valgrind定位内存问题

valgrind介绍

       Valgrind是一个GPL的软件，用于Linux（For x86, amd64 and ppc32）程序的内存调试和代码剖析。你可以在它的环境中运行你的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。使用Valgrind的工具包，你可以自动的检测许多内存管理和线程的bug，避免花费太多的时间在bug寻找上，使得你的程序更加稳固。

Valgrind的主要功能 
　　Valgrind工具包包含多个工具，如Memcheck,Cachegrind,Helgrind, Callgrind，Massif。下面分别介绍个工具的作用：

Memcheck 工具主要检查下面的程序错误：

　　1.使用未初始化的内存 (Use of uninitialised memory) 
　　2.使用已经释放了的内存 (Reading/writing memory after it has been free’d) 
　　3.使用超过 malloc分配的内存空间(Reading/writing off the end of malloc’d blocks) 
　　4.对堆栈的非法访问 (Reading/writing inappropriate areas on the stack) 
　　5.申请的空间是否有释放 (Memory leaks – where pointers to malloc’d blocks are lost forever) 
　　6.malloc/free/new/delete申请和释放内存的匹配(Mismatched use of malloc/new/new [] vs free/delete/delete []) 
　　7.src和dst的重叠(Overlapping src and dst pointers in memcpy() and related functions) 

Callgrind 
　　Callgrind收集程序运行时的一些数据，函数调用关系等信息，还可以有选择地进行cache 模拟。在运行结束时，它会把分析数据写入一个文件。callgrind_annotate可以把这个文件的内容转化成可读的形式。

Cachegrind 
它模拟 CPU中的一级缓存I1,D1和L2二级缓存，能够精确地指出程序中 cache的丢失和命中。如果需要，它还能够为我们提供cache丢失次数，内存引用次数，以及每行代码，每个函数，每个模块，整个程序产生的指令数。这对优化程序有很大的帮助。

Helgrind 
　　它主要用来检查多线程程序中出现的竞争问题。Helgrind 寻找内存中被多个线程访问，而又没有一贯加锁的区域，这些区域往往是线程之间失去同步的地方，而且会导致难以发掘的错误。Helgrind实现了名为” Eraser” 的竞争检测算法，并做了进一步改进，减少了报告错误的次数。

Massif 
　　堆栈分析器，它能测量程序在堆栈中使用了多少内存，告诉我们堆块，堆管理块和栈的大小。Massif能帮助我们减少内存的使用，在带有虚拟内存的现代系统中，它还能够加速我们程序的运行，减少程序停留在交换区中的几率。

Ubuntu 安装valgrind： 
sudo apt-get install valgrind

测试示例:

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
//动态内存泄漏
static void mem_leak1(void)
{
    char *p = malloc(1);
}
 
//资源泄漏，代码中以文件描述符为例
static void mem_leak2(void)
{
    FILE *fp = fopen("test.txt", "w");
}
 
//动态内存越界
static void mem_overrun1(void)
{
    char *p = malloc(1);
    *(short*)p = 2;
 
    free(p);
}
 
//数据越界，字符串结束符'\0'
static void mem_overrun2(void)
{
    char array[5];
    strcpy(array, "hello");
}
 
//动态内存double free
static void mem_double_free(void)
{
    char *p = malloc(1);
    free(p);
    free(p);
}
 
/*
 * 使用野指针
 * 指向一个不可用内存区域的指针（已删除或未申请内存区域），称为野指针
 */
static void mem_free_wild_pointer(void)
{
    char *p;
    free(p);
}
 
int main()
{
    mem_leak1();
    mem_leak2();
    mem_overrun1();
    mem_overrun2();
    mem_double_free();
    mem_free_wild_pointer();
 
    return 0;
}

gcc 编译后，使用valgrind运行进行内存错误检测，结果如下：

tiany@tiany-desktop:~/program/C$ valgrind --track-fds=yes --leak-check=full --undef-value-errors=yes ./memErr 
==3691== Memcheck, a memory error detector
==3691== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==3691== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==3691== Command: ./memErr
==3691== 
//此处检测到了动态内存的越界
==3691== Invalid write of size 2
==3691==    at 0x40067C: mem_overrun1 (in /home/tiany/program/C/memErr)
==3691==    by 0x400724: main (in /home/tiany/program/C/memErr)
==3691==  Address 0x51fd310 is 0 bytes inside a block of size 1 alloc'd
==3691==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x400673: mem_overrun1 (in /home/tiany/program/C/memErr)
==3691==    by 0x400724: main (in /home/tiany/program/C/memErr)
==3691== 
//检测到double free
==3691== Invalid free() / delete / delete[] / realloc()
==3691==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x4006F9: mem_double_free (in /home/tiany/program/C/memErr)
==3691==    by 0x40072E: main (in /home/tiany/program/C/memErr)
==3691==  Address 0x51fd360 is 0 bytes inside a block of size 1 free'd
==3691==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x4006ED: mem_double_free (in /home/tiany/program/C/memErr)
==3691==    by 0x40072E: main (in /home/tiany/program/C/memErr)
==3691== 
//检测到未初始化变量的问题
==3691== Conditional jump or move depends on uninitialised value(s)
==3691==    at 0x4C2BDA2: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x40070F: mem_free_wild_pointer (in /home/tiany/program/C/memErr)
==3691==    by 0x400733: main (in /home/tiany/program/C/memErr)
==3691== 
//检测到非法使用野指针
==3691== Invalid free() / delete / delete[] / realloc()
==3691==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x40070F: mem_free_wild_pointer (in /home/tiany/program/C/memErr)
==3691==    by 0x400733: main (in /home/tiany/program/C/memErr)
==3691==  Address 0x51fd360 is 0 bytes inside a block of size 1 free'd
==3691==    at 0x4C2BDEC: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x4006ED: mem_double_free (in /home/tiany/program/C/memErr)
==3691==    by 0x40072E: main (in /home/tiany/program/C/memErr)
==3691== 
==3691== 
/*
 * 检测到文件指针资源的泄漏，即就是退出时未关闭打开的文件描述符
 */
==3691== FILE DESCRIPTORS: 4 open at exit.
==3691== Open file descriptor 3: test.txt
==3691==    at 0x4F234B0: __open_nocancel (syscall-template.S:81)
==3691==    by 0x4EB1E07: _IO_file_open (fileops.c:228)
==3691==    by 0x4EB1E07: _IO_file_fopen@@GLIBC_2.2.5 (fileops.c:333)
==3691==    by 0x4EA62E3: __fopen_internal (iofopen.c:90)
==3691==    by 0x40065B: mem_leak2 (in /home/tiany/program/C/memErr)
==3691==    by 0x40071F: main (in /home/tiany/program/C/memErr)
==3691== 
==3691== Open file descriptor 2: /dev/pts/8
==3691==    <inherited from parent>
==3691== 
==3691== Open file descriptor 1: /dev/pts/8
==3691==    <inherited from parent>
==3691== 
==3691== Open file descriptor 0: /dev/pts/8
==3691==    <inherited from parent>
==3691== 
==3691== 
//堆信息
==3691== HEAP SUMMARY:
==3691==     in use at exit: 569 bytes in 2 blocks
==3691==   total heap usage: 4 allocs, 4 frees, 571 bytes allocated
==3691== 
==3691== 1 bytes in 1 blocks are definitely lost in loss record 1 of 2
==3691==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3691==    by 0x40063E: mem_leak1 (in /home/tiany/program/C/memErr)
==3691==    by 0x40071A: main (in /home/tiany/program/C/memErr)
==3691== 
==3691== LEAK SUMMARY:
==3691==    definitely lost: 1 bytes in 1 blocks
==3691==    indirectly lost: 0 bytes in 0 blocks
==3691==      possibly lost: 0 bytes in 0 blocks
==3691==    still reachable: 568 bytes in 1 blocks
==3691==         suppressed: 0 bytes in 0 blocks
==3691== Reachable blocks (those to which a pointer was found) are not shown.
==3691== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==3691== 
==3691== For counts of detected and suppressed errors, rerun with: -v
==3691== Use --track-origins=yes to see where uninitialised values come from
==3691== ERROR SUMMARY: 6 errors from 5 contexts (suppressed: 0 from 0)