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Document how to enter the debugger here. I'm sure there's some better

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canonical place, and the nit-pickers are welcome to move this
information there with a cross reference.

Differential Review: https://reviews.freebsd.org/D4860
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imp 2016-01-14 16:23:07 +00:00
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@ -1435,6 +1435,47 @@ The NMI allows one to break into the debugger on a wedged machine to
diagnose problems.
Other bus' bridge chipsets may be able to generate NMI using bus specific
methods.
There are many PCI and PCIe add-in cards which can generate NMI for
debugging.
Modern systems typically use IMPI to generate signals to enter the
debugger.
The
.Dv devel/ipmitool
port can be used to send the
.Cd chassis power diag
command which delivers an NMI to the processor.
.Pp
For serial consoles, you can break to the debugger by sending a BREAK
condition on the serial line if
.Cd options BREAK_TO_DEBUGGER
is specified in the kernel.
Most terminal emulation programs can send a break sequence with a
special key sequence or via a menu item.
However, in some setups, sending the break can be difficult to arrange
or happens spuriously, so if the kernel contains
.Cd options ALT_BREAK_TO_DEBUGGER
then the sequence of CR TILDE CTRL-B enters the debugger;
CR TILDE CTRL-P causes a panic instead of entering the
debugger; and
CR TILDE CTRL-R causes an immediate reboot.
In all the above sequences, CR is a Carriage Return and is usually
sent by hitting the Enter or Return key.
TILDE is the ASCII tilde character (~).
CTRL-x is Control x created by hitting the control key and then x
and then releasing both.
.Pp
The break to debugger behavior may also be enabled by setting the
.Xr sysctl 8
.Dv debug.kdb.break_to_debugger
to 1.
The alt break to debugger behavior may also be enabled by setting the
.Xr sysctl 8
.Dv debug.kdb.alt_break_to_debugger
to 1.
The debugger may be entered by setting the
.Xr sysctl 8
.Dv debug.kdb.enter
to 1.
.Sh FILES
Header files mentioned in this manual page can be found below
.Pa /usr/include