HP OpenVMS Systems Documentation
OpenVMS Debugger Manual
C.2.4 Compiling and Linking
The Ada predefined units in the ADA$PREDEFINED program library on your system have been compiled with the /NODEBUG qualifier. Before using the debugger to refer to names declared in the predefined units, you must first copy the predefined unit source files using the ACS EXTRACT SOURCE command. Then, you must compile the copies into the appropriate library with the /DEBUG qualifier, and relink the program with the /DEBUG qualifier.
If you use the /NODEBUG qualifier with one of the Ada compilation commands, only global symbol records are included in the modules for debugging. Global symbols in this case are names that the program exports to modules in other languages by means of the Ada export pragmas:
The /DEBUG qualifier on the ACS LINK command causes the linker to
include all debugging information in the closure of the specified unit
in the executable image.
Source code may not be available for display for the following reasons that are specific to Ada programs:
The following paragraphs explain how to control the display of source code with Ada programs.
If the compiler command's /COPY_SOURCE qualifier (the default) was in effect when you compiled your program, the debugger obtains the displayed Ada source code from the copied source files located in the program library where the program was originally compiled. If you compiled your program with the /NOCOPY_SOURCE qualifier, the debugger obtains the displayed Ada source code from the external source files associated with your program's compilation units.
The file specifications of the copied or external source files are embedded in the associated object files. For example, if you have used the ACS COPY UNIT command to copy units, or the DCL command COPY or BACKUP to copy an entire library, the debugger still searches the original program library for copied source files. If, after copying, the original units have been modified or the original library has been deleted, the debugger may not find the original copied source files. Similarly, if you have moved the external source files to another disk or directory, the debugger may not find them.
In such cases, use the SET SOURCE command to locate the correct files for source display. You can specify a search list of one or more program library or source code directories. For example (ADA$LIB is the logical name that the program library manager equates to the current program library):
The SET SOURCE command does not affect the search list for the external
source files that the debugger fetches when you use the debugger EDIT
command. To tell the EDIT command where to look for your source files,
use the SET SOURCE/EDIT command.
With Ada programs, by default the debugger EDIT command fetches the external source file that was compiled to produce the compilation unit in which execution is currently paused. You do not edit the copied source file, in the program library, that the debugger uses for source display.
The file specifications of the source files you edit are embedded in the associated object files during compilation (unless you specify /NODEBUG). If some source files have been relocated after compilation, the debugger may not find them.
In such cases, you can use the debugger SET SOURCE/EDIT command to specify a search list of one or more directories where the debugger should look for source files. For example:
The SET SOURCE/EDIT command does not affect the search list for copied source files that the debugger uses for source display.
The SHOW SOURCE/EDIT command displays the source-file search list
currently being used for the EDIT command. The CANCEL SOURCE/EDIT
command cancels the source-file search list currently being used for
the EDIT command and restores the default search mode.
Note the following points about using the GO and STEP commands with Ada programs:
C.2.8 Debugging Ada Library Packages
When an Ada main program (or a non-Ada main program that calls Ada code) is executed, initialization code is executed for the Ada run-time library and elaboration code for all library units that the program depends on. The elaboration code causes the library units to be elaborated in appropriate order before the main program is executed. Library specifications, bodies, and some of their subunits are also elaborated by this process.
The elaboration of library packages accomplishes the following operations:
When you bring an Ada program under debugger control, execution is paused initially before the initialization code is executed and before the elaboration of library units. For example:
At that point, before typing GO to get to the start of the main program, you can step through and examine parts of the library packages by setting breakpoints at the package specifications or bodies you are interested in. You then use the GO command to get to the start of each package. To set a breakpoint on a package body, specify the package unit name with the SET BREAK command. To set a breakpoint on a package specification, specify the package unit name followed by a trailing underscore character (_).
Even if you have set a breakpoint on a package body, the break will not occur if the debugger module for that body is not set. If the module is not set, the break will occur at the package specification. This effect occurs because the debugger automatically sets modules for the specifications of packages named in with clauses; it does not automatically set modules for the associated package bodies (see Section C.2.14).
Also, to set a breakpoint on a subprogram declared in a package specification, you must set the module for the package body.
Note that the compiler generates unique names for subprograms declared
in library packages that are or could be overloaded names. The debugger
uses these unique names in its output, and requires them in commands
where the names would otherwise be ambiguous. For more information on
resolving overloaded names and symbols, see Section C.2.15.
When you start the debugger with an Ada program (or a non-Ada program that calls Ada code), two breakpoints that are associated with Ada tasking exception events are automatically established. These breakpoints are established automatically during debugger initialization when the Ada run-time library is present.
When you enter a SHOW BREAK command under these conditions, the following breakpoints are displayed:
C.2.10 Monitoring Exceptions
The debugger recognizes three kinds of exceptions in Ada programs:
The following subtopics explain how to monitor such exceptions.
The SET BREAK/EXCEPTION command enables you to set a breakpoint on any exception or condition. This includes certain conditions that are signaled internally within the Ada run-time library. These conditions are an implementation mechanism; they do not represent program failures, and they cannot be handled by Ada exception handlers. If these conditions appear while you are debugging your program, you may want to consider specifying the kind of exceptions when setting breakpoints.
The following example shows a tracepoint occurring for an Ada CONSTRAINT_ERROR exception as the result of a SET TRACE/EXCEPTION command:
In the next example, the SHOW CALLS command displays a traceback of the calls leading to the subprogram where the exception occurred or to which the exception was raised:
In this example, the condition SS$_INTDIV is raised at line 17 of the subprogram DIVIDE in the package SYSTEM_OPS. The example shows an important effect: some conditions (such as SS$_INTDIV) are treated as being equivalent to some Ada predefined exceptions.
The matching of a condition and an Ada predefined exception is
performed by the condition handler provided by Ada for any frame that
includes an exception part. Therefore, when an exception breakpoint or
tracepoint is triggered by a condition that has an equivalent Ada
exception name, the message displays only the system condition
code name, and not the name of the corresponding Ada exception.
Whenever an exception is raised, the debugger sets the following built-in symbols. You can use them to qualify exception breakpoints or tracepoints so that they trigger only on certain exceptions.
C.2.10.3 Monitoring Handled Exceptions and Exception Handlers
The SET BREAK/EVENT and SET TRACE/EVENT commands let you set breakpoints and tracepoints on exceptions that are about to be handled by Ada exception handlers. These commands let you observe the execution of each Ada exception handler that gains control.
You can specify two event names with these commands:
For example, the following command sets a breakpoint that triggers whenever an exception is about to be handled by an Ada exception handler:
When the breakpoint triggers, the debugger identifies the exception that is about to be handled and the exception handler that is about to be executed. You can then use that information to set a breakpoint on a particular handler, or you can enter the GO command, and see which Ada handler next attempts to handle the exception. For example:
C.2.11 Examining and Manipulating Data
When examining and manipulating data, note the following considerations:
In most cases, the debugger enables you to specify variables and
expressions in debugger commands exactly as you would specify them in
the source code of the program, including use of qualified expressions.
The following subtopics discuss some additional points about debugger
support for records and access types.
Note the following points about debugger support for records:
C.2.11.2 Access Types
Note the following points about debugger support for access types:
The following example shows the debugger support for incomplete types. Consider the following declarations:
The debugger does not have complete information about the type T, so
you cannot manipulate the variable VAR. However, the debugger does have
information about objects declared in the package body P. Thus, you can
manipulate the variables T_PTR and T_REC.
The names of Ada debugger modules are the same as the names of the corresponding compilation units, with the following provision. To eliminate ambiguity, an underscore character (_) is appended to a specification name to distinguish it from its body name. For example, TEST (body), TEST_ (specification). To determine the exact names of the modules in your program, use the SHOW MODULE command.
In most cases when you specify a path name, the debugger can distinguish body names and specification names from the context. Therefore, use this naming convention only if needed to resolve an ambiguity.
When the debugger language is set to Ada, the debugger generally constructs pathnames that follow the Ada rules, using selected component notation to separate path name elements (with other languages, a backslash is used to separate elements). For example:
The maximum length that you can specify for a subunit path name (expanded name) is 247 characters.
When a use clause makes a symbol declared in a package directly visible outside the package, you do not need to specify an expanded name (package-name.symbol) to refer to the symbol, either in the program itself or in debugger commands.
The SHOW SYMBOL/USE_CLAUSE command identifies any package (library or otherwise) that a specified block, subprogram, or package mentions in a use clause. If the entity specified is a package (library or otherwise), the command also identifies any block, subprogram, package, and so on, that names the specified module in a use clause. For example:
If a label has been assigned to a loop statement or
declare block in the source code, the debugger
displays the label; otherwise, the debugger displays LOOP$n
for a loop statement or BLOCK$n for a declare block, where
n is the line number at which the statement or block begins.
For Ada programs, when you do not specify a path name (including an Ada expanded name), the debugger searches the run-time symbol table as follows.
C.2.14 Setting Modules
When you or the debugger sets an Ada module, by default the debugger also sets any "related" module (that is, any module whose symbols should be visible within the module being set). Such modules are related to the one being set through either a with-clause or a subunit relationship.
Related module setting takes place as follows. If M1 is the module that is being set, then the following modules are considered related and are also set:
If debugger performance becomes a problem as more modules are set, use the SET MODE NODYNAMIC command, which disables related module setting as well as dynamic module setting. You must then set individual modules explicitly with the SET MODULE command.
By default, the SET MODULE command sets related modules simultaneously with the module specified in the command.
The SET MODULE/NORELATED command sets only the modules you specify explicitly. However, if you use SET MODULE/NORELATED, you may find that a symbol that is declared in another unit and that should be visible at the point of execution is no longer visible or that a symbol which should be hidden by a redeclaration of that same symbol is now visible.
The CANCEL MODULE/NORELATED command deletes from the RST only the modules you specify explicitly. This command, which is the default, deletes related modules in a manner consistent with the intent of Ada's scope and visibility rules. The exact effect depends on module relationships.