Kernel programming and RTAI: problems with a custom module installation.

Alessandro_2 · 02-22-2011, 03:05 AM

Hi guys,
I am facing a weird problem. I am new to kernel programming and to rtai. I am trying to write a simple module that periodically set to 1 and 0 the parallel port's output.
In particular I created two .c. files (main.c and mathlib.c with the header mathlib.h) the file main.c includes the header mathlib.h, with the makefile below.
Within the main file I call a function (say funcx) in the mathlib library that essentially use the snprintf function to store in a string to print an integer value. The code compiles fine but I experience a reboot when I insmod the module. By moving the funcx form the mathlib to the top of the main function, all works fine.
I really can't understand what it is wrong.

Thanks for your help.

Alessandro

EXTRA_CFLAGS += -O -Wall -DMODULE -D__KERNEL__ -I/usr/realtime/include -I/usr/include -mhard-float # -D__KERNEL__ -DMODULE -I/usr/realtime/include -I/usr/include -D_IN_RTAI_ -mhard-float -O3 -pipe -Wall
PWD = $(shell pwd)
obj-m += main_mod.o
main_mod-objs += mathlib.o main.o
module=$(obj-m:.o=.ko)

ifneq ($(shell lsmod | grep $(module:.ko=)),)
$(shell sudo rmmod $(module))
endif

.PHONY: all clean

all: $(clean)

make -C /lib/modules/$(shell uname -r)/build SUBDIRS=$(PWD) modules

clean:
-rm -f *.o *.ko .*.cmd .*.flags *.mod.c *~ *vers
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

gnashley · 02-23-2011, 12:01 PM

Did you include linux/module.h?

Alessandro_2 · 02-24-2011, 02:58 AM

Yes, I did. These are the included headers:

Code:

#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <linux/kernel.h>
#include <stdarg.h>
#include <asm/page.h>		/* for PAGE_SIZE */
#include <asm/div64.h>

The function in question in mathlib.c is a simple function:

Code:

void float2string(char string*, float num){

sprintf(tring, "%d.%lld\n",(int)num,(long long int)((float) (num-(long long int) num))*1000);
}

The same happens commenting the sprintf function and using (just for the case) "strcpy(string, "SomeString")". Everything is ok if I do:

Quote:

string[0]='1'; string[1]='2'; .... string[n]='\0';

or, like I said, if I use the functions defined in vsnprintf.c (namely, sprintf) directly in the main.c file.

Sorry to bother for such a stupid problem, but I spent two days trying to figure out what's wrong. I want to be sure that it is neither a configuration issue nor a programming one.
Thanks, for the interest.

Alessandro

gnashley · 02-24-2011, 10:55 AM

Could it be that you are missing the trailing '\0'?