CODEWITHSUNDEEP
gcccmakeclang
flamasterrr
flamasterrr

Reputation: 315

Add linker flags only to specific libraries in CMake

Say I have a final executable called exec and I need to link it with 2 shared libraries - libA and libB. For libA I would like to pass some linker flag, the other library I would prefer not to.

This is how my simplified CMakeLists.txt file looks like at the moment:

add_executable(exec
    main.cpp
)
target_link_libraries(exec
    PRIVATE
    libA
    libB
)
target_link_options(exec PRIVATE "-Wl,--no-as-needed")

Right now CMake will treat it as if I passed --no-as-needed option to both libraries.

I want to achieve this very strict order:

-Wl,-no-as-needed -llibA -Wl,-as-needed -llibB

From what I know CMake does not guarantee that libraries will be passed to linker in the order they're written in target_link_libraries as the order can change if it results from depencencies so I cannot write:

target_link_libraries(exec
    PRIVATE
    "-Wl,-no-as-needed"
    libA
    "-Wl,-as-needed"
    libB
)

Upvotes: 1

Views: 4578

Answers (1)

Ivorne
Ivorne

Reputation: 336

You are right in the assumption that CMake does not guarantee ordering of linker flags. Additionally, duplicate entries are used only once.

To solve it, you can use target_link_options instead of target_link_librares in combination with SHELL: prefix. This prefix allows you to create a group of linker flags that will not change order within the group.

It will get more complicated if libA is a CMake target, in which case target_link_libraries( exec PRIVATE libA ) will generate something more compilicated than just -llibA. The most straightforward solution there would be to modify definition of target libA to already include the flag with the SHELL: prefix. But this does not seem to be your case.

So the solution is:

target_link_options( exec PRIVATE "SHELL:-Wl,-no-as-needed -llibA" )
target_link_options( exec PRIVATE "SHELL:-Wl,-as-needed -llibB" )

This can generate either -Wl,-no-as-needed -llibA -Wl,-as-needed -llibB or -Wl,-as-needed -llibB -Wl,-no-as-needed -llibA.

Upvotes: 3

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