c - 使用无效命令的 fork 导致 valgrind 中的内存泄漏

Question

我有以下代码，它在 fork 中执行无效命令。以下代码在 valgrind 中返回内存泄漏。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdarg.h>
#include <errno.h>
#include <unistd.h>


int external_cmd(char **argv)
{
    int pid;

    if ((pid = fork()) == -1)
        return -1;

    if (pid == 0) {
        /* child */
        execvp(argv[0], argv);
        exit(0);

    } else if (pid < 0)
        return -1;

    int status;
    while (wait(&status) != pid);

    return 0;
}

int main ()
{
    char *argv[8] = {0};
    argv[0] = "tawtaw"; //<--------- invalid command
    argv[1] = "-a";

    char *mem = strdup("anychar");

    /* fork call */
    external_cmd(argv);

    free(mem);

   return(0);
}

用 valgrind 返回执行上面的代码:

$ valgrind --leak-check=full --show-leak-kinds=all ./test
==11573== Memcheck, a memory error detector
==11573== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==11573== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==11573== Command: ./test
==11573== 
==11574== 
==11574== HEAP SUMMARY:
==11574==     in use at exit: 8 bytes in 1 blocks
==11574==   total heap usage: 1 allocs, 0 frees, 8 bytes allocated
==11574== 
==11574== 8 bytes in 1 blocks are still reachable in loss record 1 of 1
==11574==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==11574==    by 0x4EBF729: strdup (strdup.c:42)
==11574==    by 0x400747: main (in /home/mohamed/Desktop/tech/test/test)
==11574== 
==11574== LEAK SUMMARY:
==11574==    definitely lost: 0 bytes in 0 blocks
==11574==    indirectly lost: 0 bytes in 0 blocks
==11574==      possibly lost: 0 bytes in 0 blocks
==11574==    still reachable: 8 bytes in 1 blocks
==11574==         suppressed: 0 bytes in 0 blocks
==11574== 
==11574== For counts of detected and suppressed errors, rerun with: -v
==11574== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
==11573== 
==11573== HEAP SUMMARY:
==11573==     in use at exit: 0 bytes in 0 blocks
==11573==   total heap usage: 1 allocs, 1 frees, 8 bytes allocated
==11573== 
==11573== All heap blocks were freed -- no leaks are possible
==11573== 
==11573== For counts of detected and suppressed errors, rerun with: -v
==11573== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

注意:如果我使用有效命令“ls”而不是“tawtaw”执行代码，则 valgring 不会返回内存泄漏。

我缺少什么？

Answer 1

这是意料之中的。当 execve() 无法执行命令时，它将控制权返回给您的代码，然后您退出并且永远不会从 strdup() 中释放内存。

当 execve 成功时，整个文件图像被替换，并且用 strdup() 分配的内存没有任何剩余。