module is inserted if it has been compiled with the CONFIG_NETCONSOLE_DYNAMIC option.
An example configuration when inserting netconsole kernel module is as follows:
alice:~# modprobe netconsole netconsole=6666@192.168.191.130/eth0,6000@192.168.191.1/00:50:56:c0:00:08
Thus, the debug messages on the station that has the address 192.168.191.130 will be sent to the eth0 interface, having source port 6666 . The messages will be sent to 192.168.191.1 with the MAC address 00:50:56:c0:00:08 , on port 6000 .
Messages can be played on the destination station using netcat:
bob:~ # nc -l -p 6000 -u
Alternatively, the destination station can configure syslogd to intercept these messages. More information can be found in Documentation/networking/netconsole.txt .
The two oldest and most useful debugging aids are Your Brain and Printf .
For debugging, a primitive way is often used, but it is quite effective: printk debugging. Although a debugger can also be used, it is generally not very useful: simple bugs (uninitialized variables, memory management problems, etc.) can be easily localized by control messages and the kernel-decoded oop message.
For more complex bugs, even a debugger can not help us too much unless the operating system structure is very well understood. When debugging a kernel module, there are a lot of unknowns in the equation: multiple contexts (we have multiple processes and threads running at a time), interruptions, virtual memory, etc.
You can use printk to display kernel messages to user space. It is similar to printf 's functionality; the only difference is that the transmitted message can be prefixed with a string of "" , where n indicates the error level (loglevel) and has values between 0 and 7 . Instead of "" , the levels can also be coded by symbolic constants:
KERN_EMERG - n = 0 KERN_ALERT - n = 1 KERN_CRIT - n = 2 KERN_ERR - n = 3 KERN_WARNING - n = 4 KERN_NOTICE - n = 5 KERN_INFO - n = 6 KERN_DEBUG - n = 7
The definitions of all log levels are found in linux/kern_levels.h . Basically, these log levels are used by the system to route messages sent to various outputs: console, log files in /var/log etc.
To display printk messages in user space, the printk log level must be of higher priority than console_loglevel variable. The default console log level can be configured from /proc/sys/kernel/printk .
For instance, the command:
echo 8 > /proc/sys/kernel/printk
will enable all the kernel log messages to be displayed in the console. That is, the logging level has to be strictly less than the console_loglevel variable. For example, if the console_loglevel has a value of 5 (specific to KERN_NOTICE ), only messages with loglevel stricter than 5 (i.e KERN_EMERG , KERN_ALERT , KERN_CRIT , KERN_ERR , KERN_WARNING ) will be shown.
Console-redirected messages can be useful for quickly viewing the effect of executing the kernel code, but they are no longer so useful if the kernel encounters an irreparable error and the system freezes. In this case, the logs of the system must be consulted, as they keep the information between system restarts. These are found in /var/log and are text files, populated by syslogd and klogd during the kernel run. syslogd and klogd take the information from the virtual file system mounted in /proc . In principle, with syslogd and klogd turned on, all messages coming from the kernel will go to /var/log/kern.log .
A simpler version for debugging is using the /var/log/debug file. It is populated only with the printk messages from the kernel with the KERN_DEBUG log level.
Given that a production kernel (similar to the one we're probably running with) contains only release code, our module is among the few that send messages prefixed with KERN_DEBUG . In this way, we can easily navigate through the /var/log/debug information by finding the messages corresponding to a debugging session for our module.
Such an example would be the following:
# Clear the debug file of previous information (or possibly a backup) $ echo "New debug session" > /var/log/debug # Run the tests # If there is no critical error causing a panic kernel, check the output # if a critical error occurs and the machine only responds to a restart, restart the system and check /var/log/debug.
The format of the messages must obviously contain all the information of interest in order to detect the error, but inserting in the code printk to provide detailed information can be as time-consuming as writing the code to solve the problem. This is usually a trade-off between the completeness of the debugging messages displayed using printk and the time it takes to insert these messages into the text.
A very simple way, less time-consuming for inserting printk and providing the possibility to analyze the flow of instructions for tests is the use of the predefined constants __FILE__ , __LINE__ and __func__ :
__FILE__ and __LINE__ are part of the ANSI C specifications: __func__ is part of specification C99; __FUNCTION__ is a GNU C extension and is not portable; However, since we write code for the Linux kernel, we can use it without any problems.
The following macro definition can be used in this case:
#define PRINT_DEBUG \ printk (KERN_DEBUG "[% s]: FUNC:% s: LINE:% d \ n", __FILE__, __FUNCTION__, __LINE__)
Then, at each point where we want to see if it is "reached" in execution, insert PRINT_DEBUG; This is a simple and quick way, and can yield by carefully analyzing the output.
The dmesg command is used to view the messages printed with printk but not appearing on the console.
To delete all previous messages from a log file, run:
cat /dev/null > /var/log/debug
To delete messages displayed by the dmesg command, run:
dmesg -c
Dynamic dyndbg debugging enables dynamic debugging activation/deactivation. Unlike printk , it offers more advanced printk options for the messages we want to display; it is very useful for complex modules or troubleshooting subsystems. This significantly reduces the amount of messages displayed, leaving only those relevant for the debug context. To enable dyndbg , the kernel must be compiled with the CONFIG_DYNAMIC_DEBUG option. Once configured, pr_debug() , dev_dbg() and print_hex_dump_debug() , print_hex_dump_bytes() can be dynamically enabled per call.
The /sys/kernel/debug/dynamic_debug/control file from the debugfs (where /sys/kernel/debug is the path to which debugfs was mounted) is used to filter messages or to view existing filters.
mount -t debugfs none /debug
Debugfs is a simple file system, used as a kernel-space interface and user-space interface to configure different debug options. Any debug utility can create and use its own files /folders in debugfs.
For example, to display existing filters in dyndbg , you will use:
cat /debug/dynamic_debug/control
And to enable the debug message from line 1603 in the svcsock.c file:
echo 'file svcsock.c line 1603 +p' > /debug/dynamic_debug/control
The /debug/dynamic_debug/control file is not a regular file. It shows the dyndbg settings on the filters. Writing in it with an echo will change these settings (it will not actually make a write). Be aware that the file contains settings for dyndbg debugging messages. Do not log in this file.
echo 'func svc_tcp_accept +p' > /debug/dynamic_debug/control
file svcsock.c file kernel/freezer.c file /usr/src/packages/BUILD/sgi-enhancednfs-1.4/default/net/sunrpc/svcsock.c
module sunrpc
format "nfsd: SETATTR"
# Triggers debug messages between lines 1603 and 1605 in the svcsock.c file $ echo 'file svcsock.c line 1603-1605 +p' > /sys/kernel/debug/dynamic_debug/control # Enables debug messages from the beginning of the file to line 1605 $ echo 'file svcsock.c line -1605 +p' > /sys/kernel/debug/dynamic_debug/control
In addition to the above options, a series of flags can be added, removed, or set with operators + , - or = :
The kernel debugger has proven to be very useful to facilitate the development and debugging process. One of its main advantages is the possibility to perform live debugging. This allows us to monitor, in real time, the accesses to memory or even modify the memory while debugging. The debugger has been integrated in the mainline kernel starting with version 2.6.26-rci. KDB is not a source debugger, but for a complete analysis it can be used in parallel with gdb and symbol files -- see the GDB debugging section
To use KDB, you have the following options:
For the lab, we will use a serial interface connected to the host. The following command will activate GDB over the serial port:
echo hvc0 > /sys/module/kgdboc/parameters/kgdboc
KDB is a stop mode debugger, which means that, while it is active, all the other processes are stopped. The kernel can be forced to enter KDB during execution using the following SysRq command
echo g > /proc/sysrq-trigger
or by using the key combination Ctrl+O g in a terminal connected to the serial port (for example using minicom).
KDB has various commands to control and define the context of the debugged system:
For a better description of the available commands you can use the help command in the KDB shell. In the next example, you can notice a simple KDB usage example which sets a hardware breakpoint to monitor the changes of the mVar variable.
# trigger KDB echo g > /proc/sysrq-trigger # or if we are connected to the serial port issue Ctrl-O g # breakpoint on write access to the mVar variable kdb> bph mVar dataw # return from KDB kdb> go
We strongly encourage you to use the setup from this repository.
The current lab name is kernel_modules. See the exercises for the task name.
The skeleton code is generated from full source examples located in tools/labs/templates . To solve the tasks, start by generating the skeleton code for a complete lab:
tools/labs $ make clean tools/labs $ LABS= make skels
You can also generate the skeleton for a single task, using
tools/labs $ LABS=/ make skels
Once the skeleton drivers are generated, build the source:
tools/labs $ make build
Then, start the VM:
tools/labs $ make console
The modules are placed in /home/root/skels/kernel_modules/.
You DO NOT need to STOP the VM when rebuilding modules! The local skels directory is shared with the VM.
Review the Exercises section for more detailed information.
Before starting the exercises or generating the skeletons, please run git pull inside the Linux repo, to make sure you have the latest version of the exercises.
If you have local changes, the pull command will fail. Check for local changes using git status . If you want to keep them, run git stash before pull and git stash pop after. To discard the changes, run git reset --hard master .
If you already generated the skeleton before git pull you will need to generate it again.
Using cscope or LXR find the definitions of the following symbols in the Linux kernel source code:
If you have problems using cscope, it is possible that the database is not generated. To generate it, use the following command in the kernel directory:
make ARCH=x86 cscope
When searching for a structure using cscope, use only the structure name (without struct ). So, to search for the structure struct module , you will use the command
vim -t module
or, in vim, the command
