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991367c922
Memcheck, replacing the 9-bits-per-byte shadow memory representation to a 2-bits-per-byte representation (with possibly a little more on the side) by taking advantage of the fact that extremely few memory bytes are partially defined. For the SPEC2k benchmarks with "test" inputs, this speeds up Memcheck by a (geometric mean) factor of 1.20, and reduces the size of shadow memory by a (geometric mean) factor of 4.26. At the same time, Addrcheck is removed. It hadn't worked for quite some time, and with these improvements in Memcheck its raisons-d'etre have shrivelled so much that it's not worth the effort to keep around. Hooray! Nb: this code hasn't been tested on PPC. If things go wrong, look first in the fast stack-handling functions (eg. mc_new_mem_stack_160, MC_(helperc_MAKE_STACK_UNINIT)). git-svn-id: svn://svn.valgrind.org/valgrind/trunk@5791
172 lines
7.3 KiB
XML
172 lines
7.3 KiB
XML
<?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="manual-intro" xreflabel="Introduction">
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<title>Introduction</title>
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<sect1 id="manual-intro.overview" xreflabel="An Overview of Valgrind">
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<title>An Overview of Valgrind</title>
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<para>Valgrind is a suite of simulation-based debugging and profiling
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tools for programs running on Linux (x86, amd64 and ppc32). The system
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consists of a core, which provides a synthetic CPU in software, and a
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series of tools, each of which performs some kind of debugging,
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profiling, or similar task. The architecture is modular, so that new
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tools can be created easily and without disturbing the existing
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structure.</para>
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<para>A number of useful tools are supplied as standard. In
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summary, these are:</para>
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<orderedlist>
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<listitem>
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<para><command>Memcheck</command> detects memory-management problems
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in your programs. All reads and writes of memory are checked, and
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calls to malloc/new/free/delete are intercepted. As a result,
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Memcheck can detect the following problems:</para>
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<itemizedlist>
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<listitem>
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<para>Use of uninitialised memory</para>
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</listitem>
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<listitem>
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<para>Reading/writing memory after it has been
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free'd</para>
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</listitem>
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<listitem>
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<para>Reading/writing off the end of malloc'd
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blocks</para>
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</listitem>
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<listitem>
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<para>Reading/writing inappropriate areas on the
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stack</para>
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</listitem>
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<listitem>
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<para>Memory leaks -- where pointers to malloc'd
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blocks are lost forever</para>
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</listitem>
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<listitem>
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<para>Mismatched use of malloc/new/new [] vs
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free/delete/delete []</para>
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</listitem>
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<listitem>
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<para>Overlapping <computeroutput>src</computeroutput> and
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<computeroutput>dst</computeroutput> pointers in
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<computeroutput>memcpy()</computeroutput> and related
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functions</para></listitem>
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</itemizedlist>
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<para>Problems like these can be difficult to find by other means,
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often lying undetected for long periods, then causing occasional,
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difficult-to-diagnose crashes.</para>
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</listitem>
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<listitem>
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<para><command>Cachegrind</command> is a cache profiler. It
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performs detailed simulation of the I1, D1 and L2 caches in your CPU
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and so can accurately pinpoint the sources of cache misses in your
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code. If you desire, it will show the number of cache misses,
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memory references and instructions accruing to each line of source
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code, with per-function, per-module and whole-program summaries. If
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you ask really nicely it will even show counts for each individual
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machine instruction.</para>
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<para>On x86 and AMD64, Cachegrind auto-detects your machine's cache
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configuration using the <computeroutput>CPUID</computeroutput>
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instruction, and so needs no further configuration info, in most
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cases.</para>
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<para>Cachegrind is nicely complemented by Josef Weidendorfer's
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amazing KCacheGrind visualisation tool
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(<ulink url="http://kcachegrind.sourceforge.net/cgi-bin/show.cgi/KcacheGrindIndex">http://kcachegrind.sourceforge.net</ulink>),
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a KDE application which presents these profiling results in a
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graphical and easier-to-understand form.</para>
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</listitem>
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<listitem>
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<para><command>Helgrind</command> finds data races in multithreaded
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programs. Helgrind looks for memory locations which are accessed by
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more than one (POSIX p-)thread, but for which no consistently used
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(pthread_mutex_)lock can be found. Such locations are indicative of
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missing synchronisation between threads, and could cause
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hard-to-find timing-dependent problems.</para>
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<para>Helgrind ("Hell's Gate", in Norse mythology) implements the
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so-called "Eraser" data-race-detection algorithm, along with various
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refinements (thread-segment lifetimes) which reduce the number of
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false errors it reports. It is as yet somewhat of an experimental
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tool, so your feedback is especially welcomed here.</para>
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<para>Helgrind has been hacked on extensively by Jeremy
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Fitzhardinge, and we have him to thank for getting it to a
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releasable state.</para>
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<para>NOTE: Helgrind is, unfortunately, not available in Valgrind
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3.1.X, as a result of threading changes that happened in the 2.4.0
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release. We hope to reinstate its functionality in a future 3.2.0
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release.</para>
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</listitem>
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</orderedlist>
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<para>A couple of minor tools (<command>Lackey</command> and
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<command>Nulgrind</command>) are also supplied. These aren't
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particularly useful -- they exist to illustrate how to create simple
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tools and to help the valgrind developers in various ways. Nulgrind is
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the null tool -- it adds no instrumentation. Lackey is a simple example
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tool which counts instructions, memory accesses, and the number of
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integer and floating point operations your program does.</para>
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<para>Valgrind is closely tied to details of the CPU and operating
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system, and to a lesser extent, the compiler and basic C libraries.
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Nonetheless, as of version 3.1.0 it supports several platforms:
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x86/Linux (mature), AMD64/Linux (maturing), and PPC32/Linux (immature
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but works well). Valgrind uses the standard Unix
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<computeroutput>./configure</computeroutput>,
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<computeroutput>make</computeroutput>, <computeroutput>make
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install</computeroutput> mechanism, and we have attempted to ensure that
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it works on machines with kernel 2.4 or 2.6 and glibc
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2.2.X--2.3.X.</para>
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<para>Valgrind is licensed under the <xref linkend="license.gpl"/>,
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version 2. The <computeroutput>valgrind/*.h</computeroutput> headers
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that you may wish to include in your code (eg.
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<filename>valgrind.h</filename>, <filename>memcheck.h</filename>) are
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distributed under a BSD-style license, so you may include them in your
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code without worrying about license conflicts. Some of the PThreads
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test cases, <filename>pth_*.c</filename>, are taken from "Pthreads
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Programming" by Bradford Nichols, Dick Buttlar & Jacqueline Proulx
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Farrell, ISBN 1-56592-115-1, published by O'Reilly & Associates,
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Inc.</para>
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</sect1>
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<sect1 id="manual-intro.navigation" xreflabel="How to navigate this manual">
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<title>How to navigate this manual</title>
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<para>The Valgrind distribution consists of the Valgrind core, upon
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which are built Valgrind tools, which do different kinds of debugging
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and profiling. This manual is structured similarly.</para>
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<para>First, we describe the Valgrind core, how to use it, and the flags
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it supports. Then, each tool has its own chapter in this manual. You
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only need to read the documentation for the core and for the tool(s) you
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actually use, although you may find it helpful to be at least a little
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bit familar with what all tools do. If you're new to all this, you
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probably want to run the Memcheck tool. If you want to write a new
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tool, read <xref linkend="writing-tools"/>.</para>
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<para>Be aware that the core understands some command line flags, and
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the tools have their own flags which they know about. This means there
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is no central place describing all the flags that are accepted -- you
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have to read the flags documentation both for
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<xref linkend="manual-core"/> and for the tool you want to use.</para>
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</sect1>
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</chapter>
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