[CMake] Approach to both shared and static lib (again, sorry)

[Ray Donnelly]

On Sat, May 19, 2018 at 11:55 PM, Elvis Stansvik
<elvis.stansvik at orexplore.com> wrote:
> 2018-05-19 21:49 GMT+02:00 Mateusz Loskot <mateusz at loskot.net>:
>> On 19 May 2018 at 15:00, Elvis Stansvik <elvis.stansvik at orexplore.com> wrote:
>>> I know this has been asked before, but I've never seen a really
>>> authoritative answer.
>>>
>>> Say I have a simple single-library project.
>>>
>>> The advise I've seen is to not pass SHARED or STATIC to the
>>> add_library(..), but instead let the user pass
>>> -DBUILD_SHARED_LIBS:BOOL=ON/OFF to build the library as either shared
>>> or static.
>>>
>>> That's fine, but leads to packagers having to do ugly things like e.g:
>>>
>>>     https://salsa.debian.org/hle/dlib/blob/master/debian/rules
>>>
>>> That is, do two separate configure/build/install, in order to get both
>>> a shared and static version.
>>
>> IMHO, there is nothing ugly in this approach.
>> Not every system allows (or recomments) to generate both,
>> static and shared, from the same object files.
>
> Alright. Yes I'm probably personally leaning towards just using the
> recommended way, with a single add_library(..) and demand
> reconfigure/rebuild/reinstall to get both variants. I was mostly
> curious if you CMake pros on this list had some neat solution I hadn't
> seen before.
>
> Note that I wasn't necessarily suggesting building shared + static
> from the same set of object files (which is indeed not recommended,
> e.g. think of -fPIC),

Static libraries should be compiled with -fPIC on all systems that
support -fPIC. The reason for this is that you should not make
assumptions about the final target of the static library. There is no
reason it should be excluded from being linked into a shared library
or a ASLR capable executable. On Anaconda Distribution, everything is
compiled with -fPIC on Linux for this reason, and on macOS, -fPIC is
the only option and Windows has always been PIC or at least for as
long as I can remember.

but just looking for best practices when having
> CMake do the build of both libraries as part of the same build.
>
> Elvis
>
>> Why not view static vs shared as the similar to 32 vs 64 bit?
>>
>> Best regards,
>> --
>> Mateusz Loskot, http://mateusz.loskot.net
>> --
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