1<html lang="en"> 2<head> 3<title>Patching - Debugging with GDB</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Debugging with GDB"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Altering.html#Altering" title="Altering"> 9<link rel="prev" href="Calling.html#Calling" title="Calling"> 10<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 11<!-- 12Copyright (C) 1988-2013 Free Software Foundation, Inc. 13 14Permission is granted to copy, distribute and/or modify this document 15under the terms of the GNU Free Documentation License, Version 1.3 or 16any later version published by the Free Software Foundation; with the 17Invariant Sections being ``Free Software'' and ``Free Software Needs 18Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,'' 19and with the Back-Cover Texts as in (a) below. 20 21(a) The FSF's Back-Cover Text is: ``You are free to copy and modify 22this GNU Manual. Buying copies from GNU Press supports the FSF in 23developing GNU and promoting software freedom.'' 24--> 25<meta http-equiv="Content-Style-Type" content="text/css"> 26<style type="text/css"><!-- 27 pre.display { font-family:inherit } 28 pre.format { font-family:inherit } 29 pre.smalldisplay { font-family:inherit; font-size:smaller } 30 pre.smallformat { font-family:inherit; font-size:smaller } 31 pre.smallexample { font-size:smaller } 32 pre.smalllisp { font-size:smaller } 33 span.sc { font-variant:small-caps } 34 span.roman { font-family:serif; font-weight:normal; } 35 span.sansserif { font-family:sans-serif; font-weight:normal; } 36--></style> 37<link rel="stylesheet" type="text/css" href="../cs.css"> 38</head> 39<body> 40<div class="node"> 41<a name="Patching"></a> 42<p> 43Previous: <a rel="previous" accesskey="p" href="Calling.html#Calling">Calling</a>, 44Up: <a rel="up" accesskey="u" href="Altering.html#Altering">Altering</a> 45<hr> 46</div> 47 48<h3 class="section">17.6 Patching Programs</h3> 49 50<p><a name="index-patching-binaries-1053"></a><a name="index-writing-into-executables-1054"></a><a name="index-writing-into-corefiles-1055"></a> 51By default, <span class="sc">gdb</span> opens the file containing your program's 52executable code (or the corefile) read-only. This prevents accidental 53alterations to machine code; but it also prevents you from intentionally 54patching your program's binary. 55 56 <p>If you'd like to be able to patch the binary, you can specify that 57explicitly with the <code>set write</code> command. For example, you might 58want to turn on internal debugging flags, or even to make emergency 59repairs. 60 61 62<a name="index-set-write-1056"></a> 63<dl><dt><code>set write on</code><dt><code>set write off</code><dd>If you specify ‘<samp><span class="samp">set write on</span></samp>’, <span class="sc">gdb</span> opens executable and 64core files for both reading and writing; if you specify <kbd>set write 65off</kbd> (the default), <span class="sc">gdb</span> opens them read-only. 66 67 <p>If you have already loaded a file, you must load it again (using the 68<code>exec-file</code> or <code>core-file</code> command) after changing <code>set 69write</code>, for your new setting to take effect. 70 71 <br><dt><code>show write</code><dd><a name="index-show-write-1057"></a>Display whether executable files and core files are opened for writing 72as well as reading. 73</dl> 74 75 </body></html> 76 77