Valgrind是一款非常強大的工具集合,它包含有包括內存檢測、CPU監測等多種工具,其中最常用的是內存檢測功能,它能監測出以下的各種內存錯誤:
1. 訪問非法內存區域
2. 使用未被初始化的內存區域
3. 非法釋放內存,比如多次free一個內存
4. 內存泄露
1. 使用valgrind前需要使用-g參數編譯源程序以便生成debug信息
2. 在運行程序的命令行前加上valgrind,例如:valgrind myprog argvlist
爲了能夠給出內存檢測報告,需要加上--leak-check參數,那麼上述命令就變成:valgrind --leak-check=yes myprog argvlist
這個時候程序運行會非常慢,消耗資源也會大幅增加,這是正常的,不必擔心。因爲valgrind需要收集內存錯誤和泄露的詳細信息。這被有些人認爲是valgrind的缺點,但是對於一個大項目來說,這一點時間的消耗來監測程序的穩定性是值得的。
3. 閱讀valgrind給出的報告
--num-callers=N:指定報告中調用棧的層數,這在定位和跟蹤錯誤的時候會比較有用
-v :可以打印出更加詳細的信息
"Invalid write/read...":這一般是訪問非法的內存區域,比如數組越界等
"definitely lost":肯定丟失的部分,這種報告必須處理
"possibly lost":可能丟失的部分,這是由於C/C++語言指針處理的特點造成的,這部分可能不太準確
Valgrind 是在linux系統下開發應用程序時用於調試內存問題的工具。它尤其擅長髮現內存管理的問題,它可以檢查程序運行時的內存泄漏問題。
它的官方網址是 http://www.valgrind.org/
下載最新版本的Valgrind,目前是3.2.0。 wget http://www.valgrind.org/downloads/valkyrie-1.2.0.tar.bz2
執行常規的安裝步驟:./confgure && make && make install。注意: 系統必須安裝QT的開發包。即便這樣在make 時還是出現qplatformdefs.h這個文件找不到的情況,導致make失敗。查找系統中的qplatformdefs.h 之後,發現沒有存在於qt的標準頭文件目錄/usr/lib/qt-3.3/include。如是將/usr/lib/qt- 3.3/mkspecs/linux-g++/ 目錄下該頭文件複製標準頭文件目錄,重新make ,後面一切OK。
初次使用
編譯如下代碼: gcc -Wall example.c -g -o example
#include <stdlib.h> |
注意:gcc 的-g 選項讓Valgrind調試輸出時指出相應信息的代碼所在的行號。
valgrind --tool=memcheck --leak-check=yes ./example |
==6742== Memcheck, a memory error detector for x86-linux. ==6742== Copyright (C) 2002-2004, and GNU GPL'd, by Julian Seward et al. ==6742== Using valgrind-2.2.0, a program supervision framework for x86-linux. ==6742== Copyright (C) 2000-2004, and GNU GPL'd, by Julian Seward et al. ==6742== For more details, rerun with: -v ==6742== ==6742== Invalid write of size 4 ==6742== at 0x8048384: f (example.c:6) ==6742== by 0x80483AC: main (example.c:12) ==6742== Address 0x1B908050 is 0 bytes after a block of size 40 alloc'd ==6742== at 0x1B904984: malloc (vg_replace_malloc.c:131) ==6742== by 0x8048377: f (example.c:5) ==6742== by 0x80483AC: main (example.c:12) ==6742== ==6742== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 12 from 1) ==6742== malloc/free: in use at exit: 40 bytes in 1 blocks. ==6742== malloc/free: 1 allocs, 0 frees, 40 bytes allocated. ==6742== For counts of detected errors, rerun with: -v ==6742== searching for pointers to 1 not-freed blocks. ==6742== checked 1360800 bytes. ==6742== ==6742== ==6742== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==6742== at 0x1B904984: malloc (vg_replace_malloc.c:131) ==6742== by 0x8048377: f (example.c:5) ==6742== by 0x80483AC: main (example.c:12) ==6742== ==6742== LEAK SUMMARY: ==6742== definitely lost: 40 bytes in 1 blocks. ==6742== possibly lost: 0 bytes in 0 blocks. ==6742== still reachable: 0 bytes in 0 blocks. ==6742== suppressed: 0 bytes in 0 blocks. ==6742== Reachable blocks (those to which a pointer was found) are not shown. ==6742== To see them, rerun with: --show-reachable=yes |
上面的C程序存在兩個錯誤:1. 數組下標越界;2. 分配的內存沒有釋放,存在內存泄露的問題。對於錯誤1,看Valgrind的調試信息片斷
==6742== Invalid write of size 4 ==6742== at 0x8048384: f (example.c:6) ==6742== by 0x80483AC: main (example.c:12) ==6742== Address 0x1B908050 is 0 bytes after a block of size 40 alloc'd ==6742== at 0x1B904984: malloc (vg_replace_malloc.c:131) ==6742== by 0x8048377: f (example.c:5) |
對於錯誤2,看這個
==6742== malloc/free: 1 allocs, 0 frees, 40 bytes allocated. ...... ==6742== 40 bytes in 1 blocks are definitely lost in loss record 1 of 1 |
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