C Valgrind - memcpy中的源和目标重叠

Question

我是c编程的新手,我正在编写一个简单的客户端服务器应用程序.我收到这条消息:

 Source and destination overlap in memcpy(0x41f0beb, 0x41f0258, 69141077)
    ==9522==    at 0x402D9A9: memcpy (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
    ==9522==    by 0x8049C13: message_to_buffer (message.c:92)

这是具体的代码:

case CT_ENTRY://100
{
    int c=(2+2+4+strlen(msg->content.entry->key)-1+4+4+strlen(msg->content.entry->value->data));
    char *offset=malloc(c);
    *msg_buf=offset;
    memcpy(offset,&opcode,2);
    offset+=2;
    memcpy(offset,&ctype,2 );
    offset+=2;
    int ks=strlen(msg->content.entry->key);
    int ksc=host_to_net(ks);
    memcpy(offset,&ksc,4);
    offset+=4;
    memcpy(offset, msg->content.entry->key, ks);
    offset+=ks;
    int l=host_to_net(get_time());
    memcpy(offset,&l,4);
    offset+=4;
    int ds=host_to_net(msg->content.entry->value->datasize);
    memcpy(offset,&ds,4);
    offset+=4;

    // this line here!
    memcpy(offset,msg->content.entry->value->data, msg->content.value->datasize);

    return c;
    break;

违规行是

memcpy(offset,msg->content.entry->value->data, msg->content.value->datasize);

任何人都可以解释为什么会这样吗？谢谢

Answer 1

如果源和目标内存块重叠memmove,memcpy则必须使用而不是.

Answer 2

您要告知memcpy()复制69141077字节的数据.这看起来比你实际分配的大小要大得多offset(除非那些字符串真的很大).

所以,这是一个缓冲区溢出.检查msg->content.value->datasize分配的内容是否与您计算的大小相匹配offset.