How to statically build kernel module with buildroot?

Question

Is there an example package somewhere on how you might go about statically compiling in a device driver?

I know that obj-y is used for static compilation vs obj-m. I have a dynamically loadable module being built in my buildroot package right now. That dynamic module works exactly as I would expect. I even figured out that I could change the module makefile to use obj-y, and add a buildroot option where, if I clicked it it would append a line in the drivers/Makefile. The output appeared to show that my module got built. But it didn't at all seem to me that my driver's init function was being executed at startup, because I don't see my device file in /dev.

There is a problem in your driver. Perhaps initialization order is wrong when you compile in. And seems you didn't do your homework, i.e. check how to debug initcalls in kernel documentation. — 0andriy, Jan 23 '16 at 12:42
I got it working fully, I'll answer my own question with a post to an example. — Adam Miller, Jan 23 '16 at 16:12
Dynamic external kernel module: https://stackoverflow.com/questions/40307328/how-to-add-a-linux-kernel-module-driver-as-a-buildroot-package — Ciro Santilli OurBigBook.com, Jun 23 '17 at 07:15

score 2 · Accepted Answer · answered Jan 30 '16 at 23:41

Supposing you have a driver in driver.c, and a buildroot package called STATICDRVR, you can use the following Config.in and STATICDRVR.mk files to add a static module to be built when the kernel is built:

Config.in

config BR2_PACKAGE_STATICDRVR
       bool "Build & link static driver?"
       help
         This is a driver that blah blah greatness whatever

STATICDRVR.mk

STATICDRVR_VERSION = master
STATICDRVR_SITE =  /location/to/STATICDRVR_containing_src
STATICDRVR_SITE_METHOD = local
STATICDRVR_MODULE_SUBDIRS = src
STATICDRVR_INSTALL_TARGET = YES
STATICDRVR_LICENSE = GPLv2
STATICDRVR_LICENSE_FILES = COPYING
STATICDRVR_NAME = STATICDRVR

STATICDRVR_DEPENDENCIES = linux


define STATICDRVR_BUILD_CMDS
    #make sure that obj-y += STATICDRVR/ is only in the build makefile once
    sed -i '/obj-y += STATICDRVR/d' $(BUILD_DIR)/linux-$(LINUX_VERSION)/drivers/Makefile
    echo "obj-y += STATICDRVR/" >> $(BUILD_DIR)/linux-$(LINUX_VERSION)/drivers/Makefile
    rm -rf $(BUILD_DIR)/linux-$(LINUX_VERSION)/drivers/STATICDRVR
    cp -r $(@D)/src $(BUILD_DIR)/linux-$(LINUX_VERSION)/drivers/STATICDRVR
    echo "obj-y += driver.o" > $(BUILD_DIR)/linux-$(LINUX_VERSION)/drivers/STATICDRVR/Makefile
endef

define STATICDRVR_INSTALL_STAGING_CMDS
endef


define STATICDRVR_INSTALL_TARGET_CMDS
endef

endif

define STATICDRVR_DEVICES
endef

define STATICDRVR_PERMISSIONS
endef

define STATICDRVR_USERS
endef

$(eval $(kernel-module))
$(eval $(generic-package))

I'd provide a `.patch` file and apply it instead. – Ciro Santilli OurBigBook.com Aug 03 '16 at 22:57 — Ciro Santilli OurBigBook.com, Aug 03 '16 at 22:57

score 1 · Answer 2 · answered Jan 24 '16 at 14:04

1

It is not possible to statically link an external module with the kernel. To do that, you have to patch the kernel itself and add your module there.

answered Jan 24 '16 at 14:04

Arnout

2,927
16
24

I'll provide an example, I've solved my own problem. You're technically correct, but its probably more benefit to acknowledge that I mean I have driver code and I want it to be statically linked into the kernel, because I know better than to think that a .ko file can be statically linked to the vmlinux file. – Adam Miller Jan 24 '16 at 14:06
Related: http://stackoverflow.com/questions/7353851/insert-linux-kernel-module-statically – Ciro Santilli OurBigBook.com Aug 03 '16 at 22:59

How to statically build kernel module with buildroot?

2 Answers2