structure. This field keeps track of how many levels deep we are nested
into the kernel. The nesting level is bumped at the start of a trap,
interrupt, syscall, or exception and is decremented on return. This is
used to detect the case when the kernel is returning back to a kernel
context in exception_return(). If we are returning to the kernel we need
to update the globaldata pointer register saved in the stack frame in case
we have switched CPU's between taking the initial interrupt that saved the
frame and returning. If we don't do this fixup it is possible for a CPU to
use the wrong per-cpu data. On UP systems this is not a problem, so the
code is conditional on SMP.
A count was used instead of simply checking the process status register in
the frame during exception_return() since there are critical sections at
the very start and end of a trap, exception, or interrupt from userland in
which we could trash the t7 register being used in userland. The counter
is incremented after adn before these critical sections respectively so
that we will not overwrite the saved t7 register if we are interrupted
during one of these critical sections.
include:
* Mutual exclusion is used instead of spl*(). See mutex(9). (Note: The
alpha port is still in transition and currently uses both.)
* Per-CPU idle processes.
* Interrupts are run in their own separate kernel threads and can be
preempted (i386 only).
Partially contributed by: BSDi (BSD/OS)
Submissions by (at least): cp, dfr, dillon, grog, jake, jhb, sheldonh
delivering SIGBUS). This will allow a non-superuser to control unaligned
access behaviour on a per-process basis once a userland control program
(uac) is written.
Reviewed by: obrien
Tested by: obrien
* Update drivers to the latest version of the bus interface.
The ISA drivers' use of the new resource api is minimal. Garrett has
some much cleaner drivers which should be more easily shared between
i386 and alpha. This has only been tested on cia based machines. It
should work on lca and apecs but I might have broken something.
work in progress and has never booted a real machine. Initial
development and testing was done using SimOS (see
http://simos.stanford.edu for details). On the SimOS simulator, this
port successfully reaches single-user mode and has been tested with
loads as high as one copy of /bin/ls :-).
Obtained from: partly from NetBSD/alpha
(and even run). These files don't necessarily make sense for a
FreeBSD/Alpha kernel build. That will come later and these files
will be changed accordingly.
