scanf userland & kernelspace test

Makefile

.PHONY: all runtest

MODULES_DIR := /lib/modules/$(shell uname -r)
KERNEL_DIR := $(MODULES_DIR)/build

obj-m := test.o

all: test test.ko

test:
	$(CC) -Wall -o test test.c;

test.ko:
	make modules
	sudo make modules_install

modules:
	make -C $(KERNEL_DIR) M=$$PWD $@;

modules_install:
	make -C $(KERNEL_DIR) M=$$PWD $@;
	sudo depmod -a

runtest: all
	@echo === user space ===
	./test
	@echo === kernel space ===
	sudo modprobe test
	dmesg | tail -n 3
	sudo modprobe -r test

clean:
	make -C $(KERNEL_DIR) M=$$PWD $@;
	@rm -f test

shell output

=== user space ===
init, ret = 0 fp = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, after fp = 65005f5f7664, before fp = 000000000000
ret = 2 fp = aabb
ret = 20 fp = ffffffffffffffffffffffffffffffffffffffff, after fp = 65005f5f7664, before fp = 000000000000
=== kernel space ===
[386177.161037] init, ret = 0 fp = aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa, after fp = baae0dbc0000, before fp = bc0daebaffff
[386177.161044] ret = 2 fp = aabb
[386177.161061] ret = 20 fp = 000000000000000000000000ffffffffffffffff, after fp = baae0dbc0000, before fp = bc0daebaffff

test.c

/* scanf userland & kernelspace test */

#if __KERNEL__

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

MODULE_AUTHOR("Enteee (duckpond.ch) ");
MODULE_DESCRIPTION("scanf test");
MODULE_LICENSE("GPL");
MODULE_ALIAS("scanf_test");

#else

#include <stdio.h>
#include <string.h>
#define printk printf

#endif

void test(void){
    int ret = 0;
    char fp[20] = { 0 };

    memset(fp, 0xaa, sizeof(fp));
    printk("init, ret = %d fp = "
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "%2.2hhx%2.2hhx, "
            // overflow prints (hacky)
            "after fp = "
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx, "
            "before fp = "
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "\n",
            ret,
            (fp)[0],  (fp)[1],  (fp)[2],  (fp)[3],  (fp)[4],  (fp)[5],
            (fp)[6],  (fp)[7],  (fp)[8],  (fp)[9],  (fp)[10], (fp)[11],
            (fp)[12], (fp)[13], (fp)[14], (fp)[15], (fp)[16], (fp)[17],
            (fp)[18], (fp)[19],
            // overflow
            (fp)[20], (fp)[21], (fp)[22], (fp)[23], (fp)[24], (fp)[25],
            (fp)[-1], (fp)[-2], (fp)[-3], (fp)[-4], (fp)[-5], (fp)[-6]
          );

    ret = sscanf("aabb", "%2hhx%2hhx", &fp[0], &fp[1]);
    printk("ret = %d fp = %2.2hhx%2.2hhx\n", ret, fp[0], fp[1]);

    ret = sscanf(
            "ffffffffffffffffffffffffffffffffffffffff", 
            "%2hhx%2hhx%2hhx%2hhx%2hhx%2hhx"
            "%2hhx%2hhx%2hhx%2hhx%2hhx%2hhx"
            "%2hhx%2hhx%2hhx%2hhx%2hhx%2hhx"
            "%2hhx%2hhx",
            &(fp)[0],  &(fp)[1],  &(fp)[2],  &(fp)[3],  &(fp)[4],  &(fp)[5],
            &(fp)[6],  &(fp)[7],  &(fp)[8],  &(fp)[9],  &(fp)[10], &(fp)[11],
            &(fp)[12], &(fp)[13], &(fp)[14], &(fp)[15], &(fp)[16], &(fp)[17],
            &(fp)[18], &(fp)[19]
            );

    printk("ret = %d fp = "
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "%2.2hhx%2.2hhx, "
            // overflow prints (hacky)
            "after fp = "
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx, "
            "before fp = "
            "%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx%2.2hhx"
            "\n",
            ret,
            (fp)[0],  (fp)[1],  (fp)[2],  (fp)[3],  (fp)[4],  (fp)[5],
            (fp)[6],  (fp)[7],  (fp)[8],  (fp)[9],  (fp)[10], (fp)[11],
            (fp)[12], (fp)[13], (fp)[14], (fp)[15], (fp)[16], (fp)[17],
            (fp)[18], (fp)[19],
            (fp)[20], (fp)[21], (fp)[22], (fp)[23], (fp)[24], (fp)[25],
            (fp)[-1], (fp)[-2], (fp)[-3], (fp)[-4], (fp)[-5], (fp)[-6]
          );
}

#ifndef __KERNEL__

int main(void){
    test();
    return 0;
}

#else

static int __init test_init(void) {
    test();
    return 0;
}

static void __exit test_exit(void) {
}

module_init(test_init);
module_exit(test_exit);

#endif