Specifications

Driver Testing and Debugging

15-19

matically under various conditions, such as panics and breakpoint traps. Any time the

kdb>> prompt displays, you are in the debugger. I/O is performed through the console or

a serial terminal.

To exit the debugger, press CTRL-d or q.

When you exit and re-enter the debugger, its state is preserved, including the contents of

the value stack.

kdb is an extremely powerful tool, and should be used carefully to avoid accidental cor-

ruption of kernel data structures, which could lead to a system crash. kdb has few provi-

sions for preventing programmer error.

NOTE

The kernel debugger is not meant for debugging user programs.

Use an appropriate user-level debugger, such as adb(1), for

that purpose.

kdb must exist in your kernel before you can use it (just like any device driver).

kdb prints and accepts address inputs symbolically, using kernel procedure and variable

names instead of hexadecimal numbers, but you must load the debugger with the kernel's

symbols after the debugger itself has been installed into the kernel. You can do this by

using the unixsyms command, which loads the symbols into the kernel executable file

after building it and before booting it. Normally, this is done automatically for you by

idbuild(1M).

Entering kdb from a Driver 15

If you are debugging a device driver or another part of the kernel, you can directly invoke

the kernel debugger by including the following code in your driver:

#include <sys/systm.h>

(*call_demon) (DR_OTHER, NO_FRAME);

This mechanism cannot be used for debugging early kernel startup code or driver init

routines, since the debugger cannot be used until its init routine, kdb_init, has been

called.

System Panics 15

If you expect that the driver could enter a state that is invalid, the driver can halt the system

using the cmn_err(D3) function with a panic ﬂag set. For example, if the driver expects

one of three specific cases in a switch statement, the driver can add a fourth default case

that calls the cmn_err() function. The system dumps an image of memory for later