HELLO·Android
系统源代码
IT资讯
技术文章
我的收藏
注册
登录
-
我收藏的文章
创建代码块
我的代码块
我的账号
Pie
|
9.0.0_r8
下载
查看原文件
收藏
根目录
external
valgrind
docs
html
quick-start.html
<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>The Valgrind Quick Start Guide</title> <link rel="stylesheet" type="text/css" href="vg_basic.css"> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="index.html" title="Valgrind Documentation"> <link rel="up" href="QuickStart.html" title="The Valgrind Quick Start Guide"> <link rel="prev" href="QuickStart.html" title="The Valgrind Quick Start Guide"> <link rel="next" href="manual.html" title="Valgrind User Manual"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <div><table class="nav" width="100%" cellspacing="3" cellpadding="3" border="0" summary="Navigation header"><tr> <td width="22px" align="center" valign="middle"><a accesskey="p" href="QuickStart.html"><img src="images/prev.png" width="18" height="21" border="0" alt="Prev"></a></td> <td width="25px" align="center" valign="middle"><a accesskey="u" href="QuickStart.html"><img src="images/up.png" width="21" height="18" border="0" alt="Up"></a></td> <td width="31px" align="center" valign="middle"><a accesskey="h" href="index.html"><img src="images/home.png" width="27" height="20" border="0" alt="Up"></a></td> <th align="center" valign="middle">The Valgrind Quick Start Guide</th> <td width="22px" align="center" valign="middle"><a accesskey="n" href="manual.html"><img src="images/next.png" width="18" height="21" border="0" alt="Next"></a></td> </tr></table></div> <div class="article"> <div class="titlepage"> <div><div><h1 class="title"> <a name="quick-start"></a>The Valgrind Quick Start Guide</h1></div></div> <hr> </div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="quick-start.intro"></a>1.Introduction</h2></div></div></div> <p>The Valgrind tool suite provides a number of debugging and profiling tools that help you make your programs faster and more correct. The most popular of these tools is called Memcheck. It can detect many memory-related errors that are common in C and C++ programs and that can lead to crashes and unpredictable behaviour.</p> <p>The rest of this guide gives the minimum information you need to start detecting memory errors in your program with Memcheck. For full documentation of Memcheck and the other tools, please read the User Manual. </p> </div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="quick-start.prepare"></a>2.Preparing your program</h2></div></div></div> <p>Compile your program with <code class="option">-g</code> to include debugging information so that Memcheck's error messages include exact line numbers. Using <code class="option">-O0</code> is also a good idea, if you can tolerate the slowdown. With <code class="option">-O1</code> line numbers in error messages can be inaccurate, although generally speaking running Memcheck on code compiled at <code class="option">-O1</code> works fairly well, and the speed improvement compared to running <code class="option">-O0</code> is quite significant. Use of <code class="option">-O2</code> and above is not recommended as Memcheck occasionally reports uninitialised-value errors which don't really exist.</p> </div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="quick-start.mcrun"></a>3.Running your program under Memcheck</h2></div></div></div> <p>If you normally run your program like this:</p> <pre class="programlisting"> myprog arg1 arg2 </pre> <p>Use this command line:</p> <pre class="programlisting"> valgrind --leak-check=yes myprog arg1 arg2 </pre> <p>Memcheck is the default tool. The <code class="option">--leak-check</code> option turns on the detailed memory leak detector.</p> <p>Your program will run much slower (eg. 20 to 30 times) than normal, and use a lot more memory. Memcheck will issue messages about memory errors and leaks that it detects.</p> </div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="quick-start.interpret"></a>4.Interpreting Memcheck's output</h2></div></div></div> <p>Here's an example C program, in a file called a.c, with a memory error and a memory leak.</p> <pre class="programlisting"> #include <stdlib.h> void f(void) { int* x = malloc(10 * sizeof(int)); x[10] = 0; // problem 1: heap block overrun } // problem 2: memory leak -- x not freed int main(void) { f(); return 0; } </pre> <p>Most error messages look like the following, which describes problem 1, the heap block overrun:</p> <pre class="programlisting"> ==19182== Invalid write of size 4 ==19182== at 0x804838F: f (example.c:6) ==19182== by 0x80483AB: main (example.c:11) ==19182== Address 0x1BA45050 is 0 bytes after a block of size 40 alloc'd ==19182== at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130) ==19182== by 0x8048385: f (example.c:5) ==19182== by 0x80483AB: main (example.c:11) </pre> <p>Things to notice:</p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"><p>There is a lot of information in each error message; read it carefully.</p></li> <li class="listitem"><p>The 19182 is the process ID; it's usually unimportant.</p></li> <li class="listitem"><p>The first line ("Invalid write...") tells you what kind of error it is. Here, the program wrote to some memory it should not have due to a heap block overrun.</p></li> <li class="listitem"><p>Below the first line is a stack trace telling you where the problem occurred. Stack traces can get quite large, and be confusing, especially if you are using the C++ STL. Reading them from the bottom up can help. If the stack trace is not big enough, use the <code class="option">--num-callers</code> option to make it bigger.</p></li> <li class="listitem"><p>The code addresses (eg. 0x804838F) are usually unimportant, but occasionally crucial for tracking down weirder bugs.</p></li> <li class="listitem"><p>Some error messages have a second component which describes the memory address involved. This one shows that the written memory is just past the end of a block allocated with malloc() on line 5 of example.c.</p></li> </ul></div> <p>It's worth fixing errors in the order they are reported, as later errors can be caused by earlier errors. Failing to do this is a common cause of difficulty with Memcheck.</p> <p>Memory leak messages look like this:</p> <pre class="programlisting"> ==19182== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==19182== at 0x1B8FF5CD: malloc (vg_replace_malloc.c:130) ==19182== by 0x8048385: f (a.c:5) ==19182== by 0x80483AB: main (a.c:11) </pre> <p>The stack trace tells you where the leaked memory was allocated. Memcheck cannot tell you why the memory leaked, unfortunately. (Ignore the "vg_replace_malloc.c", that's an implementation detail.)</p> <p>There are several kinds of leaks; the two most important categories are:</p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"><p>"definitely lost": your program is leaking memory -- fix it!</p></li> <li class="listitem"><p>"probably lost": your program is leaking memory, unless you're doing funny things with pointers (such as moving them to point to the middle of a heap block).</p></li> </ul></div> <p>Memcheck also reports uses of uninitialised values, most commonly with the message "Conditional jump or move depends on uninitialised value(s)". It can be difficult to determine the root cause of these errors. Try using the <code class="option">--track-origins=yes</code> to get extra information. This makes Memcheck run slower, but the extra information you get often saves a lot of time figuring out where the uninitialised values are coming from.</p> <p>If you don't understand an error message, please consult <a class="xref" href="mc-manual.html#mc-manual.errormsgs" title="4.2.Explanation of error messages from Memcheck">Explanation of error messages from Memcheck</a> in the <a class="xref" href="manual.html" title="Valgrind User Manual">Valgrind User Manual</a> which has examples of all the error messages Memcheck produces.</p> </div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="quick-start.caveats"></a>5.Caveats</h2></div></div></div> <p>Memcheck is not perfect; it occasionally produces false positives, and there are mechanisms for suppressing these (see <a class="xref" href="manual-core.html#manual-core.suppress" title="2.5.Suppressing errors">Suppressing errors</a> in the <a class="xref" href="manual.html" title="Valgrind User Manual">Valgrind User Manual</a>). However, it is typically right 99% of the time, so you should be wary of ignoring its error messages. After all, you wouldn't ignore warning messages produced by a compiler, right? The suppression mechanism is also useful if Memcheck is reporting errors in library code that you cannot change. The default suppression set hides a lot of these, but you may come across more.</p> <p>Memcheck cannot detect every memory error your program has. For example, it can't detect out-of-range reads or writes to arrays that are allocated statically or on the stack. But it should detect many errors that could crash your program (eg. cause a segmentation fault).</p> <p>Try to make your program so clean that Memcheck reports no errors. Once you achieve this state, it is much easier to see when changes to the program cause Memcheck to report new errors. Experience from several years of Memcheck use shows that it is possible to make even huge programs run Memcheck-clean. For example, large parts of KDE, OpenOffice.org and Firefox are Memcheck-clean, or very close to it.</p> </div> <div class="sect1"> <div class="titlepage"><div><div><h2 class="title" style="clear: both"> <a name="quick-start.info"></a>6.More information</h2></div></div></div> <p>Please consult the <a class="xref" href="FAQ.html" title="Valgrind FAQ">Valgrind FAQ</a> and the <a class="xref" href="manual.html" title="Valgrind User Manual">Valgrind User Manual</a>, which have much more information. Note that the other tools in the Valgrind distribution can be invoked with the <code class="option">--tool</code> option.</p> </div> </div> <div> <br><table class="nav" width="100%" cellspacing="3" cellpadding="2" border="0" summary="Navigation footer"> <tr> <td rowspan="2" width="40%" align="left"> <a accesskey="p" href="QuickStart.html"><<The Valgrind Quick Start Guide</a></td> <td width="20%" align="center"><a accesskey="u" href="QuickStart.html">Up</a></td> <td rowspan="2" width="40%" align="right"><a accesskey="n" href="manual.html">Valgrind User Manual>></a> </td> </tr> <tr><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td></tr> </table> </div> </body> </html>
Html程序
|
204行
|
10.83 KB
原始内容
高亮显示
复制内容
×
已收藏
收藏成功,您可以在我收藏的代码页面中查看,其地址为:
https://www.androidos.net.cn/my/collect/code
。
登录后可以享受更多权益
您还没有登录，登录后您可以：
收藏Android系统代码
收藏喜欢的文章
多个平台共享账号
去登录
首次使用？从这里
注册