PyMem_MALLOC (was [Python-Dev] Snake farm) (original) (raw)

Martin v. Loewis martin@v.loewis.de
22 Nov 2002 19:20:48 +0100

Guido van Rossum <guido@python.org> writes:

This can be solved (as MAL suggested) by fixing configure so that malloc(0) returning 0x800 is treated the same as malloc(0) returning NULL. That way, pymalloc's free code doesn't have to special-case this.

This is nearly as bad as hard-coding the system on which it happens. If system developers come to like this trick, they may decide to return 0xFFFF0000 for malloc(0) (system developers, when confronted with a non-conformity in their implementation, always love to find a conforming but surprising implementation).

Given that this is quite hard to debug if it happens, I'd rather like to see a better test. It's not easy to find one, though.

One would be to do MALLOC_ZERO_RETURNS_ALWAYS_THE_SAME_THING, which would cover this and similar implementations (i.e. you test malloc(0) == malloc(0)).

Another test would be MALLOC_ZERO_RETURNS_NO_MEMORY: malloc(0), round down to the page beginning, read a word there, expect a crash. This tests precisely the functionality that pymalloc needs.

Regards, Martin