[Buildroot] What is the preferred way install additional cmake modules?

[Buildroot] What is the preferred way install additional cmake modules?

[Zoltan Gyarmati]

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Dear All,

i am about to add the modemmanager-qt[1] package to Buildroot, which
for building depends on a set of additional cmake modules also
provided by the KDE project, called extra-cmake-modules[2], which
itself also uses cmake for building and installing.

 I managed to set up a working configuration to install the
extra-cmake-modules package with the following in my
extra-cmake-modules/extra-cmake-modules.mk file (_VERSION and other
variables are omitted here):


EXTRA_CMAKE_MODULES_INSTALL_STAGING = YES
EXTRA_CMAKE_MODULES_INSTALL_TARGET = NO

$(eval $(cmake-package))


and in my target package i add the 'extra-cmake-modules' to the
dependencies. In this case the .cmake files get installed in the

path-to-buildroot/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/us
r/share/ECM/cmake/

directory.

 My instinct would say that extra-cmake-modules is supposed to be a
host package (as then i wouldn't need to explicitly set
EXTRA_CMAKE_MODULES_INSTALL_TARGET to NO), so i tried this to define
as a host-cmake-package, make modemmanager-qt depending on
host-extra-cmake-modules, but then the cmake modules not found by the
modemmanager-qt build config.

In this latter case the .cmake files gets installed under:
path-to-buildroot/output/host/usr/share/ECM/cmake/


What is the preferred way to install this package? Install it as a
host-package, and specify a custom install target dir, or leave it as
plain cmake-package?



Thanks, regards
zgyarmati


[1]
https://projects.kde.org/projects/frameworks/modemmanager-qt/repository

[2] https://projects.kde.org/projects/kdesupport/extra-cmake-modules
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[Buildroot] What is the preferred way install additional cmake modules?

[Yann E. MORIN]

Zoltan, All,

On 2015-10-20 18:52 +0200, Zoltan Gyarmati spake thusly:
> i am about to add the modemmanager-qt[1] package to Buildroot, which
> for building depends on a set of additional cmake modules also
> provided by the KDE project, called extra-cmake-modules[2], which
> itself also uses cmake for building and installing.
[--SNIP--]
>  My instinct would say that extra-cmake-modules is supposed to be a
> host package

My instinct says so, too. ;-)

> (as then i wouldn't need to explicitly set
> EXTRA_CMAKE_MODULES_INSTALL_TARGET to NO), so i tried this to define
> as a host-cmake-package, make modemmanager-qt depending on
> host-extra-cmake-modules, but then the cmake modules not found by the
> modemmanager-qt build config.

So:
  - if extra-cmake-modules are in staging/ then it works
  - if extra-cmake-modules are in host/ then it does not work

But what is not found? The ECM files themselves? Can you paste the few
lines that exhibit the error, please?

> In this latter case the .cmake files gets installed under:
> path-to-buildroot/output/host/usr/share/ECM/cmake/

I would have indeed expected to see them installed there.

> What is the preferred way to install this package? Install it as a
> host-package, and specify a custom install target dir, or leave it as
> plain cmake-package?

My stance:
  - it is a host-package

We need to understand why cmake can't find those modules.

I CCed Samuel, our cmake expert, so he can shine some light on this.

Regards,
Yann E. MORIN.

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[Buildroot] What is the preferred way install additional cmake modules?

[Samuel Martin]

Hi Zoltan, Yann, all,

On Tue, Oct 20, 2015 at 8:54 PM, Yann E. MORIN <yann.morin.1998@free.fr> wrote:
> Zoltan, All,
>
> On 2015-10-20 18:52 +0200, Zoltan Gyarmati spake thusly:
>> i am about to add the modemmanager-qt[1] package to Buildroot, which
>> for building depends on a set of additional cmake modules also
>> provided by the KDE project, called extra-cmake-modules[2], which
>> itself also uses cmake for building and installing.
> [--SNIP--]
>>  My instinct would say that extra-cmake-modules is supposed to be a
>> host package
>
> My instinct says so, too. ;-)
>
>> (as then i wouldn't need to explicitly set
>> EXTRA_CMAKE_MODULES_INSTALL_TARGET to NO), so i tried this to define
>> as a host-cmake-package, make modemmanager-qt depending on
>> host-extra-cmake-modules, but then the cmake modules not found by the
>> modemmanager-qt build config.
>
> So:
>   - if extra-cmake-modules are in staging/ then it works
>   - if extra-cmake-modules are in host/ then it does not work
>
> But what is not found? The ECM files themselves? Can you paste the few
> lines that exhibit the error, please?

The CMake module files installed by ECM, when configuring a target package.

As explained in [1] (in the second half of the page), CMake
(find_package) looks into a series of paths to find the modules.
The prefix of these paths is sensitive to the CMAKE_SYSROOT variable,
that's why modules installed in the host/ are not found when
configuring some package for cross-compilation.

My understanding behind this behavior is that CMake does not trust too
much 3rd-party modules.
I mean CMake has no way to know:
- that modules located in <buildroot>/output/host/usr/share/ECM/cmake/
are only for the host or for target;
- that <buildroot>/output/host/usr/share/ECM/cmake/ is a collection of
modules specially written to extend to default collection;
- if a 3rd-party module would contain absolute paths to the
libraries/programs/headers/etc, so stuff not compiled for the target.

So, CMake just assumes that everything that is for the target should
be located in the sysroot. That's a safe way IMHO;

(Side note: For pkg-config, it is the same we look for *.pc in host/
for when building for the host, and in staging/ for target, the only
difference is that it does not comes with a lot of *.pc files.)

>
>> In this latter case the .cmake files gets installed under:
>> path-to-buildroot/output/host/usr/share/ECM/cmake/
>
> I would have indeed expected to see them installed there.
>
>> What is the preferred way to install this package? Install it as a
>> host-package, and specify a custom install target dir, or leave it as
>> plain cmake-package?
>
> My stance:
>   - it is a host-package

I second.
I worked on something similar a while ago, and I ended up with a hack
I'm not really proud of: line 15 in [2] (the ugly symlink).

Another way to do this more properly is using
CMAKE_FIND_ROOT_PATH_MODE_PACKAGE [3], like this [4].
But this solution does not prevent from badly written module with
absolute paths (pointing to some host binaries).
This may be caught later during the build by the poison paths
detection, but I doubt it can spot paths to the paths like
<output>/host/usr/lib/; can it?

>
> We need to understand why cmake can't find those modules.
>
> I CCed Samuel, our cmake expert, so he can shine some light on this.

Hope this help! ;-)


[1] https://cmake.org/cmake/help/v3.3/command/find_package.html?highlight=find_package
[2] https://github.com/tSed/buildroot-2/commit/2f5c52bfc8da80461d589efa97898b51ab42021b
[3] https://cmake.org/cmake/help/v3.3/variable/CMAKE_FIND_ROOT_PATH_MODE_PACKAGE.html
[4] http://code.bulix.org/h0jy9o-89332

Regards,

-- 
Samuel

[Buildroot] Poison $(HOST_DIR)/usr/lib [was: Re: What is the preferred way install additional cmake modules?]

[Arnout Vandecappelle]

On 20-10-15 22:43, Samuel Martin wrote:
[snip]
> But this solution does not prevent from badly written module with
> absolute paths (pointing to some host binaries).
> This may be caught later during the build by the poison paths
> detection, but I doubt it can spot paths to the paths like
> <output>/host/usr/lib/; can it?

 It can't, but it probably should, since that is equally bad as /usr/lib.

 Regards,
 Arnout

[snip]

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