在Linux用户空间进程中，vsyscall页面的地址是什么？

I would like to acquire the address of the vsyscall page for my own uses. I only have two ideas here: alter the compiler to store this information in some known location after it is given to __start, or read /proc/[pid]/maps. I really don't want to read /proc/ as that is slow and shouldn't be necessary. I also don't want to make compiler modifications. Does anyone have an alternative? Is there a symbol I should know about?I would like to acquire the address of the vsys