[Python-bugs-list] [ python-Bugs-472568 ] PyBuffer_New() memory not aligned (original) (raw)

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Mon, 22 Oct 2001 13:19:18 -0700

Bugs item #472568, was opened at 2001-10-18 14:31 You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=472568&group_id=5470

Category: None Group: None Status: Open Resolution: None Priority: 5 Submitted By: Nobody/Anonymous (nobody) Assigned to: Nobody/Anonymous (nobody) Summary: PyBuffer_New() memory not aligned

Initial Comment: Memory buffer areas created by PyBuffer_New are missaligned on 32 bit machines, for doubles (64 bit).

This typically generates a bus error crash on most RISC machines when a library function tries to write a double in a memory buffer allocated by PyBuffer_New().

When looking at the bufferobject.c code, this seems to come from the fact that the memory buffer points at 'malloc() + sizeof struct PyBufferObject'; [line: b->b_ptr = (void *)(b + 1); ]

To the extent that struct PyBufferObject is not a multiple of sizeof (double), the largest value type; thus the misalignment, and the crashes on most RISC processors.

A quick and temporary solution would consist in adding a dummy double field as the last field of the PyBufferObject structure:

struct PyBufferObject { ... double dummy; } ;

and setting b->b_ptr = (void*)&b->dummy; /was (void(b+1)*/

In doing so, b->b_ptr will always by aligned on sizeof (double), on either 32 and 64 bit architectures.

Since I'm on the buffer type problem: It would be nice (and probably easy to do) to augment the buffer protocol interface with the ability to specify the basic value type stored in the buffer.

A possible list of values (enum ...) would be:

This would enable to check at runtime the type of values stored in a buffer (and prevent missalignement buserrors, as well as catching garbage situations when improper array types are passed by means of the buffer interface [e.g.: int/float/double/short...).

Frederic Giacometti

Frederic Giacometti

Comment By: Jeremy Hylton (jhylton) Date: 2001-10-22 13:19

Message: Logged In: YES user_id=31392

Note to whomever take this bug: PyBuffer_New() is not called anywhere in the Python source tree; nor are there any tests for buffer objects that I'm aware of. A few simple test cases would have caught this bug already. (And for the case of the builtin buffer() call, it might be good if it used PyBuffer_New().)

Comment By: Frederic Giacometti (giacometti) Date: 2001-10-18 14:35

Message: Logged In: YES user_id=93657

I wasn't looged in when I submitted the item. Don't think I'm becoming anonymous :))

You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=472568&group_id=5470