Building a library for use with RTEMS via CMake

[Michael Davidsaver]

On 7/19/21 6:17 AM, Andre.Nahrwold at dlr.de wrote:
> Hello,
> 
> I have built RTEMS 5 and its tools for the Xilinx Zynq Zedboard and installed the BSP and tools at a certain position on my machine.
> The tools are added to the PATH variable and RTEMS_BSPS is also available in the environment.
> 
> Now we need to build a library for the use with RTEMS via CMake.
> For this we wanted to use the toolchain files.
> Does anybody know how to correctly setup such a toolchain file using the RTEMS compiler?
> 
> We managed to get a toolchain file working which at least built the library.
> But when we wanted to link to this library during compilation of a RTEMS application we got a bunch of errors due to undefined references to standard library functions.
> Does anybody has a clue where this might origin from?

As it happens, I went through this exercise recently with libevent.
The main obstacle for me was that the CMake try_compile() command
actually tries to link an executable.  With RTEMS 5 this can't be
done generically without also adding '-lrtemsdefaultconfig'.

eg.

> string(APPEND CMAKE_EXE_LINKER_FLAGS_INIT " -lrtemsdefaultconfig")

Also, if you use networking you might want to add.

> set(CMAKE_REQUIRED_LIBRARIES "-lbsd")

for eg. CheckFunctionExists.cmake to work correctly.


The (fairly complex) result of this all can be found here:

https://github.com/mdavidsaver/pvxs/tree/master/bundle

The essential parts are:

- cmake/RTEMS.cmake@

Template toolchain file.  (expand using definitions from RTEMS makefiles)

- cmake/Platform/

Hooks into the CMake startup process.  The exact interplay between
Platform/ and toolchain file is... quite involved.  Also not well
documented.  The best I've found is:

https://github.com/Kitware/CMake/blob/f86d8009c6a4482c81221114a2b04b375564cc94/Source/cmGlobalGenerator.cxx#L461-L504



> Building a RTEMS application which does not use the own library works fine.
> 
> Our toolchain file looks like this:
> 
> # CMake toolchain file for ARM
> # The compiler is based on
> # The RTEMS_BSPS environment variable is expected to be set.
> set(ARCH arm)
> set(CMAKE_SYSTEM_NAME RTEMS5)
> 
> set(CMAKE_CXX_FLAGS "" CACHE STRING "ARM RTEMS5 gcc additional compiler flags" FORCE)
> 
> set(RTEMS_TOOLS_PATH $ENV{RTEMS_BSPS}/../../tools/bin)
> 
> set(CMAKE_C_COMPILER ${RTEMS_TOOLS_PATH}/arm-rtems5-gcc CACHE PATH "ARM RTEMS5 gcc" FORCE)
> set(CMAKE_CXX_COMPILER ${RTEMS_TOOLS_PATH}/arm-rtems5-gcc CACHE PATH "ARM RTEMS5 gcc" FORCE)
> set(CMAKE_CXX_COMPILER_AR ${RTEMS_TOOLS_PATH}/arm-rtems5-gcc-ar CACHE PATH "ARM RTEMS5 ar" FORCE)
> set(CMAKE_CXX_COMPILER_RANLIB ${RTEMS_TOOLS_PATH}/arm-rtems5-gcc-ranlib CACHE PATH "ARM RTEMS5 gcc ranlib" FORCE)
> set(CMAKE_RANLIB ${RTEMS_TOOLS_PATH}/arm-rtems5-ranlib CACHE PATH "ARM RTEMS5 ranlib" FORCE)
> set(CMAKE_READELF ${RTEMS_TOOLS_PATH}/arm-rtems5-readelf CACHE PATH "ARM RTEMS5 readelf" FORCE)
> set(CMAKE_STRIP ${RTEMS_TOOLS_PATH}/arm-rtems5-strip CACHE PATH "ARM RTEMS5 strip" FORCE)
> set(CMAKE_ADDR2LINE ${RTEMS_TOOLS_PATH}/arm-rtems5-addr2line CACHE PATH "ARM RTEMS5 addr2line" FORCE)
> set(CMAKE_LINKER ${RTEMS_TOOLS_PATH}/arm-rtems5-ld CACHE PATH "ARM RTEMS5 ld" FORCE)
> set(CMAKE_NM ${RTEMS_TOOLS_PATH}/arm-rtems5-nm CACHE PATH "ARM RTEMS5 nm" FORCE)
> set(CMAKE_OBJCOPY ${RTEMS_TOOLS_PATH}/arm-rtems5-objcopy CACHE PATH "ARM RTEMS5 objcopy" FORCE)
> set(CMAKE_OBJDUMP ${RTEMS_TOOLS_PATH}/arm-rtems5-objdump CACHE PATH "ARM RTEMS5 objdump" FORCE)
> 
> set(CMAKE_TARGET_CONFIG_POSTFIX .rtems5_gcc_arm)
> 
> Best regards
> Andre Nahrwold
> --------------------------
> Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR)
> German Aerospace Center
> Institute for Software Technolog | SRV-OSS BS | Lilienthalpl. 7 | 38108 Braunschweig | Geb. 112C Raum 001
> M.Sc. Andre Nahrwold | Telephone +49 531 295-3834 | andre.nahrwold at dlr.de
> DLR.de
> 
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