[Python-Dev] Valgrind on 2.2.2 (original) (raw)

Tim Peters tim.one@comcast.net
Mon, 28 Oct 2002 20:36:50 -0500

[Guido]

... (I wonder if pymalloc adds to the confusion, since its arenas count as a single block to malloc and hence to valgrind, but are internally cut up into many objects.)

For each arena, the address returned by malloc() is stored in the file-static arenas[] vector. So if a diagnostic program can find that vector, it can find the base address of every arena gotten from malloc.

In a debug build, though, pymalloc adds pad bytes to both ends of each request (and whether handled by pymalloc or by malloc!), and returns the address of the byte beyond the leading pad byte. This can leave any number of system-malloc blocks with no direct pointer to their start. That's specific to the debug build, which forces all Python mem API calls to go thru pymalloc (the release build only directs PyObject_{Malloc,etc}() calls to pymalloc).