Re: How to make a C++ -module?

On Tue, 21 Jun 2016, Patrick Welche wrote:

> I'm trying to create a C++ loadable module. I thought it would be as easy
> as:

[ stuff removed ]

> This fails with:
>
> /bin/sh ./libtool  --tag=CXX   --mode=link g++  -g -O2 -module -avoid-version  -o hellow.la -rpath /usr/local/lib hellow.lo
>
> *** Warning: linker path does not have real file for library -lgcc.
> *** I have the capability to make that library automatically link in when
> *** you link to this library.  But I can only do this if you have a
> *** shared version of the library, which you do not appear to have
> *** because I did check the linker path looking for a file starting
> *** with libgcc and none of the candidates passed a file format test
> *** using a regex pattern. Last file checked: /usr/lib/libgcc.a
>
> Presumably, this means that things aren't as simple as I thought.
> What am I missing?

Nothing is easy when it comes to C++-based modules.  Risks are 
elevated if a C-based program uses C++-based modules due to unhandled 
C++ exceptions or C++ exceptions possibly not working.

You are going to need a shared library for the (correct) C++ run-time 
as well as libgcc_s.so.  These need to somehow appear where libtool is 
searching for them.  They will also need to be available in a path 
where the system searches for shared libraries in order to load the 
module.

> # Dependencies to place before and after the objects being linked to
> # create a shared library.
> predep_objects="/usr/lib/crti.o /usr/lib/crtbeginS.o"
> postdep_objects="/usr/lib/crtendS.o /usr/lib/crtn.o"
> predeps=""
> postdeps="-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc"

I am not sure what libgcc is used for.  It seems to only ever be 
delivered as a static library in the GCC installation tree.  Its 
appearance in the link line may be a bug (possibly a bug in GCC).

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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