linux内核中开头带有 asmlinkage 的函数表示什么

强制通过堆栈传递参数，不要用寄存器传递
仔细看一下有asmlinkage的地方通常是系统调用的函数，因为在系统调用中，寄存器从用户空间传过来后SAVE_ALL压入堆栈，接着调用相应的系统调用函数，这样系统调用函数一定要保证是通过堆栈传递参数的
转贴一段：
The asmlinkage tag is one other thing that we should observe about this simple function. This is a #define for some gcc magic that tells the compiler that the function should not expect to find any of its arguments in registers (a common optimization), but only on the CPU's stack. Recall our earlier assertion that system_call consumes its first argument, the system call number, and allows up to four more arguments that are passed along to the real system call. system_call achieves this feat simply by leaving its other arguments (which were passed to it in registers) on the stack. All system calls are marked with the asmlinkage tag, so they all look to the stack for arguments. Of course, in sys_ni_syscall's case, this doesn't make any difference, because sys_ni_syscall doesn't take any arguments, but it's an issue for most other system calls. And, because you'll be seeing asmlinkage in front of many other functions, I thought you should know what it was about.