Debug Command 35 JIT (Just-in-Time) Debugger Registration/De-Registration Command

Parameters

Pid

Process of ID of debuggee
Cmd
DBG_C_RegDbg
Buffer
Pointer to JIT Debugger path name and arguments

Address of the buffer in which the fully-qualified path name of the JIT debugger is specified. The path name can be followed by an optional arguments to the JIT debugger. If %d is found in the arguments, the system will replace %d with the ID of the failing process. If %d is not found in the arguments, the system will assume argument one is the process ID.

A coded example of this follows

Assume the ID of the failing process is 99.

If Buffer contains "C \OS2\MYJITDBG.EXE /Tn /K /P%d", the system will launch the JIT debugger as "C \OS2\MYJITDBG.EXE /Tn /K /P99"

If Buffer contains "C \OS2\MYJITDBG.EXE /Tn /K", the system will launch the JIT debugger as "C \OS2\MYJITDBG.EXE 99 /Tn /K"

Len
0 or the size of Buffer in bytes

A Len of 0 is used to deregister the JIT debugger from the given process. Buffer is ignored in this case. If Len is 0 and no JIT debugger is registered the system will return error code ERROR_INSUFFICIENT_BUFFER.

Addr
Registration Flags

JIT_REG_INHERIT

Enable children processes to inherit registered per-process JIT debugger from parent. (This is the default.)
JIT_REG_NONINHERIT
Do not allow inheritance of per-process JIT debugger to the children of that parent process.
If Inheritance is being used with DosStartSession() on a PM application, the inheritance link is broken. This is due to the design of sessions management for DosStartSession() which causes all children processes to always inherit from the PM. The recommended way to start a child process is through DosExecPgm() under the same session type. The parent-child relationship will be set up correctly and the JIT will be inherited. Otherwise the parent application has to register the JIT on every DosStartSession() child process. The JIT could also be registered on the main PMSHELL.EXE process. This would cause all future DosStartSession() processes to inherit the JIT information from PM. This works around the DosStartSession() inheritance problem above.
Value
Return error code, if any

Returns

The only DosDebug notifications that are returned by this command are DBG_N_Success and DBG_N_Error.

Valid Field return error return code(s)

ERROR_FILE_NOT_FOUND

File was not found in specified path
ERROR_INSUFFICIENT BUFFER
Returned if JIT Debugger not registered and a Len of 0 passed into register

Restrictions

This is one of the only DosDebug commands that can be called without having to issue a DBG_C_Connect or DBG_C_Attach first. This command is usually called after starting a process using DosExecPgm() or DosStartSession() in order to gather the PID to use with the registration command. Another way of gathering PID information is to use the DosQuerySysState(). This will return all of the current Process ID's running in the system. See DosQuerySysState() for more information. The registration of the debugger must use a fully-qualified path name and executable for per-process and global registration. Registration will not occur if the debugger is not physically found on the disk upon registration. If you make multiple calls to DosDebug with the DBG_C_RegDbg command, the previous debugger will be deleted and the newest one will be registered. If the DBG_C_RegDbg is called with the size field of 0 and a JIT debugger exists, the JIT debugger will be unregistered. This only applies for per-process JIT registration. Global registration cannot be unregistered. This is set for a systemwide level.

If a per-process JIT registration exists, it will be used over the global JIT registration specified in the CONFIG.SYS.

Remarks

The JIT debugger is invoked when an application process encounters a trap or exception not serviced by that application's exception management. Under normal operations, where a JIT debugger has not been registered with the OS, the application would be terminated by the user on a Hard Error Popup. This disallowed state information from being gathered. By registering a JIT debugger with the OS, the OS will launch the JIT debugger in place of the Hard Error popup.

The JIT debugger should attach to the dying process allowing the user to debug the dying process using a conventional debug program or just gather state debugger (unattended). A state debugger would gather required information to determine the state of the process dying; e.g., stack, registers, addresses, storage, etc. Once the state is gathered, the state debugger could save it to a log and terminate the offending process and/or start a new process in place of the old. This is completely customizable in the JIT debugger.

There are two types of JIT registration supported in OS/2. The first type is global registration. This allows the user to register a global debugger for the entire OS in the CONFIG.SYS. This debugger will be launched for any process in the OS that has an error. The global debugger will not support launching a PM (Presentation Manager(R)) JIT debugger. This has to be a VIO application (or one that produces no screen output) because of the organization of the boot cycle at which a JIT debugger can be invoked. The global JIT registration is done before the loading of device drivers, IFS, CALLS, and RUNS. This enables JIT support for all of these types of files.

The syntax for the CONFIG.SYS is as follows

JITDBGREG=[JIT_PathName] [arguments]

Refer to Buffer under parameters section above to see how [JIT_PathName] and [arguments] are used.

Example

JITDBGREG=c \os2\MYJITDBG.EXE /Tn /K /PID%d

The second type of JIT registration is the per-process registration. This type of registration allows the user to register any type of debugger including PM and VIO using the DBG_C_RegDbg command above.

Attention The JIT debugger writer needs to be aware of the environment that the JIT is being used in because of PM and VIO considerations for starting the debugger in regards session management and screen groups.

Note: For kernel debugger users there is an option to turn off the JIT debugger support when trying to catch traps in the kernel debugger. See the .on, .of and .oq switches in the kernel debugger help.

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