valgrind检查代码内存泄漏，5种内存泄漏情况

2022-07-20 21:00:45

摘要：

valgrind是linux下用于调试程序和查找内存泄露的常用工具。valgrind会报告5种内存泄露，"definitely lost", "indirectly lost", "possibly lost", "still reachable", and "suppressed"。笔者于工作闲暇之余对这5种（其实是4种，有一种没研究出结果）内存泄露的出现原因及区别进行了研究，撰此文以记之。

官方解释及分析：

摘自http://valgrind.org/docs/manual/faq.html#faq.deflost

5.2.With Memcheck's memory leak detector, what's the difference between "definitely lost", "indirectly lost", "possibly lost", "still reachable", and "suppressed"?

The details are in the Memcheck section of the user manual.

In short:

  • "definitely lost" means your program is leaking memory -- fix those leaks!
  • "indirectly lost" means your program is leaking memory in a pointer-based structure. (E.g. if the root node of a binary tree is "definitely lost", all the children will be "indirectly lost".) If you fix the "definitely lost" leaks, the "indirectly lost" leaks should go away.
  • "possibly lost" means your program is leaking memory, unless you're doing unusual things with pointers that could cause them to point into the middle of an allocated block; see the user manual for some possible causes. Use --show-possibly-lost=no if you don't want to see these reports.
  • "still reachable" means your program is probably ok -- it didn't free some memory it could have. This is quite common and often reasonable. Don't use --show-reachable=yes if you don't want to see these reports.
  • "suppressed" means that a leak error has been suppressed. There are some suppressions in the default suppression files. You can ignore suppressed errors.

translate

  • "definitely lost"：确认丢失。程序中存在内存泄露，应尽快修复。当程序结束时如果一块动态分配的内存没有被释放且通过程序内的指针变量均无法访问这块内存则会报这个错误。

  • "indirectly lost"：间接丢失。当使用了含有指针成员的类或结构时可能会报这个错误。这类错误无需直接修复，他们总是与"definitely lost"一起出现，只要修复"definitely lost"即可。例子可参考我的例程。

  • "possibly lost"：可能丢失。大多数情况下应视为与"definitely lost"一样需要尽快修复，除非你的程序让一个指针指向一块动态分配的内存（但不是这块内存起始地址），然后通过运算得到这块内存起始地址，再释放它。例子可参考我的例程。当程序结束时如果一块动态分配的内存没有被释放且通过程序内的指针变量均无法访问这块内存的起始地址，但可以访问其中的某一部分数据，则会报这个错误。

  • "still reachable"：可以访问，未丢失但也未释放。如果程序是正常结束的，那么它可能不会造成程序崩溃，但长时间运行有可能耗尽系统资源，因此笔者建议修复它。如果程序是崩溃（如访问非法的地址而崩溃）而非正常结束的，则应当暂时忽略它，先修复导致程序崩溃的错误，然后重新检测。

  • "suppressed"：已被解决。出现了内存泄露但系统自动处理了。可以无视这类错误。这类错误我没能用例程触发，看官方的解释也不太清楚是操作系统处理的还是valgrind，也没有遇到过。所以无视他吧~

测试程序：

源码(C++)：

#include "stdio.h"

#include "stdlib.h"  

class c1

{

private:

    char *m_pcData;  

public:

    c1();

    ~c1();

};  

c1::c1()

{

    m_pcData=(char*)malloc(10);

}  

c1::~c1()

{

    if(m_pcData) delete m_pcData;

}  

char *Fun1()//definitely lost

{

    char *pcTemp;  

    pcTemp=(char*)malloc(10);

    return pcTemp;

}  

char *Fun2()//still reachable

{

    static char *s_pcTemp=NULL;  

    if(s_pcTemp==NULL) s_pcTemp=(char*)malloc(10);  

    return NULL;

}  

char *Fun3()//possibly lost

{

    static char *s_pcTemp;

    char *pcData;  

    pcData=(char*)malloc(10);

    s_pcTemp=pcData+1;  

    return NULL;

}  

int Fun4()//definitely and indirectly lost

{

    c1 *pobjTest;  

    pobjTest=new c1();  

    return 0;

}  

char *Fun5()//possibly lost but no need of repair,repair the breakdown then no memory leak

{

    char *pcData;

    int i,*piTemp=NULL;  

    pcData=(char*)malloc(10);

    pcData+=10;

    for(i=0;i<10;i++)

    {

        pcData--;

        *pcData=0;  

        if(i==5) *piTemp=1;//create a breakdown

    }

    free(pcData);  

    return NULL;

}  

int main()

{

    printf("This program will create various memory leak,use valgrind to observe it.\n");

    printf("Following functions are bad codes,don\'t imitate.\n");

    printf("Fun1\n");

    Fun1();

    printf("Fun2\n");

    Fun2();

    printf("Fun3\n");

    Fun3();

    printf("Fun4\n");

    Fun4();

    printf("Fun5\n");

    Fun5();

    printf("end\n");  

    return 0;

}

使用valgrind运行结果：

[root@localhost valtest]# valgrind --tool=memcheck --leak-check=yes ./valtest

==29240== Memcheck, a memory error detector

==29240== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.

==29240== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info

==29240== Command: ./valtest

==29240==

This program will create various memory leak,use valgrind to observe it.

Following functions are bad codes,don't imitate.

Fun1

Fun2

Fun3

Fun4

Fun5

==29240== Invalid write of size 4

==29240==    at 0x4007BE: Fun5() (main.cpp:73)

==29240==    by 0x40086E: main (main.cpp:93)

==29240==  Address 0x0 is not stack'd, malloc'd or (recently) free'd

==29240==

==29240==

==29240== Process terminating with default action of signal 11 (SIGSEGV)

==29240==  Access not within mapped region at address 0x0

==29240==    at 0x4007BE: Fun5() (main.cpp:73)

==29240==    by 0x40086E: main (main.cpp:93)

==29240==  If you believe this happened as a result of a stack

==29240==  overflow in your program's main thread (unlikely but

==29240==  possible), you can try to increase the size of the

==29240==  main thread stack using the --main-stacksize= flag.

==29240==  The main thread stack size used in this run was 10485760.

==29240==

==29240== HEAP SUMMARY:

==29240==     in use at exit: 58 bytes in 6 blocks

==29240==   total heap usage: 6 allocs, 0 frees, 58 bytes allocated

==29240==

==29240== 10 bytes in 1 blocks are possibly lost in loss record 2 of 6

==29240==    at 0x4A05E1C: malloc (vg_replace_malloc.c:195)

==29240==    by 0x4006D9: Fun3() (main.cpp:46)

==29240==    by 0x400850: main (main.cpp:89)

==29240==

==29240== 10 bytes in 1 blocks are possibly lost in loss record 3 of 6

==29240==    at 0x4A05E1C: malloc (vg_replace_malloc.c:195)

==29240==    by 0x400795: Fun5() (main.cpp:66)

==29240==    by 0x40086E: main (main.cpp:93)

==29240==

==29240== 10 bytes in 1 blocks are definitely lost in loss record 5 of 6

==29240==    at 0x4A05E1C: malloc (vg_replace_malloc.c:195)

==29240==    by 0x40072D: Fun1() (main.cpp:28)

==29240==    by 0x400832: main (main.cpp:85)

==29240==

==29240== 18 (8 direct, 10 indirect) bytes in 1 blocks are definitely lost in loss record 6 of 6

==29240==    at 0x4A0666E: operator new(unsigned long) (vg_replace_malloc.c:220)

==29240==    by 0x4007F0: Fun4() (main.cpp:56)

==29240==    by 0x40085F: main (main.cpp:91)

==29240==

==29240== LEAK SUMMARY:

==29240==    definitely lost: 18 bytes in 2 blocks

==29240==    indirectly lost: 10 bytes in 1 blocks

==29240==      possibly lost: 20 bytes in 2 blocks

==29240==    still reachable: 10 bytes in 1 blocks

==29240==         suppressed: 0 bytes in 0 blocks

==29240== Reachable blocks (those to which a pointer was found) are not shown.

==29240== To see them, rerun with: --leak-check=full --show-reachable=yes

==29240==

==29240== For counts of detected and suppressed errors, rerun with: -v

==29240== ERROR SUMMARY: 5 errors from 5 contexts (suppressed: 4 from 4)

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