Re: [Openexr-devel] .la and link to basename .so

[Peter Hillman]

Hi Charles,

From memory, we do libIex.so -> libIex-2_0.so.10.0.1 for the reason you 
suggest: so you can rebuild older code against EXR-2.0 without any 
change to sources or to your build system. The only reason to do 
libIex-2_0.so -> libIex-2_0.so.10.0.1 would be to allow linking against 
both old and new EXR libraries from the same binary (-lIex -lIex-2_0) 
but that seems to be an edge case which I think is unsupported unless 
you specifically make your own symlinks.

If you want to have both libraries available, and sometimes link against 
EXR-1.7 and sometimes against EXR-2.0, it might be better to install the 
libraries into two different locations by changing the prefix at 
configure time, and making sure the .so libraries can be located at runtime.

We'd also be interested to see the problem you are having building with 
./configure. I believe "make check" fails with certain versions of gcc  
on extended precision CPUs, but that shouldn't effect a standard 
"configure, make, make install" build.





On 11/09/13 03:52, Piotr Stanczyk wrote:
> Hey,
>
> Most of that stuff is just pure autoconf, I'll take a closer look at your 2nd 
> point and refresh my mind as I seem to remember we did some work on supporting 
> custom namespacing.
>
> I would like to know exactly what is failing for you regarding the build; would 
> you happen to have the output from the shell or the configure log files.
>
> Thanks
>
> - Piotr
>
> ________________________________________
> From: address@hidden address@hidden on behalf of Charles Flèche address@hidden
> Sent: 09 September 2013 14:26
> To: address@hidden
> Subject: [Openexr-devel] .la and link to basename .so
>
> Hi,
>
> As the ./configure script doesn't allow me to build IlmBase and OpenEXR
> on the latest Ubuntu, I'm taking a look at improving the current CMake
> files. Here are a couple of questions about the build :
>
> 1. the build process yields a few .la files : libHalf.la, libIex.la,
> etc... My understanding is that these .la files are legacy files from
> libtool to help linking, but this mechanism should be replaced by proper
> package-config .pc files. As OpenEXR already build valid .pc files, are
> these .la files still useful ?
>
> https://blog.flameeyes.eu/2008/04/what-about-those-la-files
>
> 2. taking libIex :
>     libIex-2_0.so.10 -> libIex-2_0.so.10.0.1
>     libIex-2_0.so.10.0.1
>     libIex.a
>     libIex.la
>     libIex.so -> libIex-2_0.so.10.0.1
>
> Now I get that renaming libIex.so to libIex-2_0.so is probably to avoid
> symbol collisions while linking two versions of OpenEXR from the same
> process. However, I don't understand the libIex.so ->
> libIex-2_0.so.10.0.1 symbolic link. Why renaming libIex-2_0 to libIex ?
> Is it to avoid modifying the build systems of the applications linking
> against OpenEXR ? Why not :
>     libIex-2_0.so.10 -> libIex-2_0.so.10.0.1
>     libIex-2_0.so.10.0.1
>     libIex-2_0.a
>     libIex-2_0.la
>     libIex-2_0.so -> libIex-2_0.so.10.0.1
>
> I probably miss something, there...
>
> Many thanks,
>
> Charles
>
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