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

[noreply@sourceforge.net]

Bugs item #472568, was opened at 2001-10-18 14:31
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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:

- undefined (backward compatibility)
- char, unsigned char, short, ....int, ... long, long
long, float, double, and void* (memory address).

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






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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 :))


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