[Python-Dev] Debug entry points for PyMalloc

[Skip Montanaro]

    >> #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.)

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