指针由shmat指向返回的地址空间的末尾，它给出seg故障 [英] pointer returned by shmat points at the end of address space which gives seg fault

问题描述

  // TeamSize是一个整数
 int Seg_id = shmget（SHM_KEY，sizeof（Word）* TeamSize，IPC_CREAT）; 
 
 void * Seg_ptr = shmat（Seg_id，0,0）; 
 
 new（Seg_ptr）Word [TeamSize]; 
  

我在此段代码中遇到问题。 Word类是用8个字节的char数组和一些解析函数定义的类。我想我使用shmget和shmat就像别人使用它们。但我不断得到seg故障。当我打印出Seg_id，它看起来正常只是一些数字。但Seg_ptr指向0xffffffffffffffff。然后下一行代码显然给我seg故障。我想知道为什么Seg_ptr指向内存空间的结尾。提前感谢！

解决方案

测试后，似乎非root用户不能使用shmat或者它将返回Permission Denied。 / p>

晚更新：
设置权限有帮助，如shmget（SHM_KEY，sizeof（...），（IPC_CREAT | 0666）这个论点;它结果是共享内存段与相同的键已经存在。然后我可以使用ipcs检查我已经有共享内存段与相同的密钥，并使用ipcrm释放它。

 //TeamSize is an integer   
int Seg_id = shmget(SHM_KEY,sizeof(Word)*TeamSize,IPC_CREAT);

void* Seg_ptr = shmat(Seg_id,0,0);

new(Seg_ptr) Word[TeamSize];

I am having trouble with this segment of code. The Word class is a class that I defined with 8 bytes char array and some parse functions. I think I am using shmget and shmat just like how others use them. But I keep getting seg fault. When I print out Seg_id, it looks normal just some number. But Seg_ptr points at 0xffffffffffffffff. Then the next line of code obviously gives me seg fault. I want to know why Seg_ptr points at the end of memory space. Thanks in advance!

解决方案

After testing, it seems that non-root user cannot use shmat or it will return Permission Denied.

late update: setting permission helps, such as shmget(SHM_KEY, sizeof(...),(IPC_CREAT | 0666)).But I kept getting invalid argument with this ; it turned out shared memory segment with the same key already existed. I could then use ipcs to check if I already have the shared memory segment with the same key and use ipcrm to free it.

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