Question

守则如下:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    char* buf = malloc(3);
    strcpy(buf, "hi");
    printf("%s
", buf);
    free(buf);
}

汇编如下:

gcc a.c && valgrind ./a.out

错误信息如下:

==1421== Memcheck, a memory error detector
==1421== Copyright (C) 2002-2010, and GNU GPL d, by Julian Seward et al.
==1421== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==1421== Command: ./a.out
==1421== 
==1421== Invalid read of size 8
==1421==    at 0x4EA96C1: ??? (in /lib/libc-2.14.1.so)
==1421==    by 0x4E92D3B: puts (in /lib/libc-2.14.1.so)
==1421==    by 0x4005BB: main (in /home/peter/a.out)
==1421==  Address 0x51b4040 is 0 bytes inside a block of size 3 alloc d
==1421==    at 0x4C2740D: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==1421==    by 0x400595: main (in /home/peter/a.out)
==1421== 
hi
==1421== 
==1421== HEAP SUMMARY:
==1421==     in use at exit: 0 bytes in 0 blocks
==1421==   total heap usage: 1 allocs, 1 frees, 3 bytes allocated
==1421== 
==1421== All heap blocks were freed -- no leaks are possible
==1421== 
==1421== For counts of detected and suppressed errors, rerun with: -v
==1421== ERROR SUMMARY: 2 errors from 1 contexts (suppressed: 6 from 6)

同样奇怪的是,如果我使用以下文字,那么四舍五入报告就不再出现错误(再加一空):

printf("%s 
", buf);

谁会帮助我?

Answer 1

这是一种诱杀,但并不是对所有机器进行再造。

在某些机器上,gcc优化了简单的<代码>f(),例如,puts(<>/code>,其中可能涉及无效读(或只是贬低)。



If it really matters, you can  complicate  the printf format.  A space between %s and 
 would do.

Here is a similar bug: C strings, strlen and Valgrind

这一答复结合了讨论中的意见。 谢谢大家。

Answer 2

我是用自己的机器管理,我没有错误:

==61755== Memcheck, a memory error detector
==61755== Copyright (C) 2002-2009, and GNU GPL d, by Julian Seward et al.
==61755== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==61755== Command: ./a.out
==61755==
hi
==61755==
==61755== HEAP SUMMARY:
==61755==     in use at exit: 0 bytes in 0 blocks
==61755==   total heap usage: 1 allocs, 1 frees, 3 bytes allocated
==61755==
==61755== All heap blocks were freed -- no leaks are possible
==61755==
==61755== For counts of detected and suppressed errors, rerun with: -v
==61755== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 6 from 6)

友情链接