Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Allow the ARM unwinder to work through modules. This will be used to add
support for unwinding from dtrace.

Tested by: gnn (with dtrace)
Sponsored by: ABT Systems Ltd

Pull the ARM ddb unwind code out to a new file. This will allow it to be
used by other places that expect to unwind the stack, e.g. dtrace and
stack(9).

As I have written most of this code I'm changing the license to the
standard FreeBSD license. I have received approval from the other
developers who have changed any of the affected code.

Approved by: ian, imp, rpaulo, eadler (all license change)

Remove the non-EABI code from the DDB stack unwinder, we only support the
ARM EABI now.

Cleanup up ARM *frame structures...

- Eliminate unused irqframe
- Eliminate unused saframe
- Instead of splitting r4-sp storage between the stack and switchframe,
just put all the registers in switchframe and eliminate the un_32 struct.

Submitted by: Svatopluk Kraus <onwahe@gmail.com>,
Michal Meloun <meloun@miracle.cz>

Fix the unwinder to get past functions with no stack but may cause an
exception. In this case no registers will be updated but the link register
will be copied to the program counter to be used to find the calling
function. In this case the program counter may be updated and we should
continue with the trace.

Remove the "Unable to unwind further" message from DDB.

The ARM version of DDB is supposedly reliable enough making this
message benign.

Remove extra parens to silence clang warning.

Fix undefined behavior: (1 << 31) is not defined as 1 is an int and this
shifts into the sign bit. Instead use (1U << 31) which gets the
expected result.

This fix is not ideal as it assumes a 32 bit int, but does fix the issue
for most cases.

A similar change was made in OpenBSD.

Discussed with: -arch, rdivacky
Reviewed by: cperciva

Indent the "scp=... rlv=..." to make it easier to read the backtrace.

Support reading registers r0-r3 when unwinding. There is a seperate
instruction to load these. We only hit it when unwinding past an trap frame
as in C r0-r3 would never have been saved onto the stack.

Fix comment block formatting.

EABI unwinder enhancements... When it's time to stop unwinding, don't
exit the loop until after printing info about the current frame. Also,
if executing the unwind function for a frame doesn't change the values of
any registers, log that and exit the loop rather than looping endlessly.

Move the __aeabi_unwind_cpp_pr{0,1,2} functions to libkern so they can be
referenced in a non-debug kernel.

Fix a typo where db_printf was spelt printf.

Update how we read the stack pointer to work on both GCC and clang.

Implement stack unwinding based on section 9 of the "Exception handling ABI
for the ARM architecture" documentation. The unwind tables are currently
not stored in the kernel but will be added later.

Final whitespace trim.

Print userspace backtrace for current thread.

Reviewed by: imp
Obtained from: Semihalf

When backtracing self, start with the current frame (i.e. the
frame of db_trace_self()) and not the caller's frame. The use
of builtin_frame_address(1) to get the caller's frame is not
reliable and can cause panics.

Implement db_trace_thread() by calling db_stack_trace_cmd() and
passing a frame pointer that comes from the thread context. This
fixes DDB backtraces by not unwinding debugger functions first.

Implement db_trace_self() by calling db_stack_trace_cmd()
and not db_trace_thread().

Break out stack(9) from ddb(4):

- Introduce per-architecture stack_machdep.c to hold stack_save(9).
- Introduce per-architecture machine/stack.h to capture any common
definitions required between db_trace.c and stack_machdep.c.
- Add new kernel option "options STACK"; we will build in stack(9) if it is
defined, or also if "options DDB" is defined to provide compatibility
with existing users of stack(9).

Add new stack_save_td(9) function, which allows the capture of a stacktrace
of another thread rather than the current thread, which the existing
stack_save(9) was limited to. It requires that the thread be neither
swapped out nor running, which is the responsibility of the consumer to
enforce.

Update stack(9) man page.

Build tested: amd64, arm, i386, ia64, powerpc, sparc64, sun4v
Runtime tested: amd64 (rwatson), arm (cognet), i386 (rwatson)

Simplify the pager support in DDB. Allowing different db commands to
install custom pager functions didn't actually happen in practice (they
all just used the simple pager and passed in a local quit pointer). So,
just hardcode the simple pager as the only pager and make it set a global
db_pager_quit flag that db commands can check when the user hits 'q' (or a
suitable variant) at the pager prompt. Also, now that it's easy to do so,
enable paging by default for all ddb commands. Any command that wishes to
honor the quit flag can do so by checking db_pager_quit. Note that the
pager can also be effectively disabled by setting $lines to 0.

Other fixes:
- 'show idt' on i386 and pc98 now actually checks the quit flag and
terminates early.
- 'show intr' now actually checks the quit flag and terminates early.

Move the prototypes of db_md_set_watchpoint(), db_md_clr_watchpoint()
and db_md_list_watchpoints() to ddb/ddb.h.

- Add support for saving stack traces and displaying them via printf(9)
and KTR.

Contributed by: Antoine Brodin <antoine.brodin@laposte.net>
Concept code from: Neal Fachan <neal@isilon.com>

Start all license statements with /*-

Don't include sys/user.h merely for its side-effect of recursively
including other headers.

Cleanup.

- Change the ddb paging "support" to use a variable (db_lines_per_page) to
control the number of lines per page rather than a constant. The variable
can be examined and changed in ddb as '$lines'. Setting the variable to
0 will effectively turn off paging.
- Change db_putchar() to force out pending whitespace before outputting
newlines and carriage returns so that one can rub out content on the
current line via '\r \r' type strings.
- Change the simple pager to rub out the --More-- prompt explicitly when
the routine exits.
- Add some aliases to the simple pager to make it more compatible with
more(1): 'e' and 'j' do a single line. 'd' does half a page, and
'f' does a full page.

MFC after: 1 month
Inspired by: kris

In db_stack_trace_cmd, remove the "pc" variable, we don't need it.

- Add support for "paging" in stack trace output. That is, when you do
a stack trace from ddb, the output will pause with a '--More--' prompt
every 18 lines. If you hit Enter, it will print another line and prompt
again. If you hit space it will output another page and then prompt.
If you hit 'q' or 'x' it will abort the rest of the stack trace.
- Fix the sparc64 userland stack trace to honor the total count of lines
to print. This is useful if your trace happens to walk back onto
0xdeadc0de and gets stuck in an endless loop.

MFC after: 1 month
Tested on: i386, alpha, sparc64

Unify db_stack_trace_cmd(). All it did was look up the thread given
the thread ID and call db_trace_thread().
Since arm has all the logic in db_stack_trace_cmd(), rename the
new DB_COMMAND function to db_stack_trace to avoid conflicts on
arm.
While here, have db_stack_trace parse its own arguments so that
we can use a more natural radix for IDs. If the ID is not a thread
ID, or more precisely when no thread exists with the ID, try if
there's a process with that ID and return the first thread in it.
This makes it easier to print stack traces from the ps output.

requested by: rwatson@
tested on: amd64, i386, ia64

Make kdb_backtrace() sort of work.

Update to kdb.

Import FreeBSD/arm kernel bits.
It only supports sa1110 (on simics) right now, but xscale support should come
soon.
Some of the initial work has been provided by :
Stephane Potvin <sepotvin at videotron.ca>
Most of this comes from NetBSD.