Malmo linux releases require specific boost versions

[DaveyBiggers]

Is it possible to avoid this?

[DaveyBiggers]

Hmm, probably not: "There is no way to build an executable or library that will be version-agnostic to the Boost version it uses." - see http://stackoverflow.com/a/32964146

Boost doesn't maintain ABI compatibility between versions, so our only option would be to link boost statically, as we currently do for Debian 7, for example.

Looking at the sizes of the binaries in the releases, it doesn't seem as though statically linking will add a huge overhead, so this might be worth considering. Going to the other extreme, we could stop providing prebuilt Linux binaries, and just ask people to build their own. (Building is pretty simple on Linux.)

[DaveyBiggers]

Turns out there's an issue with linking boost statically - the boost static libraries aren't compiled with -fPIC (which is needed to ensure the code is position independent). This is required for shared libaries (like Malmo). If I understand this correctly, since the shared library must be PIC, any code it pulls in must also be PIC.

Bottom line seems to be that anyone attempting to build Malmo from source would be forced to recompile boost with -fPIC before compiling Malmo. This seems a heavy price to pay. It makes life easier for users who just want to install a prebuilt Malmo, but it penalises anyone who wants to build it themselves.

[DaveyBiggers]

@timhutton proposed something like this:
Add a flag to the root CMakeLists.txt (along the lines of the BUILD_MOD, BUILD_DOCUMENTATION etc flags) to specify whether or not to link boost statically.
This can be off, by default, so that users who want to build from source don't need to bother with the hassle of building boost (unless they need to - eg for Debian 7 or Windows). When we build the release binaries here, we switch it on (and build boost ourselves).

That way, everyone wins.
(Except us.)

[DaveyBiggers]

Fixed in #434