Yocto Out-of-Tree Kernel Module Issues

README.md

This is a basic incremental change to the hello-mod example provided here:

• http://git.yoctoproject.org/cgit/cgit.cgi/poky/tree/meta-skeleton/recipes-kernel/hello-mod/files

At runtime, on insertion, I see the following output:

root@board:~# modprobe hello
[   41.741181] hello: Unknown symbol __class_create (err 0)
[   41.746530] hello: Unknown symbol class_destroy (err 0)
modprobe: ERROR: could not insert 'hello': Unknown symbol in module, or unknown parameter (see dmesg)

This is on an i.MX8 SOM, provided by KaRo

hello-mod_0.1.bb

SUMMARY = "Example of how to build an external Linux kernel module"
LICENSE = "GPLv2"
LIC_FILES_CHKSUM = "file://COPYING;md5=12f884d2ae1ff87c09e5b7ccc2c4ca7e"

inherit module

SRC_URI = "file://Makefile \
           file://hello.c \
           file://COPYING \
          "

S = "${WORKDIR}"

# The inherit of module.bbclass will automatically name module packages with
# "kernel-module-" prefix as required by the oe-core build environment.

RPROVIDES_${PN} += "kernel-module-hello"

hello.c

/******************************************************************************
 *
 *   Copyright (C) 2011  Intel Corporation. All rights reserved.
 *
 *   This program is free software;  you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; version 2 of the License.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY;  without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
 *   the GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program;  if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 *
 *****************************************************************************/

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

static struct class *dev_class = NULL;

int init_module(void)
{
    printk("Hello World!\n");

    dev_class = class_create(THIS_MODULE, "hello");
  
    return 0;
}

void cleanup_module(void)
{
    class_destroy(dev_class);
    printk("Goodbye Cruel World!\n");
}

MODULE_LICENSE("GPL");

Makefile

obj-m := hello.o

SRC := $(shell pwd)

all:
    $(MAKE) -C $(KERNEL_SRC) M=$(SRC)

modules_install:
    $(MAKE) -C $(KERNEL_SRC) M=$(SRC) modules_install

clean:
    rm -f *.o *~ core .depend .*.cmd *.ko *.mod.c
    rm -f Module.markers Module.symvers modules.order
    rm -rf .tmp_versions Modules.symvers