- Kernel Symbolic Debugging for OpenBoot Firmware
modload -p misc/obpsym
obpsym is a kernel module that installs OpenBoot callback handlers that provide kernel symbol information to OpenBoot. OpenBoot firmware user interface commands use the callbacks to convert numeric addresses to kernel symbol names for display purposes, and to convert kernel symbol names to numeric literals allowing symbolic names to be used as input arguments to user interface commands.
Once obpsym is installed, kernel symbolic names may be used anywhere at the OpenBoot firmware's user interface command prompt in place of a literal (numeric) string. For example, if obpsym is installed, the OpenBoot firmware commands ctrace and dis typically display symbolic names and offsets in the form modname:symbolname + offset. User interface Commands such as dis can be given a kernel symbolic name such as ufs:ufs_mount instead of a numeric address.
Placing the command
into the system(4) file forces the kernel module misc/obpsym to be loaded and activates the kernel callbacks during the kernel startup sequence.
obpsym may be useful as a kernel debugger in situations where other kernel debuggers are not useful. For example, on SPARC machines, if obpsym is loaded, you may be able to use the OpenBoot firmware's ctrace command to display symbolic names in the stack backtrace after a watchdog reset.
The syntax for a kernel symbolic name is:
[ module-name : ] symbol-name
Where module-name is the name of the kernel module that the symbol symbol-name appears in. A NULL module name is taken as “all modules, in no particular order” by obpsym. The module name unix is equivalent to a NULL module name, so that conflicts with words defined in the firmware's vocabulary can be avoided.
Typically, OpenBoot firmware reads a word from the input stream and looks the word up in its internal vocabulary before checking if the word is a literal. Thus, kernel symbols, such as reset may be given as unix:reset to avoid the unexpected side effect of the firmware finding and executing a matching word in its vocabulary.
System configuration information file.
Platform-specific kernel symbol information.
See attributes(5) for descriptions of the following attributes:
Some OpenBoot firmware user interface commands may use system resources incompatibly with the way they are used by the Unix kernel. These commands and the use of this feature as a kernel debugger may cause interactions that the Unix kernel is not prepared to deal with. If this occurs, the Unix kernel and/or the OpenBoot firmware user interface commands may react unpredictably and may panic the system, or may hang or may cause other unpredictable results. For these reasons, the use of this feature is only minimally supported and recommended to be used only as a kernel debugger of last resort.
If a breakpoint or watchpoint is triggered while the console frame buffer is powered off, the system can crash and be left in a state from which it is difficult to recover. If one of these is triggered while the monitor is powered off, you will not be able to see the debugger output.
platform-name can be found using the -i option of uname(1)
obpsym is supported only on architectures that support OpenBoot firmware.
On some systems, OpenBoot must be completely RAM resident so the obpsym symbol callback support can be added to the firmware, if the firmware doesn't include support for the symbol callbacks. On these systems, obpsym may complain that it requires that “you must use ramforth to use this module”.
See the 『OpenBoot 2.x Command Reference Manual』『OpenBoot 2.x Command Reference Manual』 for details on how to use the ramforth command, how to place the command into nvramrc, and how to set use-nvramrc? to true. On systems with version 1.x OpenBoot firmware, nvramrc doesn't exist, and the ramforth command must be typed manually after each reset, in order to use this module.
Once installed, the symbol table callbacks can be disabled by using the following OpenBoot firmware command:
0 0 set-symbol-lookup