Fady Yousry Fady Yousry - 1 month ago 24
C Question

kernel module compiler error: function declaration isn’t a prototype [-Werror=strict-prototypes]

this code: Linux kernel module that directly controls the LEDs of your PS/2 keyboard (Num Lock, Caps Lock, and Scroll Lock)

#include <linux/module.h>
#include <linux/kernel.h>

int check_bit(unsigned char status, int i) {
return (status & (1<<(i)));
}

unsigned char kbd_read_status() { // <== ERROR first appears on this line
return inb(0x64);
}

unsigned char kbd_read_data() {
unsigned char status;
do
{
status = kbd_read_status();
}
while(!check_bit(status, 0));
return inb(0x60);
}


when run makefile :

make -C /lib/modules/3.19.0-15-generic/build M=/home/fyousry/Desktop/hellokernel modules
make[1]: Entering directory '/usr/src/linux-headers-3.19.0-15-generic'
CC [M] /home/fyousry/Desktop/hellokernel/New.o
/home/fyousry/Desktop/hellokernel/New.c:9:15: error: function declaration isn’t a prototype [-Werror=strict-prototypes]
unsigned char kbd_read_status() {
^
/home/fyousry/Desktop/hellokernel/New.c:13:15: error: function declaration isn’t a prototype [-Werror=strict-prototypes]
unsigned char kbd_read_data() {
^
cc1: some warnings being treated as errors
scripts/Makefile.build:263: recipe for target '/home/fyousry/Desktop/hellokernel/New.o' failed
make[2]: *** [/home/fyousry/Desktop/hellokernel/New.o] Error 1
Makefile:1394: recipe for target '_module_/home/fyousry/Desktop/hellokernel' failed
make[1]: *** [_module_/home/fyousry/Desktop/hellokernel] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-3.19.0-15-generic'
Makefile:3: recipe for target 'all' failed
make: *** [all] Error 2


when add #include 'sys/io.h' this error show

make -C /lib/modules/3.19.0-15-generic/build M=/home/fyousry/Desktop/hellokernel modules
make[1]: Entering directory '/usr/src/linux-headers-3.19.0-15-generic'
CC [M] /home/fyousry/Desktop/hellokernel/New.o
/home/fyousry/Desktop/hellokernel/New.c:3:21: fatal error: sys/uio.h: No such file or directory
#include <sys/io.h>
^
compilation terminated.
scripts/Makefile.build:263: recipe for target '/home/fyousry/Desktop/hellokernel/New.o' failed
make[2]: *** [/home/fyousry/Desktop/hellokernel/New.o] Error 1
Makefile:1394: recipe for target '_module_/home/fyousry/Desktop/hellokernel' failed
make[1]: *** [_module_/home/fyousry/Desktop/hellokernel] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-3.19.0-15-generic'
Makefile:3: recipe for target 'all' failed
make: *** [all] Error 2

Answer

For a proper prototype, you cannot leave your parameter list empty.
If your function does not take any parameters, you must specify that it is (void).

kbd_read_status(void) instead of kbd_read_status( )

Kernel code is much more pedantic about this.
In other code, you can get away with empty parameters, but not under the most strict rules.