[Cmake] different compiler in subdirs ?

[Eric Wing]

> From: "Alexander Neundorf"
> Subject: [Cmake] different compiler in subdirs ?
> 
> Hi, 
>
> I'd like to use cmake for cross-compiling. 
> What I would like to do is to have a big source
> tree, everything "managed" 
> by cmake, where in some directories stuff for the
> local machine is 
> compiled, but in some other directories sources for
> an embedded target get 
> compiled. Therefor in these directories not gcc
> should be used, but e.g 
> arm-elf-gcc and friends.  
> Is there a way to achieve this ? I didn't find a
> starting point for this 
> until now. 
>  
> Thanks in advance 
> Alex 


Hi, I'm hoping somebody else will address this
question too because I also have almost the exact same
situation (need to invoke a vxworks compiler).

But until I can figure out a better solution, I've
been trying two different things for the embedded
stuff (the non-embedded stuff can use CMake in a
normal manner). 

First, I tried building my own rules using
ADD_CUSTOM_TARGET, where I invoke the embedded
compiler directly with the flags I need. But one of
the problems I've been having though is a "make clean"
doesn't necessarily clean up the files. I've found a
little hack where if you make the target name the path
and name of the file generated, it seems to clean it
up. However, I don't know if there are any bad issues
I should be worried about. The other problem I have is
that our source tree is large and complicated enough
that I don't know all the dependencies, and using
ADD_CUSTOM_TARGET requires you to list all the
dependencies if you expect things to rebuild when, say
a header file is changed.

So more recently, I've been trying a more convoluted
system that will invoke a Makefile directly which uses
GNU make depend to generate the dependency information
for me and build the system directly. But one problem
I haven't figured out is how to always ensure Make is
invoked because CMake will only call it if it thinks a
listed dependency is changed. I suppose I can find
some unclean hack for this if I can't find a nice
elegant solution. Another one of the problems of
course is I risk losing portability. But since all the
different platforms I need to support (Solaris, Linux,
MacOS X) have gcc and GNU tools installed on them,
this is less of an issue for me. 

But another problem I have with this technique is once
again, cleaning up the files. Since I'm now invoking
make indirectly through CMake, calling make clean will
only clean CMake's normally generated files and will
miss everything generated in my embedded target
makefile. As far as I know, I can't add any
instructions to CMake's clean process. So I use
ADD_CUSTOM_TARGET to create a special target called
vxclean which will invoke a process to call my
embedded Makefiles' clean target. However, this won't
recursively clean all my subdirectories. So my target
actually invokes a custom Perl script that I wrote
which will recurse through the CMake build
subdirectories and invoke make clean. In the end, this
seems to work, but the user must remember to
explicitly call "make vxclean" to clean up the
embedded stuff.


Anyway, I hope this might get you started, but 
I would really appreciate hearing some other ideas
from others out there.

Thanks,
Eric