[Python-Dev] GCC version compatibility (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Sun Jul 10 09:21:23 CEST 2005

David Abrahams wrote:

I'll describe it once more: If a program is compiled with the C++ compiler, is it then possible to still link it with the C compiler? This is the question this test tries to answer.

Okay, I understand that. What I have never understood is why that should be an appropriate thing to test for the Python executable. There's no reason to compile any of Python with a C++ compiler.

I hope you understand now: it is necessary if you want to link C++ extension modules into a Python interpreter (statically, not dynamically).

Wrong. The test was introduced in response to complaints that Python unnecessarily links with libstdc++ on some Linux systems.

Apparently it still does.

Not "still", but "again", since recent changes in gcc.

On these Linux systems, it was well possible to build main() with a C++ compiler

Nobody would need to build Python's main() with a C++ compiler, if you'd just comment out the 'extern "C"'.

Wrong. People that statically link C++ extensions modules on systems where the C++ compiler requires main to be compiled as C++ need to do such a thing. One such compiler is gcc on systems where the binary format does not support .init sections.

and still link the entire thing with gcc. Since main() doesn't use _any libstdc++ functionality, and since collect2/main isn't used, one would indeed expect that linking with CXX is not necessary.

It isn't.

Hmmm. It is. Try for yourself. You get an unresolved gxx_personality_v0.

I have tested Boost.Python and C++ extension modules on a wide variety of Linux systems, and have seen this phenomenon.

Did you try on Linux systems released 1994? That don't use ELF as the binary format?

I think either the ELF Linux loader changed substantially since 1995, or whoever introduced this test was just confused.

No. The ELF loader was introduced since 1995. Dynamic loading was not available before.

Regards, Martin

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