Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Commit MD parts of a loosely functional AMD64 port. This is based on
a heavily stripped down FreeBSD/i386 (brutally stripped down actually) to
attempt to get a stable base to start from. There is a lot missing still.
Worth noting:
- The kernel runs at 1GB in order to cheat with the pmap code. pmap uses
a variation of the PAE code in order to avoid having to worry about 4
levels of page tables yet.
- It boots in 64 bit "long mode" with a tiny trampoline embedded in the
i386 loader. This simplifies locore.s greatly.
- There are still quite a few fragments of i386-specific code that have
not been translated yet, and some that I cheated and wrote dumb C
versions of (bcopy etc).
- It has both int 0x80 for syscalls (but using registers for argument
passing, as is native on the amd64 ABI), and the 'syscall' instruction
for syscalls. int 0x80 preserves all registers, 'syscall' does not.
- I have tried to minimize looking at the NetBSD code, except in a couple
of places (eg: to find which register they use to replace the trashed
%rcx register in the syscall instruction). As a result, there is not a
lot of similarity. I did look at NetBSD a few times while debugging to
get some ideas about what I might have done wrong in my first attempt.

Split 4.x and 5.x signal handling so that we can keep 4.x signal
handling clean and functional as 5.x evolves. This allows some of the
nasty bandaids in the 5.x codepaths to be unwound.

Encapsulate 4.x signal handling under COMPAT_FREEBSD4 (there is an
anti-foot-shooting measure in place, 5.x folks need this for a while) and
finish encapsulating the older stuff under COMPAT_43. Since the ancient
stuff is required on alpha (longjmp(3) passes a 'struct osigcontext *'
to the current sigreturn(2), instead of the 'ucontext_t *' that sigreturn
is supposed to take), add a compile time check to prevent foot shooting
there too. Add uniform COMPAT_43 stubs for ia64/sparc64/powerpc.

Tested on: i386, alpha, ia64. Compiled on sparc64 (a few days ago).
Approved by: re

Use struct __ucontext in prototypes and associated functions instead of
ucontext_t. Forward declare struct __ucontext in <sys/signal.h> and
remove reliance on <sys/ucontext.h> being included.

While I'm here, also hide osigcontext types from userland; suggested
by bde.

Namespace pollution noticed by: Kevin Day <toasty@shell.dragondata.com>

style(9) the structure definitions.

Fix type of sf_addr.

Pointed out by: bde

Change the type of sf_addr in struct {o}sigframe from char* to
register_t.

Fix some style bugs and bitrotted comments.

Submitted by: bde

Simplification of the signal trampoline and other cleanups.

o Remove unused defines from genassym.c that were needed
by the trampoline.
o Add load_gs_param function to support.s that catches
a fault when %gs is loaded with an invalid descriptor.
The function returns EFAULT in that case.
o Remove struct trapframe from mcontext_t and replace it
with the list of registers.
o Modify sendsig and sigreturn accordingly.

This commit contains a patch by bde.

Reviewed by: luoqi, jdp

Fix style bugs caused by using the wrong file to copy from. That one
gets fixed later on.

Reinstate the mysterious 4th argument to signal handlers and add some
comments on that.

sigset_t change (part 3 of 5)
-----------------------------

By introducing a new sigframe so that the signal handler operates
on the new siginfo_t and on ucontext_t instead of sigcontext, we
now need two version of sendsig and sigreturn.

A flag in struct proc determines whether the process expects an
old sigframe or a new sigframe. The signal trampoline handles
which sigreturn to call. It does this by testing for a magic
cookie in the frame.

The alpha uses osigreturn to implement longjmp. This means that
osigreturn is not only used for compatibility with existing
binaries. To handle the new sigset_t, setjmp saves it in
sc_reserved (see NOTE).

the struct sigframe has been moved from frame.h to sigframe.h
to handle the complex header dependencies that was caused by
the new sigframe.

NOTE: For the i386, the size of jmp_buf has been increased to hold
the new sigset_t. On the alpha this has been prevented by
using sc_reserved in sigcontext.