In this book (understanding Linux kernel),
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 struc- ture 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
Why is "stack pointer(esp) & 0xffffe000" equal to the process descriptor base address?
That means the base address of process descriptor is always 0xXYZ...000, right? It is weird.
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