How to cross-compile with the Distribution Package

1. Article purpose[edit source]

This article provides simple examples for the Distribution Package of the OpenSTLinux distribution, that illustrate the cross-compilation with the devtool and BitBake tools:

modification with Linux^® Kernel (configuration, device tree, driver, ...)
modification of an external in-tree Linux Kernel module
modification of U-Boot
modification of TF-A
addition of software

These examples also show how to deploy the results of the cross-compilation on the target, through a network connection to the host machine.

Information

All the examples described on this page use devtool and/or bitbake from OpenEmbededded, see OpenEmbedded - devtool and BitBake cheat sheet for more information.

Information

There are many ways to achieve the same result; this article aims to provide at least one solution per example. You have the liberty to explore other methods that are better adapted to your development constraints.

2. Prerequisites[edit source]

The prerequisites from Installing the OpenSTLinux distribution must be executed.

The board and the host machine are connected through an Ethernet link, and a remote terminal program is started on the host machine: see How to get Terminal.

The target is started, and its IP address (<board ip address>) is known.

3. Modification with kernel[edit source]

3.1. Preamble[edit source]

To start modification with a module, you need to initialize your Distribution Package environment.

 cd <working directory path of distribution>
 DISTRO=openstlinux-weston MACHINE=stm32mp1 source layers/meta-st/scripts/envsetup.sh

You are now in the build directory, identified by <build dir> in the following paragraphs.

Initialize devtool for kernel component:

 devtool modify virtual/kernel
NOTE: Starting bitbake server...
NOTE: Creating workspace layer in /mnt/internal_storage/oetest/oe_openstlinux_rocko/build-openstlinuxweston-stm32mp1/workspace
NOTE: Enabling workspace layer in bblayers.conf
Parsing recipes: 100% |########################################################################################| Time: 0:00:54
Parsing of 2401 .bb files complete (0 cached, 2401 parsed). 3282 targets, 88 skipped, 0 masked, 0 errors.
NOTE: Mapping virtual/kernel to linux-stm32mp
NOTE: Resolving any missing task queue dependencies
...

Information

For the case of virtual/<something> component, you need to get the name of mapping between virtual component and associated recipe. In this example, the name of kernel recipe is indicated in the trace, but you can also get it by calling devtool status

A minority of devtool command supports the virtual/<something> component, like devtool modify, it is why you need to get the recipe name associated to virtual/component.
In this example, the name of kernel recipe is indicated in the trace (linux-stm32mp)

Information

The source code of kernel is located on <build dir>/workspace/sources. You can change the path where the source code is extracted by customizing the devtool modify command

Information

For all the work around the kernel, we strongly encourage some usage for deploying the binaries on board

Kernel image, device tree: use bitbake deploy command and scp (see #modifying kernel configuration ))
Kernel module: use devtool deploy-target by passing by a temporary directory (see #Modifying/adding an external Linux kernel module)

The difference of usage comes from the number of files to deploy on board. When there is only one or two files to put on board, the easiest way to do it is to deploy only the desired files .

3.2. Modifying kernel configuration[edit source]

This simple example modifies the kernel configuration via menuconfig for the CMA size.

Get the current value of the CMA size (128 Mbytes here) through the analysis of the target boot log

 dmesg | grep -i cma
[    0.000000] cma: Reserved 128 MiB at 0xf0000000

Start the Linux kernel configuration menu: see Menuconfig or how to configure kernel

Navigate to "Device Drivers - Generic Driver Options"
- select "Size in Megabytes"
- modify its value to 256
- exit and save the new configuration

Check that the configuration file (.config) has been modified

 grep -i CONFIG_CMA_SIZE_MBYTES <build dir>/workspace/sources/<name of kernel recipe>/.config.new
CONFIG_CMA_SIZE_MBYTES=256

Cross-compile the Linux kernel: see Menuconfig or how to configure kernel

Update the Linux kernel image on board: see Menuconfig or how to configure kernel

Reboot the board: see Menuconfig or how to configure kernel

Get the new value of the CMA size (256 Mbytes) through the analysis of the target boot log

 dmesg | grep -i cma
[    0.000000] cma: Reserved 256 MiB at 0xe0000000

3.3. Modifying the Linux kernel device tree[edit source]

This simple example modifies the default status of a user LED.

With the board started; check that the user LED (LD3) is disabled

Go to the <build dir>/workspace/sources/<name of kernel recipe>/ directory

 cd <build dir>/workspace/sources/<name of kernel recipe>/

Edit the arch/arm/boot/dts/stm32mp157c-ed1.dts Device Tree Source file for evaluation board or

Edit the arch/arm/boot/dts/stm32mp157c-dk2.dts Device Tree Source file for discovery board or

Change the status of the "stm32mp:green:user" led to "okay", and set its default state to "on"

	led {
		compatible = "gpio-leds";

		status = "okay";
		red {
			label = "stm32mp:red:status";
			gpios = <&gpioa 13 GPIO_ACTIVE_LOW>;

			status = "disabled";
		};
		green {
			label = "stm32mp:green:user";
			gpios = <&gpioa 14 GPIO_ACTIVE_LOW>;
			default-state = "on";

			status = "okay";
		};
	};

Go to the build directory

 cd <build dir>

If this update is accepted, then to report in other paragraph of this page}}

Generate the device tree blobs (*.dtb)

 bitbake virtual/kernel -C compile

Information

we use here bitbake command instead of devtool build because the build makes compile, compile_kernemodules and install commands whereas we only need only compile command to generate the kernel image and the device tree

Update the device tree blobs on the board

 scp <build dir>/tmp-glibc/deploy/images/<machine name>/*.dtb root@<board ip address>:/boot

Information

If the /boot mounting point doesn't exist yet, please see how to create a mounting point

Reboot the board

 cd /boot; sync; systemctl reboot

Check that the user LED (LD3) is enabled (green)

3.4. Modifying a built-in Linux kernel device driver[edit source]

This simple example adds unconditional log information when the display driver is probed.

Check that there is no log information when the display driver is probed

 dmesg | grep -i stm_drm_platform_probe

Go to the <build dir>/workspace/sources/<name of kernel recipe>/

 cd <build dir>/workspace/sources/<name of kernel recipe>/

Edit the ./drivers/gpu/drm/stm/drv.c source file
Add a log information in the stm_drm_platform_probe function

static int stm_drm_platform_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct drm_device *ddev;
	int ret;
	[...]

	DRM_INFO("Simple example - %s\n", __func__);

	return 0;
	[...]
}

Go to the build directory

 cd <build dir>

Cross-compile the Linux kernel

 bitbake virtual/kernel -C compile

Update the Linux kernel image on board

 scp <build dir>/tmp-glibc/deploy/images/<machine name>/uImage root@<board ip address>:/boot

Information

If the /boot mounting point doesn't exist yet, please see how to create a mounting point

Reboot the board

 cd /boot; sync; systemctl reboot

Check that there is now log information when the display driver is probed

 dmesg | grep -i stm_drm_platform_probe
[    5.005833] [drm] Simple example - stm_drm_platform_probe

3.5. Modifying/adding an external Linux kernel module[edit source]

Most device drivers (modules) in the Linux kernel can be compiled either into the kernel itself (built-in/internal module) or as Loadable Kernel Modules (LKM/external module) that need to be placed in the root file system under the /lib/modules directory. An external module can be in-tree (in the kernel tree structure), or out-of-tree (outside the kernel tree structure).

This simple example adds an unconditional log information when the virtual video test driver (vivid) kernel module is probed or removed.

Go to the <build dir>/workspace/sources/<name of kernel recipe>/

 cd <build dir>/workspace/sources/<name of kernel recipe>/

Edit the ./drivers/media/platform/vivid/vivid-core.c source file
Add log information in the vivid_probe and vivid_remove functions

static int vivid_probe(struct platform_device *pdev)
{
	const struct font_desc *font = find_font("VGA8x16");
	int ret = 0, i;
	[...]

	/* n_devs will reflect the actual number of allocated devices */
	n_devs = i;

	pr_info("Simple example - %s\n", __func__);

	return ret;
}

static int vivid_remove(struct platform_device *pdev)
{
	struct vivid_dev *dev;
	unsigned int i, j;
	[...]

	pr_info("Simple example - %s\n", __func__);

	return 0;
}

Go to the build directory

 cd <build dir>

Cross-compile the Linux kernel modules

 bitbake virtual/kernel -C compile

Update the vivid kernel module on the board

 devtool deploy-target -Ss <name of kernel recipe> root@<board ip address>:/

Information

Take care to have enought place available on board to receive the binaries deployed via deploy-target command.

The binaries (mainly kernel modules) are not stripped on deploy-target command and take a lot of place.

Update dependency descriptions for loadable kernel modules, and synchronize the data on disk with memory

 /sbin/depmod -a
 sync

Insert the vivid kernel module into the Linux kernel

 modprobe vivid                   
[...]
[ 3412.784638] Simple example - vivid_probe

Remove the vivid kernel module from the Linux kernel

 rmmod vivid
[...]
[ 3423.708517] Simple example - vivid_remove

4. Adding an external out-of-tree Linux kernel module[edit source]

This simple example adds a "Hello World" external out-of-tree Linux kernel module to the Linux kernel.

Create a directory for this kernel module example

 mkdir kernel_module_example
 cd kernel_module_example

Create the source code file for this kernel module example: kernel_module_example.c

// SPDX-identifier: GPL-2.0
/*
 * Copyright (C) STMicroelectronics SA 2018
 *
 * Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
 *
 */

#include <linux/module.h>    /* for all kernel modules */
#include <linux/kernel.h>    /* for KERN_INFO */
#include <linux/init.h>      /* for __init and __exit macros */

static int __init kernel_module_example_init(void)
{
	printk(KERN_INFO "Kernel module example: hello world from STMicroelectronics\n");
	return 0;
}

static void __exit kernel_module_example_exit(void)
{
	printk(KERN_INFO "Kernel module example: goodbye from STMicroelectronics\n");
}

module_init(kernel_module_example_init);
module_exit(kernel_module_example_exit);

MODULE_DESCRIPTION("STMicroelectronics simple external out-of-tree Linux kernel module example");
MODULE_AUTHOR("Jean-Christophe Trotin <jean-christophe.trotin@st.com>");
MODULE_LICENSE("GPL v2");

Create the makefile for this kernel module example: Makefile

Information

All the indentations in a makefile are tabulations

# Makefile for simple external out-of-tree Linux kernel module example

# Object file(s) to be built
obj-m := kernel_module_example.o

# Path to the directory that contains the Linux kernel source code
# and the configuration file (.config)
KERNEL_DIR ?= <Linux kernel path>

# Path to the directory that contains the source file(s) to compile
PWD := $(shell pwd) 
  
default:
	$(MAKE) -C $(KERNEL_DIR) M=$(PWD) modules

clean:
	$(MAKE) -C $(KERNEL_DIR) M=$(PWD) clean

Add a new recipe to the workspace

 cd <build dir>
 devtool add mymodule kernel_module_example/

Adapt recipe to kernel module build

 devtool edit-recipe mymodule

Modify the recipe according the following changes (see highlighted lines)

# Recipe created by recipetool
# This is the basis of a recipe and may need further editing in order to be fully functional.
# (Feel free to remove these comments when editing.)

# Unable to find any files that looked like license statements. Check the accompanying
# documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
#
# NOTE: LICENSE is being set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (it
# will not be in most cases) you must specify the correct value before using this
# recipe for anything other than initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""

# No information for SRC_URI yet (only an external source tree was specified)
SRC_URI = ""

# NOTE: this is a Makefile-only piece of software, so we cannot generate much of the
# recipe automatically - you will need to examine the Makefile yourself and ensure
# that the appropriate arguments are passed in.
DEPENDS = "virtual/kernel"
inherit module

EXTRA_OEMAKE  = "ARCH=arm"
EXTRA_OEMAKE += "KERNEL_DIR=${STAGING_KERNEL_BUILDDIR}"

S = "${WORKDIR}"

do_configure () {
	# Specify any needed configure commands here
	:
}

do_compile () {
 	# You will almost certainly need to add additional arguments here
	oe_runmake
}

do_install () {
	# NOTE: unable to determine what to put here - there is a Makefile but no
	# target named "install", so you will need to define this yourself
        install -d ${D}/lib/modules/${KERNEL_VERSION}
        install -m 0755 ${B}/kernel_module_example.ko ${D}/lib/modules/${KERNEL_VERSION}/
}

Go to the build directory

 cd <build dir>

Generated kernel module example

 devtool build mymodule

Push this kernel module example on board

 devtool deploy-target -Ss mymodule root@<board ip address>

Update dependency descriptions for loadable kernel modules, and synchronize the data on disk with memory

 /sbin/depmod -a
 sync

Insert the kernel module example into the Linux kernel

 modprobe kernel_module_example
[18167.821725] Kernel module example: hello world from STMicroelectronics

Remove the kernel module example from the Linux kernel

 rmmod kernel_module_example
[18180.086722] Kernel module example: goodbye from STMicroelectronics

5. Modifying the U-Boot[edit source]

This simple example adds unconditional log information when U-Boot starts. Within the scope of the trusted boot chain, U-Boot is used as second stage boot loader (SSBL).

Have a look at the U-Boot log information when the board reboots

 reboot
[...]
U-Boot <U-Boot version>

CPU: STM32MP1 rev1.0
Model: STMicroelectronics STM32MP157C [...]
Board: stm32mp1 in trusted mode
[...]

Go to the build directory

 cd <build dir>

Search U-boot recipe

 devtool search u-boot*
u-boot-stm32mp-extlinux  Generate 'extlinux.conf' file for U-boot
u-boot-stm32mp        Universal Boot Loader for embedded devices for stm32mp

On this example, the recipe name is u-boot-stm32mp

Start to work with u-boot

 devtool modify u-boot-stm32mp

Example:
 cd <build dir>/workspace/sources/u-boot-stm32mp

Edit the ./board/st/stm32mp1/stm32mp1.c source file
Add a log information in the checkboard function

int checkboard(void)
{
	char *mode;

	[...]

	printf("Board: stm32mp1 in %s mode\n", mode);
	printf("U-Boot simple example\n");

	return 0;
}

Cross-compile the U-Boot: trusted boot

 devtool build u-boot-stm32mp
 bitbake u-boot-stm32mp -c deploy

Go to the directory in which the compilation results are stored

 cd <build dir>/tmp-glibc/deploy/images/<machine name>/

Reboot the board, and hit any key to stop in the U-boot shell

 reboot
[...]
Hit any key to stop autoboot:  0 
STM32MP>

Connect a USB cable between the host machine and the board via the USB OTG ports

In the U-Boot shell, call the USB mass storage function

STM32MP> ums 0 mmc 0

Information

for more information about the usage of U-Boot UMS functionality, see How to use USB mass storage in U-Boot

On the host machine, check the partition associated with the secondary stage boot loader (ssbl): sdc3 here

 ls -l /dev/disk/by-partlabel/
total 0
lrwxrwxrwx 1 root root 10 Jan 17 18:05 bootfs -> ../../sdc4
lrwxrwxrwx 1 root root 10 Jan 17 18:05 fsbl1 -> ../../sdc1
lrwxrwxrwx 1 root root 10 Jan 17 18:05 fsbl2 -> ../../sdc2
lrwxrwxrwx 1 root root 10 Jan 17 18:05 rootfs -> ../../sdc5
lrwxrwxrwx 1 root root 10 Jan 17 18:05 ssbl -> ../../sdc3
lrwxrwxrwx 1 root root 10 Jan 17 18:05 userfs -> ../../sdc6

Copy the binary (u-boot.stm32) to the dedicated partition

 dd if=u-boot-<board name>-trusted.stm32 of=/dev/sdc3 bs=1M conv=fdatasync

(here u-boot-stm32mp157c-ev1-trusted.stm32 or u-boot-stm32mp157c-dk2-trusted.stm32)

Reset the U-Boot shell

STM32MP> reset

Have a look at the new U-Boot log information when the board reboots

[...]
U-Boot <U-Boot version>

CPU: STM32MP1 rev1.0
Model: STMicroelectronics STM32MP157C [...]
Board: stm32mp1 in trusted mode
U-Boot simple example
[...]

6. Modifying the TF-A[edit source]

This simple example adds unconditional log information when the TF-A starts. Within the scope of the trusted boot chain, TF-A is used as first stage boot loader (FSBL).

Have a look at the TF-A log information when the board reboots

 reboot
[...]
INFO:      System reset generated by MPU (MPSYSRST)
INFO:    Using SDMMC
[...]

Go to the build directory

 cd <build dir>

Search TF-A recipe

 devtool search tf-a*
babeltrace            Babeltrace - Trace Format Babel Tower
libunistring          Library for manipulating C and Unicode strings
lttng-tools           Linux Trace Toolkit Control
gettext               Utilities and libraries for producing multi-lingual messages
glibc                 GLIBC (GNU C Library)
tf-a-stm32mp          Trusted Firmware-A for STM32MP1
gnutls                GNU Transport Layer Security Library
gstreamer1.0          GStreamer 1.0 multimedia framework
harfbuzz              Text shaping library
glibc-locale          Locale data from glibc
kbd                   Keytable files and keyboard utilities

On this example, the recipe name is tf-a-stm32mp

Start to work with tf-a

 devtool modify tf-a-stm32mp

Go to <build dir>/workspace/sources/tf-a-stm32mp

 cd <build dir>/workspace/sources/tf-a-stm32mp

Edit the ./plat/st/stm32mp1/bl2_io_storage.c source file
Add a log information in the stm32mp1_io_setup function

void stm32mp1_io_setup(void)
{
	int io_result;
	[...]
 
	/* Add a trace about reset reason */
	print_reset_reason();

	INFO("TF-A simple example");

	[...]
}

Cross-compile the TF-A

 devtool build tf-a-stm32mp
 bitbake tf-a-stm32mp -c deploy

Go to the directory in which the compilation results are stored

 cd <build dir>/tmp-glibc/deploy/images/<machine name>/

Reboot the board, and hit any key to stop in the U-boot shell

 reboot
[...]
Hit any key to stop autoboot:  0 
STM32MP>

Connect a USB cable between the host machine and the board via the USB OTG ports

In the U-Boot shell, call the USB mass storage function

STM32MP> ums 0 mmc 0

Information

for more information about the usage of U-boot ums functionality see How to use USB mass storage in U-Boot

On the host machine, check the partition associated with the first stage boot loader (fsbl1 and fsbl2 as backup): sdc1 and sdc2 (as backup) here

 ls -l /dev/disk/by-partlabel/
total 0
lrwxrwxrwx 1 root root 10 Jan 17 18:05 bootfs -> ../../sdc4
lrwxrwxrwx 1 root root 10 Jan 17 18:05 sfsbl1 -> ../../sdc1
lrwxrwxrwx 1 root root 10 Jan 17 18:05 sfsbl2 -> ../../sdc2
lrwxrwxrwx 1 root root 10 Jan 17 18:05 rootfs -> ../../sdc5
lrwxrwxrwx 1 root root 10 Jan 17 18:05 ssbl -> ../../sdc3
lrwxrwxrwx 1 root root 10 Jan 17 18:05 userfs -> ../../sdc6

Copy the binary (tf-a-stm32mp157c-ev1-trusted.stm32) to the dedicated partition; to test the new TF-A binary, it might be useful to keep the old TF-A binary in the backup FSBL (fsbl2)

 dd if=tf-a-<board name>-trusted.stm32 of=/dev/sdc1 bs=1M conv=fdatasync

(here tf-a-stm32mp157c-ev1-trusted.stm32 or tf-a-stm32mp157c-dk2-trusted.stm32)

Reset the U-Boot shell

STM32MP> reset

Have a look at the new TF-A log information when the board reboots

[...]
INFO:      System reset generated by MPU (MPSYSRST)
INFO:    TF-A simple example
INFO:    Using SDMMC
[...]

7. Adding a "hello world" user space example[edit source]

This chapter shows how to compile and execute a simple "hello world" example.

Create a directory for this user space example

 mkdir hello_world_example
 cd hello_world_example

Create the source code file for this user space example: hello_world_example.c

// SPDX-identifier: GPL-2.0
/*
 * Copyright (C) STMicroelectronics SA 2018
 *
 * Authors: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
 *
 */

#include <stdio.h>
#include <unistd.h>

int main(int argc, char **argv)
{
	int i =11;

	printf("\nUser space example: hello world from STMicroelectronics\n");
	setbuf(stdout,NULL);
	while (i--) {
		printf("%i ", i);
		sleep(1);
	}
	printf("\nUser space example: goodbye from STMicroelectronics\n");

	return(0);
}

Add a new recipe to the workspace

 cd <build dir>
 devtool add myhelloword hello_world_example/

Adapt recipe

 devtool edit-recipe myhelloworld

Modify the recipe according the following changes (see highlighted lines)

# Recipe created by recipetool
# This is the basis of a recipe and may need further editing in order to be fully functional.
# (Feel free to remove these comments when editing.)

# Unable to find any files that looked like license statements. Check the accompanying
# documentation and source headers and set LICENSE and LIC_FILES_CHKSUM accordingly.
#
# NOTE: LICENSE is being set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (it
# will not be in most cases) you must specify the correct value before using this
# recipe for anything other than initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""

# No information for SRC_URI yet (only an external source tree was specified)
SRC_URI = ""

# NOTE: no Makefile found, unable to determine what needs to be done

do_configure () {
	# Specify any needed configure commands here
	:
}

do_compile () {
	# Specify compilation commands here
	cd ${S}
	${CC} hello_world_example.c -o hello_word_example
}

do_install () {
	# Specify install commands here
	install -d ${D}${bindir}
	install -m 755 ${S}/hello_word_example  ${D}${bindir}/
}

Compile binary

 devtool build myhelloword

Push this binary on board

 devtool deploy-target -s myhelloword root@<board ip address>

Execute this user space example

 /usr/bin/hello_world_example 

User space example: hello world from STMicroelectronics
10 9 8 7 6 5 4 3 2 1 0 
User space example: goodbye from STMicroelectronics

8. Tips[edit source]

8.1. Creating a mounting point[edit source]

The objective is to create a mounting point for the boot file system (bootfs partition)

Find the partition label associated with the boot file system

 ls -l /dev/disk/by-partlabel/
total 0
lrwxrwxrwx 1 root root 15 Dec 13 12:31 bootfs -> ../../mmcblk0p4
lrwxrwxrwx 1 root root 15 Dec 13 12:31 fsbl1 -> ../../mmcblk0p1
lrwxrwxrwx 1 root root 15 Dec 13 12:31 fsbl2 -> ../../mmcblk0p2
lrwxrwxrwx 1 root root 15 Dec 13 12:31 rootfs -> ../../mmcblk0p5
lrwxrwxrwx 1 root root 15 Dec 13 12:31 ssbl -> ../../mmcblk0p3
lrwxrwxrwx 1 root root 15 Dec 13 12:31 userfs -> ../../mmcblk0p6

Attach the boot file system found under /dev/mmcblk0p4 in the directory /boot

 mount /dev/mmcblk0p4 /boot