The similarity between these two operators assignment and equality may result in the accidental use of one in place of the other, and in many cases, the mistake does not produce an error message although some compilers produce warnings. The program prints "hello, world" to the standard outputwhich is usually a terminal or screen display. The original version was:
My name is Santiago and this is my little space on the Internet! I'm interested in computer security and here I publish things that at some point I found useful and that maybe they can be for someone else.
Sunday, January 28, Static code analysis: As I did not know much about the subject, I decided to investigate the main parts of which an analyzer is composed. After searching through the internet, I finished reading from start to finish the Dragon Booka book from which I learned a lot.
After reading this book, I realized that the construction of a static analyzer is very similar to the first half of construction of a compiler, mainly because it is much simpler and efficient to traverse the code in an intermediate representation like an AST Abstract Syntax Tree or a CFG Control Flow Graph that traverse it in its high-level Analysis of the c programming language.
Taking advantage of the effort that I invested in understanding the construction phases of an analyzer and a compiler, I decided to dedicate my career final project to the construction of a static source code analyzer for the C programming language with the aim of finding vulnerabilities in the code.
I managed to complete the tool written in Python, and for those who are interested, here I will talk a little about source code static analysis and the intermediate representations that facilitate it. The first thing I did before starting to program any line of code, was to define very well the main components that I had to develop to get an appropriate representation of the source code on which to perform the analysis.
The components that I defined were the following: Construction of a lexical analyzer that reads the string of characters that forms the source code and groups them into lexemes. Construction of a syntactic analyzer or parser that uses the lexemes produced in the previous phase to build a parse-tree.
Construction of a semantic analyzer that uses the previously produced representation to analyze the program in search of inconsistencies and perform type resolution.
Construction of an intermediate representation. Construction of a suitable representation for the analysis. Construction of a representation of calls between functions. In this case construction of a Call Graph CG.
Construction of an analysis module.
As you can see, they are a lot of components, and when we talk about developing these components for a programming language that has a grammar like that of C, it becomes anything but easy. In a general way, we could group the aforementioned components into two main groups, The construction of the intermediate representation that the static analysis algorithms will use as input.
The analysis module itself that will implement these algorithms and will provide the results. In this post, I will focus only on the first group, the construction of an intermediate representation from the source code.
Intermediate representations of the source code for the C programming language An intermediate representation of the source code, such as the AST, CFG or CG, can be used for many more things than for the construction of a static source code analyzer.
It can be used to make a compiler, a code generator or, for example, a source code syntax checker. As I mentioned before, the construction of all these components for a programming language like C, which has a relatively complex grammar, is not trivial, and since we have a finite time in our lives, I decided to investigate to see what components had already been made in Python that I could reuse for my system.
One of the first things I discovered after a lot of searching the web, is that I could skip the construction of the first four components of the list lexical analyzer, parser, semantic analyzer and AST thanks to Clang, libclang and their Python bindings.
At this point, we will stop a few minutes and explain what each of these concepts are. Some are complex to explain, so I accompany the explanation with some images or diagrams that I found online or in different books.
Lexical Analyzer It consists of reading the source code provided by the file and transforming it into a sequence of characters called lexemes. For each lexeme the lexical analyzer produces an output of the form: In a very general way, the process of recognizing tokens is usually done through the construction of Transition Diagrams.
A transition diagram is composed of a set of nodes called states and a set of vertices. Each state represents a condition that can occur during the process of scanning a lexeme that matches a certain pattern.
The vertices are labeled with a symbol or a set of symbols. Transition diagram and tokens Syntactic analyzer The parser uses the first component of the token produced by the lexical analyzer to construct an intermediate representation in the form of a tree that represents the grammatical structure of the token.
A typical representation is a syntax tree in which the inner node represents an operation, and the children the arguments of the operation. Syntax tree Abstract Syntax Tree AST It is possible to perform certain analyzes in the syntax tree because it contains a direct representation of the source code as written by the programmer.
However, to perform complex analysis tasks is not convenient due to: The nodes of the tree derive directly from the rules of grammar production, and therefore can introduce symbols that exist only for the purpose of making the parsing process easier or to eliminate ambiguities.An essential element in designing many geospatial systems is the choice of what programming language (or languages) to use.
Most of the exciting projects we can envision will involve at least some programming to customize existing tools, or to develop completely new ones.
The C Programming Language is THE VERY BEST way to learn the C programming language. Starting with the basic "Hello World" program, this book covers everything (of course, as the official guide to the language this is expected)/5. Program Analysis and Specialization for the C Programming Language Ph.D.
Thesis Lars Ole Andersen DIKU, University of Copenhagen Universitetsparken 1 Ansi C programming language. The content of this thesis is analysis and transformation of C programs.
We develop. analysis for the C programming language. F or ev ery p oin ter v ariable it computes set of abstract lo cations the p oin ter ma y t to.
In languages with p oin ters and/or call-b y-reference parameters, alias analysis is the core part of most other data o w analyses.
F or example, liv e-v ariable analysis an expression ` *p = 13 ' m ust mak e. The content of this thesis is analysis and transformation of C programs. We develop several analyses that support the transformation of a program into its generating extension.
‹ Back to Introduction to C Programming Problem Analysis [ edit ] If we are to use the computer as a problem-solving tool, then we must have a good analysis of the problem given. New techniques are required to solve this so-called software crisis. Partial evaluation is a program specialization technique that reconciles the benefits of generality with efficiency. This thesis presents an automatic partial evaluator for the Ansi C programming language. The content of this thesis is analysis and transformation of C programs. analysis for the C programming language. F or ev ery p oin ter v ariable it computes set of abstract lo cations the p oin ter ma y t to. In languages with p oin ters and/or call-b y-reference parameters, alias analysis is the core part of most other data o w analyses. F or example, liv e-v ariable analysis an expression ` *p = 13 ' m ust mak e.
A generating extension is a program that produces specialized programs when executed on parts of the input. A programming language's surface form is known as its lausannecongress2018.com programming languages are purely textual; they use sequences of text including words, numbers, and punctuation, much like written natural languages.