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From: Richard Stallman <rms@gnu.org>
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Subject: Dynamic loading of C libraries
Date: Wed, 19 May 2010 19:09:04 -0400
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I talked with our lawyer, and we determined that GCC's technique of
checking for a symbol whose name says "I am under a GPL3-compatible
license" is ok for Emacs and other GNU packages when dynamically
loading libraries at the C level.

So you can implement dynamic loading with the check for that symbol.
If the symbol is not present then the function to load should
report an error and not load it.