[fpc-pascal] Defining sonames?

[Graeme Geldenhuys]

On 2017-08-16 18:14, Sven Barth via fpc-pascal wrote:
> As you can see the program will work correctly as long as the
> libX11.so.6 file exists (even though that is a symlink itself, but the
> X11 project guarantees that different libX11.so.6.x.y are compatible to
> eachother), because the linker picks the SONAME that is set inside the
> binary. And the libX11.so.6 symlink is part of the non-devel package.

Sven, now here is an interesting problem regarding the way FPC (or 
Object Pascal in general) works with C based libraries. Martin pointed 
this out in another mailing list, and he gave me permission to forward 
it here. What is your answer or recommendation to this problem?



-------- Forwarded Message --------
Subject: Re: [MSEide-MSEgui-talk] MSE and XLib.
Date: Thu, 17 Aug 2017 14:54:16 +0200
From: Martin Schreiber
To: mseide-msegui-talk at lists.sourceforge.net

On Thursday 17 August 2017 10:54:31 Graeme Geldenhuys wrote:
 > On 2017-08-17 07:18, Martin Schreiber wrote:
 > > I don't understand why FPC uses the version-less library
 > > names instead of the mayor version names where the bindings are 
made for.
 > > Maybe a misunderstanding happened at ancient times...
 >
 > No, they are simply following the guidelines of Unix-type systems -
 > doing everything correctly by the book.

A hypothetical example:

- You make a pascal bindings file for the "greatlibrary" version 1.0.
- You set the library name in the bindings pascal file "great.pas" to 
"great" as Unix-type systems guidelines command.
- In your system great-devel package of the version 1.0.1 is installed, 
you have the c-header *.h files of libgreat 1.0.1 and the links 
libgreat.so -> libgreat.so.1 -> libgreat.so.1.0.1.
- The SONAME of libgreat.so.1.0.1 is libgreat.so.1
- You compile and run the application, libgreat.so.1 -> 
libgreat.so.1.0.1 is loaded, all is OK.

Now you give the source of the application to a colleague who has 
installed the newer but incompatible "greatlibrary" version 2.0.3 
including the devel package.
- He has the c-header *.h files of libgreat 2.0.3 and links libgreat.so 
-> libgreat.so.2 -> libgreat.so.2.0.3.
- The SONAME of libgreat.so.2.0.3 is libgreat.so.2
- He compiles your program, the linker links libgreat.so -> 
libgreat.so.2 -> libgreat.so.2.0.3 and stores the SONAME libgreat.so.2 
(remember, libgreat.so.2 and libgreat.so.1 are *not* compatible).

Now there are two possibilities, maybe the function names in 
libgreat.pas did not change between version 1 and 2 -> the program 
compiles but crashes because of changed parameters or other 
incompatibilities.
Or it does not compile and then he needs to install version 1 of 
"greatlibrary" and deinstall great-devel-2.0.3 and install 
great-devel-1.0.1 or change manually libgreat.so -> libgreat.so.2 to 
libgreat.so -> libgreat.so.1 temporarily.
This also must be done in first case in order to produce a working 
application.

The difference between a FPC bindings unit and a Unix C-header *.h file 
is that the *.h file is *included* in the devel-package and thus matches 
the installed version, the pascal file is not included but in a separate 
package or more likely taken from the FPC tar archive by the FPC install 
script because FPC Linux/FreeBSD-packages usually are too old or one 
wants to use a FPC version from SVN.
So the "guidelines for Unix-type systems" are not appropriate for Free 
Pascal C-library binding units IMHO.

Martin
---------------------------------------------------



Regards,
   Graeme

-- 
fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal
http://fpgui.sourceforge.net/

My public PGP key:  http://tinyurl.com/graeme-pgp