1 
==11136== Invalid read of size 8
==11136==    at 0x5AFC696: memrchr (memrchr.S:289)
==11136==    by 0x5B57FAF: dirname (dirname.c:45)
==11136==    by 0x405F43: push::lg_cmd_dirname(push::Env&) (LGExtension.cpp:379)
==11136==    by 0x42533C: push::Instruction::operator()(push::Env&) const (in /home/bots/svn/eco/branches/skynet_BigPUSH/src/push3.0/extension/push_bloodline)
==11136==    by 0x488ECD: push::Env::go(int) (Env.cpp:72)
==11136==    by 0x4A84D5: main (bloodline.cpp:99)
==11136==  Address 0x640daf8 is 8 bytes inside a block of size 10 alloc'd
==11136==    at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==11136==    by 0x5AEF801: strdup (strdup.c:43)
==11136==    by 0x405EF2: push::lg_cmd_dirname(push::Env&) (LGExtension.cpp:369)
==11136==    by 0x42533C: push::Instruction::operator()(push::Env&) const (in /home/bots/svn/eco/branches/skynet_BigPUSH/src/push3.0/extension/push_bloodline)
==11136==    by 0x488ECD: push::Env::go(int) (Env.cpp:72)
==11136==    by 0x4A84D5: main (bloodline.cpp:99)
==11136==

这是一个合法的错误吗？看起来读取发生在有效块内。在我的程序中，调用如下所示：

        char *path = strdup(full_path.c_str());
        cerr << "Path is : " << path << endl;
        result = dirname(path);
        if(result < 0){
                cerr << "Dirname failed for some reason. Check log." << endl;
        }

错误发生时 cerr 的输出是：

Path is : /tmp/tmp/

这是一个有效的路径。Dirname 对此应该没有任何问题，并且它在堆分配的副本上运行。

编辑：

这是一个会产生此错误的最小示例：

#include <string.h>
#include <stdio.h>
#include <iostream>
#include <libgen.h>

int main(){

        char *path = strdup("/tmp/tmp/");
        char* result = dirname(path);
        std::cerr << result << std::endl;
}

用 g++ 编译。

用 valgrind 运行，你会得到：

==32466== Memcheck, a memory error detector                                                                                                                                                                                                  
==32466== Copyright (C) 2002-2011, and GNU GPL'd, by Julian Seward et al.                                                                                                                                                                    
==32466== Using Valgrind-3.7.0 and LibVEX; rerun with -h for copyright info                                                                                                                                                                  
==32466== Command: ./a.out                                                                                                                                                                                                                   
==32466==                                                                                                                                                                                                                                    
==32466== Invalid read of size 8                                                                                                                                                                                                             
==32466==    at 0x51C7696: memrchr (memrchr.S:289)                                                                                                                                                                                           
==32466==    by 0x5222FAF: dirname (dirname.c:45)                                                                                                                                                                                            
==32466==    by 0x400865: main (in /home/j3doucet/a.out)                                                                                                                                                                                     
==32466==  Address 0x59ff048 is 8 bytes inside a block of size 10 alloc'd                                                                                                                                                                    
==32466==    at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)                                                                                                                                                   
==32466==    by 0x51BA801: strdup (strdup.c:43)                                                                                                                                                                                              
==32466==    by 0x400855: main (in /home/j3doucet/a.out)                                                                                                                                                                                     
==32466==                                                                                                                                                                                                                                    
/tmp
==32466== 
==32466== HEAP SUMMARY:
==32466==     in use at exit: 10 bytes in 1 blocks
==32466==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
==32466== 
==32466== LEAK SUMMARY:
==32466==    definitely lost: 10 bytes in 1 blocks
==32466==    indirectly lost: 0 bytes in 0 blocks
==32466==      possibly lost: 0 bytes in 0 blocks
==32466==    still reachable: 0 bytes in 0 blocks
==32466==         suppressed: 0 bytes in 0 blocks
==32466== Rerun with --leak-check=full to see details of leaked memory
==32466== 
==32466== For counts of detected and suppressed errors, rerun with: -v
==32466== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)
4

1 回答 1

1

Valgrind 指示从 10 字节块中的第 nr 8 字节开始读取大小为 8 的内容。此读取由 memrchr 完成。此类函数通常基于您可以读取比分配的块更多的字节的假设进行优化。为了避免报告此类问题，Valgrind 不得不用自己的重新定义函数替换此类优化函数。

memrchr 仅在 Valgrind 中从 3.8 版开始重新定义。

=> 你应该使用最新版本的 Valgrind (3.8.1) 重试。然后可能不再报告错误（假设由于未重新定义 memrchr 而实际上是误报）。

于 2012-10-04T20:25:38.117 回答