Sandbox tests

Test Design

Most uclasses and many functions of U-Boot have sandbox tests. This allows much of the code to be checked in an developer-friendly environment.

Sandbox provides a way to write and run unit tests. The traditional approach to unit tests is to build lots of little executables, one for each test or category of tests. With sandbox, so far as possible, all the tests share a small number of executables (e.g. ‘u-boot’ for sandbox, ‘u-boot-spl’ and ‘u-boot’ for sandbox_spl) and can be run very quickly. The vast majority of tests can run on the ‘sandbox’ build,

Available tests

Some of the available tests are:

  • command_ut: Unit tests for command parsing and handling

  • compression: Unit tests for U-Boot’s compression algorithms, useful for

    security checking. It supports gzip, bzip2, lzma and lzo.

  • image: Unit tests for images:

    • test/image/ - multi-file images

    • test/py/tests/ - FIT images

  • tracing: test/trace/ tests the tracing system (see


  • verified boot: test/py/tests/

If you change or enhance any U-Boot subsystem, you should write or expand a test and include it with your patch series submission. Test coverage in some older areas of U-Boot is still somewhat limited and we need to work to improve it.

Note that many of these tests are implemented as commands which you can run natively on your board if desired (and enabled).

To run all tests, use ‘make check’.

Running sandbox tests directly

Typically tests are run using the pytest suite. Running pytests on sandbox is easy and always gets things right. For example some tests require files to be set up before they can work.

But it is also possible to run some sandbox tests directly. For example, this runs the dm_test_gpio() test which you can find in test/dm/gpio.c:

$ ./u-boot -T -c "ut dm gpio"

U-Boot 2021.01

Model: sandbox
DRAM:  128 MiB
WDT:   Started with servicing (60s timeout)
MMC:   mmc2: 2 (SD), mmc1: 1 (SD), mmc0: 0 (SD)
In:    serial
Out:   vidconsole
Err:   vidconsole
Model: sandbox
Net:   eth0: eth@10002000, eth5: eth@10003000, eth3: sbe5, eth6: eth@10004000
Test: dm_test_gpio: gpio.c
Test: dm_test_gpio: gpio.c (flat tree)
Failures: 0

The -T option tells the U-Boot sandbox to run with the ‘test’ devicetree (test.dts) instead of -D which selects the normal sandbox.dts - this is necessary because many tests rely on nodes or properties in the test devicetree. If you try running tests without -T then you may see failures, like:

$ ./u-boot -c "ut dm gpio"

U-Boot 2021.01

DRAM:  128 MiB
WDT:   Not found!
In:    serial
Out:   serial
Err:   serial
Net:   No ethernet found.
Please run with test device tree:
    ./u-boot -d arch/sandbox/dts/test.dtb
Test: dm_test_gpio: gpio.c
test/dm/gpio.c:37, dm_test_gpio(): 0 == gpio_lookup_name("b4", &dev, &offset, &gpio): Expected 0x0 (0), got 0xffffffea (-22)
Test: dm_test_gpio: gpio.c (flat tree)
test/dm/gpio.c:37, dm_test_gpio(): 0 == gpio_lookup_name("b4", &dev, &offset, &gpio): Expected 0x0 (0), got 0xffffffea (-22)
Failures: 2

The message above should provide a hint if you forget to use the -T flag. Even running with -D will produce different results.

You can easily use gdb on these tests, without needing –gdbserver:

$ gdb --args u-boot -T -c "ut dm gpio"
(gdb) break dm_test_gpio
Breakpoint 1 at 0x1415bd: file test/dm/gpio.c, line 37.
(gdb) run -T -c "ut dm gpio"
Starting program: u-boot -T -c "ut dm gpio"
Test: dm_test_gpio: gpio.c

Breakpoint 1, dm_test_gpio (uts=0x5555558029a0 <global_dm_test_state>)
    at files/test/dm/gpio.c:37
37           ut_assertok(gpio_lookup_name("b4", &dev, &offset, &gpio));

You can then single-step and look at variables as needed.

Running tests multiple times

Some tests can have race conditions which are hard to detect on a single one. It is possible to run each individual test multiple times, before moving to the next test, with the ‘-r’ flag.

This is most useful when running a single test, since running all tests multiple times can take a while.

For example:

=> ut dm -r1000 dm_test_rtc_set_get
Test: dm_test_rtc_set_get: rtc.c (flat tree)
Test: dm_test_rtc_set_get: rtc.c
test/dm/rtc.c:257, dm_test_rtc_reset(): old_base_time == base_time: Expected 0x62e7453c (1659323708), got 0x62e7453d (1659323709)
Test: dm_test_rtc_set_get: rtc.c (flat tree)
Test: dm_test_rtc_set_get: rtc.c
Test: dm_test_rtc_set_get: rtc.c (flat tree)
Test dm_test_rtc_reset failed 3 times

Isolating a test that breaks another

When running unit tests, some may have side effects which cause a subsequent test to break. This can sometimes be seen when using ‘ut dm’ or similar.

You can use the -I argument to the ut command to isolate this problem. First use ut info to see how many tests there are, then use a binary search to home in on the problem. Note that you might need to restart U-Boot after each iteration, so the -c argument to U-Boot is useful.

For example, let’s stay that dm_test_host() is failing:

=> ut dm
Test: dm_test_get_stats: core.c
Test: dm_test_get_stats: core.c (flat tree)
Test: dm_test_host: host.c
test/dm/host.c:71, dm_test_host(): 0 == ut_check_delta(mem_start): Expected 0x0 (0), got 0xffffcbb0 (-13392)
Test: dm_test_host: host.c (flat tree)
Test <NULL> failed 1 times
Test: dm_test_host_dup: host.c
Test: dm_test_host_dup: host.c (flat tree)

You can then tell U-Boot to run the failing test at different points in the sequence:

=> ut info Test suites: 21 Total tests: 645

$ ./u-boot -T -c "ut dm -I300:dm_test_host"
Test: dm_test_pinctrl_single: pinmux.c (flat tree)
Test: dm_test_host: host.c
test/dm/host.c:71, dm_test_host(): 0 == ut_check_delta(mem_start): Expected 0x0 (0), got 0xfffffdb0 (-592)
Test: dm_test_host: host.c (flat tree)
Test dm_test_host failed 1 times (position 300)
Failures: 4

So it happened before position 300. Trying 150 shows it failing, so we try 75:

$ ./u-boot  -T  -c "ut dm -I75:dm_test_host"
Test: dm_test_autoprobe: core.c
Test: dm_test_autoprobe: core.c (flat tree)
Test: dm_test_host: host.c
Test: dm_test_host: host.c (flat tree)
Failures: 0

That succeeds, so we try 120, etc. until eventually we can figure out that the problem first happens at position 82.

$ ./u-boot -T -c “ut dm -I82:dm_test_host” … Test: dm_test_blk_flags: blk.c Test: dm_test_blk_flags: blk.c (flat tree) Test: dm_test_host: host.c test/dm/host.c:71, dm_test_host(): 0 == ut_check_delta(mem_start): Expected 0x0 (0), got 0xffffc960 (-13984) Test: dm_test_host: host.c (flat tree) Test dm_test_host failed 1 times (position 82) Failures: 1

From this we can deduce that dm_test_blk_flags() causes the problem with dm_test_host().

Running sandbox_spl tests directly

SPL is the phase before U-Boot proper. It is present in the sandbox_spl build, so you can run SPL like this:


SPL tests are special in that they run (only in the SPL phase, of course) if the -u flag is given:

./spl/u-boot-spl -u

U-Boot SPL 2021.01-00723-g43c77b51be5-dirty (Jan 24 2021 - 16:38:24 -0700)
Running 5 driver model tests
Test: dm_test_of_plat_base: of_platdata.c (flat tree)
Test: dm_test_of_plat_dev: of_platdata.c (flat tree)
Test: dm_test_of_plat_parent: of_platdata.c (flat tree)
Test: dm_test_of_plat_phandle: of_platdata.c (flat tree)
Test: dm_test_of_plat_props: of_platdata.c (flat tree)
Failures: 0

U-Boot 2021.01-00723-g43c77b51be5-dirty (Jan 24 2021 - 16:38:24 -0700)

DRAM:  128 MiB

It is not possible to run SPL tests in U-Boot proper, firstly because they are not built into U-Boot proper and secondly because the environment is very different, e.g. some SPL tests rely on of-platdata which is only available in SPL.

Note that after running, SPL continues to boot into U-Boot proper. You can add ‘-c exit’ to make U-Boot quit without doing anything further. It is not currently possible to run SPL tests and then stop, since the pytests require that U-Boot produces the expected banner.

You can use the -k flag to select which tests run:

./spl/u-boot-spl -u -k dm_test_of_plat_parent

Of course you can use gdb with sandbox_spl, just as with sandbox.

Running all tests directly

A fast way to run all sandbox tests is:

./u-boot -T -c "ut all"

It typically runs single-thread in 6 seconds on 2021 hardware, with 2s of that to the delays in the time test.

This should not be considered a substitute for ‘make check’, but can be helpful for git bisect, etc.

What tests are built in?

Whatever sandbox build is used, which tests are present is determined by which source files are built. For sandbox_spl, the of_platdata tests are built because of the build rule in test/dm/Makefile:

ifeq ($(CONFIG_SPL_BUILD),y)
obj-$(CONFIG_SPL_OF_PLATDATA) += of_platdata.o
...other tests for non-spl

You can get a list of tests in a U-Boot ELF file by looking for the linker_list:

$ nm /tmp/b/sandbox_spl/spl/u-boot-spl |grep 2_dm_test
000000000001f200 D _u_boot_list_2_dm_test_2_dm_test_of_plat_base
000000000001f220 D _u_boot_list_2_dm_test_2_dm_test_of_plat_dev
000000000001f240 D _u_boot_list_2_dm_test_2_dm_test_of_plat_parent
000000000001f260 D _u_boot_list_2_dm_test_2_dm_test_of_plat_phandle
000000000001f280 D _u_boot_list_2_dm_test_2_dm_test_of_plat_props

Writing tests

See Writing Tests for how to write new tests.