HP OpenVMS systems documentation

XDELTA and the target kernel are integrated into the same system. Normally, you choose to use one or the other. However, XDELTA and the target kernel can be used together. This section explains how they interoperate.

The XDELTA boot flag controls which debugger (XDELTA or the SCD target kernel) gets control first. If it is not set, the target kernel gets control first, and it is not possible to use XDELTA without rebooting. If it is set, XDELTA gets control first, but you can use XDELTA commands to switch to the target kernel and to switch INI$BRK behavior such that the target kernel gets control when INI$BRK is called.

Breakpoints always stick to the debugger that set them; for example, if you set a breakpoint at location "A" with XDELTA, and then you enter the commands 1;K (switch INI$BRK to the system code debugger) and ;R (start using the system code debugger) then, from SCD, you can set a breakpoint at location "B". If the system executes the breakpoint at A, XDELTA reports a breakpoint, and SCD will see nothing (though you could switch to SCD by issuing the XDELTA ;R command). If the system executes the breakpoint at B, SCD will get control and report a breakpoint (you cannot switch to XDELTA from SCD).

Notice that if you examine location A with SCD, or location B with XDELTA, you will see a BPT instruction, not the instruction that was originally there. This is because neither debugger has any information about the breakpoints set by the other debugger.

One useful way to use both debuggers together is when you have a system that exhibits a failure only after hours or days of heavy use. In this case, you can boot the system with SCD enabled (8000), but with XDELTA the default (0002) and with initial breakpoints enabled (0004). When you reach the initial breakpoint, set an XDELTA breakpoint at a location that will only be reached when the error occurs. Then proceed. When the error breakpoint is reached, possibly days later, then you can set up a remote system to debug it and enter the ;R command to XDELTA to switch control to SCD.

Here is another technique to use on Alpha when you do not know where to put an error breakpoint as previously mentioned. Boot the system with only the SCD boot flag set. When you see that the error has occurred, halt the system and initiate an IPL 14 interrupt, as you would to start XDELTA. The target kernel will get control and wait for a connection for SCD.

11.4 Setting Up the Host System

To set up the host system, you need access to all system images and drivers that are loaded (or can be loaded) on the target system. You should have access to a source listings kit or a copy of the following directories:

SYS$LOADABLE_IMAGES:
SYS$LIBRARY:
SYS$MESSAGE:

You need all the .EXE files in those directories. The .DSF files are available with the OpenVMS Alpha source listings kit.

Optionally, you need access to the source files for the images to be debugged. SCD will look for the source files in the directory where they were compiled. If your build system and host system are different, you must use the SET SOURCE command to point SCD to the location of the source code files. For an example of the SET SOURCE command, see Section 11.12.

Before making a connection to the target system, you must set up the logical name DBGHK$IMAGE_PATH, which must be set up as a search list to the area where the system images or .DSF files are kept. For example, if the copies are in the following directories:

DEVICE:[SYS$LDR] DEVICE:[SYSLIB] DEVICE:[SYSMSG]

you would define DBGHK$IMAGE_PATH as follows:

$ define dbghk$image_path DEVICE:[SYS$LDR],DEVICE:[SYSLIB],DEVICE:[SYSMSG]

This works well for debugging using all the images normally loaded on a given system. However, you might be using the debugger to test new code in an execlet or a new driver. Because that image is most likely in your default directory, you must define the logical name as follows:

$ define dbghk$image_path [],DEVICE:[SYS$LDR],DEVICE:[SYSLIB],DEVICE:[SYSMSG]

If SCD cannot find one of the images through this search path, a warning message is displayed. SCD will continue initialization as long as it finds at least two images. If SCD cannot find the SYS$BASE_IMAGE and SYS$PUBLIC_VECTORS files, which are the OpenVMS operating system's main image files, an error message is displayed and the debugger exits.

If and when this happens, check the directory for the image files and compare it to what is loaded on the target system.

11.5 Starting the System Code Debugger

To start SCD on the host side, enter the following command:

$ DEBUG/KEEP

SCD displays the DBG> prompt. With the DBGHK$IMAGE_PATH logical name defined, you can invoke the CONNECT command and the optional qualifiers /PASSWORD and /IMAGE_PATH.

To use the CONNECT command and the optional qualifiers (/PASSWORD and /IMAGE_PATH) to connect to the node with name nodename, enter the following command:

DBG> CONNECT %NODE_NAME nodename /PASSWORD="password"

If a password has been set up on the target system, you must use the /PASSWORD qualifier. If a password is not specified, a zero length string is passed to the target system as the password.

The /IMAGE_PATH qualifier is also optional. If you do not use this qualifier, SCD uses the DBGHK$IMAGE_PATH logical name as the default. The /IMAGE_PATH qualifier is a quick way to change the logical name. However, when you use it, you cannot specify a search list. You can use only a logical name or a device and directory, although the logical name can be a search list.

Usually, SCD obtains the source file name from the object file. This is put there by the compiler when the source is compiled with the /DEBUG qualifier. The SET SOURCE command can take a list of paths as a parameter. It treats them as a search list.

11.6 Summary of System Code Debugger Commands

In general, any OpenVMS debugger command can be used in SCD. For a complete list, refer to the HP OpenVMS Debugger Manual. The following are a few examples:

• Commands to manipulate the source display, such as TYPE and SCROLL.
• Commands used in OpenVMS debugger command programs, such as DO and IF.
• Commands that affect output formats, such as SET RADIX.
• Commands that manipulate symbols and scope, such as EVALUATE, SET LANGUAGE, and CANCEL SCOPE. Note that the debugger SHOW IMAGE command is equivalent to the XDELTA ;L command, and the debugger DEFINE command is equivalent to the XDELTA ;X command.
• Commands that cause code to be executed, such as STEP and GO. Note that the debugger STEP command is equivalent to the XDELTA S and O commands, and the debugger GO command is equivalent to the XDELTA ;P and ;G commands.
• Commands that manipulate breakpoints, such as SET BREAK and CANCEL BREAK. These commands are equivalent to the XDELTA ;B command. However, unlike XDELTA, there is no limit on the number of breakpoints in SCD.
• Commands that affect memory, such as DEPOSIT and EXAMINE. These commands are equivalent to the XDELTA /,!,[,",' commands.

You can also use the OpenVMS debugger command SDA to examine the target system with System Dump Analyzer semantics. This command, which is not available when debugging user programs, is described in the next section.

11.7 Using System Dump Analyzer Commands

Once a connection has been established to the target system, you can use the commands listed in the previous section to examine the target system. You can also use some System Dump Analyzer (SDA) commands, such as SHOW SUMMARY and SHOW DEVICE. This feature allows the system programmer to take advantage of the strengths of both the OpenVMS Debugger and SDA to examine the state of the target system and to debug system programs such as device drivers.

To obtain access to SDA commands, you simply type "SDA" at the OpenVMS Debugger prompt ("DBG>") at any time after a connection has been established to the target system. SDA initializes itself and then outputs the "SDA>" prompt. Enter SDA commands as required. (See Chapter 4 for more information.) To return to the OpenVMS Debugger, you enter "EXIT" at the "SDA>" prompt. Optionally, you may invoke SDA to perform a single command and then return immediately to the OpenVMS Debugger, as in the following example:

DBG>SDA SHOW SUMMARY

You may reenter SDA at any time, with or without the optional SDA command. Once SDA has been initialized, the SDA> prompt is output more quickly on subsequent occasions.

Note that there are some limitations on the use of SDA from within SCD.

• You cannot switch between processes, whether requested explicitly (SET PROCESS <name>) or implicitly (SHOW PROCESS <name>). The exception to this is that access to the system process is possible.
• You cannot switch between CPUs.
• SDA has no knowledge of the OpenVMS debugger's Motif or Windows interfaces. Therefore, all SDA input and output occurs at the terminal or window where the OpenVMS debugger was originally invoked. Also, while using SDA, the OpenVMS debugger window is not refreshed; you must exit SDA to allow the OpenVMS debugger window to be refreshed.
• When you invoke SDA from SCD with an immediate command, and that command produces a full screen of output, SDA displays the message "Press RETURN for more." followed by the "SDA>" prompt before continuing. If you enter another SDA command at this prompt, SDA does not automatically return to SCD upon completion. To do this, you must enter an EXIT command.

The SCD host and the target kernel use a private Ethernet protocol to communicate. The best way to ensure that the two systems can see each other is for them both to be on the same Ethernet segment. Otherwise, your network and its bridges must be set up to pass through the packets with the protocol 08-00-2B-80-4B and multicast address 09-00-2B-02-01-0F.

The network portion of the target system uses the specified Ethernet device and communicates through it. The network portion of the host system finds the first Ethernet device and communicates through it. If the host SCD picks the wrong device for your needs, then you can force it to use the correct device by defining the logical DBGHK$ADAPTOR as the template device name for the appropriate adaptor.

11.9 Troubleshooting Checklist

If you have trouble starting a connection, perform the following tasks to correct the problem:

• Check SCSNODE on the target system.
  It must match the name you are using in the host CONNECT command.
• Make sure that both the Ethernet and boot device have been specified correctly.
• Make sure that the host system is using the correct Ethernet device, and that the host and target systems are connected to the same Ethernet segment.
• Check the version of the operating system and make sure that both the host and target systems are running the same version of the OpenVMS operating system.

There are three possible network errors:

• NETRETRY
  Indicates the system code debugger connection is lost
• SENDRETRY
  Indicates a message send failure
• NETFAIL
  Results from the two previous errors

The netfail error message has a status code that can be one of the following values:

Value	Status
2, 4, 6	Internal network error, submit a problem report to HP.
8,10,14,16,18,20,26,28,34,38	Network protocol error, submit a problem report to HP.
22,24	Too many errors on the network device most likely due to congestion. Reduce the network traffic or switch to another network backbone.
30	Target system scratch memory not available. Check DBGTK_SCRATCH. If increasing this value does not help, submit a problem report to HP.
32	Ran out of target system scratch memory. Increase value of DBGTK_SCRATCH.
All others	There should not be any other network error codes printed. If one occurs that does not match the previous ones, submit a problem report to HP.

11.11 Access to Symbols in OpenVMS Executive Images

Accessing OpenVMS executive images' symbols is not always straightforward with SCD. Only a subset of the symbols may be accessible at one time and in some cases, the symbol value the debugger currently has may be stale. To understand these problems and their solutions, you must understand how the debugger maintains its symbol tables and what symbols exist in the OpenVMS executive images. The following sections briefly summarize these topics.

11.11.1 Overview of How the OpenVMS Debugger Maintains Symbols

The debugger can access symbols from any image in the OpenVMS loaded system image list by reading in either the .DSF or .EXE file for that particular image. The .EXE file contains information only about symbols that are part of the symbol vector for that image. The current image symbols for any set module are defined. (You can tell if you have the .DSF or .EXE file by doing a SHOW MODULE. If there are no modules, you have the .EXE file.) This includes any symbols in the SYS$BASE_IMAGE.EXE symbol vector for which the code or data resides in the current image. However, you cannot access a symbol that is part of the SYS$BASE_IMAGE.EXE symbol vector that resides in another image.

In general, at any one point in time, the debugger can access only the symbols from one image. It does this to reduce the time it takes to search for a symbol in a table. To load the symbols for a particular image, use the SET IMAGE command. When you set an image, the debugger loads all the symbols from the new image and makes that image the current image. The symbols from the previous image are in memory, but the debugger will not look through them to translate symbols. To remove symbols from memory for an image, use the CANCEL IMAGE command (which does not work on the main image, SYS$BASE_IMAGE).

There is a set of modules for each image the debugger accesses. The symbol tables in the image that are part of these modules are not loaded with the SET IMAGE command. Instead they can be loaded with the SET MODULE <module-name> or SET MODULE/ALL commands. As they are loaded, a new symbol table is created in memory under the symbol table for the image. Figure 11-1 shows what this looks like.

Figure 11-1 Maintaining Symbols

When the debugger needs to look up a symbol name, it first looks at the current image to find the information. If it does not find it there, it then looks into the appropriate module. It determines which module is appropriate by looking at the module range symbols which are part of the image symbol table.

To see the symbols that are currently loaded, use the debugger's SHOW SYMBOL command. This command has a few options to obtain more than just the symbol name and value. (See the HP OpenVMS Debugger Manual for more details.)

11.11.2 Overview of OpenVMS Executive Image Symbols

Depending on whether the debugger has access to the .DSF or .EXE file, different kinds of symbols could be loaded. Most users will have the .EXE file for the OpenVMS executive images and a .DSF file for their private images---that is, the images they are debugging.

The OpenVMS executive consists of two base images, SYS$BASE_IMAGE.EXE and SYS$PUBLIC_VECTORS.EXE, and a number of separately loadable executive images.

The two base images contain symbol vectors. For SYS$BASE_IMAGE.EXE, the symbol vector is used to define symbols accessible by all the separately loadable images. This allows these images to communicate with each other through cross-image routine calls and memory references. For SYS$PUBLIC_VECTORS.EXE, the symbol vector is used to define the OpenVMS system services. Because these symbol vectors are in the .EXE and the .DSF files, the debugger can load these symbols no matter which one you have.

All images in the OpenVMS executive also contain global and local symbols. However, none of these symbols ever gets into the .EXE file for the image. These symbols are put in the specific module's section of the .DSF file if that module was compiled using /DEBUG and the image was linked using /DSF.

11.11.3 Possible Problems You May Encounter

• Access to All Executive Image Symbols
  When the current image is not SYS$BASE_IMAGE, but one of the separately loaded images, the debugger does not have access to any of the symbols in the SYS$BASE_IMAGE symbol vector. This means you cannot access (set breakpoints, and so on) any of the cross-image routines or data cells. The only symbols you have access to are the ones defined by the current image.
  If the debugger has access only to the .EXE file, then only symbols that have vectors in the base image are accessible. For .DSF files, the current image symbols for any set module are defined. (You can tell if you have the .DSF or .EXE by using the SHOW MODULE command---if there are no modules you have the .EXE). This includes any symbols in the SYS$BASE_IMAGE.EXE symbol vector for which the code or data resides in the current image. However, the user cannot access a symbol that is part of the SYS$BASE_IMAGE.EXE symbol vector that resides in another image. For example, if you are in one image and you want to set a breakpoint in a cross-image routine from another image, you do not have access to the symbol. Of course, if you know in which image it is defined, you can do a SET IMAGE, SET MODULE/ALL, and then a SET BREAK.
  There is a debugger workaround for this problem. The debugger and SCD let you use the SET MODULE command on an image by prefixing the image name with SHARE$ (SHARE$SYS$BASE_IMAGE, for example). This treats that image as a module which is part of the current image. In the previous figure, think of it as another module in the module list for an image. Note, however, that only the symbols for the symbol vector are loaded. None of the symbols for the modules of the SHARE$xxx image are loaded. Therefore, this command is only useful for base images.
  So, in other words, by doing SET MODULE SHARE$SYS$BASE_IMAGE, the debugger gives you access to all cross-image symbols for the OpenVMS executive.
• Stale Data from the Symbol Vector
  When an OpenVMS executive based image is loaded, the values in the symbol vectors are only correct for information that resides in that based image. For all symbols that are defined in the separately loaded images, the based image contains a pointer to a placeholder location. For routine symbols this is a routine that just returns "an image not loaded" failure code. A symbol vector entry is fixed to contain the real symbol address when the image in which the data resides is loaded.
  Therefore, if you do a SET IMAGE command to a base image before all the symbol entries are corrected, the SET IMAGE obtains the placeholder value for those symbols. Then, once the image containing the real data is loaded, the debugger will still have the placeholder value. This means that you are looking at stale data. One solution to this is to make sure to do a SET IMAGE command on the base image in order to get the most up-to-date symbol vector loaded into memory.
  The CANCEL IMAGE/SET IMAGE combination does not currently work for SYS$BASE_IMAGE because it is the main image and DEBUG does not allow you to CANCEL the main image. Therefore, if you connect to the target system early in the boot process, you will have stale data as part of the SYS$BASE_IMAGE symbol table. However, the SET MODULE SHARE$xxx command always reloads the information from the symbol vector. So, to solve this problem you could SET IMAGE to an image other than SYS$BASE_IMAGE and then use the CANCEL MODULE SHARE$SYS$BASE_IMAGE and SET MODULE SHARE$SYS$BASE_IMAGE commands to do the same thing. The only other solution is to always connect to the target system once all images are loaded that define the real data for values in the symbol vectors. You could also enter the following commands, and you would obtain the latest values from the symbol vector:

  SET IMAGE EXEC_INIT SET MODULE/ALL SET MODULE SHARE$SYS$BASE_IMAGE

• Problems with SYS$BASE_IMAGE.DSF
  For those who have access to the SYS$BASE_IMAGE.DSF file, there may be another complication with accessing symbols from the symbol vector. The problem is that the module SYSTEM_ROUTINES contains the placeholder values for each symbol in the symbol vector. So, if SYSTEM_ROUTINES is the currently set module (which is the case if you are sitting at the INI$BRK breakpoint) then the debugger will have the placeholder value of the symbol as well as the value in the symbol vector. You can see what values are loaded with the SHOW SYMBOL/ADDRESS command. The symbol vector version should be marked with (global); the local one is not.
  To set a breakpoint at the correct code address for a routine when in this state, use the SHOW SYMBOL/ADDRESS command on the routine symbol name. If the global and local values for the code address are the same, then the image with the routine has not yet been loaded. If not, set a breakpoint at the code address for the global symbol.

11.12 Sample System Code Debugging Session

To reproduce this sample session, the host system needs access to the SYSTEM_DEBUG.DSF matching the SYSTEM_DEBUG.EXE file on your target system, and to the source file C_TEST_ROUTINES.C, which is available in SYS$EXAMPLES. The target system is booted with the boot flags 0, 8004, so it stops at an initial breakpoint. The system disk is DKB200, and the network device is ESA0 in the Alpha examples and EIA0 in the I64 examples.

Example 11-1 Booting an Alpha Target System

>>> b -fl 0,8004 dkb200,esa0 INIT-S-CPU... INIT-S-RESET_TC... INIT-S-ASIC... INIT-S-MEM... INIT-S-NVR... INIT-S-SCC... INIT-S-NI... INIT-S-SCSI... INIT-S-ISDN... INIT-S-TC0... AUDIT_BOOT_STARTS ... AUDIT_CHECKSUM_GOOD AUDIT_LOAD_BEGINS AUDIT_LOAD_DONE %SYSBOOT-I-GCTFIL, Using a configuration file to boot as a Galaxy instance. OpenVMS (TM) Alpha Operating System, Version V7.2 DBGTK: Initialization succeeded. Remote system debugging is now possible. DBGTK: Waiting at breakpoint for connection from remote host.

A sample I64 Boot Menu follows (long lines wrapped for clarity).

Example 11-2 Booting an I64 Target System

Please select a boot option EFI Shell [Built-in] PESOS - X8.2-AHI (Topaz BL2) on $1$DGA3890:[SYS2.] PESOS - X8.2-AHI (Topaz BL2) on $1$DGA3890:[SYS2.] sysboot PESOS - E8.2-ADH (Topaz BL1) on $1$DGA3891:[SYS2.] PESOS - E8.2-ADH (Topaz BL1) on $1$DGA3891:[SYS2.] sysboot Boot Option Maintenance Menu System Configuration Menu Select the "EFI Shell [Built-in]" Loading.: EFI Shell [Built-in] EFI Shell version 1.10 [14.61] Device mapping table fs0 : Acpi(HWP0002,100)/Pci(1|1)/Scsi(Pun0,Lun0)/HD(Part2, SigB3A4A931-1F2A-11D8-9EA1-AA000400FEFF) fs1 : Acpi(HWP0002,100)/Pci(1|1)/Scsi(Pun2,Lun0)/HD(Part1, SigF7B864C3) fs2 : Acpi(HWP0002,300)/Pci(1|0)/Fibre(WWN50001FE10011B15D, Lun2200)/HD(Part1,Sig51C7BEE1-070B-11D9-8099-AA000400FEFF) fs3 : Acpi(HWP0002,300)/Pci(1|0)/Fibre(WWN50001FE10011B15D, Lun2200)/HD(Part4,Sig51C7BEE0-070B-11D9-809A-AA000400FEFF) . . . Shell> Select the desired device/partion: Shell> fs1: fs1:\>

Use the utilities in \efi\vms. Use vms_show to list the devices and vms_set to set ethernet device (debug_dev), if necessary. Note that this set is sticky so it only needs to be done once. Then load the operating system with the desired flags. Note that Alpha and I64 use the same flags with the same meanings.

fs1:\> dir \efi\vms Directory of: fs1:\efi\vms 09/13/04 10:13a <DIR> 2,048 . 09/13/04 10:13a <DIR> 2,048 .. 09/13/04 10:13a <DIR> 2,048 tools 09/13/04 10:13a 3,101,184 ipb.exe 09/13/04 10:13a <DIR> 2,048 update 09/13/04 10:13a 846,336 vms_loader.efi 09/13/04 10:13a 244,224 vms_bcfg.efi 09/13/04 10:13a 218,112 vms_set.efi 09/13/04 10:13a 215,040 vms_show.efi 5 File(s) 4,624,896 bytes 4 Dir(s) fs1:\> \efi\vms\vms_show device VMS: EIA0 EFI: Acpi(000222F0,0)/Pci(3|0)/Mac(00306E39F77B) VMS: DKB200 EFI: fs1: Acpi(000222F0,100)/Pci(1|1)/Scsi(Pun2,Lun0) VMS: DKB0 EFI: fs0: Acpi(000222F0,100)/Pci(1|1)/Scsi(Pun0,Lun0) VMS: EWA0 EFI: Acpi(000222F0,100)/Pci(2|0)/Mac(00306E3977C5) . . .

Set the debug_dev to one of the connected ethernet devices:

fs1:\> \efi\vms\vms_set debug_dev eia0 VMS: EIA0 0-30-6E-39-F7-CF EFI: Acpi(000222F0,0)/Pci(3|0)/Mac(00306E39F7CF) fs1:\> \efi\vms\vms_show debug_dev VMS: EIA0 0-30-6E-39-F7-CF EFI: Acpi(000222F0,0)/Pci(3|0)/Mac(00306E39F7CF)

Boot up the OS. In this example, the boot is with the SCD and initial (early) breakpoint flags, using root 2 (SYS2), that will vary with system setups:

fs1:\> \efi\vms\vms_loader -flags "2,8004" hp OpenVMS Industry Standard 64 Operating System, Version XAHI-T3Z © Copyright 1976-2004 Hewlett-Packard Development Company, L.P. %EIA-I-BOOTDRIVER, Starting auto-negotiation %EIA-I-BOOTDRIVER, Auto-negotiation selected 100BaseTX FDX DBGTK: Initialization succeeded. Remote system debugging is now possible. DBGTK: Waiting at breakpoint for connection from remote host.