Re: cross-compiling vm, confusion over output directory

[shuah <shuah@kernel.org>]

Hi Tim,

You are using an ancient email address for me.

Use either shuah@kernel.org or skhan@linuxfoundation.org

On 3/13/20 4:14 PM, Bird, Tim wrote:
> I was working on fixing the cross-compilation for the selftests/vm tests.
> Currently, there are two issues in my testing:
> 
> 1) problem: required library missing from some cross-compile environments:
> tools/testing/selftests/vm/mlock-random-test.c requires libcap
> be installed.  The target line for mlock-random-test in
> tools/testing/selftests/vm/Makefile looks like this:
> 
> $(OUTPUT)/mlock-random-test: LDLIBS += -lcap

You can use TEST_GEN_PROGS and define LDFLAGS for lcap

> 
> and mlock-random-test.c has this include line:
> #include <sys/capability.h>
> 
> this is confusing, since this is different from the header file
> linux/capability.h.  It is associated with the capability library (libcap)
> and not the kernel.  In any event, on some distros and in some
> cross-compile SDKs the package containing these files is not installed
> by default.
> 
> Once this library is installed, things progress farther.  Using an Ubuntu
> system, you can install the cross version of this library (for arm64) by doing:
> $ sudo apt install libcap-dev:arm64
> 
> 1) solution:
> I would like to add some meta-data about this build dependency, by putting
> something in the settings file as a hint to CI build systems.  Specifically, I'd like to
> create the file 'tools/testing/selftests/vm/settings', with the content:
> NEED_LIB=cap
> 
> We already use settings for other meta-data about a test (right now, just a
> non-default timeout value), but I don't want to create a new file or syntax
> for this build dependency data.
> 
> Let me know what you think.
> 
> I may follow up with some script in the kernel source tree to check these
> dependencies, independent of any CI system.  I have such a script in Fuego
> that I could submit, but it would need some work to fit into the kernel build
> flow for kselftest.  The goal would be to provide a nicely formatted warning,
> with a recommendation for a package install.  But that's more work than
> I think is needed right now just to let developers know there's a build dependency
> here.
> 
> 2) problem: reference to source-relative header file
> the Makefile for vm uses a relative path for include directories.
> Specifically, it has the line:
> CFLAGS = -Wall -I ../../../../../usr/include $(EXTRA_CFLAGS)
> 
> I believe this needs to reference kernel include files from the
> output directory, not the source directory.
> 
> With the relative include directory path, the program userfaultfd.c
> gets compilation error like this:
> 
> userfaultfd.c:267:21: error: 'UFFD_API_RANGE_IOCTLS_BASIC' undeclared here (not in a function)
>    .expected_ioctls = UFFD_API_RANGE_IOCTLS_BASIC,
>                       ^
> userfaultfd.c: In function 'uffd_poll_thread':
> userfaultfd.c:529:8: error: 'UFFD_EVENT_FORK' undeclared (first use in this function)
>     case UFFD_EVENT_FORK:
>          ^
> userfaultfd.c:529:8: note: each undeclared identifier is reported only once for each function it appears in
> userfaultfd.c:531:18: error: 'union <anonymous>' has no member named 'fork'
>      uffd = msg.arg.fork.ufd;
>                    ^
> 
> 2) incomplete solution:
> I originally changed this line to read:
> CFLAGS = -Wall -I $(KBUILD_OUTPUT)/usr/include $(EXTRA_CFLAGS)
> 

Take a look at seccomp patch I sent out. Use the approach used
in this patch.

https://lore.kernel.org/linux-kselftest/20200313212404.24552-1-skhan@linuxfoundation.org/T/#u

> This works when the output directory is specified using KBUILD_OUTPUT,
> but not when the output directory is specified using O=
> I'm not sure what happens when the output directory is specified
> with a non-source-tree current working directory.
> 
> In any event, while researching a proper solution to this, I found
> the following in tools/testing/selftests/Makefile:
> 
> If compiling with ifneq ($(O),)
>      BUILD := $(O)
> else
>      ifneq ($(KBUILD_OUTPUT),)
>          BUILD := $(KBUILD_OUTPUT)/kselftest
>      else
>          BUILD := $(shell pwd)
>          DEFAULT_INSTALL_HDR_PATH := 1
>      endif
> endif
> 
> This doesn't seem right.  It looks like the selftests Makefile treats a directory
> passed in using O= different from one specified using KBUILD_OUTPUT
> or the current working directory.
> In the KBUILD_OUTPUT case, you get an extra 'kselftest' directory layer
> that you don't get for the other two.

Are you using

git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git 
kernelci branch

This is fixed and that is the very first patch I sent.

I also applied the patch to

git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git next 
branch

thanks,
-- Shuah