[Python-Dev] Linux Python linking with G++? (original) (raw)

David Abrahams dave at boost-consulting.com
Mon Jul 11 00:51:55 CEST 2005

"Martin v. Löwis" <martin at v.loewis.de> writes:

David Abrahams wrote:

- we add a configure test that runs after the existing test determines that --with-cxx is needed (but not when --with-cxx is explicitly specified on the command line)

- This test runs a 'C' executable that tries to load a C++ dynamic library with dlopen. - The test returns an error code if the the dynamic library's static and dynamic initializers have not been run properly - If the test fails we disable --with-cxx ?? What would be the purpose of such a test? The test may fail for many reasons, for example, dlopen might not be available.

I was assuming we only disable --with-cxx if the test builds successfully. I presume dlopen will fail linking if it's unavailable?

OTOH, on current Linux systems the test would succeed, so configure would conclude to link with g++.

Uhh, whoops. Change the sense of my last bullet

I'm trying to intrude on the existing behavior as little as possible, yet get the semantics we want for ELF/Linux in a way that stands a good chance of generalizing to other platforms. I now think that the code should be made more simple, not more complex. Aspects of a solution I could accept: - ccpython.cc and linking with g++ is removed entirely. or,

That would be bad for C++ users on HP/UX. Is that acceptable?

- the logic is fixed so that linking with g++ is only done if main is in ccpython.o

I don't see how that works. Somehow we need to decide whether to put main in ccpython.o in the first place, don't we?

- the configure test is extended to better match current g++ behaviour.

What do you have in mind?

Well, that would certainly be an easy "solution," but it would break HP/UX, and it would break anyone that needs to statically link C++ modules on some platforms. It's a much more drastic change than it would be to only have the system use --with-cxx when the person running configure asks for it explicitly. I just checked, and it seems that the logic in use is still somewhat different. If the configure test determines that a C++ main() must be linked with CXX, it unconditionally changes the linker to CXX. The test, in turn, is run always if a C++ compiler was found, i.e. independently of whether --with-cxx was provided.

That doesn't match up with reports from my testers who say they can run with C++ extension modules from many different GCC versions if they just configure their Python --without-cxx. If what you were saying were true, wouldn't --without-cxx be ignored on ELF/Linux?

-- Dave Abrahams Boost Consulting www.boost-consulting.com

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