Linux: Ode to valgrind

[Z-Man]

It works. End.

Well, it's a short ode. But I can't think of anything better to say about a tool.

For the uninformed: Valgrind is a powerful debugging tool. It runs your program inside a virtual machine where it has full control over what the program does. By default, it checks for all kinds of memory handling errors: read/writes to unallocated memory, double deallocation, memory leaks, and most amazingly, reads from allocated, but uninitialized memory.

[wrtlprnft]

sorry for digging out this old thread, but I tried it (mostly to check my own code), and out of frustration that it didn't find anything in my code I'll post this (CVS HEAD):

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==21111== Conditional jump or move depends on uninitialised value(s)
==21111==    at 0x81E4B73: tMemManager::tMemManager(int) (tMemManager.cpp:619)
==21111==    by 0x81E654A: __static_initialization_and_destruction_0(int, int) (tMemManager.cpp:964)
==21111==    by 0x81E72F9: _GLOBAL__I__Z4leakv (sstream.tcc:80)
==21111==    by 0x81EE7E4: (within /home/mathias/armagetronad/src/armagetronad_main)
==21111==    by 0x804EDA8: (within /home/mathias/armagetronad/src/armagetronad_main)
==21111==    by 0x81EE6DA: __libc_csu_init (in /home/mathias/armagetronad/src/armagetronad_main)
==21111==    by 0x4493081: (below main) (in /lib/libc-2.3.5.so)

Not sure exactly, but for reference, this is tMemManager.cpp:619:

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            if (cs>=0 && cs < MAXCHECKSUM && (ln < leaks[cs] || leaks[cs] == 0))

That might have something to do with the special nature of the memory manager, but the only time something writes to the leaks array is inside this if block...

[Z-Man]

Two cascading memory managers give bad karma. Use either the internal one or valgrind, valgrind can't do its job fully when the internal manager is used.
But the warning is realy anyway and should be fixed now (in b0_2_8).

[Z-Man]

Valgrind is constantly cooler. Release 3.3 includes exp-omega, a memory checker that can report leaks as they happen, i.e. when the last pointer to a memory block gets assigned to point somewhere else. At the end, you'll get told where the block was allocated, and what bit of code lost it. Immensely useful.