[cmake-developers] [PATCH 3/3] FindQt4: document cross compilation

[Pascal Bach]

Am 30.07.2015 um 17:20 schrieb Clinton Stimpson:
> On Thursday, July 30, 2015 10:56:02 AM Brad King wrote:
>> On 07/30/2015 09:29 AM, Pascal Bach wrote:
>>> CMAKE_FIND_ROOT_PATH_MODE would then need to be extended to support
>>> something like NATIVE and TARGET that one could use to choose where
>>> to look for files.
>>> This way every find_* call could explicitly tell if it wants a host
>>> or a target version.
>> Are you proposing new keyword arguments to find_* commands to specify
>> this?  The problem is that find modules don't necessarily know which
>> kind of binary the application wants.  That is why we have the
>> CMAKE_FIND_ROOT_PATH_MODE_<type> variables.
>>
>> The existing CMAKE_FIND_ROOT_PATH* and CMAKE_SYSROOT options have been
>> sufficient for most packages for a long time.  We regularly get
>> complaints that FindPythonLibs does not ask the python executable
>> where to get its libraries, and our answer every time is that it is
>> wrong to do that for cross compiling.  FindQt4 is making that mistake,
>> and that is the cause of these troubles.
>>
>> FindQt4 should be taught not to ask qmake for anything when cross
>> compiling.
> FindQt4 supports 2 use cases when cross compiling.
>
> 1. One Qt installation with a mix of native and non-native files.
>
> 2. Two Qt installations, one native and one non-native.  In this case, qmake 
> may still be queried to find other tools, but CMAKE_FIND_ROOT_PATH is used to 
> find the non-native includes and libraries.
>
> The second case is what you are asking for, right?
Yes case 2 is exactly what Yocto does, one qt-native and one qt-target.
There might also be a third installation from the host machine (installed via apt-get for example).

I need to check if I can modify FindQt4 to not use qmake for libary and header finding if CROSS_COMPILING is set.
But just rely on plain find_* commands.
>
> This why I previously suggested changing 
> from
> SET(CMAKE_FIND_ROOT_PATH /sysroot/arm ...)
> to 
> SET(CMAKE_FIND_ROOT_PATH /sysroot/arm/usr ...)
I could not get this to work.
It seems that the variables returned by qmake take priority over everything else.

Pascal

>
> Because its a find root, not a sysroot.
>