Program animation
Encyclopedia
Program animation or Stepping refers to the very common debugging
method of executing code one "line" at a time. The programmer may examine the state of the program, machine, and related data
before and after execution of a particular line of code. This allows evaluation of the effects
of that statement or instruction in isolation and thereby gain insight into the behavior (or misbehavior) of the executing program. Nearly all modern IDE
s and debugger
s support this mode of execution.
Some Testing tools allow programs to be executed step-by-step optionally at either source code
level or machine code
level depending upon the availability of data collected at compile
time.
Instruction stepping or single cycle also referred to the related, more microscopic, but now obsolete method of debugging
code by stopping the processor clock
and manually advancing it one cycle at a time. For this to be possible, three things are required:
On the IBM
System 360 processor range, these facilities were provided by front panel switches, buttons and banks of neon lights.
Other systems such as the PDP-11
provided similar facilities, again on some models. The precise configuration was also model-dependent. It would not be easy to provide such facilities on LSI processors such as the Intel x86 and Pentium lines, owing to cooling considerations.
As multiprocessing
became more commonplace, such techniques would have limited practicality, since many independent processes would be stopped simultaneously. This led to the development of proprietary software from several independent vendors that provided similar features but deliberately restricted breakpoints and instruction stepping to particular application programs in particular address spaces and threads. The program state (as applicable to the chosen application/thread) was saved for examination at each step and restored before resumption, giving the impression of a single user environment. This is normally sufficient for diagnosing problems at the application layer.
Instead of using a physical stop button to suspend execution - to then begin stepping through the application program, a breakpoint
or "Pause" request must usually be set beforehand, usually at a particular statement/instruction in the program (chosen beforehand or alternatively, by default, at the first instruction).
To provide for full screen "animation" of a program, a suitable I/O device such as a video monitor is normally required that can display a reasonable section of the code (e.g. in dis-assembled machine code or source code
format) and provide a pointer (e.g. <) to the current instruction or line of source code. For this reason, the widespread use of these full screen animators in the mainframe
world had to await the arrival of transaction processing
systems - such as CICS
in the early 1970's and were initially limited to debugging application programs operating within that environment. Later versions of the same products provided cross region monitoring/debugging of batch programs and other operating systems and platforms.
With the much later introduction of Personal computers from around 1980 onwards, integrated debuggers were able to be incorporated more widely into this single user domain and provided similar animation by splitting the user screen and adding a debugging "console" to provide programmer interaction.
Borland Turbo Debugger was a stand-alone product introduced in 1989, that provided full-screen program animation for PC's. Later versions added support for combining the animation with actual source lines extracted at compilation time.
Techniques for program animation
There are at least three distinct software techniques for creating 'animation' during programs execution.
Comparison of methods
The advantage of the last method is that no changes are made to the compiled program to provide the diagnostic and there is almost unlimited scope for extensive diagnostics since the tool can augment the host system diagnostics with additional software tracing features. It is also possible to diagnose (and prevent) many program errors automatically using this technique, including storage violation
s and buffer overflow
s. Loop detection is also possible using automatic instruction trace together with instruction count thresholds (e.g. pause after 10,000 instructions; display last n instructions)
The second method only alters the instruction that will halt before it is executed and may also then restore it before optional resumption by the programmer.
Some animators optionally allow the use of more than one method depending on requirements. For example, using method 2 to execute to a particular point at full speed and then using instruction set simulation thereafter.
, dump, conditional breakpoint
and memory
alteration, program flow alteration, code coverage
analysis, "hot spot" detection or similar.
Examples of program animators
External links and references
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
method of executing code one "line" at a time. The programmer may examine the state of the program, machine, and related data
State (computer science)
In computer science and automata theory, a state is a unique configuration of information in a program or machine. It is a concept that occasionally extends into some forms of systems programming such as lexers and parsers....
before and after execution of a particular line of code. This allows evaluation of the effects
Side effect (computer science)
In computer science, a function or expression is said to have a side effect if, in addition to returning a value, it also modifies some state or has an observable interaction with calling functions or the outside world...
of that statement or instruction in isolation and thereby gain insight into the behavior (or misbehavior) of the executing program. Nearly all modern IDE
Integrated development environment
An integrated development environment is a software application that provides comprehensive facilities to computer programmers for software development...
s and debugger
Debugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
s support this mode of execution.
Some Testing tools allow programs to be executed step-by-step optionally at either source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
level or machine code
Machine code
Machine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...
level depending upon the availability of data collected at compile
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
time.
History
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
code by stopping the processor clock
Clock signal
In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits...
and manually advancing it one cycle at a time. For this to be possible, three things are required:
- A control that allows the clock to be stopped (e.g. a "Stop" button).
- A second control that allows the stopped clock to be manually advanced by one cycle (e.g. An "instruction step" switch and a "Start" button).
- Some means of recording the state of the processor after each cycle (e.g. register and memory displays).
On the IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
System 360 processor range, these facilities were provided by front panel switches, buttons and banks of neon lights.
Other systems such as the PDP-11
PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
provided similar facilities, again on some models. The precise configuration was also model-dependent. It would not be easy to provide such facilities on LSI processors such as the Intel x86 and Pentium lines, owing to cooling considerations.
As multiprocessing
Multiprocessing
Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor and/or the ability to allocate tasks between them...
became more commonplace, such techniques would have limited practicality, since many independent processes would be stopped simultaneously. This led to the development of proprietary software from several independent vendors that provided similar features but deliberately restricted breakpoints and instruction stepping to particular application programs in particular address spaces and threads. The program state (as applicable to the chosen application/thread) was saved for examination at each step and restored before resumption, giving the impression of a single user environment. This is normally sufficient for diagnosing problems at the application layer.
Instead of using a physical stop button to suspend execution - to then begin stepping through the application program, a breakpoint
Breakpoint
In software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause....
or "Pause" request must usually be set beforehand, usually at a particular statement/instruction in the program (chosen beforehand or alternatively, by default, at the first instruction).
To provide for full screen "animation" of a program, a suitable I/O device such as a video monitor is normally required that can display a reasonable section of the code (e.g. in dis-assembled machine code or source code
Source code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
format) and provide a pointer (e.g. <) to the current instruction or line of source code. For this reason, the widespread use of these full screen animators in the mainframe
Mainframe
Mainframe may refer to either of the following:* Mainframe computer, large and powerful data processing systems* Mainframe Entertainment, a Canadian computer animation and design company* Mainframe , a 1980s Electropop band...
world had to await the arrival of transaction processing
Transaction processing
In computer science, transaction processing is information processing that is divided into individual, indivisible operations, called transactions. Each transaction must succeed or fail as a complete unit; it cannot remain in an intermediate state...
systems - such as CICS
CICS
Customer Information Control System is a transaction server that runs primarily on IBM mainframe systems under z/OS and z/VSE.CICS is a transaction manager designed for rapid, high-volume online processing. This processing is mostly interactive , but background transactions are possible...
in the early 1970's and were initially limited to debugging application programs operating within that environment. Later versions of the same products provided cross region monitoring/debugging of batch programs and other operating systems and platforms.
With the much later introduction of Personal computers from around 1980 onwards, integrated debuggers were able to be incorporated more widely into this single user domain and provided similar animation by splitting the user screen and adding a debugging "console" to provide programmer interaction.
Borland Turbo Debugger was a stand-alone product introduced in 1989, that provided full-screen program animation for PC's. Later versions added support for combining the animation with actual source lines extracted at compilation time.
Techniques for program animation
There are at least three distinct software techniques for creating 'animation' during programs execution.
- instrumentationInstrumentation (computer programming)In context of computer programming, instrumentation refers to an ability to monitor or measure the level of a product's performance, to diagnose errors and to write trace information. Programmers implement instrumentation in the form of code instructions that monitor specific components in a system...
involves adding additional source code to the program at compileCompileCompile may refer to:* Compile , a Japanese video game company founded in 1983 that specialized in shoot 'em up and computer puzzle game genres...
time to call the animator before or after each statement to halt normal execution. - Induced interrupt This technique involves forcing a breakpoint at certain points in a program at execution time, usually by altering the machine code instruction at that point (this might be an inserted system call or deliberate invalid operation) and waiting for an interrupt. When the interrupt occurs, it is handled by the testing tool to report the status back to the programmer. This method allows program execution at full speed (until the interrupt occurs) but suffers from the disadvantage that most of the instructions leading up to the interrupt are not monitored by the tool.
- Instruction Set SimulatorInstruction Set SimulatorAn instruction set simulator is a simulation model, usually coded in a high-level programming language, which mimics the behavior of a mainframe or microprocessor by "reading" instructions and maintaining internal variables which represent the processor's registers.Instruction simulation is a...
This technique treats the compiled programs machine codeMachine codeMachine code or machine language is a system of impartible instructions executed directly by a computer's central processing unit. Each instruction performs a very specific task, typically either an operation on a unit of data Machine code or machine language is a system of impartible instructions...
as its input 'data' and fully simulates the host machine instructions, monitors the code for conditional or unconditional breakpointBreakpointIn software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause....
s or programmer requested "single cycle" animation requests between every step.
Comparison of methods
The advantage of the last method is that no changes are made to the compiled program to provide the diagnostic and there is almost unlimited scope for extensive diagnostics since the tool can augment the host system diagnostics with additional software tracing features. It is also possible to diagnose (and prevent) many program errors automatically using this technique, including storage violation
Storage violation
A storage violation occurs when a task modifies, or attempts to modify, computer storage that it does not own.-Types of storage violation:Storage violation can, for instance, consist of writing to or freeing storage not owned by the task....
s and buffer overflow
Buffer overflow
In computer security and programming, a buffer overflow, or buffer overrun, is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory. This is a special case of violation of memory safety....
s. Loop detection is also possible using automatic instruction trace together with instruction count thresholds (e.g. pause after 10,000 instructions; display last n instructions)
The second method only alters the instruction that will halt before it is executed and may also then restore it before optional resumption by the programmer.
Some animators optionally allow the use of more than one method depending on requirements. For example, using method 2 to execute to a particular point at full speed and then using instruction set simulation thereafter.
Additional features
The animator may, or may not, combine other test/debugging features within it such as program traceTracing (software)
In software engineering, tracing is a specialized use of logging to record information about a program's execution. This information is typically used by programmers for debugging purposes, and additionally, depending on the type and detail of information contained in a trace log, by experienced...
, dump, conditional breakpoint
Breakpoint
In software development, a breakpoint is an intentional stopping or pausing place in a program, put in place for debugging purposes. It is also sometimes simply referred to as a pause....
and memory
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
alteration, program flow alteration, code coverage
Code coverage
Code coverage is a measure used in software testing. It describes the degree to which the source code of a program has been tested. It is a form of testing that inspects the code directly and is therefore a form of white box testing....
analysis, "hot spot" detection or similar.
Examples of program animators
- Firebug (Firefox extension)Firebug (Firefox extension)Firebug is a web development tool that facilitates the debugging, editing, and monitoring of any website's CSS, HTML, DOM, XHR, and JavaScript; it also provides other web development tools. Firebug's JavaScript panel can log errors, profile function calls, and enable the developer to run arbitrary...
- IBM OLIVER (CICS interactive test/debug)
- SIMON (Batch Interactive test/debug)SIMON (Batch Interactive test/debug)SIMON was a proprietary test/debugging toolkit for interactively testing Batch programs designed to run on IBM's System 360/370/390 architecture....
External links and references
Firebug (Firefox extension)
Firebug is a web development tool that facilitates the debugging, editing, and monitoring of any website's CSS, HTML, DOM, XHR, and JavaScript; it also provides other web development tools. Firebug's JavaScript panel can log errors, profile function calls, and enable the developer to run arbitrary...
SIMON (Batch Interactive test/debug)
SIMON was a proprietary test/debugging toolkit for interactively testing Batch programs designed to run on IBM's System 360/370/390 architecture....
- Stepping (Visual Studio) Overview of stepping support in Microsoft Corporation'sMicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
IDEIntegrated development environmentAn integrated development environment is a software application that provides comprehensive facilities to computer programmers for software development...
, Visual Studio - Tarraingim - A Program Animation Environment
- Program Animation as a way to teach and learn about Program Design and Analysis
- Structured information on software testing (such as the History of Software Testing) published by Testing references