Using ELF section in LKM

Using ELF section in LKM

I have this POC in C that saves a few structs in a custon section and then
iterates over those structs, showing their content.
#include <stdio.h>
char a, b, c;
struct counter_info {
int counter;
char *name;
} __attribute__((packed));
#define __PUT_STUFF_IN_SECTION(_name) \
do{ \
static struct counter_info __counter_info_##_name \
__attribute((__section__("counters"))) \
__attribute((__used__)) = { \
.name = #_name, \
.counter = 0, \
}; \
}while(0)
extern struct counter_info __start_counters;
extern struct counter_info __stop_counters;
int main(int argc, char **argv){
printf("Start %p\n", &__start_counters);
__PUT_STUFF_IN_SECTION(a);
__PUT_STUFF_IN_SECTION(b);
__PUT_STUFF_IN_SECTION(c);
struct counter_info *iter = &__start_counters;
for(; iter < &__stop_counters; ++iter){
printf("Name: %s | Counter: %d.\n", iter->name, iter->counter);
}
printf("End %p\n", &__stop_counters);
return 0;
}
Output:
Name: c | Counter: 0.
Name: b | Counter: 0.
Name: a | Counter: 0.
The output is as expected, so I'm trying to do that same thing in a kernel
module:
hello-1.c
#include <linux/module.h>
#include <linux/kernel.h>
char a, b, c;
struct counter_info {
int counter;
char *name;
} __attribute__((packed));
#define __PUT_STUFF_IN_SECTION(_name) \
do{ \
static struct counter_info __counter_info_##_name \
__attribute((__section__("counters"))) \
__attribute((__used__)) = { \
.name = #_name, \
.counter = 0, \
}; \
}while(0)
extern struct counter_info __start_counters;
extern struct counter_info __stop_counters;
int init_module(void){
__PUT_STUFF_IN_SECTION(a);
__PUT_STUFF_IN_SECTION(b);
__PUT_STUFF_IN_SECTION(c);
return 0;
}
void cleanup_module(void){
struct counter_info *iter = &__start_counters;
for(; iter < &__stop_counters; ++iter){
printk(KERN_INFO "Name: %s | Counter: %d.\n", iter->name,
iter->counter);
}
}
Makefile:
obj-m += hello-1.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
But I get those warnings when I compile the module:
WARNING: "__stop_counters"
[/media/sf_procmon/procmon_kmodule/test/hello-1.ko] undefined!
WARNING: "__start_counters"
[/media/sf_procmon/procmon_kmodule/test/hello-1.ko] undefined!
My question is: Why isn't working and how am I supposed to use the section
attribute inside a LKM?