CMake: Embed ELF into executable - c++

Question

I have a project that needs access to an ELF file embedded into the executable in a special section.
I was handcrafting Makefiles before and simply had a shell script where I used objcopy to copy the target I wanted to embed into an .o file, then link to this file in the executable.
# Create a new section and copy the binary there ($1=input $2=output name)
objcopy --input-target binary --output-target elf64-x86-64 \
--binary-architecture i386 $1 $2.o
Now I want to get rid of the custom Makefiles and use CMake to generate them. However, I don't see an easy way to link to such a file. I am able to create and add this file, but not to link against it:
# Invoke script to package module as a library
add_custom_command(OUTPUT ${PACKAGED_FILE}
COMMAND ./package.sh ${MODULE_FILE} ${PACKAGED_FILE}
WORKING_DIRECTORY ${MODULE_DIR}
DEPENDS ${MODULE_FILE}
COMMENT packaging file into ELF object
VERBATIM
)
add_custom_target(${PACKAGED_NAME} ALL DEPENDS ${PACKAGED_FILE})
I have tried to add it with:
target_link_libraries(binary ${PROJECT_BINARY_DIR}/${PACKAGED_FILE})
However, this fails because the file isn't there yet. It will be, but CMake doesn't know that. Adding the target name as a link library doesn't help either because it can't be found. Adding it as a also dependency doesn't help. Does anyone have an idea how this could be accomplished?

Answer 1

We are doing a similar thing in our project - the following part of our CMakeLists.txt does the trick:
set(PROJECT_EMBED_OBJ_FILES "")
set(PROJECT_EMBED_FILES "file1.elf" "file2.elf")
foreach(FILENAME ${PROJECT_EMBED_FILES})
get_filename_component(FILENAME_ONLY ${FILENAME} NAME)
get_filename_component(FILEPATH_ONLY ${FILENAME} PATH)
add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${FILENAME_ONLY}.o
WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/${FILEPATH_ONLY}
COMMAND ${CMAKE_OBJCOPY}
ARGS -I binary -O elf64-x86-64 -B i386 ${FILENAME_ONLY} ${CMAKE_CURRENT_BINARY_DIR}/${FILENAME_ONLY}.o )
list(APPEND PROJECT_EMBED_OBJ_FILES ${CMAKE_CURRENT_BINARY_DIR}/${FILENAME_ONLY}.o)
message(STATUS "Objcopy'ing ${FILENAME}")
endforeach(FILENAME)
And then in the call to add_executable:
add_executable(projectname ${PROJECT_SOURCES} ${PROJECT_EMBED_OBJ_FILES})

Answer 2

You may try
add_custom_command(TARGET $(PROJECT_NAME).elf
POST_BUILD
COMMAND ${CMAKE_OBJCOPY} ARGS -O binary ${PROJECT_NAME}.elf \
${PROJECT_NAME}.bin)
Put this after your add_executable().
The POST_BUILD means execute after build.