[CMake] installing source (or object) files

Thu Jan 19 16:40:00 EST 2017

If you are using symbol visibility/exports, then marking the symbol as
exported may prevent the linker from removing it if the code is going into
a shared library (including static libraries that are built up into a
shared library). It's not a trivial topic though, so you would need to do
some reading up to get up to speed. Some starting points which may help:

https://cmake.org/cmake/help/latest/policy/CMP0063.html

https://cmake.org/cmake/help/latest/module/GenerateExportHeader.html

https://gcc.gnu.org/wiki/Visibility

On Fri, Jan 20, 2017 at 8:23 AM, Kris Thielemans <
kris.f.thielemans at gmail.com> wrote:

> Thanks Mike
>
> The motivation for linking explicitly with the object file was in the PS
> at the bottom, although only very brief of course.
>
> The registry.cxx file has static variables with constructors with side
> effects (they add entries to a std:::map that registers "factories").
> Therefore, registry.cxx refers to stuff in mylib, but neither
> wonderful_program.cxx nor mylib refers to stuff in registry.cxx. If I stick
> registry.cxx into a library (I could have used mylib for instance), the
> linker happily removes it from the wonderful_program executable (as it
> thinks its an irrelevant object file). Result: the std::map never gets
> initialised. The only way (that I know) to fix this is to link explicitly
> with registry.o. Then the linker keeps it, hence the variables get
> initialised, hence the std::map does.
>
> This is I believe a relatively standard trick, although I'm not 100% happy
> with it. If anyone has a replacement for that, I'd be happy to know (but
> it's probably not for the CMake list).
>
> Hope this clarifies why I need to export registry.cxx (or its object file).
>
> Kris
>
> -----Original Message-----
> From: Michael Ellery
> Sent: 19 January 2017 16:07
> To: Kris Thielemans
> Cc: cmake at cmake.org
> Subject: Re: [CMake] installing source (or object) files
>
> I think my initial reaction to installing a source (cxx) file is that you
> should install a static library instead (.a) - which is basically what you
> are suggesting. Just define a new static library target that includes the
> cxx file and install it…should work fine. If there are headers needed to
> use that static lib, you install those as well. There is a third type of
> library target called OBJECT, but those are usually just for use in the
> context of a build and not meant to be installed (if i recall correctly…).
>
> HTH,
> Mike Ellery
>
> > On Jan 18, 2017, at 11:49 PM, Kris Thielemans wrote:
> >
> > Hi
> >
> > I haven’t had any replies to my message below, hopefully because it was
> sent at the wrong time of year… So I’m reposting, but with some
> clarifications.
> >
> > I wrote the message about include_flags only. I’ve currently solved
> > this by adding a variable
> >
> >                Set(STIR_INCLUDE_DIRS blabla)
> >
> > in my STIRConfig.cmake.in (which is at
> > https://github.com/UCL/UCL-STIR/blob/master/src/cmake/STIRConfig.cmake
> > .in)
> >
> > and tell the user of the library that they have to do
> >
> > include_directories(${STIR_INCLUDE_DIRS})
> >
> > This works but only for include directories, not for other compiler
> flags. I’ve currently solved that by putting all (most?) of these in a
> STIRConfig.h.in.
> >
> > I don’t particularly like the include_directories solution however. I
> believe CMake’s eport facility is trying to get away from this. Indeed, for
> the library, its include path (and other compilation flags) get
> automatically exported, so the user doesn’t have to do anything else than
> target_link_libraries to inherit all necessary flags.
> >
> > Also, my current solution relies on exporting the .cxx. It seems safer
> to export the object file as that is guaranteed to have been compiled with
> the correct flags, but I don’t know how to do that.
> >
> > I hope my message below makes more sense now.
> >
> > Thanks
> >
> > Kris
> > From: Kris Thielemans
> > Sent: 27 December 2016 16:12
> > To: cmake at cmake.org
> > Subject: installing source (or object) files
> >
> > Hi all
> >
> > I have a non-standard set-up where I have a library that needs to be
> > linked together with some extra source files that contain
> > “registries”). So in my CMakeLists.txt I use
> >
> > Add_executable(wonderful_program wonderful_program.cxx registry.cxx)
> > target_link_libraries(wonderful_program mylib)
> >
> > registry.cxx needs to be compiled with some of my include files.
> >
> > For that, I added
> >
> > include_directories(“${PROJECT_SOURCE_DIR}/src/include”)
> >
> > I guess I could just as well have added
> >
> > SET_PROPERTY(SOURCE registry.cxx PROPERTY COMPILE_FLAG
> > "-I${STIR_INCLUDE_DIR}")
> >
> >
> > This works fine, but now I want to export my library (relocatable). I
> > have created a config file etc, added mylib as an install target,
> > installed the include files etc. All of that works great for the
> > library. However, I have no idea how to install registry.cxx. I could
> > just
> >
> > INSTALL(FILES registry.cxx …)
> >
> > However, that doesn’t copy the properties of the source files anywhere.
> In particular, it means that a “client” doesn’t know what compilation flags
> to use.
> >
> > Any ideas?
> >
> > Best wishes for 2017!
> >
> > Kris
> >
> > PS: The reason that I need registry.cxx is that it contains some
> variables that have a funky constructor that initialises some registries
> somewhere.
> > PS: Full source code is at https://github.com/UCL/STIR
> > --
> >
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-- 
Craig Scott
Melbourne, Australia
https://crascit.com
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