From: Andy Lutomirski
> Sent: 25 January 2018 21:31
...
> Another potentially useful if rather minor optimization would be to
> rejigger the SYSCALL_DEFINE macros a bit. Currently we treat all
> syscalls like this:
>
> long func(long arg0, long arg1, long arg2, long arg3, long arg4, long arg5);
>
> I wonder if we'd be better off doing:
>
> long func(const struct pt_regs *regs);
>
> and autogenerating:
>
> static long SyS_read(const struct pt_regs *regs)
> {
> return sys_reg(regs->di, ...);
> }
Hmmm....
NetBSD (and the other BSD?) defines a structure for the arguments to each
syscall.
On systems where all function arguments are put on stack the user stack that
contains the arguments is copied into a kernel buffer.
For amd64 I changed the register save area layout so that the arguments were in
the right order [1]. Then added an extra area for the extra arguments that had
to be
read from the user stack.
Just passing a pointer into the save area has to be better than reading
all the values again.
[1] There was some horrid fallout from that :-(
David
