[fpc-pascal] Is it possible to link to SO libraries that have filename ending like '.so.0'

[Peter Vreman]

> Hi
>
> This problem arised with recent change to JEDI-SDL, but it seems a
> general problem with linking to libraries under UNIXes.
>
> Before the change, JEDI-SDL headers linked to libraries named like
> 'libSDL.so', using constructs that looked like (after removing preproc
> $ifdefs and resolving constants)
>
>    procedure SDL_Quit; cdecl; external 'libSDL.so';
>
> and it worked OK. Of course, libSDL.so was on all systems only a symlink
> to an actual so file, e.g. to 'libSDL-1.2.so.0.7.0' on my system.
>
> However, recently we're trying to link to 'libSDL-1.2.so.0', to make
> sure that at compilation time we're linking to proper SDL version (since
> JEDI-SDL headers were always supposed to work only with "rather new" SDL
> version, not with "every possible SDL version". As is the case with most
> header units.) But the problem is that doing
>
>    procedure SDL_Quit; cdecl; external 'libSDL-1.2.so.0';
>
> fails at linking with
>
>    /usr/bin/ld: cannot find -lSDL-1.2
>    link_so_filename.dpr(4,1) Error: Error while linking
>
> So it seems that fpc passes to ld -lSDL-1.2, and ld looks for
> 'libSDL-1.2.so' (without '.0' suffix). Honestly, I don't know what one
> should pass to ld to tell it to link to 'libSDL-1.2.so.0'.
>
> Question: Can this be somehow fixed in FPC ? Or is it just impossible
> for FPC to say such thing to ld (so we have another problem that can't
> be solved because FPC uses external linker) ?
>
> In another words, should this be considered something that must be fixed
> in JEDI-SDL (by changing lib name back to 'libSDL.so') or can this be
> fixed in newer FPC versions ? Or maybe it's all already working, but I
> have to pass some command-line parameter to FPC or use some {$...}
> preprocessor directive to make it work ?

It is not possible for the compiler to detect if you want to link to a
specific version or to the generic .so file. If you specify a complete
filename then you must also pass the correct path where the file is
located (In most cases /usr/lib) otherwise the linker can't find it. That
means that the compiler needs to search for the file. This is not
implemented.