HP OpenVMS Systems Documentation
OpenVMS Debugger Manual
4.4.2 Processor Status (Alpha Only)
On Alpha processors, the processor status (PS) is a register whose value represents a number of processor state variables. The first three bits of the PS are reserved for the use of the software. The values of these bits can be controlled by a user program. The remainder of the bits, bits 4 to 64, contain privileged information and cannot be altered by a user-mode program.
The following example shows how to examine the contents of the PS:
See the Alpha Architecture Reference Manual for complete information about the PS, including the values of the various bits.
You can also display the information in the PS in other formats. For example:
The command EXAMINE/PS displays the value at any location in PS format.
This is useful for examining the combined current and saved PS values.
The preceding sections explain how to use the EXAMINE and DEPOSIT commands with program locations that have a symbolic name and, therefore, are associated with a compiler-generated type.
Section 4.5.1 describes how the debugger formats (types) data for program locations that do not have a symbolic name and explains how you can control the type for those locations.
Section 4.5.2 explains how to override the type associated with any
program location, including a location that has a symbolic name.
Program locations that do not have a symbolic name and, therefore, are not associated with a compiler-generated type have the type longword integer by default. Section 4.1.5 explains how to examine and deposit into such locations using the default type.
The SET TYPE command enables you to change the default type in order to examine and display the contents of a location in another type, or to deposit a value of one type into a location associated with another type. Table 4-3 lists the type keywords for the SET TYPE command.
For example, the following commands set the type for locations without a symbolic name to, respectively, byte integer, G_floating, and ASCII with 6 bytes of ASCII data. Each successive SET TYPE command resets the type.
Note that the SET TYPE command, when used without the /OVERRIDE qualifier, does not affect the type for program locations that have a symbolic name (locations associated with a compiler-generated type).
The SHOW TYPE command identifies the current type for locations without
a symbolic name. To restore the default type for such locations, enter
the SET TYPE LONGWORD command.
The SET TYPE/OVERRIDE command enables you to change the type associated with any program location, including locations with compiler-generated types. For example, after the following command is executed, an unqualified EXAMINE command displays the contents of only the first byte of the location specified and interprets the contents as byte integer data. An unqualified DEPOSIT command modifies only the first byte of the location specified and formats the data deposited as byte integer data.
See Table 4-3 for the valid type keywords for the SET TYPE/OVERRIDE command.
To identify the current override type, enter the SHOW TYPE/OVERRIDE command. To cancel the current override type and restore the normal interpretation of locations that have a symbolic name, enter the CANCEL TYPE/OVERRIDE command.
The EXAMINE and DEPOSIT commands have qualifiers that enable you to override the type currently associated with a program location for the duration of the EXAMINE or DEPOSIT command. These qualifiers override any previous SET TYPE or SET TYPE/OVERRIDE command as well as any compiler-generated type. See the DEPOSIT and EXAMINE commands for the type qualifiers available to each command.
When used with a type qualifier, the EXAMINE command displays the entity specified by the address expression in that type. For example:
When used with a type qualifier, the DEPOSIT command deposits a value of that type into the location specified by the address expression, which overrides the type associated with the address expression.
The remaining sections provide examples of specifying integer, string,
and user-declared types with type qualifiers and the SET TYPE command.
The following examples show the use of the EXAMINE and DEPOSIT commands with integer-type qualifiers (/BYTE, /WORD, /LONGWORD). These qualifiers enable you to deposit a value of a particular integer type into an arbitrary program location.
220.127.116.11 ASCII String Type
The following examples show the use of the EXAMINE and DEPOSIT commands with the /ASCII:n type qualifier.
When used with the DEPOSIT command, this qualifier enables you to deposit an ASCII string of length n into an arbitrary program location. In the example, the location has a symbolic name (I) and, therefore, is associated with a compiler-generated integer type. The command syntax is as follows:
The default value of n is 4 bytes.
To enter several DEPOSIT/ASCII commands, you can establish an override ASCII type with the SET TYPE/OVERRIDE command. Subsequent EXAMINE and DEPOSIT commands then have the effect of specifying the /ASCII qualifier with these commands. For example:
18.104.22.168 User-Declared Types
The following examples show the use of the EXAMINE and DEPOSIT commands with the /TYPE=(name) qualifier. The qualifier enables you to specify a user-declared override type when examining or depositing.
For example, assume that a Pascal program contains the following code, which declares the enumeration type COLOR with the three values RED, GREEN, and BLUE:
During the debugging session, the SHOW SYMBOL/TYPE command identifies the type COLOR as it is known to the debugger:
The next example displays the value at address 1000, which is not associated with a symbolic name. Therefore, the value 0 is displayed in the type longword integer, by default.
The next example displays the value at address 1000 in the type COLOR. The preceding SHOW SYMBOL/TYPE command indicates that each enumeration element is stored in 1 byte. Therefore, the debugger converts the first byte of the longword integer value 0 at address 1000 to the equivalent enumeration value, RED (the first of the three enumeration values):
The following DEPOSIT command deposits the value GREEN into address 1000 with the override type COLOR. The EXAMINE command displays the value at address 1000 in the default type, longword integer:
The following SET TYPE command establishes the type COLOR for locations, such as address 1000, that do not have a symbolic name. The EXAMINE command now displays the value at 1000 in the type COLOR:
DBG> SET BREAK COUNTER %DEBUG-E-NOSYMBOL, symbol 'COUNTER' is not in the symbol table DBG>
You must then set the module where COUNTER is defined, as explained in Section 5.2.
The debugger might display the following message if the same symbol X is defined (declared) in more than one module, routine, or other program unit:
DBG> EXAMINE X %DEBUG-E-NOUNIQUE, symbol 'X' is not unique DBG>
You must then resolve the symbol ambiguity, perhaps by specifying a path name for the symbol, as explained in Section 5.3.
This chapter explains how to handle these and other situations related to accessing symbols in your program.
The chapter discusses only the symbols (typically address expressions) that are derived from your source program:
The following types of symbols are discussed in other chapters:
Also, see Section 4.1.11 for information about how to obtain the memory addresses and register names associated with symbolic address expressions and how to symbolize program locations.
If your program was optimized during compilation, certain variables in the program might be removed by the compiler. If you then try to reference such a variable, the debugger issues a warning (see Section 1.2 and Section 14.1).
Before you try to reference a nonstatic (stack-local or register) variable, its defining routine must be active on the call stack. That is, program execution must be paused somewhere within the defining routine (see Section 3.4.3).
To take full advantage of symbolic debugging, you must compile and link your program with the /DEBUG qualifier as explained in Section 1.2.
The following sections describe how symbol information is created and
passed to the debugger when compiling and linking.
When you compile a source file using the /DEBUG qualifier, the compiler creates symbol records for the debug symbol table (DST records) and includes them in the object module being created.
DST records provide not only the names of symbols but also all relevant information about their use. For example:
Most compilers allow you to vary the amount of DST information put in an object module by specifying different options with the /DEBUG qualifier. Table 5-1 identifies the options for most compilers (see the documentation supplied with your compiler for complete information).
|Compiler Command Qualifier||DST Information in Object Module|
|/DEBUG=TRACEBACK 2||Traceback only (module names, routine names, and line numbers)|
The TRACEBACK option is a default for most compilers. That is, if you omit the /DEBUG qualifier, most compilers assume /DEBUG=TRACEBACK. The TRACEBACK option enables the traceback condition handler to translate memory addresses into routine names and line numbers so that it can give a symbolic traceback if a run-time error has occurred. For example:
$ RUN FORMS . . . %PAS-F-ERRACCFIL, error in accessing file PAS$OUTPUT %PAS-F-ERROPECRE, error opening/creating file %RMS-F-FNM, error in file name %TRACE-F-TRACEBACK, symbolic stack dump follows module name routine name line rel PC abs PC PAS$IO_BASIC _PAS$CODE 00000192 00001CED PAS$IO_BASIC _PAS$CODE 0000054D 000020A8 PAS$IO_BASIC _PAS$CODE 0000028B 00001DE6 FORMS FORMS 59 00000020 000005A1 $
Traceback information is also used by the debugger's SHOW CALLS command.
5.1.2 Local and Global Symbols
DST records contain information about all of the symbols that are defined in your program. These are either local or global symbols.
Typically, a local symbol is a symbol that is referenced only within the module where it is defined; a global symbol is a symbol such as a routine name, procedure entry point, or a global data name, that is defined in one module but referenced in other modules.
A global symbol that is defined in a shareable image and is referenced in another image (for example the main, executable image of a program) is called a universal symbol. When creating a shareable image, you must explicitly define any universal symbols as such at link time. See Section 5.4 for information about universal symbols and shareable images.
Generally, the compiler resolves references to local symbols, and the linker resolves references to global symbols.
The distinction between local and global symbols is discussed in
various parts of this chapter in connection with symbol lookup and with
shareable images and universal symbols.
When you enter the LINK/DEBUG command to link object modules and produce an executable image, the linker performs several functions that affect debugging:
Section 5.4 explains how to link shareable images for debugging, including how to define universal symbols (global symbols that are defined within a shareable image and referenced from another image).
Table 5-2 summarizes the level of DST and GST information passed to the debugger depending on the compiler or LINK command option. The compiler command qualifier controls the level of DST information passed to the linker. The LINK command qualifier controls not only how much DST and GST information is passed to the debugger but also whether the program can be brought under debugger control (see Section 1.2).
| DST Data in
| LINK Command
| DST Data
| GST Data
|/DEBUG=TRACE||Traceback only||/DEBUG||Traceback only||Full|
|/DEBUG||Full||/DSF 4||Full||Full 5|
|/DEBUG=TRACE||Traceback only||/DSF 4||Traceback only||Full 5|
|/NODEBUG||None||/DSF 4||None||Full 5|
|/DEBUG||Full||/TRACE 6||Traceback only||Full|
|/DEBUG=TRACE||Traceback only||/TRACE||Traceback only||Full|
%DEBUG-I-NOLOCALS, image does not contain local symbols
The previous message, which occurs whether you linked with the /TRACEBACK or /DEBUG qualifier, indicates that no DST has been created for that image. Therefore, you have access only to global symbols contained in the GST.