[Python-Dev] mingw32 and gc-header weirdness

[Christian Tismer]

Hi all,

I was hacking to get mingw32 builds of psyco to work
and found a pretty weird thing:

I used mingw32 (stable distro) to build the psyco extension
on top of standard python2.6, built with Visual Studio,
and got weird crashes.

The reason is in objimpl.h:

typedef union _gc_head {
	struct {
		union _gc_head *gc_next;
		union _gc_head *gc_prev;
		Py_ssize_t gc_refs;
	} gc;
	long double dummy;  /* force worst-case alignment */
} PyGC_Head;

Mingw32 behaves funny here. The size of long double is 12 ! 8-)

I happened to use the _PyObject_GC_UNTRACK macro in psyco, instead
of the function, and that caused the errors, because psython
and the extension disagreed on the location of the gc pointers...
Using PyObject_GC_Untrack instead fixed the problem,
but there is a bad feeling left.

Question:
Is that considered a mingw bug?
Should we change the above union to a safer construct?

Or maybe I just missed something obvious and made a fool out of me?

cheers - chris

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