[CMake] How to hundle gcc link options(like whole-archive, --allow-multiple-definition) in CMake？

[Chaos Zhang]

Thanks for your generous Mr. Atkins, what you answer me worked well and
solved my question. I would keep 'always use target names in a
CMakeLists.txt instead of the actual output file' in my mind. :-)

Chao

Chuck Atkins wrote
> Hi Chao,
> 
> You want to let CMake to as much of the work for you as possible.  You're
> still trying to explicitly pass the path to the library file to
> target_link_libraries.  If you look at the line:
> 
> target_link_library(exe1 "-Wl, --whole-archive ../sub_dir1/liblib1.a
> --no-whole-archive")
> 
> there's no CMake target name so CMake can't know about the dependency.
> However, if you use the target name instead:
> 
> top_dir/CMakeLists.txt:
> cmake_minimum_required(VERSION 3.0)
> project(foo)
> add_subdirectory(sub_dir2)
> add_subdirectory(sub_dir1)
> 
> top_dir/sub_dir1/CMakeLists.txt
> add_library(L1 1.c)
> 
> top_dit/sub_dir2/CMakeLists.txt
> add_executable(exe1 main.c)
> target_link_libraries(exe1 "-Wl,--whole-archive" *L1*
> "-Wl,--no-whole-archive")
> 
> Notice how in the target_link_libraries line for exe1, the link options
> are
> separate instead of 1 big string combining them all and the actual CMake
> target name, L1, is used instead of the output file libL1.a.  You can see
> the resulting output is what you want:
> 
> $ make VERBOSE=1
> ...
> [100%] Linking C executable exe1
> ...
> /usr/bin/cc     CMakeFiles/exe1.dir/main.c.o  -o exe1 -rdynamic
> *-Wl,--whole-archive
> ../sub_dir1/libL1.a -Wl,--no-whole-archive*
> 
> Generally speaking, always use target names in a CMakeLists.txt instead of
> the actual output file.  There are a few situations where you may need the
> actual file name but they are uncommon and even then you would do it
> through target properties and generator expressions rather than hard code
> the library file name.
> 
> - Chuck
> 
> On Mon, May 30, 2016 at 8:35 AM, Chaos Zhang <

> zcsd2012@

> > wrote:
> 
>> Hi, all,
>>
>> Thanks for taking your time to review my email. I have a demo project and
>> it's structure like as below:
>>
>> top_dir
>>     CMakeLists.txt
>>     sub_dir1
>>         CMakeLists.txt
>>     sub_dir2
>>         CMakeLists.txt
>>
>> top_dir/sub_dir1/CMakeLists.txt used to build `lib1` by using
>> `add_library(lib1 ...)`,
>> top_dir/sub_dir2/CMakeLists.txt used to build `exe1` with linking lib1 by
>> `target_link_library(exe1 lib1)`.
>> And the content of top_dir/CMakeLists.txt is as below:
>>
>> add_subdirectory(sub_dir2)
>> add_subdirectory(sub_dir1)
>>
>> Normally, when build target exe1, cmake will check dependency so `lib1`
>> will
>> be built before building exe1. The problem is I am transfering an existed
>> makefile project into CMake, and there are many gcc link options, like
>> "whole-archive ... no-whole-archive, allow-mutiple-definition", if use
>> like
>> `target_link_library(exe1 "-Wl, --whole-archive ../sub_dir1/liblib1.a
>> --no-whole-archive")`(The form like this, and this may not work, it just
>> a
>> e.g.), cmake seem don't built `lib1` any more. Is there any way i can use
>> target_link_library like `target_link_library(exe1 "-Wl, --whole-archive
>> ../sub_dir1/liblib1.a")` and cmake link dependency checking still work,
>> or
>> other way i can transfer these gcc link options into cmake?
>>
>> Thanks a lot,
>> Chao
>>
>>
>>
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