Updated: 11 December 1998

OpenVMS VAX System Dump Analyzer Utility Manual

In a uniprocessor system only one CPU exists, and the concept of SDA CPU context is not an issue. However, for a multiprocessor system with more than one active CPU, SDA must maintain an idea of CPU context to provide a way of displaying information bound to a specific CPU, such as the reason for the bugcheck exception, the currently executing process, the current IPL, the contents of CPU registers, and any owned spin locks. When you first invoke SDA to analyze a crash dump, the "SDA current CPU" is the CPU that induced the system failure.

Changing the CPU Context

You can use several SDA commands to change the CPU context. When you change the CPU context, the "SDA current process" is changed to the current process on the "SDA current CPU" to synchronize CPU context and process context. If no current process is on the "SDA current CPU," the "SDA current process" is undefined; no process context information will be available until you set SDA process context to a specific process.

Type HELP PROCESS_CONTEXT for specific information about the "SDA current process."

The following SDA commands change the "SDA current CPU":

Command	Description
SET CPU cpu_id	Changes the "SDA current CPU" to CPU cpu_id
SHOW CPU cpu_id	Changes the "SDA current CPU" to CPU cpu_id
SHOW CRASH	Changes the "SDA current CPU" to the CPU that induced the system failure

If you select a process that is the current process on a CPU, the following commands change the "SDA current CPU" to that CPU:

• SET PROCESS name
• SET PROCESS/INDEX=nn
• SHOW PROCESS name
• SHOW PROCESS/INDEX=nn

No other SDA commands affect the "SDA current CPU."

In a uniprocessor system, process context might be the process that is current on the CPU or the process in whose context process-specific SDA commands are interpreted. For a multiprocessor system with more than one active CPU, however, the meaning of "SDA process context" changes so that it includes a way to display information relevant to a specific process both when the process is current on a processor and when the process is not.

You can use several SDA commands to change SDA process context. Following is a list of the results of some of these changes:

• When you change the "SDA current process" to the current process on a CPU, the "SDA current CPU" is changed to the new CPU to synchronize CPU context and process context.
• When you change the "SDA current process" to a process that is not current on any processor, the "SDA current CPU" is not changed.
• When you change the SDA CPU context to a CPU that has no current process, the "SDA current process" is undefined; no process context information is available until you set SDA process context to a specific process.

Type HELP CPU_CONTEXT for specific information about the "SDA current CPU."

The following SDA commands change the "SDA current process":

Command	Description
SET PROCESS name	Changes the "SDA current process" to the named process
SET PROCESS /INDEX=n	Changes the "SDA current process" to the process with index n
SHOW PROCESS name	Changes the "SDA current process" to the named process
SHOW PROCESS /INDEX=n	Changes the "SDA current process" to the process with index n

The following commands change the SDA process context if the "SDA current process" is not the current process on the selected CPU:

Command	Description
SET CPU cpu_id	Changes the "SDA current process" to the current process on CPU cpu_id
SHOW CPU cpu_id	Changes the "SDA current process" to the current process on CPU cpu_id
SHOW CRASH	Changes the "SDA current process" to the current process on the CPU that induced the system failure

No other SDA commands affect the "SDA current process."

Changing the SDA CPU Context

When you invoke SDA to analyze a crash dump from a multiprocessing system with more than one active CPU, SDA maintains a second dimension of context---its CPU context---that allows it to display certain processor-specific information, such as the reason for the bugcheck exception, the currently executing process, the current IPL, the contents of processor-specific registers, the interrupt stack pointer (ISP), and the spin locks owned by the processor. When you invoke SDA to analyze a multiprocessor's crash dump, its CPU context defaults to that of the processor that induced the system failure.³

You can change the SDA CPU context by using any of the following commands:

• SET CPU cpu-id
• SHOW CPU cpu-id
• SHOW CRASH

Changing CPU context involves an implicit change in process context in either of the following ways:

• If there is a current process on the CPU made current, SDA process context is changed to that of that CPU's current process.
• If there is no current process on the CPU made current, SDA process context is undefined and no process-specific information is available until you set SDA process context to that of a specific process.

Likewise, changing process context can involve a switch of CPU context as well. For instance, if you issue a SET PROCESS command for a process that is current on another CPU, SDA automatically changes its CPU context to that of the CPU on which that process is current. The following commands can have this effect if the name or index number (nn) refers to a current process:

• SET PROCESS name
• SET PROCESS/INDEX=nn
• SHOW PROCESS name
• SHOW PROCESS/INDEX=nn

7 SDA Command Format

The following sections describe the format of SDA commands and the expressions you can use with SDA commands.

7.1 General Command Format

SDA uses a command format similar to that used by the DCL interpreter. You issue commands in this general format:

command-name[/qualifier...] [parameter][/qualifier...] [!comment]

where:

command-name	Is an SDA command. Each command tells the utility to perform a function. Commands can consist of one or more words, and can be abbreviated to the number of characters that make the command unique. For example, SH stands for SHOW and SE stands for SET.
/qualifier	Modifies the action of an SDA command. A qualifier is always preceded by a slash (/). Several qualifiers can follow a single parameter or command name, but a slash must precede each. You can abbreviate qualifiers to the shortest string of characters that uniquely identifies the qualifier.
parameter	Is the target of the command. For example, SHOW PROCESS RUSKIN tells SDA to display the context of the process RUSKIN. The command EXAMINE 80104CD0;40 displays the contents of 40 bytes of memory, beginning with location 80104CD0. When you supply part of a file specification as a parameter, SDA assumes default values for the omitted portions of the specification. The default device SYS$DISK and default directory are those specified in your most recent SET DEFAULT command. See the OpenVMS DCL Dictionary for a description of the DCL command SET DEFAULT.
!comment	Consists of text that describes the command, but this text is not actually part of the command. Comments are useful for documenting SDA command procedures. When executing a command, SDA ignores the exclamation point (!) and all characters that follow it on the same line.

7.2 Expressions

You can use expressions as parameters for some SDA commands, such as SEARCH and EXAMINE. To create expressions, you can use any of the following elements:

• Numerals
• Radix operators
• Arithmetic and logical operators
• Precedence operators
• Symbols

The following sections describe elements other than numerals.

7.2.1 Radix Operators

Radix operators determine which numeric base SDA uses to evaluate expressions. You can use one of three radix operators to specify the radix of the numeric expression that follows the operator:

• ^X (hexadecimal)
• ^O (octal)
• ^D (decimal)

The default radix is hexadecimal. SDA displays hexadecimal numbers with leading zeros and decimal numbers with leading spaces.

7.2.2 Arithmetic and Logical Operators

There are two types of arithmetic and logical operators, both of which are listed in Table SDA-8.

• Unary operators affect the value of the expression that follows them.
• Binary operators combine the operands that precede and follow them.

In evaluating expressions containing binary operators, SDA performs logical AND, OR, and XOR operations, and multiplication, division, and arithmetic shifting before addition and subtraction. Note that the SDA arithmetic operators perform integer arithmetic on 32-bit operands.

Table SDA-8 SDA Operators

Operator	Action
Unary Operators
#	Performs a logical NOT of the expression
+	Makes the value of the expression positive
--	Makes the value of the expression negative
@	Evaluates the following expression as a virtual address, then uses the contents of that address as value
G	Adds 80000000 16 to the value of the expression 1
H	Adds 7FFE0000 16 to the value of the expression 2
Binary Operators
+	Addition
--	Subtraction
*	Multiplication
&	Logical AND
|	Logical OR
\	Logical XOR
/	Division 3
@	Arithmetic shifting

SDA uses parentheses as precedence operators. Expressions enclosed in parentheses are evaluated first. SDA evaluates nested parenthetical expressions from the innermost to the outermost pairs of parentheses.

7.2.4 Symbols

Names of symbols can contain from 1 to 31 alphanumeric characters and can include the dollar sign ($) and underscore (_) characters. Symbols can take values from --7FFFFFFF₁₆ to 7FFFFFFF₁₆.

By default, SDA copies symbols into its symbol table from the files SYS$SYSTEM:SYS.STB and SYS$SYSTEM:REQSYSDEF.STB. To add more symbols to the symbol table, you can use the following SDA commands:

• READ---to add symbols from other symbol tables or object modules
• DEFINE---to create symbols and add them to the symbol table

In addition, SDA provides the symbols described in Table SDA-9.

Table SDA-9 SDA Symbols

Symbol	Meaning
. (period)	Current location
2P_CDDB	Address of alternate CDDB for MSCP-served device 1
2P_UCB	Address of alternate UCB for dual-pathed device 1
AMB	Associated mailbox UCB pointer 1
AP	Argument pointer 2
CDDB	Address of class driver descriptor block for MSCP-served device 1
CLUSTRLOA	Base address of loadable VAXcluster code
CRB	Address of channel request block 1
DDB	Address of device data block 1
DDT	Address of driver dispatch table 1
nnDRIVER	Base address of a driver prologue table (DPT); such a symbol exists for each loaded device driver in the system 3
ESP	Executive stack pointer 2
FP	Frame pointer 2
FPEMUL	Base address of the code that emulates floating-point instructions
G	80000000 16, the base address of system space
H	7FFE0000 16
IRP	Address of I/O request packet 1
JIB	Job information block
KSP	Kernel stack pointer 2
LNM	Address of logical name block for mailbox 1
MCHK	Address within loadable CPU-specific routines
MSCP	Address of loadable MSCP server code
ORB	Address of object rights block 1
P0BR	Base register for the program region (P0) 2
P0LR	Length register for the program region (P0) 2
P1BR	Base register for the control region (P1) 2
P1LR	Length register for the control region (P1) 2
PC	Program counter 2
PCB	Process control block
PDT	Address of port descriptor table 1
PHD	Process header
PSL	Processor status longword 2
R0 through R11	General registers 2
RMS	Base address of the RMS image
RWAITCNT	Resource wait count for MSCP-served device 1
SB	Address of system block 1
SCSLOA	Base address of loadable common SCS services
SP	Current stack pointer of a process 2
SSP	Supervisor stack pointer 2
SYSLOA	Base address of loadable processor-specific system code
TMSCP	Address of loadable TMSCP server code
UCB	Address of unit control block 1
USP	User stack pointer 2
VCB	Address of volume control block for mounted device 1

When SDA displays an address, it displays that address both in hexadecimal and as a symbol, if possible. If the address is within FFF₁₆ of the value of a symbol, SDA displays the symbol plus the offset from the value of that symbol to the address. If more than one symbol's value is within FFF₁₆ of the address, SDA displays the symbol whose value is the closest. If no symbols have values within FFF₁₆ of the address, SDA displays no symbol. (For an example, see the description of the SHOW STACK command.)

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