c - Valgrind 内存检查输出

Question

我正在使用 valgrind 查找我系统上的内存泄漏，我收到了这个输出

==9697== Memcheck, a memory error detector
==9697== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.
==9697== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info
==9697== Command: bin/vfirewall-monitor
==9697== 
==9697== 
==9697== HEAP SUMMARY:
==9697==     in use at exit: 0 bytes in 0 blocks
==9697==   total heap usage: 1 allocs, 1 frees, 37 bytes allocated
==9697== 
==9697== All heap blocks were freed -- no leaks are possible
==9697== 
==9697== For counts of detected and suppressed errors, rerun with: -v
==9697== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
==9700== Thread 2:
==9700== Conditional jump or move depends on uninitialised value(s)
==9700==    at 0x56DE3B1: vfprintf (vfprintf.c:1630)
==9700==    by 0x5706441: vsnprintf (vsnprintf.c:120)
==9700==    by 0x56E6971: snprintf (snprintf.c:35)
==9700==    by 0x403A1A: save_interfaces_info (interfaces.c:351)
==9700==    by 0x403DC4: get_all_system_info (kernel.c:135)
==9700==    by 0x547DE99: start_thread (pthread_create.c:308)
==9700==    by 0x57873FC: clone (clone.S:112)
==9700==  Uninitialised value was created by a heap allocation
==9700==    at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==9700==    by 0x403D6F: get_all_system_info (kernel.c:118)
==9700==    by 0x547DE99: start_thread (pthread_create.c:308)
==9700==    by 0x57873FC: clone (clone.S:112)
==9700== 

它说没有错误，但我在 kernel.c:118 上有一个未初始化的值。

这是我在 118 处的 1kernel.c1:

117    Interface * ifaces;
118    ifaces = malloc(sizeof (Interface));
119    ifaces->next_interface = NULL;

我不明白这里有什么问题。我找错地方了吗？或者我读错了 valgrind 日志？

Answer 1

错误在 interfaces.c:351，它正在调用 snprintf 一个未初始化的值。

该值是使用 malloc 在 kernel.c:118 分配的。您可能知道，malloc 不会初始化它返回的内存，它可能包含垃圾。这就是它的提示。

您的 Interface 对象很可能有一个 char name[] 或诸如第一个成员之类的某些成员，您将该成员传递给 snprintf无需设置。

编辑:我知道问题出在 Interface 的第一个成员是因为如果它是其他内存，valgrind 会说类似 Uninitialised value is 4 bytes into a block created by堆分配 而不仅仅是 未初始化的值是由堆分配创建的。