2008/11/28 Hrvoje Niksic <[EMAIL PROTECTED]> > A friend pointed out that running python under valgrind (simply "valgrind > python") produces a lot of "invalid read" errors. Reading up on > Misc/README.valgrind only seems to describe why "uninitialized reads" should > occur, not invalid ones. For example: > > $ valgrind python > [... lots of output ...] > ==31428== Invalid read of size 4 > ==31428== at 0x808EBDF: PyObject_Free (in /usr/bin/python2.5) > ==31428== by 0x810DD0A: (within /usr/bin/python2.5) > ==31428== by 0x810DD34: PyNode_Free (in /usr/bin/python2.5) > ==31428== by 0x80EDAD9: PyRun_InteractiveOneFlags (in > /usr/bin/python2.5) > ==31428== by 0x80EDDB7: PyRun_InteractiveLoopFlags (in > /usr/bin/python2.5) > ==31428== by 0x80EE515: PyRun_AnyFileExFlags (in /usr/bin/python2.5) > ==31428== by 0x80595E6: Py_Main (in /usr/bin/python2.5) > ==31428== by 0x8058961: main (in /usr/bin/python2.5) > ==31428== Address 0x43bf010 is 3,112 bytes inside a block of size 6,016 > free'd > ==31428== at 0x4024B4A: free (vg_replace_malloc.c:323) > ==31428== by 0x8059C07: (within /usr/bin/python2.5) > ==31428== by 0x80EDAA5: PyRun_InteractiveOneFlags (in > /usr/bin/python2.5) > ... > > valgrind claims that Python reads 4 bytes inside a block on which free() > has already been called. Is valgrind wrong, or is Python really doing that? > Googling revealed previous reports of this, normally answered by a > reference to README.valgrind. But README.valgrind justifies reading from > ununitialized memory, which doesn't help me understand how reading from the > middle of a block of freed memory (more precisely, memory on which the libc > free() has already been called) would be okay. > > I suppose valgrind could be confused by PyFree's pool address validation > that intentionally reads the memory just before the allocated block, and > incorrectly attributes it to a previously allocated (and hence freed) block, > but I can't prove that. Has anyone investigated this kind of valgrind > report?
I can't answer your question directly, but I can tell you that whenever I have to debug memory problems with python extensions is usually use my own python compiled with --with-pydebug --without-pymalloc. It really helps with valgrind. -- Gustavo J. A. M. Carneiro INESC Porto, Telecommunications and Multimedia Unit "The universe is always one step beyond logic." -- Frank Herbert
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