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Re: How to make a C++ -module?
From: |
Bob Friesenhahn |
Subject: |
Re: How to make a C++ -module? |
Date: |
Tue, 21 Jun 2016 08:30:17 -0500 (CDT) |
User-agent: |
Alpine 2.20 (GSO 67 2015-01-07) |
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
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/