fix backtrace. it was broken.
- use db_read_bytes() to avoid faults.
- quite a few functions do not use frame pointers,
therefore always detect stack depth without a frame pointer.
however, since the framepointer(=r14) is used as a trapframe,
the code to detect the frame pointer is still needed.
- dump the contents of trapframe during backtracing.
- KNF

remove unused code

db_stack_trace_print: support trace/[at], starting trace from switchframe.

branches: 1.23.32; 1.23.42; 1.23.48;
Use "pc" and "sr" instead of "spc" and "ssr" to refer to those
registers in DDB. Names with initial "s" (for "saved") are somewhat
confusing to use. The fact that we use SPC/SSR registers to retrieve
values of PC/SR at the moment of trap is an immaterial implementation
detail.

branches: 1.22.2; 1.22.4; 1.22.6;
Handle leaf routines that were interrupted.
Clean up/prettify debug printfs and compile them unconditionally,
but only enable them if db_trace_debug is set.

branches: 1.21.42;
TRUE -> true, FALSE -> false

Replace the Mach-derived boolean_t type with the C99 bool type. A
future commit will replace use of TRUE and FALSE with true and false.

branches: 1.19.24;
CONSTCOND.

branches: 1.18.2;
bare asm -> __asm

merge ktrace-lwp.

branches: 1.16.2;
adapt to const changes.

Teach db_stack_trace_print() to step through trap frames so that
backtraces on kernel exceptions are actually useful. Stop tracing at
traps from user mode for now.

Fix pasto in comment.

branches: 1.13.8;
Wrap "unknown instruction in prologue" in TRACE_DEBUG. gcc3 reorders
instructions so that prologue code and function code get mixed, and
you get a lot of noice from this printf, making traceback very hard to
read if not useless.

Don't compare an integer variable to NULL.

__KERNEL_RCSID()

branches: 1.10.2;
Fix typo in printf message.

branches: 1.9.6;
Use "#define<tab>", white space nits.

_start -> start.

ANSIfy KNF.

branches: 1.6.4;
make db_[e]regs[] const

Add support stacktrace when a function contains "mov #n,r3; sub r3,r15"

DDB single step and stack trace support.

Rename the machine-specific stack trace printing functions
from db_stack_trace_cmd() to db_stack_trace_print(),
and add an additional argument, a function pointer for an
output routine (i.e. printf() or db_printf()).

Add db_stack_trace_cmd() in db_command.[ch], calling
db_stack_trace_print() with db_printf() as the printer.

Move count==-1 special handling from db_stack_trace_print() [nee
db_stack_trace_cmd()] to db_stack_trace_cmd() [nascent here].

Again, I'm unable to test compilation on all affected platforms,
so advance apologies for potential brokenness.

Interface change: db_printsym() takes a third argument, pr, a function
pointer indicating how to print the symbol. This allows db_printsym()
to called in places where db_printf() is not an appropriate output
function.

While straightforward, apologies in advance if I've introduced any minor
syntax errors; I was unable to test compilation this on all the affected
platforms.

branches: 1.1.2;
Merge in NetBSD/sh3 from cvs.kame.net repository.

Tree structure:
- sys/arch/sh3: sh3 generic code
As commented, in-chip device drivers are put into sys/arch/sh3/dev.
- sys/arch/evbsh3: sh3 evaluation boards (pure sh3 CPU, no fancy external HW)
- sys/arch/mmeye: Brains mmEye, www.brains.co.jp
MI source code includes couple of #ifdef for sh3-coff support.
(sh3 uses coff or elf)

Needs some more improvements, especialy in sys/arch/sh3/conf/files.sh3,
to compile the tree (due to last minute tree structure change).