On Thursday 14 March 2013, Tom Z wrote:
> Hi,
ditto.
>
> I am writing a kernel module that calls rt_task_add_hook() to add a
> hook when context switch occurs. I built a kernel module called
> *switch_hook.ko*, but when I /insmod switch_hook.ko/, it complains
> "*switch_hook: Unknown symbol rt_task_add_hook (err 0)*". I think I
dmesg will probably show you have tainted your kernel by loading a
non-GPL module.
> missed something during the build process (failed to include Xenomai
> source?) but I do not how to fix it. Below is my system settings, any
> help is greatly appreciated.
> *Patched Linux kernel source* is at "/usr/src/linux-3.5.7"
> *Xenomai source* is at "/usr/src/xenomai-2.6.2.1"
> *Xenomai libraries and binaries* is at "/usr/xenomai"
> *My kernel module source code* is at **"/home/tomz/switch_hook_mod/",
> and under this folder there are only two files: *Makefile* and
> *switch_hook.c*. Here is how I make this module, and Makefile and
> switch_hook.c's contents are attached as well:
> /home/tomz/switch_hook_mod# *make
> EXTRA_CFLAGS="-I/usr/xenomai/include -D_GNU_SOURCE -D_REENTRANT
> -D__XENO" EXTRA_LDFLAGS="-lnative -L/usr/xenomai/lib -lxenomai
> -lpthread -lrt -lxenomai -lnative"*
Ugly way of passing flags and prone to error.
>
> *Makefile's content*
> obj-m += switch_hook.o
# Use cflags instead of passing on the command line.
# Read Documentation/kbuild/makefiles.txt for other options.
cflags-y = $(shell xeno-config --skin native --cflags)
>
> all:
> make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
>
> clean:
> make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
>
> *switch_hook.c's content*
> #include <linux/module.h> /* Needed by all modules */
> #include <linux/kernel.h> /* Needed for KERN_INFO */
> #include <linux/init.h> /* Needed for the macros */
>
> #include <native/task.h>
> #include <native/timer.h>
> #include <rtdk.h>
>
> void hook_func(void *cookie){
> printk(KERN_INFO "Context switch occured\n");
> }
>
> static int __init switch_hook_init(void)
> {
> rt_print_auto_init(1);
> rt_printf("Add hook\n");
> rt_task_add_hook(T_HOOK_SWITCH, &hook_func);
> return 0;
> }
>
> static void __exit switch_hook_exit(void)
> {
> printk(KERN_INFO "Goodbye\n");
> }
>
> module_init(switch_hook_init);
> module_exit(switch_hook_exit);
MODULE_LICENSE("GPL"); /* See: linux/module.h for other valid options */
MODULE_AUTHOR("DRIVER_AUTHOR"); /* Who wrote this module? */
MODULE_DESCRIPTION("DRIVER_DESC"); /* What does this module do */
> //end of switch_hook.c
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