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

"Martin v. Löwis" martin at v.loewis.de
Sun Jul 10 19:53:31 CEST 2005

David Abrahams wrote:

I well remember that gcc 2.5.8 on Linux a.out required this sort of setup.

Sorry, a.out? Isn't that the default name a C compiler gives to the executable it builds on Unix? Is it also (part of) the name of an OS?

Yes, and somewhat. It is also the name of a binary format, see /usr/include/a.out.h (*). There are different types of object files: OMAGIC (.o), NMAGIC,ZMAGIC,QMAGIC (executable), CMAGIC (core file). The Linux inplementation is now called binfmt_aout, but it used to be the only binary format that Linux supported up to Linux 1.2 (which introduced ELF in 1.1.52). Originally, a.out did not support shared libraries, but was extended to do so by allocating fixed virtual addresses to well-known shared libraries, so that no relocation was necessary (the a.out dynamic loader did not support either dynamic relocation nor PIC code on Linux; the SunOS dynamic linker did support relocation AFAIR).

Even after Linux implemented ELF, it took some time for distributions to switch to ELF. Because of the startup overhead, there was some reluctance that ELF is "slower"; it also created larger executables. Only when developers realized how powerful dynamic linking and shared libraries are, they gave up their concerns.

Understood, and I retract my former incredulity. I believe HP-UX requires it, and I believe that some systems where you have to link in extension modules explicitly require it. But the "--with-cxx if configure says you can get away with it" behavior is hurting on a major platform: ELF Linux.

Indeed.

Regards, Martin

(*) Actually, the format is called this way because it is the format of the compiler output file.

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