Re: selftests/bpf doesn't compile

From: Shuah Khan
Date: Fri Sep 15 2017 - 13:00:48 EST

On 09/15/2017 10:02 AM, Alexei Starovoitov wrote:
> On Thu, Sep 14, 2017 at 09:33:48AM -0600, Shuah Khan wrote:
>> Hi Alexei and Daniel,
>> bpf test depends on clang and fails to compile when
>> ------------------------------------------------------
>> make -C tools/testing/selftests/bpf run_tests
>> make: clang: Command not found
>> Makefile:39: recipe for target '.linux-kselftest/tools/testing/selftests/bpf/test_pkt_access.o' failed
>> make: *** [./linux-kselftest/tools/testing/selftests/bpf/test_pkt_access.o] Error 127
>> make: Leaving directory '.linux-kselftest/tools/testing/selftests/bpf'
>> With "make TARGETS=bpf kselftest" it fails earlier:
>> make[3]: Entering directory './linux-kselftest/tools/lib/bpf'
>> Makefile:40: tools/scripts/Makefile.arch: No such file or directory
>> Makefile:84: tools/build/Makefile.feature: No such file or directory
>> Makefile:143: tools/build/Makefile.include: No such file or directory
>> make[3]: *** No rule to make target 'tools/build/Makefile.include'. Stop.
>> make[3]: Leaving directory '.linux-kselftest/tools/lib/bpf'
>> Makefile:34: recipe for target './linux-kselftest/tools/testing/selftests/bpf/libbpf.a' failed
>> make[2]: *** [./linux-kselftest/tools/testing/selftests/bpf/libbpf.a] Error 2
>> make[2]: Leaving directory './linux-kselftest/tools/testing/selftests/bpf'
>> Makefile:69: recipe for target 'all' failed
>> make[1]: *** [all] Error 2
>> Makefile:1190: recipe for target 'kselftest' failed
>> make: *** [kselftest] Error 2
>> --------------------------------------------------------------
>> Is bpf test intended to be run in kselftest run? The clang dependency might
>> not be met on majority of the systems. Is this a hard dependency??
> It is a hard dependency and clang should be present on majority of the systems.
> More details are in samples/bpf/README.rst
> which was written long ago. Nowadays apt-get/yum will install clang
> with bpf support builtin.

Thanks for the clarification.

>> Would it make sense to create a special target for bpf test? We do have a few
>> tests that do that now.
>> TARGETS_HOTPLUG = cpu-hotplug
>> TARGETS_HOTPLUG += memory-hotplug
>> I could add a special target for bpf TARGET_BPF perhaps and exclude it from
>> the run_test>
> I'm not sure what was the motivation to exclude hotplug from default testing,

These are considered a bit more disruptive and were excluded a while
back. These take cpus and memory on and off-line. Also require
root access. So even if they are included in the regular run, these
won't run.

> since I think it diminishes the value of selftests overall.

I agree. We do have some timer tests that are destructive/stress that
et run using a special target. It is the idea that if somebody wants
to test all them, there is a way to do that.

In any case, I didn't think bpf falls into this category of tests that
belong in the destructive category. I am looking to understand the failures
and your take on those.

> Not running all tests all the time risks breaking them
It is balance of providing a choice to users if they don't want to
run destructive tests. For example, suspend test which requires root
access. So the idea is for users to run these by choice as opposed
to running them in the normal run and cause disruption.

> selftest makefile refactoring broke selftests/bpf in the past,

Yeah. We have had some fallout from the KBUILD_OUTPUT work that didn't
take all the use-cases into account and tests that require custom
builds such as the bpf tests. Using common build infrastructure doesn't
work for all tests.

Looks like there are other patches that went in later with lcap work.

> so I strongly suggest to install clang and make sure the tests are passing
> on the test servers

You will have to request kernelci, stable, and It is a choice to be made by
kernelci/zero-day folks.

otherwise we'd need to move selftests/bpf out of
> selftests to avoid further headaches for us when selftests infra keeps
> changing.

Let's not go to extreme options. :) I am merely looking for more information
and trying to understand the dependencies for this test.

Let's look for a constructive option to fix the build failures I am seeing.

The first failure due to clang dependency is not a problem. The second one
in the case of "make kselftest" is the one that requires some work when bpf
make is run from the main Makefile. A lots of users run tests using the
kselftest target from the mail Makefile. hence I would like to get this
working, so it would be easier to run this test on test servers.

-- Shuah