Dear FPC colleagues,
I'm reporting some experience matured with FPC under Linux, hoping that it will provide useful hints for fututre development directions. Recently, as Michael Van Canneyt knows very well (since I have been helped very much by him), my team has experimented a Linux porting of the Dynamic Electrical Power Simulator (SICRE,
http://WWW.CESI.IT/services/psa/psw/sicre/index.cfm). The original software is written for HP-UX 9000 machine, but automatic converter procedures supplies versions for Digital-OSF (now Compaq-TRU64), AIX-RS6000 and now partially also for Linux. The code is written in different languages. The simulation engine (consisting in about 2500 files, more than 50000 lines of code) is written essentially in Apollo Pascal with something in Fortran and C; the automatic procedures essentially translate the Apollo Pascal into the Pascals for the other target machines and in particular for FreePacal in Linux. The Human Machine Iterface (some thousands of files, 70000 lines of code) is written essentially in C++ (plus Motif+X libraries) but links and includes the Pascal code in order to share database structures. In the past, above all for the lack of standardisation of Pascal, we examined the possibility to port all the Pascal code into C code, using some automatic translator. Problems related to the readability of the translated code and to the lack of reliable automatic Pascal2C translators discouraged us to do this. Essentially today we consider the Pascal code as a "elite" code (even if Pascal is a very good language, much better then C) to be linked as a library with other C/C++ codes that can guarantee standardisation. But to make this kind of use, Pascal compilers should provide code very open and flexible. In particular we experimented difficulty in solving some problems caused by the constraints today imposed by FreePascal. As Michael knows, as far as today some of this problems remain unresolved. In order to provide a useful feedback from a very fruitful experience (and obviously hoping in your future considerations of such issues) I tried to make a list of the major difficulties:
- C (using gcc) main programs including (linking) Pascal code. The problem is that it is not possible to use a FPC object file (or library) into a C-main program (problems related to initialization/finalization of units, even if we didn't use any and code including "writeln"). This problem has been solved in a non elegant way, simply supplying a Pascal-shell program using the (ex) main of C. It worked. The engine of the simulator works under Linux and we are happy.
- C++ (using g++) main programs including (linking) Pascal code. Same thing that C, even if there is the additional problem (for some target machine, like HPUX) to provide a call to a C++ initialisation function (called "_main") for C++ objects (constructors/destructors). It seems not to work properly in some cases, anyway. Till now, the porting of the HMI is not working and this is a big problem for us.
- Fortran (using g77) main programs including (linking) Pascal code. We didn't use, till now.
- linking stage. One of the most important things for an open code is the possibility to use standard linkers (such as ld) in order to provide the executable linking together object files from different language in a very standard and controllable way. The compilers should provide all the necessary libraries in order to create autonomous object files and not requiring the use of their own linker for this stage. I can add that for us any modification on the code in Pascal should be replicated and verified on the other three platforms, hoping that they all are compatible for the modifications (obviously it would not happen if FPC works also on the other three platforms)

After having said so much, I should say again a big "thank you", since I experimented a very helpful and exciting FPC environment, from a technical and a human viewpoint. A special thank to Michael who constantly and promptly helped me during these months.

Fabio Casamatta

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