Cross compiling linux drivers

Cross compile FTDI VCP Driver for embedded linux arm

I’m trying to cross compile the FTDI VCP Driver for my embedded arch linux arm machine. I downloaded the source files from http://www.ftdichip.com/Drivers/VCP.htm onto my host machine which is running kernel: 2.6.32-54-generic-pae When running the Makefile, I get errors related to kernel headers, ie: asm/thread_info.h file not found. I realize that this means that my asm symlink is broken, so I tried linking it to linux-headers-2.6.32-54/include/asm-generic but the contents of that directory does not include thread_info.h either, which I’m trying to find. Has anyone cross compiled the FTDI VCP Driver for embedded arch linux arm using Ubuntu as their host and can point me in the right direction? I’m new to building kernel modules and cross compiling and any help would be appreciated. If anyone requires more information I’d be more than happy to add it.

What’s your target kernel version? If it is also 2.6.32, then FTDI driver is already there and if it is not activated it must be activated via make menuconfig .

My kernel version is 2.6.32. I know that it is already there and activated on my Ubuntu (host) machine, but I need to cross compile the driver to add usb to serial port functionality to my embedded linux machine (the target I’m cross compiling for).

Can I use make menuconfig to activate it on my embedded linux arm? I used dmesg to search for installed FTDI modules, but none exist.

You should be able to, check and see if it’s in the source tree. Building something already there will likely be easier than trying to merge isolated vendor code back into your tree.

I have no experience with Arch Linux. But on embedded Debian you have gcc and other needed tools, so one can compile the kernel directly on the machine, but it will be very slow process. So normally you just have a toolchain on your host PC and you specify ARCH and CROSS_COMPILE env vars and do your make menuconfig and then make .

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Cross compiling Linux ARM kernel modules

This guide will allow you to cross-compile a loadable kernel module (LKM; a.k.a. device driver) for a ARM Linux system.

1. Target system

I will use this configuration as an example, but you can apply the same method for other environments.

2. Download linux kernel source

You must download the exact version which is running in the qemu.

Note that source for 3.2.0 is named linux-3.2.tar.gz , not linux-3.2.0.tar.gz .

3. Download cross compiler toolchain

Linaro’s prebuilt toolchain generally works well. Download one from https://releases.linaro.org/components/toolchain/binaries.

Pick a version, and choose the appropriate architecture. In our case, it would be arm-linux-gnueabihf (ARM 32-bit, linux, little endian, hard float).

There are three kinds of files: gcc-linaro- , runtime-gcc-linaro- , and sysroot-eglibc-linaro- . You only need the first one. For more info, refer to this Linaro wiki page.

For instance, go to 4.9-2017.01/arm-linux-gnueabihf/ directory and download gcc-linaro-4.9.4-2017.01-x86_64_arm-linux-gnueabihf.tar.xz .

4. Take out kernel build config

We need to build the kernel first, and then build a kernel module. But to compile a kernel, we must have the exact build configuration of the currently running Linux system. Fortunately, you can get a copy from a running system. Look at these locations:

Copy the file out of the qemu using scp or something.

5. Build the kernel

You need auto-generated files in order to build a kernel module. Otherwise you may encounter an error message like this:

/home/ubuntu/linux-3.2/include/linux/kconfig.h:4:32: fatal error: generated/autoconf.h: No such file or directory #include ^ 

To build a kernel with given config file,

cd cp .config make ARCH=arm CROSS_COMPILE=/bin/arm-linux-gnueabihf- oldconfig make ARCH=arm CROSS_COMPILE=/bin/arm-linux-gnueabihf- 

Complete kernel build may not be necessary because what you need is generated header files.

6. Build the module

Write a Makefile as follows:

PWD := $(shell pwd) obj-m += hello.o all: make ARCH=arm CROSS_COMPILE=$(CROSS) -C $(KERNEL) SUBDIRS=$(PWD) modules clean: make -C $(KERNEL) SUBDIRS=$(PWD) clean 

And create a hello world module.

// hello.c #include #include  int init_module(void)  printk(KERN_INFO "Hello world.\n"); return 0; > void cleanup_module(void)  printk(KERN_INFO "Goodbye world.\n"); > 

make KERNEL= CROSS=/bin/arm-linux-gnueabihf- 

Then you will get hello.ko compatible with the running ARM Linux.

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Driver/module cross compilation

I am trying to cross compile a driver for an arm based board. In the make file the search path for include files is that of the host machine’s kernel i.e it points to the linux headers that come with ubuntu. I also have the kernel source tree of target board present on the host system(i7/ubuntu). My Question is that which include path is needed for cross compilation (native system’s linux headers path or the path to the kernel source tree of board ? Does same thing applies to all modules including drivers?

it should point to the kernel source tree of the board. This is because the include files that the driver you are compiling may need platform based header files. For eg. if you are cross compiling for ARM the include files should be pointing to arch/arm/include rather then the generic linux include folders.

When i use the include files of board, i get many file missing errors. and when i use include files of host machine(running ubuntu 12.04) there are no errors but the driver(module) gets compiled in an invalid format that is not compatible with the board. in both cases i am using the arm-linux-gcc compiler in the tool chain supplied by the vendor.

When you say «the driver gets compiled in an invalid format» what is the error exactly? Could you elaborate on that? If it is compiling fine that is the error shown during module insertion?

yes The compilation goes fine. but when i try to insmod the .ko file of driver i get an invalid format error, pasting the error below insmod: error inserting e1000e.ko: -1 Invalid module format

3 Answers 3

Here is a Makefile for an out of tree driver. The architecture, toolchain and kernel dir specified :

ifneq ($(KERNELRELEASE),) # We were called by kbuild obj-m += fpgacam.o else # We were called from command line KDIR := path/to/your/target/kernel PWD := $(shell pwd) CROSS=arm-none-linux-gnueabi- default: @echo ' Building Cam drivers for 2.6 kernel.' @echo ' PLEASE IGNORE THE "Overriding SUBDIRS" WARNING' $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS) modules install: ./do_install.sh *.ko endif # End kbuild check ######################### Version independent targets ########################## clean: rm -f -r *.o *.ko .*cmd .tmp* core *.i 

When make is called from the module directory, the command line path is taken, and make is redirected to the kernel directory build system using make -C . The kernel build system then the different variable passed to it to go back into the module directory with everything setup (include path, toolchain etc ..) to compile a module. This second time through the Makefile, the kbuild path is taken, and the module is built as if it was in-tree.

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Cross Compiling Linux Arm Kernel with new driver module

I am trying to include a driver for use on my arch linux arm machine. I tried using these steps to include the driver module, but my cross-compiled kernel with the added driver doesn’t load.

1) Include the driver I want to add by making it have < M >beside it's name in make ARCH=arm menuconfig 2) run: make ARCH=arm CROSS_COMPILE=/home/z3/bin/arm- (the path for my cross-compiling toolchain) 3) run: make ARCH=arm CROSS_COMPILE=/home/z3/bin/arm- modules 4) run: make ARCH=arm CROSS_COMPILE=/home/z3/bin/arm- install 5) run: make ARCH=arm CROSS_COMPILE=/home/z3/bin/arm- modules_install 6) copy my uImage from: arch/arm/boot to my boot location: /tftpboot/ 

Then when my embedded linux arm tries to load the kernel uImage, it hangs with: EDIT: Changed the entry point address to 80008000, so now it hangs with:

Filename '/tftpboot/uImage'. Load address: 0x81800000 Loading: ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# ################################################################# #################################### done 

Booting kernel from Legacy Image at 81800000 .

Image Name: 2.6.35-ModifiedEntry
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 3174784 Bytes = 3 MiB
Load Address: 80008000
Entry Point: 80008000
Verifying Checksum . OK
Loading Kernel Image . OK
OK Starting kernel . Am I cross-compiling my kernel wrong? It cannot load the uImage. All I want to do is cross compile my kernel for the linux arm machine with a newly included driver (included in the config from make menuconfig). Am I missing any additional steps?

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