Gateway function is missing error using qpOASES and Matlab 2019a

[Giulero]

I've encountered this problem calling qpOASES in Matlab2019a (Ubuntu 18.04).

The error message was:
Invalid MEX-file '~/robotology-superbuild/build/install/mex/qpOASES.mexa64': Gateway function is missing

@traversaro solved the problem commenting these lines:

set_target_properties(${${prefix}_NAME}
  PROPERTIES
    CXX_VISIBILITY_PRESET "hidden"
    C_VISIBILITY_PRESET "hidden"
    VISIBILITY_INLINES_HIDDEN "hidden"
)

in robotology-superbuild/external/qpOASES/cmake/FindMatlab.cmake

[traversaro]

Sorry @Giulero , yesterday I was a bit in an hurry, and I could not give a nice explanation of the problem.

To understand the problem, you should first be familiar with the concept of "Symbol Visibility". A nice explanation of what "symbols" are is provided in https://github.com/green7ea/cpp-compilation#symbol-tables (but read all the document, otherwise it is difficult to get the big picture). This gist has some useful links about Symbol Visibility instead: https://gist.github.com/ax3l/ba17f4bb1edb5885a6bd01f58de4d542 .

To load a mexFunction contained in a library compiled from a C++ source code, Matlab needs to find some "symbols" in the library, so this symbols need to be visible. All other symbols of the library are made non visible to avoid symbol collisions, by the CMake code provided in FindMatlab.cmake. Unfortunately the amount of symbols that need to be visible change from Matlab version to Matlab version, so this means that the FindMatlab.cmake needs to be update to work with the latest Matlab version. This is the reason why we "vendor" the FindMatlab.cmake file instead of using the one from CMake, so we can quickly update it if necessary. The workaround that I did on your machine and that you mention in your comment was basically to make all the symbols in the mex library visible, hopefully including the symbols that Matlab needed.

Related issues:

• The S-function does not compile with Matlab R2018b  robotology/blockfactory#4

@Giulero Are you able to correctly compile/run WB-Toolbox blocks without the need of custom modifications? What OS are you using?

@prashanthr05 Did you experienced the same problem?

[prashanthr05]

@traversaro Yes, I experienced the same problem. Thanks for the heads up.

[Giulero]

Thanks a lot @traversaro. I got slightly the intuition behind.

Now everything I've tested works. I'm using Ubuntu 18.04.

[traversaro]

Fixed by #11 .