Linux C/C++ 內存泄漏檢測工具：Valgrind

Valgrind 是一款 Linux下（支持 x8六、x86_64和ppc32）程序的內存調試工具，它能夠對編譯後的二進制程序進行內存使用監測（C語言中的malloc和free，以及C++中的new和delete），找出內存泄漏問題。

　　Valgrind 中包含的 Memcheck 工具能夠檢查如下的程序錯誤：

　　使用未初始化的內存 (Use of uninitialised memory)
　　使用已經釋放了的內存 (Reading/writing memory after it has been free’d)
　　使用超過malloc分配的內存空間(Reading/writing off the end of malloc’d blocks)
　　對堆棧的非法訪問 (Reading/writing inappropriate areas on the stack)
　　申請的空間是否有釋放 (Memory leaks – where pointers to malloc’d blocks are lost forever)
　　malloc/free/new/delete申請和釋放內存的匹配(Mismatched use of malloc/new/new [] vs free/delete/delete [])
　　src和dst的重疊(Overlapping src and dst pointers in memcpy() and related functions)
　　重複free

　　一、編譯安裝 Valgrind：

wget  http://valgrind.org/downloads/valgrind-3.4.1.tar.bz2
tar xvf valgrind-3.4.1.tar.bz2
cd valgrind-3.4.1/
./configure --prefix=/usr/local/webserver/valgrind
make
make install

　　二、使用示例：對「ls」程序進程檢查，返回結果中的「definitely lost: 0 bytes in 0 blocks.」表示沒有內存泄漏。

[root@xoyo42 /]#  /usr/local/webserver/valgrind/bin/valgrind --tool=memcheck --leak-check=full ls /
==1157== Memcheck, a memory error detector.
==1157== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al.
==1157== Using LibVEX rev 1884, a library for dynamic binary translation.
==1157== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.
==1157== Using valgrind-3.4.1, a dynamic binary instrumentation framework.
==1157== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.
==1157== For more details, rerun with: -v
==1157== 
bin   data0  dev  home  lib64       media  mnt  opt   root  selinux  sys       tcsql.db.idx.pkey.dec  ttserver.pid  var
boot  data1  etc  lib   lost+found  misc   net  proc  sbin  srv      tcsql.db  tmp                    usr
==1157== 
==1157== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 5 from 1)
==1157== malloc/free: in use at exit: 28,471 bytes in 36 blocks.
==1157== malloc/free: 166 allocs, 130 frees, 51,377 bytes allocated.
==1157== For counts of detected errors, rerun with: -v
==1157== searching for pointers to 36 not-freed blocks.
==1157== checked 174,640 bytes.
==1157== 
==1157== LEAK SUMMARY:
==1157==     definitely lost: 0 bytes in 0 blocks.
==1157==      possibly lost: 0 bytes in 0 blocks.
==1157==    still reachable: 28,471 bytes in 36 blocks.
==1157==         suppressed: 0 bytes in 0 blocks.
==1157== Reachable blocks (those to which a pointer was found) are not shown.
==1157== To see them, rerun with: --leak-check=full --show-reachable=yes

　　三、使用示例：對一個使用libevent庫編寫的「httptest」程序進程檢查，返回結果中的「definitely lost: 255 bytes in 5 blocks.」表示發生內存泄漏。

[root@xoyo42 tcsql-0.1]#  /usr/local/webserver/valgrind/bin/valgrind --tool=memcheck --leak-check=full ./httptest
==1274== Memcheck, a memory error detector.
==1274== Copyright (C) 2002-2008, and GNU GPL'd, by Julian Seward et al.
==1274== Using LibVEX rev 1884, a library for dynamic binary translation.
==1274== Copyright (C) 2004-2008, and GNU GPL'd, by OpenWorks LLP.
==1274== Using valgrind-3.4.1, a dynamic binary instrumentation framework.
==1274== Copyright (C) 2000-2008, and GNU GPL'd, by Julian Seward et al.
==1274== For more details, rerun with: -v
==1274== 
==1274== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1005 from 2)
==1274== malloc/free: in use at exit: 402,291 bytes in 74 blocks.
==1274== malloc/free: 15,939 allocs, 15,865 frees, 6,281,523 bytes allocated.
==1274== For counts of detected errors, rerun with: -v
==1274== searching for pointers to 74 not-freed blocks.
==1274== checked 682,468,160 bytes.
==1274== 
==1274== 255 bytes in 5 blocks are definitely lost in loss record 17 of 32
==1274==    at 0x4A05FBB: malloc (vg_replace_malloc.c:207)
==1274==    by 0x3C1D809BC6:  evhttp_decode_uri (http.c:2105)
==1274==    by 0x401C75: tcsql_handler (in /data0/tcsql/cankao/tcsql-0.1/tcsql)
==1274==    by 0x3C1D80C88F: evhttp_get_body (http.c:1582)
==1274==    by 0x3C1D8065F7: event_base_loop (event.c:392)
==1274==    by 0x403E2F: main (in /data0/tcsql/cankao/tcsql-0.1/tcsql)
==1274== 
==1274== LEAK SUMMARY:
==1274==     definitely lost: 255 bytes in 5 blocks.
==1274==      possibly lost: 0 bytes in 0 blocks.
==1274==    still reachable: 402,036 bytes in 69 blocks.
==1274==         suppressed: 0 bytes in 0 blocks.
==1274== Reachable blocks (those to which a pointer was found) are not shown.
==1274== To see them, rerun with: --leak-check=full --show-reachable=yes

　　檢查httptest程序，發現有一處「char *decode_uri = evhttp_decode_uri(evhttp_request_uri(req));」中的「decode_uri」沒有被free，再程序處理完成後加上「free(decode_uri);」後，再使用Valgrind檢查，結果已是「definitely lost: 0 bytes in 0 blocks.」。