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USENIX 2005 Annual Technical Conference, General Track — Abstract
Pp. 17–30 of the Proceedings
Using Valgrind to Detect Undefined Value Errors with Bit-Precision
Julian Seward, OpenWorks LLP; Nicholas Nethercote, University of Texas at Austin
Abstract
We present Memcheck, a tool that has been implemented with the
dynamic binary instrumentation framework Valgrind. Memcheck detects a
wide range of memory errors in programs as they run. This paper
focuses on one kind of error that Memcheck detects: undefined value errors.
Such errors are common, and often cause bugs that are hard to find in programs
written in languages such as C, C++ and Fortran. Memcheck's definedness
checking improves on that of previous tools by being accurate to the level of
individual bits. This accuracy gives Memcheck a low false positive and false
negative rate.
The definedness checking involves shadowing every bit of data in
registers and memory with a second bit that indicates if the bit has a
defined value. Every value-creating operation is instrumented with a
shadow operation that propagates shadow bits appropriately. Memcheck
uses these shadow bits to detect uses of undefined values that could
adversely affect a program's behaviour.
Under Memcheck, programs typically run 20-30 times slower than
normal. This is fast enough to use with large programs. Memcheck
finds many errors in real programs, and has been used during the
past two years by thousands of programmers on a wide range of systems,
including OpenOffice, Mozilla, Opera, KDE, GNOME, MySQL, Perl, Samba,
The GIMP, and Unreal Tournament.
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