Question

我正在尝试在redhat 2.4.18上进行新的系统调用，并且我为其中一个系统调用创建了一个包装函数。
我现在将添加系统调用代码和包装代码添加说明如下系统调用：

int sys_read_TODO(pid_t pid, int TODO_index, char *TODO_description, ssize_t description_size, int* status){
    struct task_struct *curTask = current;
    struct task_struct *requestedTask = find_task_by_pid(pid);

    // check if the requested process is valid
    // check if he even exsits, and than whether he is this process, or one of his descendants.
    if(!isValidProcess(curTask,requestedTask)){
        return -ESRCH;
    }

    // the given process is ourself or one of our decendants.
    // now check if the arguments are valid
    if(TODO_description == NULL || status == NULL || TODO_index < 1 || TODO_index > requestedTask->todoQueueLength){
        return -EINVAL;
    }

    // search for the requested todo and get his description
    struct list_head *pos;
    struct todoNode *curNode;
    int counter = 0;
    char *reqDesc = NULL;
    int reqStatus = 0;
    int reqDescLen = 0;
    list_for_each(pos,&(requestedTask->todoQueue)){
        counter +=1;
        if(counter == TODO_index){
            curNode = (todoNode*)list_entry(pos,todoNode,listNode);
            reqDesc = curNode->description;
            reqStatus = curNode->status;
            reqDescLen = curNode->descLen;
        }
    }
    // we got the description, now lets see if his size is bigger than the size they requested
    if(description_size < reqDescLen){
        return -EINVAL;
    }

    // try to update the status
    int bytes_left = copy_to_user(status,&(reqStatus),sizeof(int));
    // should we update the status using *status = reqStatus ?
    if(bytes_left > 0){
        return -EFAULT;
    }

    // now we will try to copy the description to user space
    bytes_left = copy_to_user(TODO_description,reqDesc,reqDescLen);
    if(bytes_left > 0){
        return -EFAULT;
    }

    // successful. return the number of description bytes copied, which is len.
    return reqDescLen;

}

包装器：

int read_TODO(pid_t pid, int TODO_index, char *TODO_description, ssize_t description_size, int* status){
    int res;
    __asm__
    (
        "pushl %%eax;"
        "pushl %%ebx;"
        "pushl %%ecx;"
        "pushl %%edx;"
        "movl $244, %%eax;"
        "movl %1, %%ebx;"
        "movl %2, %%ecx;"
        "movl %3, %%edx;"
        "movl %4, %%esi;"
        "movl %5, %%edi;"
        "int $0x80;"
        "movl %%eax,%0;"
        "popl %%edi;"
        "popl %%esi;"
        "popl %%edx;"
        "popl %%ecx;"
        "popl %%ebx;"
        "popl %%eax;"
        : "=m" (res)
        : "m" (pid) ,"m" (TODO_index) ,"m"(TODO_description) ,"m" (description_size) ,"m"(status)
    );
    printf("read_TODO: res = %d\n",res);
    if (res < 0)
    {
        printf("read_TODO: res = %d\n",res);
        errno = res;
        printf("read_TODO: errno = %d\n",errno);
        printf("read_TODO: res = %d\n",res);
        res = -1;
    }
    return res;


}

所以故事如下：
我为每个进程添加了一个todo赋值列表，这个系统调用应该读取给定的todo赋值的描述。
系统调用可能会返回错误代码。在这种情况下，我被指示将错误代码放在errno中，并使函数返回-1 所以在包装器中我检查了系统调用的结果值是否为负数，如果是，则更新errno并返回-1。
问题是我在打印时注意到，当我尝试将res的值放入errno的值时，errno和res都会被分配奇怪的值。

从运行示例中我得到了这些照片：

read_TODO: res = -3
read_TODO: res = -3
read_TODO: errno = 134513874
read_TODO: res = 134513874

有什么问题？我该如何解决？

无法正确分配到errno

0 个答案: