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If the linker detects any errors while linking object modules, it displays messages about their cause and severity. If any errors or fatal conditions occur (severities E or F), the linker does not produce an image file.
Linker messages are descriptive; you do not normally need additional information to determine the specific error. Some of the more common errors that occur during linking are as follows:
If an error occurs when you link object modules, you can often correct it simply by reentering the command string and specifying the correct object files or libraries.
You can use the OpenVMS HELP/MESSAGE facility to view error recovery descriptions associated with messages from any OpenVMS facility.
On using the HELP/MESSAGE command, see OpenVMS System Messages: Companion Guide for Help Message Users.
3.3 Running HP Fortran Programs
This section describes the following considerations for executing HP Fortran programs on an OpenVMS operating system:
The RUN command initiates execution of a program. The command has the following form:
|
RUN[/[NO]DEBUG] file-spec |
You must specify the file name. If you omit optional elements of the file specification, the system automatically provides a default value. The default file type is EXE.
The /DEBUG qualifier allows you to use the debugger, even if you
omitted this qualifier on the FORTRAN and LINK command lines. Refer to
Section 3.4 for details.
3.3.2 System Processing at Image Exit
When the main program executes an END statement, or when any program
unit in the program executes a STOP statement, the image is terminated.
With the OpenVMS operating system, the termination of an image, or
image exit, causes the system to perform a variety of clean-up
operations during which open files are closed, system resources are
freed, and so on.
3.3.3 Interrupting a Program
When you execute the RUN command interactively, you cannot execute any other program images or DCL commands until the current image completes. However, if your program is not performing as expected---if, for instance, you have reason to believe it is in an endless loop---you can interrupt it by using the Ctrl/Y key sequence. (You can also use the Ctrl/C key sequence, unless your program takes specific action in response to Ctrl/C.) For example:
$ RUN APPLIC [Ctrl/Y] $ |
This command interrupts the program APPLIC. After you have interrupted a program, you can terminate it by entering a DCL command that causes another image to be executed or by entering the DCL commands EXIT or STOP.
Following a Ctrl/Y interruption, you can also force an entry to the debugger by entering the DEBUG command.
Some of the other DCL commands you can enter have no direct effect on the image. After using them, you can resume the execution of the image with the DCL command CONTINUE. For example:
$ RUN APPLIC [Ctrl/Y] $ SHOW LOGICAL INFILE %SHOW-S-NOTRAN, no translation for logical name INFILE $ DEFINE INFILE $1$DUA1:[TESTFILES]JANUARY.DAT $ CONTINUE |
As noted previously, you can use Ctrl/C to interrupt your program; in most cases, the effect of Ctrl/C and Ctrl/Y is the same. However, some programs (including programs you may write) establish particular actions to take to respond to Ctrl/C. If a program has no Ctrl/C handling routine, then Ctrl/C is the same as Ctrl/Y.
If you run your program as part of a command procedure, it is often useful to return a status value to the command procedure. This indicates whether the program actually executed properly.
To return such a status value, call the EXIT system subroutine rather than terminating execution with a STOP, RETURN, or END statement. The EXIT subroutine can be called from any executable program unit. It terminates your program and returns the value of the argument as the return status value of the program.
When the command interpreter receives a status value from a terminating program, it attempts to locate a corresponding message in a system message file or a user-defined message file. Every message that can be issued by a system program, command, or component, has a unique 32-bit numeric value associated with it. These 32-bit numeric values are called condition symbols. Condition symbols are described in Section 14.4.3.
The command interpreter does not display messages on completion of a program under the following circumstances:
On the EXIT subroutine, see the HP Fortran for OpenVMS Language Reference Manual.
3.4 Symbol Table and Traceback Information: Locating Run-Time Errors
Both the compiler and the OpenVMS Run-Time Library include facilities
for detecting and reporting errors. You can use the OpenVMS Debugger
and the traceback facility to help you locate errors that occur during
program execution.
3.4.1 Effects of Error-Related Command Qualifiers
At each step in compiling, linking, and executing your program, you can specify command qualifiers that affect how errors are processed.
Table 3-2 summarizes the /DEBUG and /TRACEBACK qualifiers.
| Command | Qualifier | Effect |
|---|---|---|
| FORTRAN | /DEBUG |
The HP Fortran compiler creates symbolic data needed by the debugger.
Default: /DEBUG=(NOSYMBOLS,TRACEBACK) |
| LINK | /DEBUG |
Symbolic data created by the HP Fortran compiler is passed to the
debugger.
Default: /NODEBUG |
| /TRACEBACK |
Traceback information is passed to the debugger. Traceback will be
produced.
Default: /TRACEBACK |
|
| RUN | /DEBUG | Invokes the debugger. The DBG> prompt will be displayed. Not needed if LINK/DEBUG was specified. |
| /NODEBUG | If /DEBUG was specified in the LINK command line, RUN/NODEBUG starts program execution without first invoking the debugger. |
If an exception occurs and these qualifiers are not specified at any point in the compile-link-execute sequence, a traceback list is generated by default.
To perform symbolic debugging, you must use the /DEBUG qualifier with both the FORTRAN and LINK command lines; you do not need to specify it with the RUN command. If /DEBUG is omitted from either the FORTRAN or LINK command lines, you can still use it with the RUN command to invoke the debugger. However, any debugging you perform must then be done by specifying virtual addresses rather than symbolic names.
If you linked your program with the debugger, but wish to execute the program without debugger intervention, specify the following command:
$ RUN/NODEBUG program-name |
If you specify LINK/NOTRACEBACK, you receive no traceback if there are
errors.
3.4.2 Sample Source Program and Traceback
Example 3-1 shows a sample source program and a traceback.
| Example 3-1 Sample HP Fortran Program |
|---|
PROGRAM TRACE_TEST
REAL ST
ST = 2.4E20 ! Constant inside range for REAL*4 formats
CALL SUB1(ST)
END PROGRAM TRACE_TEST
SUBROUTINE SUB1(RV)
REAL RV,RES
RV = RV * RV ! Generates overflow value
RES=LOG(RV) ! Uses + Infinity value for IEEE floating-point data
RETURN
END SUBROUTINE SUB1
|
The program (TRACEBK.F90) shown in Example 3-1 is compiled, linked, and run to generate the traceback information shown after the RUN command:
$ FORTRAN/NOOPTIMIZ/DEBUG=TRACEBACK/SYNCHRONOUS_EXCEPTIONS/ FLOAT=IEEE_FLOAT TRACEBK.F90
$ LINK TRACEBK
$ RUN TRACEBK
%SYSTEM-F-HPARITH, high performance arithmetic trap, Imask=00000000,
Fmask=00000001, summary=08, PC=0002007C, PS=0000001B
-SYSTEM-F-FLTOVF, arithmetic trap,floating overflow at PC=0002007C,PS=0000001B
%TRACE-F-TRACEBACK, symbolic stack dump follows
Image Name Module Name Routine Name Line Number rel PC abs PC
LINK_TRACEBA TRACE_TEST SUB1 10 0000007C 0002007C
LINK_TRACEBA TRACE_TEST TRACE_TEST 6 00000030 00020030
0 88EEFA50 88EEFA50
|
On the FORTRAN command line, the following qualifiers are used:
When an error condition is detected, you receive the appropriate message, followed by the traceback information. The Run-Time Library displays a message indicating the nature of the error and the address at which the error occurred (user PC). This is followed by the traceback information, which is presented in inverse order to the calls.
Values can be produced for relative and absolute PC, with no corresponding values for routine name and line. These PC values reflect procedure calls internal to the Run-Time Library.
Of particular interest are the values listed under "Routine Name" and "Line Number":
With this information, you can usually isolate the error in a short time.
If you specify either LINK/DEBUG or RUN/DEBUG, the debugger assumes control of execution and you do not receive a traceback list if an error occurs. To display traceback information, you can use the debugger command SHOW CALLS.
You should use the /NOOPTIMIZE qualifier on the FORTRAN command line whenever you use the debugger.
This chapter describes:
A debugger is a tool that helps you locate run-time errors quickly. It is used with a program that has already been compiled and linked successfully, but does not run correctly. For example, the output may be obviously wrong, or the program goes into an infinite loop or terminates prematurely. The debugger enables you to observe and manipulate the program's execution interactively so you can locate the point at which the program stopped working correctly.
The OpenVMS Debugger is a symbolic debugger, which means that you can refer to program locations by the symbols (names) you used for those locations in your program---the names of variables, subroutines, labels, and so on. You do not need to use virtual addresses to refer to memory locations.
By issuing debugger commands at your terminal, you can perform the following operations:
Such techniques allow you to isolate an error in your code much more quickly than you could without the debugger.
Once you have found the error in the program, you can then edit the
source code and compile, link, and run the corrected version.
4.2 Getting Started with the Debugger
This section explains how to use the debugger with HP Fortran programs. The section focuses on basic debugger functions, to get you started quickly. It also provides any debugger information that is specific to HP Fortran.
Before you can use the debugger, you must compile and link your program. The following example shows how to compile and link a HP Fortran program (consisting of a single compilation unit in the file INVENTORY.F90) prior to using the debugger.
$ FORTRAN/DEBUG/NOOPTIMIZE INVENTORY $ LINK/DEBUG INVENTORY |
The /DEBUG qualifier on the FORTRAN command line causes the compiler to write the debug symbol records associated with INVENTORY.F90 into the object module INVENTORY.OBJ. These records allow you to use the names of variables and other symbols declared in INVENTORY.F90 in debugger commands. (If your program has several compilation units, each of the program units that you want to debug must be compiled with the /DEBUG qualifier.)
Use the /NOOPTIMIZE qualifier when you compile a program in preparation for debugging. Otherwise, the object code is optimized (to reduce the size of the program and make it run faster), so that the symbolic evaluation of some program locations may be inconsistent with what you might expect from viewing the source code. For example, a variable in an optimized program may not be available. (After debugging the program, recompile it without the /NOOPTIMIZE qualifier.) For a description of the various optimizations performed by the compiler, see Chapter 5.
The /DEBUG qualifier on the LINK command line causes the linker to include all symbol information that is contained in INVENTORY.OBJ in the executable image. This qualifier also causes the OpenVMS image activator to start the debugger at run time. (If your program has several object modules, you may need to specify the other modules on the LINK command line.)
On the effects of specifying the /DEBUG qualifier on the FORTRAN, LINK,
and RUN command lines, see Section 2.3.14 and Section 3.4.
4.2.2 Establishing the Debugging Configuration and Interface
Before invoking the debugger, check that the debugging configuration is appropriate for the kind of program you want to debug.
The configuration depends on the current value of the logical name DBG$PROCESS. Before invoking the debugger, issue the DCL command SHOW LOGICAL DBG$PROCESS to determine the current definition of DBG$PROCESS.
The default configuration is appropriate for almost all programs. To request the default debugging configuration. the logical name DBG$PROCESS is undefined or has the value DEFAULT. For example, the following command shows when DBG$PROCESS is undefined:
$ SHOW LOGICAL DBG$PROCESS %SHOW-S-NOTRAN, no translation for logical name DBG$PROCESS |
To define DBG$PROCESS to have a value of DEFAULT, enter:
$ DEFINE DBG$PROCESS DEFAULT |
To remove (deassign) a logical name definition, use the DEASSIGN command.
If the DECwindows Motif product is installed and running on your workstation, by default the OpenVMS Debugger uses the DECwindows Motif interface. To use the character cell interface on a DECwindows system, define the logical:
$ DEFINE/PROCESS DBG$DECW$DISPLAY " " |
To define this logical name for multiple users, use other logical name tables.
To enable use of the DECwindows interface, deassign the logical:
$ DEASSIGN/PROCESS DBG$DECW$DISPLAY |
The DECwindows interface provides a main window in which portions are updated as the program executes, including the source code, entered commands, and debugger messages. This interface provides pull-down menus and uses the kept debugger (equivalent of DEBUG/KEEP).
The examples in this chapter show the command line (character cell) interface to the OpenVMS Debugger.
The character cell interface to the OpenVMS Debugger provides the following debugging interfaces:
Screen mode is activated by pressed PF3 on the keypad (or enter the command SET MODE SCREEN). Screen mode allows the debugger character cell interface to simultaneously display separate groups of data similar to the DECwindows interface. For example, your screen might show the source code (SRC), debugger output (OUT), and debugger command input (PROMPT) displays.
While in screen mode, use the SHOW DISPLAY command to view the predefined displays and the DISPLAY command to define a new display. To view the keypad definitions in screen mode, press PF2 on the keypad.
To leave screen mode and resume line-oriented mode, press PF1 PF3 (or enter the command SET SCREEN NOSCREEN).
On the DECwindows Motif debugger interface (including a source browser)
and screen mode, see the HP OpenVMS Debugger Manual.
4.2.3 Invoking the Debugger
After you compile and link your program and establish the appropriate debugging configuration, you can then invoke the debugger. To do so, enter the DCL command RUN, specifying the executable image of your program as the parameter. For example, enter the following command to debug the program INVENTORY:
$ RUN INVENTORY
OpenVMS DEBUG (IA64 Debug64) Version x.x-xxx
%DEBUG-I-INITIAL, language is FORTRAN, module set to INVENTORY
DBG> GO
%DEBUG-I-EXITSTATUS, is '%SYSTEM-S-NORMAL, normal successful completion'
DBG> EXAMINE N
INVENTORY\N: 4
DBG> EXIT
$
|
The diagnostic message that is displayed at the debugger startup indicates that this debugging session is initialized for an HP Fortran program and that the name of the main program unit is INVENTORY. In the initial "%DEBUG-I-INITIAL" message, the OpenVMS Debugger term "module" is equivalent to an HP Fortran "procedure."
When some qualifiers are used to compile (/WARNINGS=ALIGNMENT or most /CHECK keywords), the debugger does not start up in the main program. When this happens, enter GO once to get to the beginning of the main program.
The DBG> prompt indicates that you can now enter debugger commands. At this point, if you enter the GO command, program execution begins and continues until it is forced to pause or stop (for example, if the program prompts you for input or an error occurs).
You can specify the DEBUG command /KEEP qualifier to use the kept debugger. The kept debugger allows you to run one (or more) programs with the RUN command, rerun the last program run with a RERUN command, and connect and disconnect to a running process. For example:
$ DEBUG /KEEP
OpenVMS DEBUG (IA64 Debug64) Version x.x-xxx
DBG> RUN SQUARES
%DEBUG-I-INITIAL, language is FORTRAN, module set to SQUARES
DBG> GO
%DEBUG-I-EXITSTATUS, is '%SYSTEM-S-NORMAL, normal successful completion'
DBG> RERUN
DBG> STEP
stepped to SQUARES\%LINE 4
4: OPEN(UNIT=8, FILE='DATAFILE.DAT', STATUS='OLD')
DBG> EXAMINE N
DEBUGEX$MAIN\N: 0
DBG> GO
%DEBUG-I-EXITSTATUS, is '%SYSTEM-S-NORMAL, normal successful completion'
DBG> EX N
DEBUGEX$MAIN\N: 4
DBG> EXIT
|
For more information on using the debugger and invoking the debugger for other display modes, see the HP OpenVMS Debugger Manual.
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