how to put compiler command line args in specific places using cmake

Question

So I'm building a shared library, out of two static libraries.

This answer says the way to do it is to insert -Wl,--whole-archive before my static libs, the -Wl,--no-whole-archive after them.

So what I have in cmake at the moment for the shared library is:

add_library(wittyPlus SHARED empty.cpp)
target_link_libraries(wittyPlus 
    ${wtdbosqlite}
    ${WT_LIBRARIES}
    ${DB_LIBRARIES}
    ${Boost_LIBRARIES}
    app models
)

So what I need is for it to add the -Wl,--whole-archive before app and models, then -Wl,--no-whole-archive after them (so that the standard library imports don't get exported by the shared lib).

What's the easiest way to do this in CMake ?

Addition: So I'd like to use the standard cmake stuff as much as possible, that way I don't have to do any extra work for windows builds, as CMake kindly removes the compiler definitions that aren't supported on the platform being built.

score 20 · Accepted Answer · edited May 23 '17 at 12:18

20

OK, it was much easier than I thought.

So according to the cmake docs:

Item names starting with '-', but not '-l' or '-framework', are treated as linker flags.

So the fix was just to:

add_library(wittyPlus SHARED empty.cpp)
target_link_libraries(wittyPlus 
    ${wtdbosqlite}
    ${WT_LIBRARIES}
    ${DB_LIBRARIES}
    ${Boost_LIBRARIES}
    "-Wl,--whole-archive"
    app models
    "-Wl,--no-whole-archive"
)

I don't know if it'll work on windows or not, I expect it will as cmake is super clever.

Looking at the result with objdump, it does seem to have a lot of boost stuff in the exports, so I might be doing something wrong.

objdump -C -t wittyPlus/libwittyPlus.so | grep -i boost

But it does have the stuff I need to link against it so, that's a step forward.

Any other answers still appreciated. Basically what I'm trying to do is the same as this question:

CMake: how create a single shared library from all static libraries of subprojects?

edited May 23 '17 at 12:18

Community

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answered Jan 15 '13 at 21:43

matiu

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Have you found a work around that doesn't require a null `empty.cpp` file? – Mark Lakata Jun 01 '15 at 23:15
No, I use empty.cpp all the time. – matiu Jun 02 '15 at 02:16
3

I looks like you can do `file(WRITE empty.cpp "")` if you don't want to pollute your real source tree with junk files. – Mark Lakata Jun 02 '15 at 03:21
In case your compiler doesn't like to compile empty cpp files (error message), sacrifice a few bytes in your binary and replace the "" with something like "int dummy = 0;". – dubbaluga Sep 20 '17 at 09:31
on windows it's /WHOLEARCHIVE – Erik Aronesty Mar 09 '20 at 19:30
Thanks for the answer. Saved a lot of time – Yug Singh Mar 12 '20 at 14:02

score 1 · Answer 2 · edited May 23 '17 at 12:18

1

If you are building the static libraries yourself, you can use this approach: https://stackoverflow.com/a/29824424/4069571 namely building them as object libraries first, then linking them into the respective shared and static libs.

edited May 23 '17 at 12:18

Community

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answered Dec 19 '16 at 19:02

GPMueller

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how to put compiler command line args in specific places using cmake

2 Answers2