[CMake] Getting the path to object files?

[Robert Maynard]

CMake only provides an official way to get the location of the object
files for OBJECT targets ( $<TARGET_OBJECTS:objLib> ). For other
target types the location is an implementation detail.

On Sat, Feb 23, 2019 at 3:24 PM Paul Smith <paul at mad-scientist.net> wrote:
>
> Hi all.  I'm using CMake 3.13.4 across Linux, MacOS, and Windows, with
> various generators.
>
> I need to write a script (this only runs on Linux actually) that will
> do some processing on all the object files in a shared library and
> generate a linker version file.  I'm trying to write a custom command
> using PRE_LINK that will invoke that script and pass along enough
> information to find all those object files so it can generate the
> version file, and I can't come up with it.
>
> For example, using a Makefile generator for a file "libsrc.cpp" built
> for a library "solib" in a directory "LibDir" on Linux my object file
> paths look like:
>
>   LibDir/CMakeFiles/solib.dir/libsrc.cpp.o
>
> I can use something like this:
>
>   get_target_property(srcs solib SOURCES)
>
>   add_custom_command(TARGET solib PRE_LINK
>       COMMAND foo ${srcs}
>       VERBATIM)
>
> (for some reason if I try to use a generator expression like
> $<TARGET_PROPERTY:SOURCES> etc. it's always passed as a single quoted
> argument and I can't figure out how break it up, but if I use
> get_target_property() then it works correctly).
>
> However this only gives me the source file names, not the object file
> names, and no directory information to search.  My problem is I'm
> actually compiling these same source files multiple times in different
> ways for different libraries, so I can't just search for "libsrc.cpp.o"
> I need to get this particular .o.
>
> So then I added $<TARGET_PROPERTY:BINARY_DIR> which looked promising,
> but it only gives me the path to the source directory; i.e. above it
> gives me LibDir.
>
> I tried lots of different likely-looking properties, but I can't find
> any property which will tell me the path I'm looking for.
>
> Can I get CMake to tell me the path where the object files being
> created will be put for a given target?  Or do I just need to hard-code
> it based on my observations of how cmake generators actually create the
> output?
>
> --
>
> Powered by www.kitware.com
>
> Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ
>
> Kitware offers various services to support the CMake community. For more information on each offering, please visit:
>
> CMake Support: http://cmake.org/cmake/help/support.html
> CMake Consulting: http://cmake.org/cmake/help/consulting.html
> CMake Training Courses: http://cmake.org/cmake/help/training.html
>
> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>
> Follow this link to subscribe/unsubscribe:
> https://cmake.org/mailman/listinfo/cmake