HP OpenVMS Systems Documentation

HP OpenVMS Delta/XDelta Debugger Manual

On VAX 8530, 8550, 8600, 8650, 8810 (8700), 8820, 8820-N (8800), 8830, 8840, VAX-11/780, or VAX-11/785 computers, enter the following commands at the console terminal to request the interrupt:

$ [Ctrl/P]
>>> HALT
>>> D/I 14 E
>>> C

For a VAX 9000 computer, enter the following commands at the console terminal to request the interrupt:

$ [Ctrl/P]
>>> HALT/CPU=ALL
>>> D/I 14 E
>>> C/CPU=ALL

For a VAX 6000 series, 8200, 8250, 8300, 8350, VAX-11/730, or a VAX-11/750 computer, enter the following commands:

$ [Ctrl/P]
>>> D/I 14 E
>>> C

For a VAXstation 3520 or 3540 computer, perform the following steps:

1. Press and release the Halt button on the CPU control panel. When you release the Halt button, make sure it is popped out or the system will remain halted. You can also press the Break key (if enabled) on the console terminal.
2. Enter the following commands:

   >>> D/I 14 E >>> C/ALL

For a VAXft-3000, VAXft-410, VAXft-610, or VAXft-612 computer, enter the following commands at the console terminal to request the interrupt:

$  [Break] or [F5]
>>> HALT
>>> D/I 14 E
>>> CONT
>>> PIO

For a VAX 7000 or VAX 10000 series computer, enter the following commands at the console terminal to request the interrupt. If you are operating in secure mode, first set the keyswitch to ENABLE before entering these commands.

$  [Ctrl/P]
>>> D IPR:14 E
>>> CONT

For a VAXstation 2000, MicroVAX 2000, MicroVAX 3300/3400 series, MicroVAX or VAXstation 3500/3600 series, MicroVAX 3800/3900 series, VAX 4000 series, or MicroVAX II computer, perform the following steps:

1. Press and release the Halt button on the CPU control panel. When you release the Halt button, make sure it is popped out or the system will remain halted. You can also press the Break key (if enabled) on the console terminal.
2. Enter the following commands:

   >>> D/I 14 E >>> C

For an alternative method of accessing OpenVMS through a lower priority interrupt, see the HP OpenVMS System Manager's Manual.

1.8.2 Requesting Interrupts on Alpha

On Alpha systems, perform the following steps to request an interrupt:

1. Halt the processor with the following command:

   ^P

2. Request an IPL 14 software interrupt with the following command:

   >>> DEP SIRR E

   
   This command deposits a 14₁₀ into the software interrupt request register.
3. Reactivate the processor by issuing the CONTINUE command as follows:

   >>> CONT

The process should enter XDELTA as soon as IPL drops to 14.

The following message is displayed:

Brk 0 at address
address! instruction

At this point, the exception frame is on the stack. The saved PC/PS in the exception frame tells you where you were in the program when you requested the interrupt.

1.8.3 Requesting Interrupts on I64

To request an interrupt on I64, type CTRL/P on the console terminal. Note that XDELTA must have been loaded previously.

When you press CTRL/P, the system is halted at the current PC and at the current IPL. The system must be executing below IPL 8. When the system reaches this state, execution is suspended at the PC that was executing at the time of the interrupt.

1.9 Accessing the Initial Breakpoint

When debugging a program, you can set a breakpoint in the code so that XDELTA gains control of program execution.

To set a breakpoint, place a call to the system routine INI$BRK in the source code.

On systems that are booted with XDELTA, the INI$BRK routine executes a breakpoint instruction. On systems that are not booted with XDELTA, INI$BRK is effectively a NOP instruction.

You can use the INI$BRK routine as a debugging tool, placing calls to this routine in any part of the source code you want to debug.

On VAX, the instruction following the breakpoint is RSB. After the break is taken, the return address (the address in the program to which control returns when you proceed from the breakpoint) is on the top of the stack.

The following command calls the INI$BRK system routine to reach the breakpoint:

JSB G^INI$BRK

On Alpha, the instruction following the breakpoint is JSR R31,(R26). After the break is taken, the return address (the address in the program to which control returns when you proceed from the breakpoint) is in R26.

On I64, simply step until you reach a br.ret instruction.

The following C routine calls the INI$BRK system routine to reach the breakpoint:

extern void ini$brk(void);

main()
{
 ini$brk();
}

On VAX, when XDELTA reaches one of its breakpoints, it displays the following message:

1 BRK AT nnnnnnnn

address/instruction operands

On I64 and Alpha, when XDELTA reaches one of its breakpoints, it displays the following message:

BRK 1 AT nnnnnnnn

address!instruction operands

On multiprocessor computers, the XDELTA breakpoint is taken on the processor upon which the XDELTA software interrupt was requested, which is generally the primary processor.

At this point, XDELTA is waiting for input. If you want to proceed with program execution, enter the ;P command. If you want to do step-by-step program execution, enter the S command. If you know where you have set breakpoints, examine them using the ;B command. You can also set additional breakpoints or modify existing ones.

If you entered the ;P command to proceed with program execution and the system halts with a fatal bugcheck, the system prints the bugcheck information on the console terminal. Bugcheck information consists of the following:

• Type of bugcheck
• Contents of the registers
• A dump of one or more stacks
• A list of loaded executive images

The contents of the program counter (PC) and the stack indicate where the failure was detected. Then, if the system parameter BUGREBOOT was set to 0, XDELTA issues a prompt. You can examine the system's state further by entering XDELTA commands.

1.11 Exiting from XDELTA

XDELTA remains in memory with the operating system until you reboot without it.

This chapter describes how to form the symbolic expressions used as arguments to many DELTA and XDELTA commands.

2.1 Symbols Supplied by DELTA and XDELTA

DELTA and XDELTA define symbols that are useful in forming expressions and referring to registers.

• Table 2-1 shows the symbols that pertain to OpenVMS I64 systems.
• Table 2-2 shows symbols that pertain to OpenVMS Alpha systems.
• Table 2-3 shows symbols that pertain to OpenVMS VAX systems.

On OpenVMS Alpha, floating point registers can be accessed from DELTA and from XDELTA but only if floating point arithmetic is enabled in the current process. On OpenVMS I64, floating point registers FP6 through FP11 are always available. The other floating point registers are available if floating point arithmetic is enabled in the current process.

DELTA runs in the context of a process. On OpenVMS Alpha, access to floating-point registers is enabled as soon as the first floating point instruction in the code being examined is executed. Access is disabled as soon as that image completes execution. On OpenVMS I64, floating-point registers are always available to DELTA.

Table Table 2-4 shows these relationships:

When the system enters XDELTA, it may not be obvious which process is the current process. If the current process happens to have floating point enabled (because a floating point instruction has executed and the image containing the floating point instruction is still executing), then you can access the floating point registers. Otherwise, you cannot. XDELTA checks the FEN (floating point enable) IPR (internal processor register) to see whether it needs to provide access to floating point registers.

2.3 Forming Numeric Expressions

Expressions are combinations of numbers, symbols that have numeric values, and arithmetic operators.

On all platforms, DELTA and XDELTA store and display all numbers in hexadecimal. They also interpret all numbers as hexadecimal.

Expressions are formed using regular (infix) notation. Both DELTA and XDELTA ignore operators that trail the expression. The following is a typical expression (in hexadecimal):

G4A32+24

DELTA and XDELTA recognize five binary arithmetic operators, one of which also acts as a unary operator. They are listed in Table 2-5.

The following example shows the arguments required by the arithmetic-shift operator:

In this example, n is the number to be shifted, and j is the number of bits to shift it. If j is positive, n is shifted to the left; if j is negative, n is shifted to the right. Argument j must be less than 20₁₆ and greater than -20₁₆. Bits shifted beyond the limit of the longword are lost; therefore, the result must fit into a longword.