5# deepwhite
我看的是深入理解Linux内核，然后在看Linux内核设计和实现里，有相似的表述，应该不会错吧！深入理解lLinux内核里是这么说的:
Figure 3-2 shows how the two data structures are stored in the 2- ...
wucongdonglai 发表于 2010-8-12 11:49
5#deepwhite 我看的是深入理解Linux内核，然后在看Linux内核设计和实现里，有相似的表述，应该不会错吧！深入理解lLinux内核里是这么说的:
Figure 3-2 shows how the two data structures are stored in the 2-page (8 KB) memory area. The thread_info structure resides at the beginning of the memory area, and the stack grows downward from the end. The figure also shows that the tHRead_info structure and the task_struct structure are mutually linked by means of the fields task and tHRead_info, respectively.
Figure 3-2. Storing the thread_info structure and the process kernel stack in two page frames
[attach]31786[/attach]
……
The close association between the thread_info structure and the Kernel Mode stack just described offers a key benefit in terms of efficiency: the kernel can easily obtain the address of the thread_info structure of the process currently running on a CPU from the value of the esp register. In fact, if the thread_union structure is 8 KB (213 bytes) long, the kernel masks out the 13 least significant bits of esp to obtain the base address of the thread_info structure; on the other hand, if the thread_union structure is 4 KB long, the kernel masks out the 12 least significant bits of esp. This is done by the current_thread_info( ) function, which produces assembly language instructions like the following:
movl $0xffffe000,%ecx /* or 0xfffff000 for 4KB stacks */
andl %esp,%ecx
movl %ecx,p
After executing these three instructions, p contains the tHRead_info structure pointer of the process running on the CPU that executes the instruction.
这里面esp寄存器是存放着栈指针的，以那图做例子：在那图中的栈指针的位置是0x015fa878,而thread-info的位置是在于0x015fa000，它通过那段汇编指令，也就是0x015fa878减去0x00002000，得到的是0x015f8878啊，怎么都不可能是0x015fa000啊？所以我就疑惑嘛
于 2013-04-26 20:22:10发表:
movl $-8192,%eax,其中$非代表当前地址，是AT&T格式汇编语言格式，代表立即数。将-8192的补码0xffffe000存入寄存器eax
h.hbhychl 于 2010-10-03 18:49:51发表:
任务中，顶一下！
木头128 于 2010-10-03 12:41:29发表:
学习中
wucongdonglai 于 2010-08-13 08:29:24发表:
9# deepwhite
恩，的确，是我想歪了
csac2650 于 2010-08-12 23:28:43发表:
很不错，支持楼主！
希望和楼主可以做个朋友！
yanlong938 于 2010-08-12 22:53:58发表:
不明白。。。。。
taoe29 于 2010-08-12 17:42:12发表:
任务中，顶一下！
deepwhite 于 2010-08-12 13:57:23发表:
这段意思很明显啊。
假设现在的 esp 是 0x15fa878 ，它是在两个Page组成的一个大小为8K的 thread_unio
里面，且 thread_info 这个数据结构在这 8K 内存空间的起始位置。那么只要计算一下：
esp & 0xFFFFE000
就可以得到这 8K 空间起始地址了，也就是 thread_info的地址。
wucongdonglai 于 2010-08-12 13:03:59发表:
7# ahnuzq
对哦。理解错误，呵呵，多谢啦
ahnuzq 于 2010-08-12 11:58:13发表:
让哥来告诉你吧 -8129=2的32次方减去8192就是二进制的11111111111111111110000000000000。这就是-8192在内存中的存储。这个值再与上 $sp 不就是只保留上面的19位吗，不也就是一8k也就是两页的 最低地址吗 明白了吗
wucongdonglai 于 2010-08-12 11:49:04发表:
5# deepwhite
我看的是深入理解Linux内核，然后在看Linux内核设计和实现里，有相似的表述，应该不会错吧！深入理解lLinux内核里是这么说的:
Figure 3-2 shows how the two data structures are stored in the 2-page (8 KB) memory area. The thread_info structure resides at the beginning of the memory area, and the stack grows downward from the end. The figure also shows that the tHRead_info structure and the task_struct structure are mutually linked by means of the fields task and tHRead_info, respectively.
Figure 3-2. Storing the thread_info structure and the process kernel stack in two page frames
[attach]31786[/attach]
……
The close association between the thread_info structure and the Kernel Mode stack just described offers a key benefit in terms of efficiency: the kernel can easily obtain the address of the thread_info structure of the process currently running on a CPU from the value of the esp register. In fact, if the thread_union structure is 8 KB (213 bytes) long, the kernel masks out the 13 least significant bits of esp to obtain the base address of the thread_info structure; on the other hand, if the thread_union structure is 4 KB long, the kernel masks out the 12 least significant bits of esp. This is done by the current_thread_info( ) function, which produces assembly language instructions like the following:
movl $0xffffe000,%ecx /* or 0xfffff000 for 4KB stacks */
andl %esp,%ecx
movl %ecx,p
After executing these three instructions, p contains the tHRead_info structure pointer of the process running on the CPU that executes the instruction.
这里面esp寄存器是存放着栈指针的，以那图做例子：在那图中的栈指针的位置是0x015fa878,而thread-info的位置是在于0x015fa000，它通过那段汇编指令，也就是0x015fa878减去0x00002000，得到的是0x015f8878啊，怎么都不可能是0x015fa000啊？所以我就疑惑嘛
deepwhite 于 2010-08-12 09:18:13发表:
我查了一下，多数的资料里面都说，栈指针的底13位是thread_info的地址，这样的话将 栈地址减去 8192得到的是 thread_info，这样才说的通。
你是不是看错了，或者理解错了，还是你看的书有问题？
wucongdonglai 于 2010-08-12 08:45:14发表:
3# shenhao0129
完整的是这样的：
假定栈的大小为8KB，也就是说thread-info和栈所占的空间为8KB，栈从高位往低位增长！X86通过把栈指针的后13个有效位屏蔽掉来计算thread-info的偏移！该操作通过current-thread-info（）函数完成，汇编代码如下：
movl $-8192, %eax
andl %eap, %eax
其实这讲的是内核中由于X86没有设置一个专门的寄存器来存放指向进程描述符的指针，所以就只能通过栈指针来找到thread-info，然后在thread-info的task域找到进程描述符的地址！具体实现就是把那栈指针的后13位有效位给屏蔽掉!而我想问的也就是：这段汇编在我的理解中，只是把栈指针-8192，而不是屏蔽掉后13位有效位！对这比较不理解
shenhao0129 于 2010-08-11 18:34:24发表:
刚才找了一下资料，发现栈区都是页对齐的，并且是屏蔽低13位的。你给出来的那部分资料太简略了点，不知道你的是个什么情况
ecfarther1 于 2010-08-11 17:12:11发表:
好多东西需要学习的哦