Control Flow
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Writing Fast Fortran Routines for Python
Writing fast Fortran routines for Python Table of contents Table of contents ............................................................................................................................ 1 Overview ......................................................................................................................................... 2 Installation ...................................................................................................................................... 2 Basic Fortran programming ............................................................................................................ 3 A Fortran case study ....................................................................................................................... 8 Maximizing computational efficiency in Fortran code ................................................................. 12 Multiple functions in each Fortran file ......................................................................................... 14 Compiling and debugging ............................................................................................................ 15 Preparing code for f2py ................................................................................................................ 16 Running f2py ................................................................................................................................. 17 Help with f2py .............................................................................................................................. -
7. Control Flow First?
Copyright (C) R.A. van Engelen, FSU Department of Computer Science, 2000-2004 Ordering Program Execution: What is Done 7. Control Flow First? Overview Categories for specifying ordering in programming languages: Expressions 1. Sequencing: the execution of statements and evaluation of Evaluation order expressions is usually in the order in which they appear in a Assignments program text Structured and unstructured flow constructs 2. Selection (or alternation): a run-time condition determines the Goto's choice among two or more statements or expressions Sequencing 3. Iteration: a statement is repeated a number of times or until a Selection run-time condition is met Iteration and iterators 4. Procedural abstraction: subroutines encapsulate collections of Recursion statements and subroutine calls can be treated as single Nondeterminacy statements 5. Recursion: subroutines which call themselves directly or indirectly to solve a problem, where the problem is typically defined in terms of simpler versions of itself 6. Concurrency: two or more program fragments executed in parallel, either on separate processors or interleaved on a single processor Note: Study Chapter 6 of the textbook except Section 7. Nondeterminacy: the execution order among alternative 6.6.2. constructs is deliberately left unspecified, indicating that any alternative will lead to a correct result Expression Syntax Expression Evaluation Ordering: Precedence An expression consists of and Associativity An atomic object, e.g. number or variable The use of infix, prefix, and postfix notation leads to ambiguity An operator applied to a collection of operands (or as to what is an operand of what arguments) which are expressions Fortran example: a+b*c**d**e/f Common syntactic forms for operators: The choice among alternative evaluation orders depends on Function call notation, e.g. -
A Survey of Hardware-Based Control Flow Integrity (CFI)
A survey of Hardware-based Control Flow Integrity (CFI) RUAN DE CLERCQ∗ and INGRID VERBAUWHEDE, KU Leuven Control Flow Integrity (CFI) is a computer security technique that detects runtime attacks by monitoring a program’s branching behavior. This work presents a detailed analysis of the security policies enforced by 21 recent hardware-based CFI architectures. The goal is to evaluate the security, limitations, hardware cost, performance, and practicality of using these policies. We show that many architectures are not suitable for widespread adoption, since they have practical issues, such as relying on accurate control flow model (which is difficult to obtain) or they implement policies which provide only limited security. CCS Concepts: • Security and privacy → Hardware-based security protocols; Information flow control; • General and reference → Surveys and overviews; Additional Key Words and Phrases: control-flow integrity, control-flow hijacking, return oriented programming, shadow stack ACM Reference format: Ruan de Clercq and Ingrid Verbauwhede. YYYY. A survey of Hardware-based Control Flow Integrity (CFI). ACM Comput. Surv. V, N, Article A (January YYYY), 27 pages. https://doi.org/10.1145/nnnnnnn.nnnnnnn 1 INTRODUCTION Today, a lot of software is written in memory unsafe languages, such as C and C++, which introduces memory corruption bugs. This makes software vulnerable to attack, since attackers exploit these bugs to make the software misbehave. Modern Operating Systems (OSs) and microprocessors are equipped with security mechanisms to protect against some classes of attacks. However, these mechanisms cannot defend against all attack classes. In particular, Code Reuse Attacks (CRAs), which re-uses pre-existing software for malicious purposes, is an important threat that is difficult to protect against. -
Control-Flow Analysis of Functional Programs
Control-flow analysis of functional programs JAN MIDTGAARD Department of Computer Science, Aarhus University We present a survey of control-flow analysis of functional programs, which has been the subject of extensive investigation throughout the past 30 years. Analyses of the control flow of functional programs have been formulated in multiple settings and have led to many different approximations, starting with the seminal works of Jones, Shivers, and Sestoft. In this paper, we survey control-flow analysis of functional programs by structuring the multitude of formulations and approximations and comparing them. Categories and Subject Descriptors: D.3.2 [Programming Languages]: Language Classifica- tions—Applicative languages; F.3.1 [Logics and Meanings of Programs]: Specifying and Ver- ifying and Reasoning about Programs General Terms: Languages, Theory, Verification Additional Key Words and Phrases: Control-flow analysis, higher-order functions 1. INTRODUCTION Since the introduction of high-level languages and compilers, much work has been devoted to approximating, at compile time, which values the variables of a given program may denote at run time. The problem has been named data-flow analysis or just flow analysis. In a language without higher-order functions, the operator of a function call is apparent from the text of the program: it is a lexically visible identifier and therefore the called function is available at compile time. One can thus base an analysis for such a language on the textual structure of the program, since it determines the exact control flow of the program, e.g., as a flow chart. On the other hand, in a language with higher-order functions, the operator of a function call may not be apparent from the text of the program: it can be the result of a computation and therefore the called function may not be available until run time. -
Scope in Fortran 90
Scope in Fortran 90 The scope of objects (variables, named constants, subprograms) within a program is the portion of the program in which the object is visible (can be use and, if it is a variable, modified). It is important to understand the scope of objects not only so that we know where to define an object we wish to use, but also what portion of a program unit is effected when, for example, a variable is changed, and, what errors might occur when using identifiers declared in other program sections. Objects declared in a program unit (a main program section, module, or external subprogram) are visible throughout that program unit, including any internal subprograms it hosts. Such objects are said to be global. Objects are not visible between program units. This is illustrated in Figure 1. Figure 1: The figure shows three program units. Main program unit Main is a host to the internal function F1. The module program unit Mod is a host to internal function F2. The external subroutine Sub hosts internal function F3. Objects declared inside a program unit are global; they are visible anywhere in the program unit including in any internal subprograms that it hosts. Objects in one program unit are not visible in another program unit, for example variable X and function F3 are not visible to the module program unit Mod. Objects in the module Mod can be imported to the main program section via the USE statement, see later in this section. Data declared in an internal subprogram is only visible to that subprogram; i.e. -
Subroutines – Get Efficient
Subroutines – get efficient So far: The code we have looked at so far has been sequential: Subroutines – getting efficient with Perl do this; do that; now do something; finish; Problem Bela Tiwari You need something to be done over and over, perhaps slightly [email protected] differently depending on the context Solution Environmental Genomics Thematic Programme Put the code in a subroutine and call the subroutine whenever needed. Data Centre http://envgen.nox.ac.uk Syntax: There are a number of correct ways you can define and use Subroutines – get efficient subroutines. One is: A subroutine is a named block of code that can be executed as many times #!/usr/bin/perl as you wish. some code here; some more here; An artificial example: lalala(); #declare and call the subroutine Instead of: a bit more code here; print “Hello everyone!”; exit(); #explicitly exit the program ############ You could use: sub lalala { #define the subroutine sub hello_sub { print "Hello everyone!\n“; } #subroutine definition code to define what lalala does; #code defining the functionality of lalala more defining lalala; &hello_sub; #call the subroutine return(); #end of subroutine – return to the program } Syntax: Outline review of previous slide: Subroutines – get efficient Syntax: #!/usr/bin/perl Permutations on the theme: lalala(); #call the subroutine Defining the whole subroutine within the script when it is first needed: sub hello_sub {print “Hello everyone\n”;} ########### sub lalala { #define the subroutine The use of an ampersand to call the subroutine: &hello_sub; return(); #end of subroutine – return to the program } Note: There are subtle differences in the syntax allowed and required by Perl depending on how you declare/define/call your subroutines. -
COBOL-Skills, Where Art Thou?
DEGREE PROJECT IN COMPUTER ENGINEERING 180 CREDITS, BASIC LEVEL STOCKHOLM, SWEDEN 2016 COBOL-skills, Where art Thou? An assessment of future COBOL needs at Handelsbanken Samy Khatib KTH ROYAL INSTITUTE OF TECHNOLOGY i INFORMATION AND COMMUNICATION TECHNOLOGY Abstract The impending mass retirement of baby-boomer COBOL developers, has companies that wish to maintain their COBOL systems fearing a skill shortage. Due to the dominance of COBOL within the financial sector, COBOL will be continually developed over at least the coming decade. This thesis consists of two parts. The first part consists of a literature study of COBOL; both as a programming language and the skills required as a COBOL developer. Interviews were conducted with key Handelsbanken staff, regarding the current state of COBOL and the future of COBOL in Handelsbanken. The second part consists of a quantitative forecast of future COBOL workforce state in Handelsbanken. The forecast uses data that was gathered by sending out a questionnaire to all COBOL staff. The continued lack of COBOL developers entering the labor market may create a skill-shortage. It is crucial to gather the knowledge of the skilled developers before they retire, as changes in old COBOL systems may have gone undocumented, making it very hard for new developers to understand how the systems work without guidance. To mitigate the skill shortage and enable modernization, an extraction of the business knowledge from the systems should be done. Doing this before the current COBOL workforce retires will ease the understanding of the extracted data. The forecasts of Handelsbanken’s COBOL workforce are based on developer experience and hiring, averaged over the last five years. -
Obfuscating C++ Programs Via Control Flow Flattening
Annales Univ. Sci. Budapest., Sect. Comp. 30 (2009) 3-19 OBFUSCATING C++ PROGRAMS VIA CONTROL FLOW FLATTENING T. L¶aszl¶oand A.¶ Kiss (Szeged, Hungary) Abstract. Protecting a software from unauthorized access is an ever de- manding task. Thus, in this paper, we focus on the protection of source code by means of obfuscation and discuss the adaptation of a control flow transformation technique called control flow flattening to the C++ lan- guage. In addition to the problems of adaptation and the solutions pro- posed for them, a formal algorithm of the technique is given as well. A prototype implementation of the algorithm presents that the complexity of a program can show an increase as high as 5-fold due to the obfuscation. 1. Introduction Protecting a software from unauthorized access is an ever demanding task. Unfortunately, it is impossible to guarantee complete safety, since with enough time given, there is no unbreakable code. Thus, the goal is usually to make the job of the attacker as di±cult as possible. Systems can be protected at several levels, e.g., hardware, operating system or source code. In this paper, we focus on the protection of source code by means of obfuscation. Several code obfuscation techniques exist. Their common feature is that they change programs to make their comprehension di±cult, while keep- ing their original behaviour. The simplest technique is layout transformation [1], which scrambles identi¯ers in the code, removes comments and debug informa- tion. Another technique is data obfuscation [2], which changes data structures, 4 T. L¶aszl¶oand A.¶ Kiss e.g., by changing variable visibilities or by reordering and restructuring arrays. -
Subroutines and Control Abstraction
Subroutines and Control Abstraction CSE 307 – Principles of Programming Languages Stony Brook University http://www.cs.stonybrook.edu/~cse307 1 Subroutines Why use subroutines? Give a name to a task. We no longer care how the task is done. The subroutine call is an expression Subroutines take arguments (in the formal parameters) Values are placed into variables (actual parameters/arguments), and A value is (usually) returned 2 (c) Paul Fodor (CS Stony Brook) and Elsevier Review Of Memory Layout Allocation strategies: Static Code Globals Explicit constants (including strings, sets, other aggregates) Small scalars may be stored in the instructions themselves Stack parameters local variables temporaries bookkeeping information Heap 3 dynamic allocation(c) Paul Fodor (CS Stony Brook) and Elsevier Review Of Stack Layout 4 (c) Paul Fodor (CS Stony Brook) and Elsevier Review Of Stack Layout Contents of a stack frame: bookkeeping return Program Counter saved registers line number static link arguments and returns local variables temporaries 5 (c) Paul Fodor (CS Stony Brook) and Elsevier Calling Sequences Maintenance of stack is responsibility of calling sequence and subroutines prolog and epilog Tasks that must be accomplished on the way into a subroutine include passing parameters, saving the return address, changing the program counter, changing the stack pointer to allocate space, saving registers (including the frame pointer) that contain important values and that may be overwritten by the callee, changing the frame pointer to refer to the new frame, and executing initialization code for any objects in the new frame that require it. Tasks that must be accomplished on the way out include passing return parameters or function values, executing finalization code for any local objects that require it, deallocating the stack frame (restoring the stack pointer), restoring other saved registers (including the frame pointer), and restoring the program counter. -
Control Flow Statements
Control Flow Statements Christopher M. Harden Contents 1 Some more types 2 1.1 Undefined and null . .2 1.2 Booleans . .2 1.2.1 Creating boolean values . .3 1.2.2 Combining boolean values . .4 2 Conditional statements 5 2.1 if statement . .5 2.1.1 Using blocks . .5 2.2 else statement . .6 2.3 Tertiary operator . .7 2.4 switch statement . .8 3 Looping constructs 10 3.1 while loop . 10 3.2 do while loop . 11 3.3 for loop . 11 3.4 Further loop control . 12 4 Try it yourself 13 1 1 Some more types 1.1 Undefined and null The undefined type has only one value, undefined. Similarly, the null type has only one value, null. Since both types have only one value, there are no operators on these types. These types exist to represent the absence of data, and their difference is only in intent. • undefined represents data that is accidentally missing. • null represents data that is intentionally missing. In general, null is to be used over undefined in your scripts. undefined is given to you by the JavaScript interpreter in certain situations, and it is useful to be able to notice these situations when they appear. Listing 1 shows the difference between the two. Listing 1: Undefined and Null 1 var name; 2 // Will say"Hello undefined" 3 a l e r t( "Hello" + name); 4 5 name= prompt( "Do not answer this question" ); 6 // Will say"Hello null" 7 a l e r t( "Hello" + name); 1.2 Booleans The Boolean type has two values, true and false. -
A Subroutine's Stack Frames Differently • May Require That the Steps Involved in Calling a Subroutine Be Performed in Different Orders
Chapter 04: Instruction Sets and the Processor organizations Lesson 14 Use of the Stack Frames Schaum’s Outline of Theory and Problems of Computer Architecture 1 Copyright © The McGraw-Hill Companies Inc. Indian Special Edition 2009 Objective • To understand call and return, nested calls and use of stack frames Schaum’s Outline of Theory and Problems of Computer Architecture 2 Copyright © The McGraw-Hill Companies Inc. Indian Special Edition 2009 Calling a subroutine Schaum’s Outline of Theory and Problems of Computer Architecture 3 Copyright © The McGraw-Hill Companies Inc. Indian Special Edition 2009 Calls to the subroutines • Allow commonly used functions to be written once and used whenever they are needed, and provide abstraction, making it easier for multiple programmers to collaborate on a program • Important part of virtually all computer languages • Function calls in a C language program • Also included additional functions from library by including the header files Schaum’s Outline of Theory and Problems of Computer Architecture 4 Copyright © The McGraw-Hill Companies Inc. Indian Special Edition 2009 Difficulties when Calling a subroutine Schaum’s Outline of Theory and Problems of Computer Architecture 5 Copyright © The McGraw-Hill Companies Inc. Indian Special Edition 2009 Difficulties involved in implementing subroutine calls 1. Programs need a way to pass inputs to subroutines that they call and to receive outputs back from them Schaum’s Outline of Theory and Problems of Computer Architecture 6 Copyright © The McGraw-Hill Companies Inc. Indian Special Edition 2009 Difficulties involved in implementing subroutine calls 2. Subroutines need to be able to allocate space in memory for local variables without overwriting any data used by the subroutine-calling program Schaum’s Outline of Theory and Problems of Computer Architecture 7 Copyright © The McGraw-Hill Companies Inc. -
Chapter 9: Functions and Subroutines – Reusing Code. Page 125 Chapter 9: Functions and Subroutines – Reusing Code
Chapter 9: Functions and Subroutines – Reusing Code. Page 125 Chapter 9: Functions and Subroutines – Reusing Code. This chapter introduces the use of Functions and Subroutines. Programmers create subroutines and functions to test small parts of a program, reuse these parts where they are needed, extend the programming language, and simplify programs. Functions: A function is a small program within your larger program that does something for you. You may send zero or more values to a function and the function will return one value. You are already familiar with several built in functions like: rand and rgb. Now we will create our own. Illustration 22: Block Diagram of a Function © 2014 James M. Reneau (CC BY-NC-SA 3.0 US) Chapter 9: Functions and Subroutines – Reusing Code. Page 126 Function functionname( argument(s) ) statements End Function Function functionname$( argument(s) ) statements End Function The Function statement creates a new named block of programming statements and assigns a unique name to that block of code. It is recommended that you do not name your function the same name as a variable in your program, as it may cause confusion later. In the required parenthesis you may also define a list of variables that will receive values from the “calling” part of the program. These variables belong to the function and are not available to the part of the program that calls the function. A function definition must be closed or finished with an End Function. This tells the computer that we are done defining the function. The value being returned by the function may be set in one of two ways: 1) by using the return statement with a value following it or 2) by setting the function name to a value within the function.