HP OpenVMS systems documentation

Formats and types a single line to SYS$OUTPUT.

Format

int sda$type (char *ctrstr, __optional_params);

Arguments

ctrstr

OpenVMS usage	char_string
type	character-coded text string
access	read only
mechanism	by reference

Address of a zero-terminated FAO control string.

prmlst

OpenVMS usage	varying_arg
type	quadword (signed or unsigned)
access	read only
mechanism	by value

Optional FAO parameters. All arguments after the control string are copied into a quadword parameter list, as used by $FAOL_64.

Description

Formats and prints a single line to the terminal. This is unaffected by the use of the SDA commands SET OUTPUT or SET LOG.

Condition Values Returned

SDA$_SUCCESS	Indicates a successful completion.
SDA$_CNFLTARGS	Indicates more than twenty FAO parameters given.
Other	Returns from the $PUT issued by SDA$TYPE (the error is also signaled). If the $FAOL_64 call issued by SDA$TYPE fails, the control string is output.

Example

int status; 
... 
status = sda$type ("Invoking SHOW SUMMARY to output file..."); 
      

This example displays the message "Invoking SHOW SUMMARY to output file..." to the terminal.

Validates queue structures.

Format

void sda$validate_queue (VOID_PQ queue_header, __optional_params);

Arguments

queue_header

OpenVMS usage	address
type	quadword (unsigned)
access	read only
mechanism	by value

Address from which to start search.

options

OpenVMS usage	mask_longword
type	longword (unsigned)
access	read only
mechanism	by value

The following table shows the flags that indicate the type of queue:

Description

You can use this routine to validate the integrity of doubly-linked, singly-linked or self-relative queues either with longword or quadword links. If you specify the option SDA_OPT$M_QUEUE_LISTQUEUE, the queue elements are displayed for debugging. Otherwise a one-line summary indicates how many elements were found and whether the queue is intact.

Condition Values Returned

None

If an error occurs, it is signaled by SDA$VALIDATE_QUEUE.

Example

int64 temp; 
int64 *queue; 
... 
sda$symbol_value ("EXE$GL_NONPAGED", &temp); 
temp += 4; 
sda$reqmem ((VOID_PQ)temp, &queue, 4); 
sda$validate_queue (queue, SDA_OPT$M_QUEUE_SINGLINK); 
      

This sequence validates the nonpaged pool free list, and outputs a message of the form:

        Queue is zero-terminated, total of 204 elements in the queue 
      

• Building a system image to be debugged
• Setting up the target system for connections
• Setting up the host system
• Starting SCD
• Troubleshooting connections and network failures
• Looking at a sample SCD session
• Analyzing memory as recorded in a system dump
• Looking at a sample SDD session

This chapter describes the OpenVMS System Code Debugger (SCD) and how it can be used to debug nonpageable system code and device drivers running at any interrupt priority level (IPL).

You can use SCD to perform the following tasks:

• Control the system software's execution----stop at points of interest, resume execution, intercept fatal exceptions, and so on
• Trace the execution path of the system software
• Monitor exception conditions
• Examine and modify the values of variables
• Test the effect of modifications, in some cases, without having to edit the source code, recompile, and relink

The use of SCD requires two systems:

• The host system, probably also the system where the image to be debugged has been built
• The target system, usually a standalone test system, where the image being debugged is executed
• Host and target systems must be the same architecture, that is, both must be Alpha systems or I64 systems.

SCD is a symbolic debugger. You can specify variable names, routine names, and so on, precisely as they appear in your source code. SCD can also display the source code where the software is executing, and allow you to step by source line.

SCD recognizes the syntax, data typing, operators, expressions, scoping rules, and other constructs of a given language. If your code or driver is written in more than one language, you can change the debugging context from one language to another during a debugging session.

To use SCD, you must do the following:

• Build a system image or device driver to be debugged.
• Set up the target kernel on a standalone system.
  The target kernel is the part of SCD that resides on the system that is being debugged. It is integrated with XDELTA and is part of the SYSTEM_DEBUG execlet.
• Set up the host system environment, which is integrated with the OpenVMS Debugger.

The following sections cover these tasks in more detail, describe the available user-interface options, summarize applicable OpenVMS Debugger commands, and provide a sample SCD session.

11.1 User-Interface Options

SCD has the following user-interface options:

• A DECwindows Motif interface for workstations
  When using this interface, you interact with SCD by using a mouse and pointer to choose items from menus, click on buttons, select names in windows, and so on.
  Note that you can also use OpenVMS Debugger commands with the DECwindows Motif interface.
• A character cell interface for terminals and workstations
  When using this interface, you interact with SCD by entering commands at a prompt. The sections in this chapter describe how to use the system code debugger with the character cell interface.

For more information about using the OpenVMS DECwindows Motif interface and OpenVMS Debugger commands with SCD, see the HP OpenVMS Debugger Manual.

11.2 Building a System Image to Be Debugged

1. Compile the sources you want to debug, and be sure to use the /DEBUG and /NOOPT qualifiers.

   Note Debugging optimized code is much more difficult and is not recommended unless you know the Alpha or I64 architecture well. The instructions are reordered so much that single-stepping by source line will look like you are randomly jumping all over the code. Also note that you cannot access all variables. SCD reports that they are optimized away.

2. Link your image using the /DSF (debug symbol file) qualifier. Do not use the /DEBUG qualifier, which is for debugging user programs. The /DSF qualifier takes an optional filename argument similar to the /EXE qualifier. For more information, see the HP OpenVMS Linker Utility Manual. If you specify a name in the /EXE qualifier, you will need to specify the same name for the /DSF qualifier. For example, you would use the following command:

   $ LINK/EXE=EXE$:MY_EXECLET/DSF=EXE$:MY_EXECLET OPTIONS_FILE/OPT

   
   The .DSF and .EXE file names must be the same. Only the extensions will be different, that is .DSF and .EXE.
   The contents of the .EXE file should be exactly the same as if you had linked without the /DSF qualifier. The .DSF file will contain the image header and all the debug symbol tables for .EXE file. It is not an executable file, and cannot be run or loaded.

3. Put the .EXE file on your target system.
4. Put the .DSF file on your host system, because when you use SCD to debug code in your image, it will try to look for a .DSF file first and then look for an .EXE file. The .DSF file is better because it has symbols in it. Section 11.4 describes how to tell SCD where to find your .DSF and .EXE files.

The target kernel is controlled by flags and devices specified when the system is booted, by XDELTA commands, by a configuration file, and by several system parameters. The following sections contain more information about these items.

Boot Flags

You can specify flags on the boot command line. Boot flags are specified as a hex number; each bit of the number represents a true or false value for a flag. The following flag values are relevant to the system code debugger.

• 8000
  This is the SCD boot flag. It enables operation of the target kernel. If this SCD boot flag is not set, not only will it be impossible to use SCD to debug the system, but the additional XDELTA commands related to the target kernel will generate an XDELTA error message. If this boot flag is set, SYSTEM_DEBUG is loaded, and SCD is enabled.
• 0004
  This is the initial breakpoint boot flag. It controls whether the system calls INI$BRK at the beginning and end of EXEC_INIT. Notice that if SCD is the default debugger, the first breakpoint is not as early as it is for XDELTA. It is delayed until immediately after the PFN database is set up.
• 0002
  This is the XDELTA boot flag, which controls whether XDELTA is loaded. It behaves slightly differently when the SCD boot flag is also set.
  If the SCD boot flag is clear, this flag simply determines if XDELTA is loaded. If the SCD boot flag is set, this flag determines whether XDELTA or the system code debugger is the default debugger. If the XDELTA flag is set, XDELTA will be the default debugger. In this state, the initial system breakpoints and any calls to INI$BRK trigger XDELTA, and you must enter an XDELTA command to start using SCD. If the XDELTA boot flag is clear, the initial breakpoints and calls to INI$BRK go to SCD. You cannot use XDELTA if the XDELTA boot flag is clear.

Boot Command

The form of the boot command varies depending on the platform and type OpenVMS system. However, all SCD boot commands have the concept of boot flags, boot device, and dedicated Ethernet device. In all environments, you must specify an Ethernet device on the target system to use to communicate with the host debugger. It is currently a restriction that this device must not be used for anything else (either for booting or network software such as DECnet, TCP/IP products, and LAT products).

To use Alpha SCD, you must specify the Ethernet device with boot command. In this example, we are using DEC 3000 Model 400 Alpha Workstation syntax. We are booting from the DKB100 disk and using the ESA0 Ethernet device. We are also setting the SCD, XDELTA, and initial (earliest) breakpoint flags:

>>> show device . . . >>> boot dkb100,esa0 -fl 0,8006

You can set these devices and flags to be the default values so that you will not have to specify them each time you boot:

>>> set bootdef_dev dkb100,esa0 >>> set boot_osflags 0,8006

To use I64 SCD, you can specify an Ethernet device (debug_dev) BEFORE loading the Operating System and AFTER you have selected the device/partition. Setting debug_dev is sticky. That is, you only need to set it once. Using a HP rx2600 syntax:

A sample I64 Boot Menu follows.

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|0)/Scsi(Pun0,Lun0)/HD(Part1,SigA02952 fs1 : Acpi(HWP0002,300)/Pci(1|0)/Fibre(WWN50001FE10011B15D,Lun2200) fs2 : Acpi(HWP0002,300)/Pci(1|0)/Fibre(WWN50001FE10011B15D,Lun2200) fs3 : Acpi(HWP0002,300)/Pci(1|0)/Fibre(WWN50001FE10011B15D,Lun2300) . . . Shell>

Select the desired device/partition:

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.

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 Ethernet device.

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)

Finally, load the OS. In this example, the boot is with the SCD and initial (earliest) breakpoint flags using root 2 (SYS2), that will vary with system setups.

fs1:\> \efi\vms\vms_loader -flags "2,8004"

You can set the flags to be the default value instead of specifying them for each and every OS load:

fs1:\> set vms_flags "2,8004"

You can also build the entire boot device, OS load command with flags setting as a Boot Option. See the Boot Option Maintenance Menu.

SCD Configuration File

The SCD target system reads a configuration file in SYS$SYSTEM named DBGTK$CONFIG.SYS. The first line of this file contains a default password, which must be specified by the host debug system to connect to the target. The default password may be the null string; in this case the host must supply the null string as the password (/PASSWORD="") on the connect command as described in Section 11.5, or no password at all. Other lines in this file are reserved by HP. Note that you must create this file because HP does not supply it. If this file does not exist prior to booting with SCD enabled, you can only run SCD by specifying a default password with the XDELTA ;R command described in the following section.

XDELTA Commands

When the system is booted with both the XDELTA boot flag and the SCD boot flag, the following two additional XDELTA commands are enabled:

• n,\xxxx;R ContRol SCD connection
  You can use this command to do the following:
  • Change the password which the SCD host must present
  • Disconnect the current session from SCD
  • Give control to SCD by simulating a call to INI$BRK
  • Any combination of these
  
  Optional string argument xxxx specifies the password that the system code debugger must present for its connection to be accepted. If this argument is left out, the required password is unchanged. The initial password is taken from the first line of the SYS$SYSTEM:DBGTK$CONFIG.SYS file. The new password does not remain in effect across a boot of the target system.
  The optional integer argument n controls the behavior of the ;R command as follows:

  Value of N	Action
  +1	Gives control to SCD by simulating a call to INI$BRK
  +2	Returns to XDELTA after changing the password. 2;R without a password is a no-op
  0	Performs the default action
  -1	Changes the password, breaks any existing connection to SCD, and then simulates a call to INI$BRK (which will wait for a new connection to be established and then give control to SCD)
  -2	Returns to XDELTA after changing the password and breaking an existing connection

  
  Currently, the default action is the same action as +1.
  If SCD is already connected, the ;R command transfers control to SCD, and optionally changes the password that must be presented the next time a system code debugger tries to make a connection. This new password does not last across a boot of the target system.
• n;K Change inibrK behavior
  If optional argument n is 1, future calls to INI$BRK will result in a breakpoint being taken by SCD. If the argument is 0, or no argument is specified, future calls to INI$BRK will result in a breakpoint being taken by XDELTA.

SYSTEM Parameters

• DBGTK_SCRATCH
  Bits 0 through 7 specify how many pages of memory are allocated for SCD. This memory is allocated only if system code debugging is enabled with the SCD boot flag (described earlier in this section). Usually, the default value of 1 is adequate; however, if SCD displays an error message, increase this value.
  Bits 8 through 31 are reserved by HP.
• SCSNODE
  Identifies the target kernel node name for SCD. See Section 11.3.1 for more information.
• POOLPAGING
  If the image you are debugging uses paged pool, set POOLPAGING to zero to ensure that paged pool is always resident in memory. SCD cannot examine or deposit to any locations in paged pool that are not currently valid.
• S0_PAGING
  If the image you are debugging includes pageable code or data, set S0_PAGING to 3 to ensure that such code and data are always resident in memory. SCD cannot examine, deposit to, set breakpoints at, and so on, any locations in pageable sections that are not currently valid. [This applies only to Alpha. I64 executive images and drivers do not contain pageable code or data.]

It is always SCD on the host system that initiates a connection to the target kernel. When SCD initiates this connection, the target kernel accepts or rejects the connection based on whether the remote debugger presents it with a node name and password that matches the password in the target system (either the default password from the SYS$SYSTEM:DBGTK$CONFIG.SYS file, or a different password specified via XDELTA). SCD obtains the node name from the SCSNODE system parameter.

The target kernel can accept a connection from SCD any time the system is running below IPL 22, or if XDELTA is in control (at IPL 31). However, the target kernel actually waits at IPL 31 for a connection from the SCD host in two cases: when it has no existing connection to an SCD host and (1) it receives a breakpoint caused by a call to INI$BRK (including either of the initial breakpoints), or (2) when you enter a 1;R or -1;R command to XDELTA.