| 2009年2月27日
介绍
Valgrind是x86架构Linux上的多重用途代码剖析和内存调试工具。但它的主要功能还是对内存的调试，默认工具也是启动 memcheck。用户可以在它的环境中运行程序来监视内存的使用情况，比如C语言中的malloc和free或者C++中的new和delete。
Valgrind主要检测如下内存问题：
- （1）使用未初始化的内存。
- （2）使用已经释放了的内存。
- （3）使用超过malloc分配的内存空间。
- （4）对堆栈的非法访问。
- （5）内存泄漏。
- （6）malloc/free/new/delete非匹配的使用内存申请和释放函数。
- （7）使用memcpy等函数时源地址和目的地址的重叠错误。
示例程序1：
#include <stdio.h>
#include <stdlib.h>
int main() {
struct mm{
int a;
int b;
}kk,*p;
kk.a = 10;
printf("kk.a : %d \n",kk.a);
p = (struct mm *)malloc(sizeof(struct mm));
p->a = 9;
printf("p->a : %d \n",p->a);
return 0;
}
编译源码：
helight@helight:test$ vim hello.c
helight@helight:test$ gcc -g -o hello hello.c
helight@helight:test$
使用valgrind检测内存问题：
helight@helight:test$ valgrind --tool=memcheck --leak-check=yes --show-reachable=yes ./hello
==6448== Memcheck, a memory error detector. 。。。
==6448== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 13 from 1)
==6448== malloc/free: in use at exit: 8 bytes in 1 blocks.
==6448== malloc/free: 1 allocs, 0 frees, 8 bytes allocated.
==6448== For counts of detected errors, rerun with: -v
==6448== searching for pointers to 1 not-freed blocks.
==6448== checked 59,964 bytes.
==6448==
==6448== 8 bytes in 1 blocks are definitely lost in loss record 1 of 1
==6448== at 0x4023D6E: malloc (vg_replace_malloc.c:207)
==6448== by 0x804840A: main (hello.c:12)
==6448== ==6448== LEAK SUMMARY:
==6448== definitely lost: 8 bytes in 1 blocks.
==6448== possibly lost: 0 bytes in 0 blocks.
==6448== still reachable: 0 bytes in 0 blocks.
==6448== suppressed: 0 bytes in 0 blocks.
helight@helight:test$
可以看出上面提示“malloc/free: 1 allocs, 0 frees, 8 bytes allocated.”，“definitely lost: 8 bytes in 1 blocks.”。即丢失了8个字节。
实例程序2：
#include <stdio.h>
#include <stdlib.h>
int main() {
struct mm{
int a;
int b;
}kk;
printf("kk.a : %d \n",kk.a);
return 0;
}
编译源码：
helight@helight:test$ vim hello.c
helight@helight:test$ gcc -g -o hello hello.c
helight@helight:test$
使用valgrind检测内存问题：
helight@helight:test$ valgrind --tool=memcheck --leak-check=yes --show-reachable=yes ./hello
==6635== Memcheck, a memory error detector.
==6635== Copyright (C) 2002-2007, and GNU GPL'd, by Julian Seward et al.
==6635== Using LibVEX rev 1854, a library for dynamic binary translation.
==6635== Copyright (C) 2004-2007, and GNU GPL'd, by OpenWorks LLP.
==6635== Using valgrind-3.3.1-Debian, a dynamic binary instrumentation framework.
==6635== Copyright (C) 2000-2007, and GNU GPL'd, by Julian Seward et al.
==6635== For more details, rerun with: -v
==6635==
==6635== Use of uninitialised value of size 4
==6635== at 0x40734C6: (within /lib/i686/cmov/libc-2.7.so)
==6635== by 0x4076CA3: vfprintf (in /lib/i686/cmov/libc-2.7.so)
==6635== by 0x407E46F: printf (in /lib/i686/cmov/libc-2.7.so)
==6635== by 0x80483C7: main (hello.c:10) ... kk.a : 134513673
==6635==
==6635== ERROR SUMMARY: 21 errors from 5 contexts (suppressed: 13 from 1)
==6635== malloc/free: in use at exit: 0 bytes in 0 blocks.
==6635== malloc/free: 0 allocs, 0 frees, 0 bytes allocated.
==6635== For counts of detected errors, rerun with: -v
==6635== All heap blocks were freed -- no leaks are possible.
helight@helight:test$
可以看出上面提示“Use of uninitialised value of size 4“，”by 0x80483C7: main (hello.c:10) ”。即使用了未初始化的值。
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