[CMake] CMake link order

[Juan Sanchez]

Hello,

I have always used all of the libraries at once to the
TARGET_LINK_LIBRARIES command.

In the following example, the link line order appears the same as the
libraries are listed on the line.

TARGET_LINK_LIBRARIES(devsim_tcl ${LIBRARIES} ${TCL_ARCHIVE}
${SUPERLU_ARCHIVE} ${BLAS_ARCHIVE} ${SQLITE3_ARCHIVE}
${SYMDIFF_ARCHIVE} ${OPTIONAL_LIBS} ${PTHREAD_LIB} ${DLOPEN_LIB})

This is important because my LIBRARIES need to all be on the link line
before the other libraries I am using.

Another option is to explicitly us ADD_DEPENDENCY to add dependencies
between the libraries:
https://cmake.org/cmake/help/latest/command/add_dependencies.html

If I had multiple libraries hopelessly intertwined, I would list them
multiple times:
A B A C

or force the linker to do multiple passes:

 -Wl,--start-group A B C  -Wl,--end-group

This is by using the start-group and end-group flags in your
TARGET_LINK_LIBRARIES line.
https://cmake.org/pipermail/cmake/2011-May/044478.html

Regards,

Juan






On Fri, Oct 18, 2019 at 9:56 AM Bon, William <william.bon at caldera.com>
wrote:

> Hello,
>
> we are facing an issue while using cmake and we have no idea how to solve
> or debug it.
> We have a complex and huge project (about 50 subdirectories and
> dependencies everywhere), and we are facing issue regarding the link order.
> There is a lot of dependencies between those projects, and to summarize,
> we have two libraries A and B
> A is an imported library from headers and shared lib .so declared like this
> ```
> add_library(A SHARED IMPORTED GLOBAL)
> set_target_properties(A PROPERTIES
>         IMPORTED_LINK_INTERFACE_LANGUAGES "C"
>         IMPORTED_LOCATION ${A_LIBRARY})
> ```
>
> B is a system library part of a package.
>
> We need to link A before B in every case.
>
> In every project, we include A before B using
> ```
> find_package(B)
> target_link_libraries(${library_produced} PUBLIC A)
> target_link_libraries(${library_produced} PUBLIC B)
> ```
>
> but from time to time, we don't know why, the library produced link in the
> wrong order (checked with ldd and make VERBOSE=1).
> it links B before A.
>
> Is there a way to find out what happens and why cmake change the link
> order for some project and not all projects ?
>
> Best regards,
>
> Bill
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