Valgrind检测内存读写越界

迈不过友情╰ 2021-09-19 11:24 316阅读 0赞

**一 点睛**

内存读写越界是指访问了没有权限访问的内存地址空间，比如访问数组时越界，对动态内存访问超出了申请时内存的大小范围。

**二 内存读写越界例子**

#include<stdlib.h>
    #include<iostream>
    using namespace std;
    int main(){
        int len=4;
        int *pt=(int *)malloc(len*sizeof(int));
        int *p=pt;
        for(int i=0;i<len;i++)
                p++;
        *p=5;
        cout<<"the value of p is "<<*p<<endl;
        return 0;
    }

**三 编译并运行**

[root@localhost charpter05]# g++ -g 0511.cpp -o 0511
    [root@localhost charpter05]# ./0511
    the value of p is 5

**四 用Valgrind检测内存**

[root@localhost charpter05]# valgrind ./0511
    ==18335== Memcheck, a memory error detector
    ==18335== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
    ==18335== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
    ==18335== Command: ./0511
    ==18335==
    ==18335== Invalid write of size 4
    ==18335==    at 0x400948: main (0511.cpp:10)
    ==18335==  Address 0x5a1a050 is 0 bytes after a block of size 16 alloc'd
    ==18335==    at 0x4C29EC3: malloc (vg_replace_malloc.c:309)
    ==18335==    by 0x40091D: main (0511.cpp:6)
    ==18335==
    ==18335== Invalid read of size 4
    ==18335==    at 0x400952: main (0511.cpp:11)
    ==18335==  Address 0x5a1a050 is 0 bytes after a block of size 16 alloc'd
    ==18335==    at 0x4C29EC3: malloc (vg_replace_malloc.c:309)
    ==18335==    by 0x40091D: main (0511.cpp:6)
    ==18335==
    the value of p is 5
    ==18335==
    ==18335== HEAP SUMMARY:
    ==18335==     in use at exit: 16 bytes in 1 blocks
    ==18335==   total heap usage: 1 allocs, 0 frees, 16 bytes allocated
    ==18335==
    ==18335== LEAK SUMMARY:
    ==18335==    definitely lost: 16 bytes in 1 blocks
    ==18335==    indirectly lost: 0 bytes in 0 blocks
    ==18335==      possibly lost: 0 bytes in 0 blocks
    ==18335==    still reachable: 0 bytes in 0 blocks
    ==18335==         suppressed: 0 bytes in 0 blocks
    ==18335== Rerun with --leak-check=full to see details of leaked memory
    ==18335==
    ==18335== For lists of detected and suppressed errors, rerun with: -s
    ==18335== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

**五 分析**

1 下面这个输出说明第10行，进行了非法写错误。

==18335== Invalid write of size 4
    ==18335==    at 0x400948: main (0511.cpp:10)
    ==18335==  Address 0x5a1a050 is 0 bytes after a block of size 16 alloc'd
    ==18335==    at 0x4C29EC3: malloc (vg_replace_malloc.c:309)
    ==18335==    by 0x40091D: main (0511.cpp:6)

2 下面这个输出说明第11行，进行了非法读操作

==18335== Invalid read of size 4
    ==18335==    at 0x400952: main (0511.cpp:11)
    ==18335==  Address 0x5a1a050 is 0 bytes after a block of size 16 alloc'd
    ==18335==    at 0x4C29EC3: malloc (vg_replace_malloc.c:309)
    ==18335==    by 0x40091D: main (0511.cpp:6)