Re: EPICS compilation for gcc and clang

["Johnson, Andrew N. via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Philipp,

Welcome to the EPICS community!

On Jul 20, 2021, at 10:34 AM, Philipp Kampmann via Tech-talk <tech-talk at aps.anl.gov> wrote:

I am relatively new to EPICS and in our project we would like to share
some software variables via EPICS. Therefore I implemented a first
version of channel access interface using the cadef.h header, which
works well in one program we are using, which uses only gcc to compile.

However, another program uses partially clang (as part of the
CERN-ROOT-libraries if someone is familiar) to compile, which gives me
the error:

In file included from
/home/philipp/software/EPICS/epics-base/include/cadef.h:40:
In file included from
/home/philipp/software/EPICS/epics-base/include/epicsThread.h:131:
In file included from
/home/philipp/software/EPICS/epics-base/include/epicsMutex.h:13:
In file included from
/home/philipp/software/EPICS/epics-base/include/epicsAssert.h:20:
In file included from
/home/philipp/software/EPICS/epics-base/include/compilerDependencies.h:19:
/home/philipp/software/EPICS/epics-base/include/compiler/gcc/compilerSpecific.h:24:5:
error: compiler/gcc/compilerSpecific.h is not for use with the clang
compiler

A corresponding "compiler/clang" path does not exist in my build. I
would like to compile epics headers with both, g++ and clang. Does
someone know if it works and how I can build EPICS with both compilers
supported?

I am using EPICS version 3.15 here.

Assuming your EPICS_HOST_ARCH is linux-x86_64 you can switch the compiler that EPICS uses from gcc to clang by editing the file base-3.15/configure/os/CONFIG_SITE.Common.linux-x86_64 and following the instructions in the comments there. However as Lewis just pointed out there might be problems with mixing the two different compilers, because the CA library is coded in C++ even though its API is pure C. Apparently on x64 both compilers adhere to an Itanium standard ABI for name mangling, but that doesn’t guarantee that they’ll be compatible.

I can suggest two solutions to avoid that problem, one simpler than the other. The easy one is to have a second installation of EPICS Base that was built using clang (follow the directions above to switch the compiler for the second one). Alternatively it is possible to build the libraries for both into the same installation of Base, but you would have to create and use a different EPICS_HOST_ARCH which should be named linux-x86_64-clang for the second one which requires adding 2 or 3 new files to your configure/os directory – if you want to go this route I can help you to do that.

HTH,

- Andrew

-- 

Complexity comes for free, simplicity you have to work for.