[CMake] Do an execute_process before compilation

[Michael Wild]

On 15. Aug, 2009, at 14:00, Darius Blaszyk wrote:

> On Sat, 2009-08-15 at 11:05 +0200, Michael Wild wrote:
>> On 15. Aug, 2009, at 10:21, Darius Blaszyk wrote:
>>
>>> My application links an object file in. This objectfile is not a c+ 
>>> + -
>>> code file but some other file that needs to be linked in. The
>>> problem I
>>> have now is that each time I change this file I need to run the  
>>> linker
>>> from a shell script manually and only then I can issue a make  
>>> command.
>>> Is there a way to automate that? In other words can cmake do an
>>> execute_process before attempting to compile my application if I
>>> issue a
>>> make?
>>>
>>> Regards, Darius
>>>
>>
>> Have a look at ADD_CUSTOM_COMMAND(TARGET PRE_LINK ...)
>>
>> Michael
>
> I did a test, but the make process complained "Cannot find source file
> myobj.o". Which seems to be logical because the .o file needs to be
> created first by ADD_CUSTOM_COMMAND.
> What I have now is:
>
> ADD_CUSTOM_COMMAND(TARGET mytest_gui PRE_LINK COMMAND ld -r -b  
> binary -o
> mytest_glade.o mytest.glade)
> ADD_CUSTOM_COMMAND(TARGET mytest_gui PRE_LINK COMMAND objcopy
> --rename-section .data=.rodata,alloc,load,readonly,data,contents
> mytest_glade.o mytest_glade.o)
> ADD_EXECUTABLE(mytest_gui main.cpp mytest_glade.o)
> TARGET_LINK_LIBRARIES(mytest_gui ${GTKMM_LIBRARIES})
>
> This obviously does not work because of a missing mytest_glade.o, but
> how to circumvent that?
>
> Darius
>

Well then, how do you create the mytest_glade.o in the first place  
(say, without CMake)?

Besides, you are adding two custom commands in the PRE_LINK stage to a  
target, both operating on the same file. However, their execution  
order is not specified. Am I assuming correctly, that you are using  
the "ld -r -b" command to create a "resource file" from the glade file  
which you then link into your binary (I never do such "crazy" stuff,  
hence the question)? I probably would do that like this:

-- >8 --

set( GLADE_BIN_RSRC ${CMAKE_CURRENT_BINARY_DIR}$ 
{CMAKE_FILES_DIRECTORY}/mytest_gui.dir/mytest_glade.o )
add_custom_command( OUTPUT ${GLADE_BIN_RSRC}
   COMMAND ld -r -b binary -o ${GLADE_BIN_RSRC} $ 
{CMAKE_CURRENT_SOURCE_DIR}/mytest.glade
   COMMAND objcopy --rename- 
section .data=.rodata,alloc,load,readonly,data,contents $ 
{GLADE_BIN_RSRC} ${GLADE_BIN_RSRC}
   DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/mytest.glade
   COMMENT "Creating resource file ${GLADE_BIN_RSRC}
   VERBATIM
)

add_executable( mytest_gui main.cpp ${GLADE_BIN_RSRC} )

-- 8< --

This specifies a single rule how to generate the mytest_glade.o file  
from the mytest.glade and then simply adds it to the add_executable  
call. CMake now knows that mytest_gui depends on mytest_glade.o, and  
also how to create it from mytest.glade.

HTH and works

Michael