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<?xml version="1.0"?> <!-- -*- sgml -*- -->
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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<chapter id="o-manual" xreflabel="Omega">
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<title>Omega: an instant memory leak detector</title>
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<para>Omega is a Valgrind tool that traces pointers to memory
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allocations and produces debug output as the last reference
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is removed to a block that has not been de-allocated.</para>
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<para>Omega works by tracking pointers with the use of p-bits.
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In similar fashion to the methods used by memcheck and
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addrcheck, each memory location is flagged by a p-bit which
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indicates if the location is holding a pointer to an allocated
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block. Since pointers are multibyte, we gain by only requiring
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a single p-bit per pointer thus needing one p-bit per 4 bytes
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on 32bit machines and one p-bit per 8 bytes on 64bit
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<para>Whilst this simplifies and reduces the memory footprint of
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one aspect of the tracking methodology, the other aspect can be
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a bit of a memory hog. As each block is allocated, we need to
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maintain data about the block and hold back-references to any
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live pointers. There are various ways of doing this and as the
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tool evolves further upon its release, doubtless you will all
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improve upon it (and that's why I love open source).</para>
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<para>This tool has been checked against the simple test cases in
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the tests directory. Again, you will all have many more that
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<para>Note that in order to reduce the overheads that this tool
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incurs, it is assumed that the only problems left are memory
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leaks. This assumption allows many corner cases to be left
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un-coded. As we stumble upon those that cannot be avoided,
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they can be added. A major assumption in the tracking is
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that all pointers are aligned in memory. If this one fails,
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the tracking code will have to be re-jigged.</para>
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<para>Bryan "Brain Murders" Meredith, 2006</para>
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