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fox2mike 05/07/13 05:55:39 |
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Added: xml/htdocs/doc/en/draft debugging-howto.xml |
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Log: |
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Initial Version of the debugging-guide, originally part of the bugzilla-howto. |
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Revision Changes Path |
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1.1 xml/htdocs/doc/en/draft/debugging-howto.xml |
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|
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file : http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/draft/debugging-howto.xml?rev=1.1&content-type=text/x-cvsweb-markup&cvsroot=gentoo |
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plain: http://www.gentoo.org/cgi-bin/viewcvs.cgi/xml/htdocs/doc/en/draft/debugging-howto.xml?rev=1.1&content-type=text/plain&cvsroot=gentoo |
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|
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Index: debugging-howto.xml |
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=================================================================== |
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<?xml version="1.0" encoding="UTF-8"?> |
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd"> |
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/draft/debugging-howto.xml,v 1.1 2005/07/13 05:55:39 fox2mike Exp $ --> |
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|
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<guide link="/doc/en/debugging-howto.xml"> |
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<title>Gentoo Linux Debugging Guide</title> |
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|
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<author title="Author"> |
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<mail link="chriswhite@g.o">Chris White</mail> |
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</author> |
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<author title="Editor"> |
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<mail link="fox2mike@g.o">Shyam Mani</mail> |
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</author> |
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|
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<abstract> |
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This document aims at helping the user debug various errors they may encounter |
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during day to day usage of Gentoo. |
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</abstract> |
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|
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<!-- The content of this document is licensed under the CC-BY-SA license --> |
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<!-- See http://creativecommons.org/licenses/by-sa/2.5 --> |
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<license/> |
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|
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<version>1.0</version> |
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<date>2005-07-13</date> |
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|
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<chapter> |
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<title>Introduction</title> |
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<section> |
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<title>Preface</title> |
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<body> |
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|
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<p> |
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One of the factors that delay a bug being fixed is the way it is reported. By |
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creating this guide, we hope to help improve the communication between |
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developers and users in bug resolution. Getting bugs fixed is an important, if |
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not crucial part of the quality assurance for any project and hopefully this |
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guide will help make that a success. |
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</p> |
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|
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</body> |
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</section> |
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<section> |
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<title>Bugs!!!!</title> |
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<body> |
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|
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<p> |
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You're emerge-ing a package or working with a program and suddenly the worst |
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happens -- you find a bug. Bugs come in many forms like emerge failures or |
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segmentation faults. Whatever the cause, the fact still remains that such a bug |
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must be fixed. Here is a few examples of such bugs. |
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</p> |
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|
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<pre caption="A run time error"> |
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$ <i>./bad_code `perl -e 'print Ax100'`</i> |
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Segmentation fault |
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</pre> |
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|
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<pre caption="An emerge failure"> |
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/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.2/include/g++-v3/backward/backward_warning.h:32:2: |
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warning: #warning This file includes at least one deprecated or antiquated |
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header. Please consider using one of the 32 headers found in section 17.4.1.2 of |
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the C++ standard. Examples include substituting the <X> header for the <X.h> |
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header for C++ includes, or <sstream> instead of the deprecated header |
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<strstream.h>. To disable this warning use -Wno-deprecated. |
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In file included from main.cc:40: |
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menudef.h:55: error: brace-enclosed initializer used to initialize ` |
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OXPopupMenu*' |
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menudef.h:62: error: brace-enclosed initializer used to initialize ` |
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OXPopupMenu*' |
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menudef.h:70: error: brace-enclosed initializer used to initialize ` |
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OXPopupMenu*' |
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menudef.h:78: error: brace-enclosed initializer used to initialize ` |
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OXPopupMenu*' |
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main.cc: In member function `void OXMain::DoOpen()': |
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main.cc:323: warning: unused variable `FILE*fp' |
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main.cc: In member function `void OXMain::DoSave(char*)': |
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main.cc:337: warning: unused variable `FILE*fp' |
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make[1]: *** [main.o] Error 1 |
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make[1]: Leaving directory |
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`/var/tmp/portage/xclass-0.7.4/work/xclass-0.7.4/example-app' |
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make: *** [shared] Error 2 |
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|
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!!! ERROR: x11-libs/xclass-0.7.4 failed. |
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!!! Function src_compile, Line 29, Exitcode 2 |
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!!! 'emake shared' failed |
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</pre> |
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|
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<p> |
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These errors can be quite troublesome. However, once you find them, what do |
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you do? The following sections will look at two important tools for handling |
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run time errors. After that, we'll take a look at compile errors, and how to |
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handle them. Let's start out with the first tool for debugging run time |
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errors -- <c>gdb</c>. |
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</p> |
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|
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</body> |
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</section> |
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</chapter> |
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|
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|
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<chapter> |
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<title>Debugging using GDB</title> |
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<section> |
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<title>Introduction</title> |
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<body> |
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|
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<p> |
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GDB, or the (G)NU (D)e(B)ugger, is a program used to find run time errors that |
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normally involve memory corruption. First off, let's take a look at what |
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debugging entails. One of the main things you must do in order to debug a |
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program is to <c>emerge</c> the program with <c>FEATURES="nostrip"</c>. This |
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prevents the stripping of debug symbols. Why are programs stripped by default? |
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The reason is the same as that for having gzipped man pages -- saving space. |
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Here's how the size of a program varies with and without debug symbol stripping. |
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</p> |
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|
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<pre caption="Filesize Comparison"> |
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<comment>(debug symbols stripped)</comment> |
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-rwxr-xr-x 1 chris users 3140 6/28 13:11 bad_code |
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<comment>(debug symbols intact)</comment> |
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-rwxr-xr-x 1 chris users 6374 6/28 13:10 bad_code |
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</pre> |
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|
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<p> |
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Just for reference, <e>bad_code</e> is the program we'll be debugging with |
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<c>gdb</c> later on. As you can see, the program without debugging symbols is |
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3140 bytes, while the program with them is 6374 bytes. That's close to double |
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the size! Two more things can be done for debugging. The first is adding ggdb3 |
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to your CFLAGS and CXXFLAGS. This flag adds more debugging information than is |
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generally included. We'll see what that means later on. This is how |
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<path>/etc/make.conf</path> <e>might</e> look with the newly added flags. |
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</p> |
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|
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<pre caption="make.conf settings"> |
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CFLAGS="-O2 -pipe -ggdb3" |
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CXXFLAGS="${CFLAGS}" |
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</pre> |
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|
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<p> |
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Lastly, you can also add debug to the package's USE flags. This can be done with the |
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<path>package.use</path> file. |
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</p> |
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|
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<pre caption="Using package.use to add debug USE flag"> |
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# <i>echo "category/package debug" >> /etc/portage/package.use</i> |
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</pre> |
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|
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<note> |
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The directory <path>/etc/portage</path> does not exist by default and you may |
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have to create it, if you have not already done so. If the package already has |
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USE flags set in <path>package.use</path>, you will need to manually modify them |
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in your favorite editor. |
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</note> |
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|
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<p> |
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Then we re-emerge the package with the modifications we've done so far as shown |
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below. |
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</p> |
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|
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<pre caption="Re-emergeing a package with debugging"> |
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# <i>FEATURES="nostrip" emerge package</i> |
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</pre> |
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|
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<p> |
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Now that debug symbols are setup, we can continue with debugging the program. |
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</p> |
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|
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</body> |
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</section> |
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<section> |
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<title>Running the program with GDB</title> |
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<body> |
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|
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<p> |
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Let's say we have a program here called "bad_code". Some person claims that the |
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program crashes and provides an example. You go ahead and test it out: |
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</p> |
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|
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<pre caption="Breaking The Program"> |
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$ <i>./bad_code `perl -e 'print Ax100'`</i> |
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Segmentation fault |
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</pre> |
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<p> |
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It seems this person was right. Since the program is obviously broken, we have |
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a bug at hand. Now, it's time to use <c>gdb</c> to help solve this matter. First |
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we run <c>gdb</c> with <c>--args</c>, then give it the full program with |
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arguments like shown: |
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</p> |
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|
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<pre caption="Running Our Program Through GDB"> |
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$ <i>gdb --args ./bad_code `perl -e 'print Ax100'`</i> |
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GNU gdb 6.3 |
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Copyright 2004 Free Software Foundation, Inc. |
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GDB is free software, covered by the GNU General Public License, and you are |
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welcome to change it and/or distribute copies of it under certain conditions. |
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Type "show copying" to see the conditions. |
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There is absolutely no warranty for GDB. Type "show warranty" for details. |
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-- |
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