[CMake] One project, one platform, 2 compilers

[Paul Hansen]

Thank you very much for the answers, David and Michael.

I am trying to get a QNX compiler to work with CMake. My host comp runs
Ubuntu.
I did:

cmake -G "Unix Makefiles -D CMAKE_C_COMPILER=qcc -D CMAKE_CXX_COMPILER=QCC
..
but get
dpkg-architecture: warning: Couldn't determine gcc system type, falling
back to default (native compilation)
cc: unknown option: '-dumpmachine'

I have of course google'd and found out that I probably have to make a new
toolchain file.
Does that seem correct?

qcc is basicly gcc with modifications and other libraries.
Is there an example toolchain file I can use as basis?

Is there any documentation about what should be set up in a toolchain file?

Thank you very much
paul




On Fri, Nov 18, 2011 at 2:26 PM, Michael Hertling <mhertling at online.de>wrote:

> On 11/17/2011 05:18 PM, Paul Hansen wrote:
> > Hi
> >
> > I have a project that has to be compiled with two different compilers on
> > the same computer.
> >
> > Can I do that from the same CMakeLists.txt file?
>
> What do you mean exactly?
>
> (1) Compile the project twice, each time completely with a different
> compiler? If so, use two different build trees, as already outlined
> in the meantime.
>
> (2) A part of your project must be compiled with a different compiler
> than the remaining parts? Difficult - besides a custom-command-based
> approach, you might outsource the concerned part and reintegrate it
> as an external project which can be configured independently with a
> different toolchain. Look at the following example:
>
> # CMakeLists.txt:
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(MAIN C)
> SET(CMAKE_VERBOSE_MAKEFILE ON)
> SET(SUBCC ${CMAKE_C_COMPILER} CACHE FILEPATH "Subproject C compiler")
> INCLUDE(ExternalProject)
> ExternalProject_Add(sub
>    SOURCE_DIR ${CMAKE_SOURCE_DIR}/sub
>    CMAKE_CACHE_ARGS
>        -DCMAKE_C_COMPILER:FILEPATH=${SUBCC}
>        -DCMAKE_INSTALL_PREFIX:PATH=${CMAKE_BINARY_DIR}/sub)
> ADD_LIBRARY(f SHARED IMPORTED)
> SET_TARGET_PROPERTIES(f PROPERTIES
>    IMPORTED_LOCATION ${CMAKE_BINARY_DIR}/sub/lib/libf.so)
> ADD_DEPENDENCIES(f sub)
> FILE(WRITE ${CMAKE_BINARY_DIR}/main.c "int main(void){return 0;}\n")
> ADD_EXECUTABLE(main main.c)
> TARGET_LINK_LIBRARIES(main f)
> ADD_DEPENDENCIES(main f)
>
> sub/CMakeLists.txt:
> CMAKE_MINIMUM_REQUIRED(VERSION 2.8 FATAL_ERROR)
> PROJECT(SUB C)
> SET(CMAKE_VERBOSE_MAKEFILE ON)
> FILE(WRITE ${CMAKE_BINARY_DIR}/f.c "void f(void){}\n")
> ADD_LIBRARY(f SHARED f.c)
> INSTALL(TARGETS f LIBRARY DESTINATION lib)
>
> Configure with the desired SUBCC to see the subproject being built with
> that instead of the overall project's C compiler. The downside is that
> you can't use FIND_*() on the subproject's targets since they're built
> after the overall project is already configured, so you must predict
> their locations. Additionally, there may be issues w.r.t. the correct
> handling of dependencies. Moreover, if the subproject is to share the
> overall project's cache, you need to pass the concerned variables to
> ExternalProject_Add() individually, or do some trickery with LOAD_
> CACHE(). Alternatively, you might use the so-called super-build
> approach, but be prepared for other issues then, cf. [1].
>
> > Specifically I am wondering:
> > - CMake finds a compiler and makes a test. A colleague has tried to
> change
> > the compiler variables but CMake made the test and overwrote his settings
> > (from the CMakeLists.txt file) in CMakeCache.txt
>
> The toolchain can't be changed without a complete reconfiguration, and
> during the latter, CMake even forgets the cache settings specified on
> the command line, cf. [2].
>
> > - With target_link_directories I can point out specifically which
> libraries
> > should be used with each executable. But what about header files?
> > include_directories() is not specified for each executable. Is there
> anyway
> > to control what is in the include path at different points in the
> > CMakeLists.txt. I have tried to use set_directory_properties(PROPERTIES
> > INCLUDE_DIRECTORIES "") to reset include path at one point. The deletion
> > works but just not at that specific point on CMakeLists.txt.
>
> The INCLUDE_DIRECTORIES directory property is read-only.
>
> > - If split up into compiler1.cmake and compiler2.cmake I still get the
> > include_directories() problem since values are "inherited"
>
> In general, I'd recommend to invoke INCLUDE_DIRECTORIES() sufficiently
> deep within the CMakeLists.txt files' hierarchy to limit the scope of
> its impact. Possibly, you even need to reorganize your project a bit,
> i.e. split one CMakeLists.txt in two and have INCLUDE_DIRECTORIES()
> called for the latters with the correct directories separately.
>
> Regards,
>
> Michael
>
> [1] http://www.mail-archive.com/cmake@cmake.org/msg36170.html
> [2] http://www.mail-archive.com/cmake@cmake.org/msg37060.html
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