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Linux系统中怎么使用valgrind检查内存

时间:2021-04-10 来源:大神到 人气:

在使用Linux系统编写代码过程中,有可能会发送内存泄露的问题。所以用户就应该要学会检查内存,那么Linux如何检查内存呢?一般都是使用一些工具,本文就来介绍一下Linux系统中怎么使用valgrind检查内存。

请看一下代码:

#include 《stdlib.h》

#include 《stdio.h》

#include 《string.h》

static void mem_leak1(void)

{

char *p = malloc(1);

}

static void mem_leak2(void)

{

FILE *fp = fopen(;test.txt;, ;w;);

}

static void mem_overrun1(void)

{

char *p = malloc(1);

*(short*)p = 2;

free(p);

}

static void mem_overrun2(void)

{

char array[5];

strcpy(array, ;hello;);

}

static void mem_double_free(void)

{

char *p = malloc(1);

free(p);

free(p);

}

static void mem_use_wild_pointer(void)

{

char *p = (void*)0x80184800;

*p = 1;

}

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_use_wild_pointer();

mem_free_wild_pointer();

return 0;

}

常见的内存问题:

1. 动态内存泄露;

2. 资源泄露,这里以文件描述符为例;

3. 动态内存越界;

4.数组内存越界;

5.动态内存double free;

6.使用野指针,即未初始化的指针;

7.释放野指针,即未初始化的指针;

其中由于本示例代码过于简单,第6中情况,使用野指针会直接导致crash,所以在main中,并没有真正的调用那个示例代码。由于 valgrind只能检测执行到的代码,所以在后面的报告中,不会报告第6种错误情况。但是,在大型的项目中,有可能使用野指针并不会导致程序 crash。另外上面的7中情况,有些情况严格的说,实际上可以归为一类。

执行valgrind来检测内存错误:

valgrind --track-fds=yes --leak-check=full --undef-value-errors=yes 。/a.out

上面那些option的具体含义,可以参加valgrind --help,其中有些option默认就是打开的,不过我习惯于明确的使用option,以示清晰。

执行后的报告:

==2326== Memcheck, a memory error detector

==2326== Copyright (C) 2002-2009, and GNU GPLlsquo;d, by Julian Seward et al.

==2326== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info

==2326== Command: 。/a.out

==2326==

/* 这里检测到了动态内存的越界,提示Invalid write。*/

==2326== Invalid write of size 2

==2326== at 0x80484B4: mem_overrun1 (in /home/fgao/works/test/a.out)

==2326== by 0x8048553: main (in /home/fgao/works/test/a.out)

==2326== Address 0x40211f0 is 0 bytes inside a block of size 1 allocrsquo;d

==2326== at 0x4005BDC: malloc (vg_replace_malloc.c:195)

==2326== by 0x80484AD: mem_overrun1 (in /home/fgao/works/test/a.out)

==2326== by 0x8048553: main (in /home/fgao/works/test/a.out)

==2326==

/* 这里检测到了double free问题,提示Invalid Free */

==2326== Invalid free() / delete / delete[]

==2326== at 0x40057F6: free (vg_replace_malloc.c:325)

==2326== by 0x8048514: mem_double_free (in /home/fgao/works/test/a.out)

==2326== by 0x804855D: main (in /home/fgao/works/test/a.out)

==2326== Address 0x4021228 is 0 bytes inside a block of size 1 freelsquo;d

==2326== at 0x40057F6: free (vg_replace_malloc.c:325)

==2326== by 0x8048509: mem_double_free (in /home/fgao/works/test/a.out)

==2326== by 0x804855D: main (in /home/fgao/works/test/a.out)

==2326==

/* 这里检测到了未初始化变量 */

==2326== Conditional jump or move depends on uninitialised value(s)

==2326== at 0x40057B6: free (vg_replace_malloc.c:325)

==2326== by 0x804853C: mem_free_wild_pointer (in /home/fgao/works/test/a.out)

==2326== by 0x8048562: main (in /home/fgao/works/test/a.out)

==2326==

/* 这里检测到了非法是否野指针 */

==2326== Invalid free() / delete / delete[]

==2326== at 0x40057F6: free (vg_replace_malloc.c:325)

==2326== by 0x804853C: mem_free_wild_pointer (in /home/fgao/works/test/a.out)

==2326== by 0x8048562: main (in /home/fgao/works/test/a.out)

==2326== Address 0x4021228 is 0 bytes inside a block of size 1 freersquo;d

==2326== at 0x40057F6: free (vg_replace_malloc.c:325)

==2326== by 0x8048509: mem_double_free (in /home/fgao/works/test/a.out)

==2326== by 0x804855D: main (in /home/fgao/works/test/a.out)

==2326==

==2326==

/*

这里检测到了文件指针资源的泄露,下面提示说有4个文件描述符在退出时仍是打开的。

描述符0,1,2无需关心,通过报告,可以发现程序中自己明确打开的文件描述符没有关闭。

*/

==2326== FILE DESCRIPTORS: 4 open at exit.

==2326== Open file descriptor 3: test.txt

==2326== at 0x68D613: __open_nocancel (in /lib/libc-2.12.so)

==2326== by 0x61F8EC: __fopen_internal (in /lib/libc-2.12.so)

==2326== by 0x61F94B: fopen@@GLIBC_2.1 (in /lib/libc-2.12.so)

==2326== by 0x8048496: mem_leak2 (in /home/fgao/works/test/a.out)

==2326== by 0x804854E: main (in /home/fgao/works/test/a.out)

==2326==

==2326== Open file descriptor 2: /dev/pts/4

==2326==

==2326==

==2326== Open file descriptor 1: /dev/pts/4

==2326==

==2326==

==2326== Open file descriptor 0: /dev/pts/4

==2326==

==2326==

==2326==

/* 堆信息的总结:一共调用4次alloc,4次free。之所以正好相等,因为上面有一函数少了free,有一个函数多了一个free */

==2326== HEAP SUMMARY:

==2326== in use at exit: 353 bytes in 2 blocks

==2326== total heap usage: 4 allocs, 4 frees, 355 bytes allocated

==2326==

/* 检测到一个字节的内存泄露 */

==2326== 1 bytes in 1 blocks are definitely lost in loss record 1 of 2

==2326== at 0x4005BDC: malloc (vg_replace_malloc.c:195)

==2326== by 0x8048475: mem_leak1 (in /home/fgao/works/test/a.out)

==2326== by 0x8048549: main (in /home/fgao/works/test/a.out)

==2326==

/* 内存泄露的总结 */

==2326== LEAK SUMMARY:

==2326== definitely lost: 1 bytes in 1 blocks

==2326== indirectly lost: 0 bytes in 0 blocks

==2326== possibly lost: 0 bytes in 0 blocks

==2326== still reachable: 352 bytes in 1 blocks

==2326== suppressed: 0 bytes in 0 blocks

==2326== Reachable blocks (those to which a pointer was found) are not shown.

==2326== To see them, rerun with: --leak-check=full --show-reachable=yes

==2326==

==2326== For counts of detected and suppressed errors, rerun with: -v

==2326== Use --track-origins=yes to see where uninitialised values come from

==2326== ERROR SUMMARY: 5 errors from 5 contexts (suppressed: 12 from 8)

这个只是一个简单的示例程序,即使没有Valgrind,我们也可以很轻易的发现问题。但是在真实的项目中,当代码量达到万行,十万行,甚至百 万行时。由于申请的内存可能不是在一个地方使用,不可避免的被传来传去。这时,如果光是看review代码来检查问题,可能很难找到根本原因。这时,使用 Valgrind则可以很容易的发现问题所在。

以上就是Linux系统中怎么使用valgrind检查内存的介绍了,当然还有一些错误时valgrind检查不到的,用户应该尽量避免出现太多的错误。

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