Valgrind 报告过多的 malloc

Question

考虑这段代码：

int main(int argc, char const *argv[])
{
    char *string = NULL;
    string = malloc(sizeof(char) * 30);
    free(string);
    return 0;
}

我 malloc 一个 char 指针，然后我释放它。现在考虑 valgrind 的输出：

==58317== Memcheck, a memory error detector
==58317== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==58317== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==58317== Command: ./a.out
==58317== 
==58317== 
==58317== HEAP SUMMARY:
==58317==     in use at exit: 34,941 bytes in 424 blocks
==58317==   total heap usage: 505 allocs, 81 frees, 41,099 bytes allocated
==58317== 
==58317== LEAK SUMMARY:
==58317==    definitely lost: 0 bytes in 0 blocks
==58317==    indirectly lost: 0 bytes in 0 blocks
==58317==      possibly lost: 0 bytes in 0 blocks
==58317==    still reachable: 0 bytes in 0 blocks
==58317==         suppressed: 34,941 bytes in 424 blocks
==58317== 
==58317== For counts of detected and suppressed errors, rerun with: -v
==58317== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

怎么可能有这么多的 malloc 和 free？

编辑：这是我使用valgrind --leak-check=yes --gen-suppressions=all ./a.out 运行时得到的，我正在尝试制作一个 supp 文件。

==60943== Memcheck, a memory error detector
==60943== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==60943== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==60943== Command: ./a.out
==60943== 
==60943== 
==60943== HEAP SUMMARY:
==60943==     in use at exit: 34,941 bytes in 424 blocks
==60943==   total heap usage: 505 allocs, 81 frees, 41,099 bytes allocated
==60943== 
==60943== LEAK SUMMARY:
==60943==    definitely lost: 0 bytes in 0 blocks
==60943==    indirectly lost: 0 bytes in 0 blocks
==60943==      possibly lost: 0 bytes in 0 blocks
==60943==    still reachable: 0 bytes in 0 blocks
==60943==         suppressed: 34,941 bytes in 424 blocks
==60943== 
==60943== For counts of detected and suppressed errors, rerun with: -v
==60943== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 15 from 15)

Answer 1

这些块由链接到您的可执行文件的系统库分配（其中一些也被释放）。

Valgrind 有一个默认的 suppression 文件，可以抑制系统库中的泄漏，您可以在输出中进一步看到：

==58317==         suppressed: 34,941 bytes in 424 blocks

如果您想详细了解究竟是什么被抑制了，您可以使用-v 选项。