[Python-Dev] valgrind (original) (raw)
"Martin v. Löwis" martin at v.loewis.de
Tue Nov 7 15:31:18 CET 2006
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Neal Norwitz schrieb:
at 0x44FA06: PyADDRESSINRANGE (obmalloc.c:1741)
Note that the free is inside qsort. The memory freed under qsort should definitely not be the bases which we allocated under PyTypeReady. I'll file a bug report with valgrind to help determine if this is a problem in Python or valgrind. http://bugs.kde.org/showbug.cgi?id=136989
As Tim explains, a read from Py_ADDRESS_IN_RANGE is fine, and by design. If p is the pointer, we do
pool = ((poolp)((Py_uintptr_t)(p) & ~(Py_uintptr_t)((4 * 1024) - 1)));
i.e. round down p to the start of the page, to obtain "pool". Then we do
f (((pool)->arenaindex < maxarenas && (Py_uintptr_t)(p) - arenas[(pool)->arenaindex].address < (Py_uintptr_t)(256 << 10) && arenas[(pool)->arenaindex].address != 0))
i.e. access pool->arenaindex. If this is our own memory, we really find a valid arena index there. If this is malloc'ed memory, we read garbage
- due to the page size, we are guaranteed to read successfully, still. To determine whether it's garbage, we look it up in the arenas array.
One other thing that is weird is that the complaint is about 4 bytes which should not be possible. All pointers should be 8 bytes AFAIK since this is amd64.
That's because the arenaindex is unsigned int. We could widen it to size_t, if we don't, PyMalloc can "only" manage 1 PiB (with an arena being 256kiB, and 4Gi arena indices being available).
I also ran this on x86. There were 32 errors and all of their addresses were 0x4...010.
That's because we round down to the beginning of the page.
Regards, Martin
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