[cmake-developers] New OBJECT library feature

[Ruben Geeroms]

Brad King <brad.king at ...> writes:

> 
> On 3/19/2012 2:25 PM, Eric Noulard wrote:
> > 2012/3/19 Brad King<brad.king at ...>:
> >> Can you enumerate use cases when the order of objects matters?  Unlike
> >> static libraries *all* objects will be included.  If there are duplicate
> >> symbols it is an error.  If there are not duplicate symbols then how
> >> does order matter?
> >
> > The custom command likn step looks like:
> > COMMAND ${CMAKE_LINKER} --oformat binary -Ttext ${BM_IMAGE_ADDRESS}
> > -melf_i386 -e _start -o ${BM_APPNAME}.bin ${BM_STARTUPOBJ}
> > --start-group $<TARGET_LINKER_FILE:system>  $<TARGET_LINKER_FILE:xc>
> > $<TARGET_LINKER_FILE:${BM_APPNAME}>  --end-group ${BM_LDSCRIPT}
> >
> > ${BM_STARTUPOBJ} is the specific object file compiled on its own using
> > custom command.
> 
> I can imagine some cross compiling toolchains may want the object with
> the entry point to come first.
> 
> > Now that I think about it, before that I was forced to create a custom
> > command in order
> > to compile the file ('with the same option as the one compiled by
add_library)
> > but now I will be able to build an "OBJECT library" containing a single file
> > and refer to it using $<TARGET_OBJECTS:objlib>  which is perfectly fine for
> > ensuring the ordering I may need for the link step.
> 
> Note that $<TARGET_OBJECTS:...> is not a full generator expression that
> can be used from add_custom_command.  That is also reserved for the
> future (which is why I chose that syntax).  Currently it is just a
> special source file syntax recognized by add_library and add_executable.
> 

Are there any plans to add support for using object lists in custom commands
yet?

I need to create a custom type of library from objects created using a cross
compiling toolchain, so I would like to do something like:

ADD_LIBRARY( myLibObjects OBJECT a.cpp b.cpp ) # creates a.cpp.o and b.cpp.o
ADD_CUSTOM_COMMAND( OUTPUT  myLib
                    COMMAND myCustomArchiver --objects
$<TARGET_OBJECTS:myLibObjects> --output myLib ..
                    DEPENDS $<TARGET_OBJECTS:myLibObjects>
                  ) # puts a.cpp.o and b.cpp.o in custom library myLib
ADD_CUSTOM_TARGET( myLib_created ALL DEPENDS myLib )

Best regards,
Ruben