ftruncate(), but without the pad arg.
There are several reasons for this. Consider 'mmap()'. On AMD64, the
function call (and syscall) ABI allow for 6 register arguments. Additional
arguments go on the stack. mmap(2) has 6 arguments. However, the syscall
definition has an extra 'int pad' argument. This pushes it to 7 arguments,
which means one must spill into the memory stack. Since the kernel API
doesn't match userland API, we have a hack in libc - libc/sys/mmap.c.
This implements the userland API by calling __syscall() with an extra
argument and the pad argument, for a total of 8 args. This is all
unnecessary and inconvenient for several things, including the kernel's
syscall handler code which now has to handle merging stack arguments with
register arguments. It is a big deal for certain 3rd party code.
I'm adding libc glue to make the transition totally painless. I had
intended to mark the old syscalls as COMPAT6, but the potential to shoot
your feet by building a new kernel without COMPAT_FREEBSD6 but with a
slighly older userland was too great. For now, they have manual
"freebsd6_" prefixes rather than being COMPAT6. They will go back to
being marked 'COMPAT6' after 7-stable starts.
Approved by: re (kensmith)
51504d9ac4