[CMake] Adding cross-compiler support to CMake ...

[William A. Hoffman]

At 02:39 AM 9/8/2006, Michael Casadevall wrote:
>I've been working on determining on how to do the platform part of this. My first guess is we could do something like this in the platform files:
>
>(from gcc.cmake)
>IF(CMAKE_COMPILER_IS_GNUCC)
>  SET (CMAKE_C_FLAGS_INIT "")
>  SET (CMAKE_C_FLAGS_DEBUG_INIT "-g")
>  SET (CMAKE_C_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
>  SET (CMAKE_C_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
>  SET (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
>  SET (CMAKE_C_CREATE_PREPROCESSED_SOURCE "<CMAKE_C_COMPILER> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
>  SET (CMAKE_C_CREATE_ASSEMBLY_SOURCE "<CMAKE_C_COMPILER> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
>ENDIF(CMAKE_COMPILER_IS_GNUCC)
>
>We could add something like this under it:
>IF(CROSS_COMPILING)
>IF(CMAKE_CROSSCOMPILER_IS_GNUCC)
>SET (CMAKE_CROSS_C_FLAGS_INIT "")
>   SET (CMAKE_CROSS_C_FLAGS_DEBUG_INIT "-g")
>SET (CMAKE_CROSS_C_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
>SET (CMAKE_CROSS_C_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
>SET (CMAKE_CROSS_C_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
>SET (CMAKE_CROSS_C_CREATE_PREPROCESSED_SOURCE "<CMAKE_CROSS_C_COMPILER> <FLAGS> -E <SOURCE> > <PREPROCESSED_SOURCE>")
>   SET (CMAKE_CROSS_C_CREATE_ASSEMBLY_SOURCE "<CMAKE_CROSS_C_COMPILER> <FLAGS> -S <SOURCE> -o <ASSEMBLY_SOURCE>")
>ENDIF(CMAKE_COMPILER_IS_GNUCC)
>ENDIF(CROSS_COMPILING)
>
>Now this isn't ideal because it means adding quite a bit of information to each platform file, but its also very powerful because there cases where you don't want the platform to be same. For instance, if you were cross-compiling to Mac OS X, your not going to want Universial Binary settings there since (to my knowledge), it's nearly impossible to do that.
>
>Now, we also need a way to denote if a tool should be built natively, or if it should both built natively or crosscompiled, We could go to ADD_EXECUTABLE, and friends, and add a switch. NATIVE|BOTH. Native would build the tool with the local tool-chain instead of cross-compiler, and both would, obviously enough, compile both for native and cross. This is a fairly large change, so at the moment, I was hoping some of the CMake developers could give so more input on their opinions.
>
>Finally, in regards to systems that cross-compile packages often (like OpenEmbedded or only of the many firmware packages for the Linkssy WRT54G(S)), it should be as easy to setup cross-compiling from the command line as it is for ./configure. I also believe a few distributions cross-compile their packages (I believe debian does this with their builddd system, but I don't really know for sure). It should be like this:
>
>cmake -DCROSS_COMPILE_HOST=armvt5eb-unknown-linux
>
>which is comparable to:
>./configure --host=armvt5eb-unknown-linux
>
>I'm aware that CMake doesn't really use the *arch*-*vendor*-*platform* style, but it does have variables for them. The hardest part will be figuring out which platform file to load at compile time. It doesn't seem we can have a multiple choice thing in so I'm interested in any ideas.
>
>For those unfamiliar with cross-compilers, GCC will build with a name like this, which should be the default when cross-compilng:
>*host*-*vendor*-*style*-gcc
>*host*-*vendor*-*style*-g++
>etc.
>Michael

Are we sure that we need both compilers?   I mean do we need a CMAKE_C_COMPILER and
a CMAKE_C_CROSS_COMPILER?   Did you see my idea of running cmake twice on the same
tree, and creating a local and host build tree?   So, we use the same variables
and makefile generator that we have now, just run everything twice, and create two
build trees, the local one would have all targets marked local or both, and the
target one would have all targets marked as target or both.   If an executable is
referenced for use at build time, cmake would get it out of the local tree.

So, cmake -DCROSS_COMPILE_HOST=xxxx would create:

local/CMakeFiles/Makefile
target/CMakeFiles/Makefile
And a top level makefile that would navigate both of the trees.


-Bill