Re: libSDL2_image: configure behaves differently on Debian vs Ubuntu?

On 03/02/2017 10:34 PM, Gianfranco Berardi wrote:
>
> I could always using LD_LIBRARY_PATH or do what the README.txt says
> about setting environment variables myself, but I am curious why running
> configure on one system without doing those things results in behavior
> that is different from the other system.
>

For posterity's sake, I thought I would respond with the latest 
information I have. Please correct me if I am wrong.

When I built the test code that configure was trying, I found that the 
issue is with the difference in linkers.

Debian Wheezy is using gcc 4.7, and 4.7's linker seems to add 
dependencies because you told it that it that a library should be linked 
in. That is, if you tell it to link in SDL2, it will have a dependency 
on libSDL2. configure fails because it builds a test program that fails 
to find the dependency because the run-time linker doesn't know where to 
find it.

Ubuntu 14.04 uses gcc 4.8, which has a linker that is smarter about 
checking if your resulting binary actually uses anything in the library 
before deciding if it is a dependency. If you tell it to link in SDL2, 
but none of the SDL2 library is actually used, it won't have a a 
dependency. configure passes because the test program doesn't have a 
dependency on something in a weird place and so avoids the need to have 
its run-time linker pointed in the right direction.

So, in the end, I updated my build scripts so they use LD_LIBRARY_PATH 
to point to the lib directory of my custom libraries when running 
configure, and it works on both older and newer systems.

Hopefully this information helps someone.

-Gianfranco

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