Valgrind显示的空闲空间大于分配的空间

Question

我在程序上运行valgrind，它没有返回任何内存泄漏。但是，它显示的释放空间多于分配空间，并且我不确定为什么。

提前感谢

==4234== HEAP SUMMARY:
==4234==     in use at exit: 0 bytes in 0 blocks
==4234==   total heap usage: 304 allocs, 542 frees, 81,820 bytes allocated
==4234== 
==4234== All heap blocks were freed -- no leaks are possible
==4234== 
==4234== For counts of detected and suppressed errors, rerun with: -v
==4234== Use --track-origins=yes to see where uninitialised values come from
==4234== ERROR SUMMARY: 3555 errors from 13 contexts (suppressed: 0 from 0)

Answer 1

您可以使用--trace-malloc=yes选项检查正在分配的地址。我建议不要在大型​​应用程序上使用它！

例如，对于这个小应用程序

int main()
{
   int* pi = new int;
   delete pi;
}

我知道

paulf> ./vg-in-place --trace-malloc=yes ../vg_examples/noleak
==88971== Memcheck, a memory error detector
==88971== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==88971== Using Valgrind-3.16.0.GIT and LibVEX; rerun with -h for copyright info
==88971== Command: ../vg_examples/noleak
==88971== 
--88971-- _Znwm(4) = 0x5800040
--88971-- _ZdlPv(0x5800040)
==88971== 
==88971== HEAP SUMMARY:
==88971==     in use at exit: 0 bytes in 0 blocks
==88971==   total heap usage: 1 allocs, 1 frees, 4 bytes allocated
==88971== 
==88971== All heap blocks were freed -- no leaks are possible
==88971== 
==88971== For lists of detected and suppressed errors, rerun with: -s
==88971== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

一些注意事项

1. 除非您自己构建Valgrind，否则您可能想运行valgrind而不是vg-in-place。>
2. 函数名称被修饰。如果您想查看非混杂名称，可以运行

paulf>  ./vg-in-place --trace-malloc=yes ../vg_examples/noleak 2>&1 | /usr/bin/c++filt 

[snip]

--89034-- operator new(unsigned long)(4) = 0x5800040
--89034-- operator delete(void*)(0x5800040)