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SF bug [#467145] Python 2.2a4 build problem on HPUX 11.0.

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The platform requires 8-byte alignment for doubles, but the GC header
was 12 bytes and that threw off the natural alignment of the double
members of a subtype of complex.  The fix puts the GC header into a
union with a double as the other member, to force no-looser-than
double alignment of GC headers.  On boxes that require 8-byte alignment
for doubles, this may add pad bytes to the GC header accordingly; ditto
for platforms that *prefer* 8-byte alignment for doubles.  On platforms
that don't care, it shouldn't change the memory layout (because the
size of the old GC header is certainly greater than the size of a double
on all platforms, so unioning with a double shouldn't change size or
alignment on such boxes).
This commit is contained in:
Tim Peters 2001-10-11 18:31:31 +00:00
parent f3623f310e
commit 9e4ca10ce4
2 changed files with 71 additions and 68 deletions
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27
Include/objimpl.h
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@ -266,10 +266,13 @@ extern DL_IMPORT(void) _PyObject_GC_UnTrack(PyObject *);
#ifdef WITH_CYCLE_GC
/* GC information is stored BEFORE the object structure */
typedef struct _gc_head {
struct _gc_head *gc_next; /* not NULL if object is tracked */
struct _gc_head *gc_prev;
int gc_refs;
typedef union _gc_head {
struct {
union _gc_head *gc_next; /* not NULL if object is tracked */
union _gc_head *gc_prev;
int gc_refs;
} gc;
double dummy; /* force worst-case alignment */
} PyGC_Head;
extern PyGC_Head _PyGC_generation0;
@ -278,20 +281,20 @@ extern PyGC_Head _PyGC_generation0;
* collector it must be safe to call the ob_traverse method. */
#define _PyObject_GC_TRACK(o) do { \
PyGC_Head *g = (PyGC_Head *)(o)-1; \
if (g->gc_next != NULL) \
if (g->gc.gc_next != NULL) \
Py_FatalError("GC object already in linked list"); \
g->gc_next = &_PyGC_generation0; \
g->gc_prev = _PyGC_generation0.gc_prev; \
g->gc_prev->gc_next = g; \
_PyGC_generation0.gc_prev = g; \
g->gc.gc_next = &_PyGC_generation0; \
g->gc.gc_prev = _PyGC_generation0.gc.gc_prev; \
g->gc.gc_prev->gc.gc_next = g; \
_PyGC_generation0.gc.gc_prev = g; \
} while (0);
/* Tell the GC to stop tracking this object. */
#define _PyObject_GC_UNTRACK(o) do { \
PyGC_Head *g = (PyGC_Head *)(o)-1; \
g->gc_prev->gc_next = g->gc_next; \
g->gc_next->gc_prev = g->gc_prev; \
g->gc_next = NULL; \
g->gc.gc_prev->gc.gc_next = g->gc.gc_next; \
g->gc.gc_next->gc.gc_prev = g->gc.gc_prev; \
g->gc.gc_next = NULL; \
} while (0);
#define PyObject_GC_Track(op) _PyObject_GC_Track((PyObject *)op)