[Python-Dev] Debug entry points for PyMalloc (original) (raw)

Skip Montanaro skip@pobox.com
Sat, 23 Mar 2002 15:44:49 -0600 

>> #define PYMALLOC_CLEANBYTE      0xCB    /* uninitialized memory */
>> #define PYMALLOC_DEADBYTE       0xDB    /* free()ed memory */
>> #define PYMALLOC_FORBIDDENBYTE  0xFB    /* unusable memory */
>> 
>> The debug malloc/free/realloc use these as follows.  Note that this
>> stuff is done regardless of whether PyMalloc handles the request
>> directly or passes it on to the platform malloc (in fact, the debug
>> entry points won't know and won't care).

Any possibility that the LINE or FILE:LINE at which a chunk of memory was freed could be imprinted as ASCII in freed memory without changing the API? I'd find something like

<0340><0340><0340><0340><0340>

or

<object.c:0340><object.c:0340>

more useful than a string of 

0xDB0xDB0xDB0xDB0xDB0xDB0xDB0xDB

bytes. I did something similar in a small single-file library I've been working on, though I didn't pay much attention to preserving the malloc/free API because, like I said, it was something small. I simply changed all free() calls to something like

MARK_TERRITORY(s, strlen(s), __LINE__);
free(s);

(The second arg was appropriate to the size of the memory chunk being freed.)

Skip