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1 Purpose[edit]

This article describes the process used for building several OP-TEE components from sources and deploying them the target.

The build example is based on the OpenSTLinux Developer Package or Distribution Package, and also presents build instructions for a bare environment.

2 Overview[edit]

OP-TEE is a trusted execution environment for Arm®v7-A and Arm®v8-A platforms. OP-TEE is made of several components described in OP-TEE architecture overview.

OP-TEE components generate boot images and files stored in the filesystem embedded in the target.

  • OP-TEE OS generates 3 boot image files to be loaded in the platform boot media, in the predefined partitions. The generated boot images include a STM32 binary header enabling the use of the authenticated boot and flash programming facilities.
  • OP-TEE client (package optee_client) can be built to generate non-secure services for the OP-TEE OS. The files generated from optee_client build are stored in the embedded filesystem.
  • OP-TEE project releases other packages intended for test and demonstration. These can be built and embedded in the target filesystem. Building optee_examples and optee_test generates client and trusted applications together with libraries which are all stored in the target filesystem. Note the OP-TEE Linux driver is built into the Linux kernel image and is part of the OP-TEE ecosystem.

OP-TEE can be embedded in the STM32MP1 platform for the ST trusted configuration.

3 Build with the Distribution Package[edit]

The Distribution Package provides means to build the following OP-TEE components from their related bitbake target:

 bitbake optee-os-stm32mp                # OP-TEE core firmware
 bitbake optee-os-sdk-stm32mp            # OP-TEE development kit for Trusted Applications
 bitbake optee-client                    # OP-TEE client
 bitbake optee-test                      # OP-TEE test suite (optional)
 bitbake optee-examples                  # TA and CA examples

Distribution Package build process includes fetching the source files, compiling them and installing them to the target images.

The Yocto recipes for the OP-TEE packages can be found in:


4 Build with the Developer Package or a Bare Environment[edit]

Both Developer Package and bare build environments expect you to fetch/download the OP-TEE package source file trees in order to build the embedded binary images.

The instruction set below assumes all OP-TEE package source trees are available in the base directory referred as <sources>/. The source files are available from the github repositories:

 cd <sources>/
 git clone
 git clone
 git clone
 git clone
 ls -1 <sources>/
Warning white.png Warning
The STM32MP1 platform is not yet fully merged in the official OP-TEE repository [1] hence the URL provided above refers to the ST distribution [2]

4.1 Initialize the cross compile environment[edit]

The compilation toolchain provided by the Developer Package can be used, refer to Setup Cross Compile Environment.

Alternatively other bare toolchains can be used to build the OP-TEE secure parts. In such case, the instructions below expect the toolchain to be part of the PATH and its prefix is defined by CROSS_COMPILE. One can use something like:

 export PATH=<path-to-toolchain>:$PATH
 export CROSS_COMPILE=<toolchain-prefix>-

4.2 Build OP-TEE OS[edit]

4.2.1 Developer Package SDK[edit]

The OP-TEE OS can be built from the Developer Package Makefile.sdk script that is present in the tarball. It automatically sets the proper configuration for the OP-TEE OS build. To build from shell command:

 make -f Makefile.sdk CFG_SECURE_DT=stm32mp157c-<board>

4.2.2 Bare Environment[edit]

Alternatively one can also build OP-TEE OS based a bare cross compilation toolchains, for example for the stm32mp157c-ev1 board:

 cd <optee-os>
 make PLATFORM=stm32mp1 \
           CFG_SECURE_DT=stm32mp157c-ev1 \
           CFG_TEE_CORE_LOG_LEVEL=2 O=out all

4.2.3 Generated Files[edit]

The 3 OP-TEE boot images are generated at following paths:


One can get the configuration directives used for the build are available in this file:


The build also generates a development kit used to build Trusted Application binaries:


4.2.4 Details on build directives[edit]

Mandatory directives to build OP-TEE OS:

  • PLATFORM=stm32mp1: builds an stm32mp1 platform
  • CFG_SECURE_DT=<device-tree-source-file>: in-tree (core/arch/arm/dts/) device tree filename without its .dts extension.

Common optional directives:

  • CFG_TEE_CORE_DEBUG={n|y}: disable/enable debug support
  • CFG_TEE_CORE_LOG_LEVEL={0|1|2|3|4}: define the trace level (0: no trace, 4: overflow of traces)
  • CFG_UNWIND={n|y}: disable/enable stack unwind support

Note: internal memory size constrains the debug support level that can be provided.

4.2.5 Troubleshoot[edit]

The Developer Package toolchain may report dependency error in the traces such as:

 make PLATFORM=stm32mp1 ...
arm-openstlinux_weston-linux-gnueabi-ld.bfd: cannot find libgcc.a: No such file or directory

To overcome the issue, add the directive comp-cflagscore=--sysroot=$SDKTARGETSYSROOT. I.e:

 cd <optee-os>
 make PLATFORM=stm32mp1 \
           CFG_SECURE_DT=stm32mp157c-ev1 \
           CFG_TEE_CORE_LOG_LEVEL=2 \
           comp-cflagscore=--sysroot=$SDKTARGETSYSROOT \
           O=out all

Another issue one may face with the Developer Package toolchain is a linker issue reported with a the trace message such as:

 make PLATFORM=stm32mp1 ...
arm-ostl-linux-gnueabi-ld.bfd: unrecognized option '-Wl,-O1'
arm-ostl-linux-gnueabi-ld.bfd: use the --help option for usage information
core/arch/arm/kernel/ recipe for target 'out/core/tee.elf' failed
make: *** [out/core/tee.elf] Error 1

This may be due to the exported shell variable LDFLAGS. One can overcome the link issue by dropping the environment variable:

 unset LDFLAGS
 make PLATFORM=stm32mp1 ...

4.3 Build commands for other OP-TEE components[edit]

This section describes how the several OP-TEE components (excluding OP-TEE OS described in above section) can be built. All those components generate files targeting the embedded Linux OS based filesystem (i.e the rootfs). These files are the secure Trusted Applications (TAs) binaries as well as non-secure Client Applications (CAs), libraries and test files.

There are several ways to build the OP-TEE components. The examples given below refer to OP-TEE client, test and examples source file tree paths as <optee-client>, <optee-test> and <optee-examples>.

Building these components expect, at least for the trusted applications, that the OP-TEE OS was built and the generated TA development kit is available at <optee-os>/out/export-ta_arm32/.

It is recommended to use CMake for building the Linux userland part whereas secure world binaries (TAs) must be build from their GNU makefiles as the OP-TEE project has not yet ported the secure world binaries build process over CMake.

4.3.1 Build the secure components[edit]

Build the TAs: This step expects OP-TEE OS is built to generate the 32bit TA development kit. Assuming OP-TEE OS was built at path <optee-os>/out, the TA development kit is available from path <optee-os>/out/export-ta_arm32/.

Instructions below build and copy the Trusted Application binaries to a local ./target/ directory that can be used to populate the target filesystem.

 export TA_DEV_KIT_DIR=$PWD/optee_os/out/export-ta_arm32
 mkdir -p ./target/lib/optee_armtz
 for f in optee_test/ta/*/Makefile; do \
            make -C `dirname $f` O=out; \
            cp -f `dirname $f`/out/*.ta ./target/lib/optee_armtz; \

Content in local directory ./target/ are the TA binary files:

 tree target/
└── lib
  └── optee_armtz
   ├── 614789f2-39c0-4ebf-b235-92b32ac107ed.ta
   ├── 731e279e-aafb-4575-a771-38caa6f0cca6.ta
   └── (...)

These files need to be copied to the the target filesystem.

4.3.2 Build the non-secure components[edit]

Download the OP-TEE source files in a base directory and create a CMakeLists.txt file in the base directory that lists all package to be built through CMake. For example:

 cat CMakeLists.txt
add_subdirectory (optee_client)
add_subdirectory (optee_test)
add_subdirectory (optee_examples)

From base directory, run cmake then make. The example below also creates the tree file system ./target/ that is populated with files generated that need to be installed in the target file system.
Note this examples also sets the toolchain environment:

 cmake -DOPTEE_TEST_SDK=$PWD/optee_os/out/export-ta_arm32 \
 make DESTDIR=target install 

Note the empty CMAKE_INSTALL_PREFIX value to get thing installed from root /, not from /usr/. DESTDIR=target makes the embedded files be populated in the local ./target/ directory.

Note also that stm32mp15 expects tool tee-supplicant to be located in directory /usr/bin whereas CMake installs it in directory /usr/sbin. To overcome this issue, one can build a link to the effective location, i.e:

 ln -s ../bin/tee-supplicant target/sbin/tee-supplicant

Once done, local directory ./target/ contains the files to be copied in the target filesystem.

 tree target/
├── bin
│   ├── benchmark
│   ├── optee_example_acipher
│   ├── optee_example_aes
│   ├── optee_example_hello_world
│   ├── optee_example_hotp
│   ├── optee_example_random
│   ├── optee_example_secure_storage
│   ├── tee-supplicant
│   └── xtest
├── include
│   ├── tee_bench.h
│   ├── tee_client_api_extensions.h
│   ├── tee_client_api.h
│   └── teec_trace.h
├── lib
│   ├── ->
│   ├── ->
│   └──
│   └── optee_armtz
│       └── (...)                 # This directory was previously filled with TAs
└── sbin
    └── tee-supplicant -> ../bin/tee-supplicant

5 Update software on board[edit]

The OP-TEE OS boot images shall be loaded into the related partitions of the boot media.
The other OP-TEE images are stored in the target filesystem.

For example, if using an SD card as target boot media, the card can be plugged in its PC card reader and the images copied. OP-TEE core boot images can be loaded using tool dd while other files can be simply copied into the mounted rootfs.

5.1 Update OP-TEE Core Boot Partitions in an SD card[edit]

If booting the target from an SD card, the core OP-TEE firmware can be updated using the tool dd.
Plug the SD card into the computer slot reader and copy the binary to the dedicated partition; on an SDCard/USB disk the OP-TEE OS boot partitions are partition 4 to 6.

The target partition is located from the partition labels of the SD card, i.e:

 ls -l /dev/disk/by-partlabel/
total 0
lrwxrwxrwx 1 root root 10 Jan 28 16:35 bootfs -> ../../sdd7        (Linux kernel boot filesystem)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 fsbl1 -> ../../sdd1         (part#1 is TF-A)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 fsbl2 -> ../../sdd2         (part#2 is TF-A backup)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 rootfs -> ../../sdd9        (Linux kernel root filesystem)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 ssbl -> ../../sdd3          (part#3# is U-Boot)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 teed -> ../../sdd5          (OP-TEE OS paged data)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 teeh -> ../../sdd4          (OP-TEE OS header image)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 teex -> ../../sdd6          (OP-TEE OS resident core)
lrwxrwxrwx 1 root root 11 Jan 28 16:35 userfs -> ../../sdd10       (Linux kernel user filesystem)
lrwxrwxrwx 1 root root 10 Jan 28 16:35 vendorfs -> ../../sdd8      (Linux kernel vendor filesystem)

For the SD card described above, the 3 OP-TEE core images can then be updated with:

 dd conv=fdatasync of=/dev/sdd4 if=<optee-os>/out/core/tee-header_v2.stm32
 dd conv=fdatasync of=/dev/sdd5 if=<optee-os>/out/core/tee-pageable_v2.stm32
 dd conv=fdatasync of=/dev/sdd6 if=<optee-os>/out/core/tee-pager_v2.stm32 

5.2 Update OP-TEE Linux Files in a SD card[edit]

The OP-TEE files that need to be copied to the target filesystem were installed in a local directory ./target/.

They can now be copied to the target SD card rootfs partition once the SD card is plugged to the host computer and its filesystems are mounted in the host, i.e

 cp -ar target/* /media/$USERNAME/rootfs/

5.3 Update via USB mass storage on U-boot[edit]

See How to use USB mass storage in U-Boot and follow the previous sections to load binary files tee-*_v2.stm32 onto target partitions.

5.4 Update your boot device (including SD card on the target)[edit]

Refer to the STM32CubeProgrammer documentation to update your target.

6 References[edit]