This is rather a theoretical interest for me for now (what else to do Friday evening) , but I see how it can be used in current dual-licensed mixed open / closed source storage engines MySQL world.
So problem is:
Let’s keep MySQL aside for simplicity and imagine we have fully open-source GPLvX licensed “MoonOffice” software. MoonOffice uses libsupercompress library which also distributed under GPL, and provide two functions: “superCompressFile”, “superDecompressFile”. MoonOffice can be both statically or shared linked with this library. This all fine.
Now imagine one provides library libquickcompress, which is closed sourced, available only in binary formats .so and .la, but the license on it is “use it as you want, link it with whathever you want, distribute it as you want”. Of course library also exports two functions “superCompressFile”, “superDecompressFile”.
Now questions: can we link our GPLed “MoonOffice” with libquickcompress ? Can we distribute binary build of MoonOffce linked with libquickcompress ? What is license of final binary ?
May be it is simple question and answer is obvious, but I am not sure what is correct answer.