garghub / joernantlr

C Parser based on JOERN : https://github.com/fabsx00/joern

Joern

This repository is a maven adaptation of the joern project (warning: some parts have been removed).

Author:

Fabian Yamaguchi [email protected]

Contributors:

Alwin Maier [email protected]

Introduction

This library allows one to parse a C file under the form of a string from a java program. An AST, CFG or DDG can then be computed from this parsed file.

Use

This library is used in this project by the FileMetrics project

In order to retrieve the AST of a file the following steps are required (code in Kotlin):

1. create a Walker

    class TestASTWalker : ASTWalker() {
   
        var codeItems: MutableList<ASTNode>
   
        init {
            codeItems = LinkedList<ASTNode>()
        }
   
        override fun startOfUnit(ctx: ParserRuleContext, filename: String) {
   
        }
   
        override fun endOfUnit(ctx: ParserRuleContext, filename: String) {
   
        }
   
        override fun processItem(item: ASTNode, itemStack: Stack<ASTNodeBuilder>) {
            codeItems.add(item)
        }
   
    }
   

2. create the parser and walker elements

    val parser = ANTLRCModuleParserDriver()
    val walker = TestASTWalker()
    parser.addObserver(walker)  
   

3. Then lexe your file, note that if a tokenize file is enough, you cat stop after this step

    val inputStream = ANTLRInputStream(compatibleFileContent())
    val lex = ModuleLexer(inputStream)
    val token = TokenSubStream(lex)
   

4. If you need the AST, the following step are necessary:

    parser.parseAndWalkTokenStream(token)
    val listofNode: MutableList<ASTNode> = walker.codeItems
   

5. To compute the CFG, you first need to iterate over the list of node, and in case it is a function, you can do the following:

    for (node in listnode) {
        if (node is FunctionDef) {
            val cfg = CCFGFactory.convert(node.content)
         }
    }
   

6. In case you want to use UseDef Graph

    val cfgToUdg = CFGToUDGConverter()
    val udg = cfgToUdg.convert(cfg)
   

7. you can also add taint source

    cfgToUdg.addTaintSource("foo", 0);
   

8. Once this done, you can access the DDG by doing so:

    val udgToDefUse = CFGAndUDGToDefUseCFG();
    val defUseCfg = udgToDefUse.convert(cfg,udg)
    val ddg = DDGCreator().createForDefUseCFG(defUseCfg)
   

Known Issue

• The library is not handling correctly function containing __
• No handling of the NULL keyword