@specs-feup/alpakka/src-api/alpakka/graphs/cfg/flow/FlowGraphGenerator.ts

Alpakka is a [LARA Framework](https://github.com/specs-feup/lara-framework) source-to-source compiler for Android's [smali](https://github.com/google/smali) syntax. It enables the analysis and transformation of Android apps through APK files.

import FlowGraph from "./FlowGraph.js";
import {
  MethodNode,
  Joinpoint,
  Program,
  Statement,
  ReturnStatement,
  Label,
  Goto,
  IfComparison,
  IfComparisonWithZero,
  Switch,
  LabelReference,
  PackedSwitch,
  SparseSwitch,
  SparseSwitchElement,
  ThrowStatement,
  Catch,
  Instruction,
  MethodReference,
  ClassType,
} from "../../../../Joinpoints.js";
import UnknownInstructionNode from "./node/instruction/UnknownInstructionNode.js";
import FlowNode from "./node/FlowNode.js";
import InstructionNode from "./node/instruction/InstructionNode.js";
import { NodeBuilder } from "../graph/Node.js";
import StatementNode from "./node/instruction/StatementNode.js";
import FunctionEntryNode from "./node/instruction/FunctionEntryNode.js";
import FunctionExitNode from "./node/instruction/FunctionExitNode.js";
import ReturnNode from "./node/instruction/ReturnNode.js";
import LabelNode from "./node/instruction/LabelNode.js";
import GotoNode from "./node/instruction/GotoNode.js";
import SwitchNode from "./node/instruction/SwitchNode.js";
import ThrowNode from "./node/instruction/ThrowNode.js";
import IfComparisonNode from "./node/condition/IfComparisonNode.js";
import CaseNode from "./node/condition/CaseNode.js";

export default class FlowGraphGenerator {
  #$jp: Joinpoint;
  #graph: FlowGraph.Class;
  #temporaryNodes: UnknownInstructionNode.Class[];

  constructor($jp: Program | MethodNode, graph: FlowGraph.Class) {
    this.#$jp = $jp;
    this.#graph = graph;
    this.#temporaryNodes = [];
  }

  build(): FlowGraph.Class {
    if (this.#$jp instanceof Program) {
      this.#$jp.classes.forEach((child) => {
        child.methods.forEach((method) => {
          this.#processFunction(method);
        });
      });
    } else if (this.#$jp instanceof MethodNode) {
      this.#processFunction(this.#$jp);
    }

    for (const node of this.#temporaryNodes) {
      node.removeFromFlow();
      node.remove();
    }

    return this.#graph;
  }

  #processJp(
    $jp: Joinpoint,
    context: ProcessJpContext,
  ): [FlowNode.Class, InstructionNode.Class?] {
    if (context.preprocessedStatementStack.length > 0) {
      const [head, tail] = context.preprocessedStatementStack.pop()!;
      return [head, tail];
    }

    if ($jp instanceof Label) {
      return this.#processLabelStmt($jp, context);
    } else if ($jp instanceof Switch) {
      return this.#processSwitch($jp, context);
    } else if (
      $jp instanceof IfComparison ||
      $jp instanceof IfComparisonWithZero
    ) {
      return this.#processIf($jp, context);
    } else if ($jp instanceof Goto) {
      return this.#processGoto($jp, context);
    } else if ($jp instanceof Catch) {
      return this.#processCatchDirective($jp, context);
    } else if ($jp instanceof ReturnStatement) {
      return this.#addReturnStmt(new ReturnNode.Builder($jp));
    } else if ($jp instanceof ThrowStatement) {
      return this.#addThrowStmt(new ThrowNode.Builder($jp));
    } else if ($jp instanceof Statement) {
      return this.#addInstruction(new StatementNode.Builder($jp));
    } else {
      throw new Error(
        `Cannot build graph for joinpoint "${$jp.joinPointType}"`,
      );
    }
  }

  #processFunction(
    $jp: MethodNode,
  ): [FunctionEntryNode.Class, FunctionExitNode.Class?] {
    const processedFunction = this.#graph.getFunction($jp.referenceName);

    if (processedFunction !== undefined) {
      return [processedFunction, undefined];
    }

    const context = {
      labels: new Map(),
      preprocessedStatementStack: new Array<
        [FlowNode.Class, InstructionNode.Class?]
      >(),
      tryCatchDirectives: new Array<Catch>(),
    };

    const body = $jp.children.map((child) => {
      const [head, tail] = this.#processJp(child, context);
      return [head, tail ? [tail] : []] as [
        FlowNode.Class,
        InstructionNode.Class[],
      ];
    });

    const functionTail: InstructionNode.Class[] = [];

    if (body.length === 0) {
      return this.#graph.addFunction($jp, undefined, functionTail);
    }

    for (let i = 0; i < body.length - 1; i++) {
      const [head, tail] = body[i];
      const [nextHead] = body[i + 1];

      if (head instanceof ReturnNode.Class || head instanceof ThrowNode.Class) {
        functionTail.push(head);
      }

      for (const tailNode of tail) {
        tailNode.nextNode = nextHead;
      }
    }

    const [lastHead, lastTail] = body[body.length - 1];
    if (
      lastTail.length === 0 &&
      (lastHead instanceof ReturnNode.Class ||
        lastHead instanceof ThrowNode.Class)
    ) {
      functionTail.push(lastHead);
    }

    for (const directive of context.tryCatchDirectives) {
      const tryStartLabel = context.labels.get(
        directive.tryStart.decl.name,
      ) as LabelNode.Class;
      if (tryStartLabel === undefined) {
        throw new Error("Could not find try start label node");
      }

      const tryEndLabel = context.labels.get(
        directive.tryEnd.decl.name,
      ) as LabelNode.Class;
      if (tryEndLabel === undefined) {
        throw new Error("Could not find try end label node");
      }

      const catchLabel = context.labels.get(
        directive.catch.decl.name,
      ) as LabelNode.Class;

      let exception = "Ljava/lang/Exception;";

      if (!(directive.code.startsWith(".catchall"))) {
        exception = directive.exception.code;
      }

      const tryEndIndex = body.findIndex(([head]) => head === tryEndLabel);
      const tryStartIndex = body.findIndex(([head]) => head === tryStartLabel);

      for (let i = tryEndIndex - 1; i > tryStartIndex; i--) {
        const [head, tail] = body[i];

        // TODO: Check if exception being thrown is caught by this catch directive

        if (head instanceof ThrowNode.Class) {
          if (functionTail.includes(head)) {
            functionTail.splice(functionTail.indexOf(head), 1);
          }

          this.#connectArbitraryJump(head, catchLabel);
        } else if (
          head.jp instanceof Instruction &&
          this.canThrow(head.jp, exception)
        ) {
          if (tail.length === 0) {
            continue;
          }
          const nextNode = tail[0].nextNode;
          if (nextNode === undefined) {
            continue;
          }
          body[i] = [
            this.#graph.addTryCatch(head.jp, nextNode, catchLabel),
            [],
          ];

          const [prevHead, previousTail] = body[i - 1];
          for (const previousTailNode of previousTail) {
            previousTailNode.nextNode = body[i][0];
          }

          if (prevHead instanceof IfComparisonNode.Class) {
            // The true node in an if condition will always be a label
            prevHead.falseNode = body[i][0];
          }

          head.removeFromFlow();
          head.remove();
        }
      }
    }

    const bodyHead = body[0][0];

    return this.#graph.addFunction($jp, bodyHead, functionTail);
  }

  canThrow($jp: Instruction, $exception: String): boolean {
    // return $jp.canThrow;

    if (
      $jp.opCodeName === "check-cast" &&
      ($exception === "Ljava/lang/ClassCastException;" ||
        $exception === "Ljava/lang/RuntimeException;" ||
        $exception === "Ljava/lang/Exception;")
    ) {
      return true;
    }

    if (
      ($jp.opCodeName.startsWith("rem") || $jp.opCodeName.startsWith("div")) &&
      ($exception === "Ljava/lang/ArithmeticException;" ||
        $exception === "Ljava/lang/RuntimeException;" ||
        $exception === "Ljava/lang/Exception;")
    ) {
      return true;
    }

    // These can use dynamic dispatch, I think
    // Would need further analysis to accurately determine if they can throw
    if ($jp.opCodeName.startsWith("invoke-virtual") ||
      $jp.opCodeName.startsWith("invoke-interface")) {
      return $jp.canThrow;
    }

    if ($jp.opCodeName.startsWith("invoke")) {
      const methodRef = $jp.children[1];
      if (methodRef === undefined || !(methodRef instanceof MethodReference)) {
        return false;
      }

      let classDescriptor = methodRef.parentClassDescriptor as ClassType;

      let processedFunction: FunctionEntryNode.Class | undefined;

      while (
        classDescriptor.decl !== undefined &&
        processedFunction === undefined
      ) {
        classDescriptor.decl.children.forEach((child) => {
          if (
            child instanceof MethodNode &&
            child.referenceName === methodRef.code
          ) {
            // Calling this might lead to maximum call stack size exceeded, needs to be reworked
            processedFunction = this.#processFunction(child)[0];
          }
        });

        if (classDescriptor.decl.superClassDescriptor === undefined) {
          break;
        }

        classDescriptor = classDescriptor.decl.superClassDescriptor;
      }

      if (processedFunction === undefined) {
        // returning $jp.canThrow since we don't have access to system apis
        return $jp.canThrow;
      }

      let instruction = undefined;

      if (processedFunction.nextNodes[0] !== undefined) {
        instruction = processedFunction.nextNodes[0].jp;
      }

      while (instruction !== undefined) {
        if (instruction instanceof ThrowStatement) {
          // TODO: Needs to move backwards and check exception type
          return true;
        }

        instruction = (instruction as Statement).nextStatement;
      }
    }

    // Not sure if there are more exceptions
    return false;
  }

  #processIf(
    $jp: IfComparison | IfComparisonWithZero,
    context: ProcessJpContext,
  ): [IfComparisonNode.Class, InstructionNode.Class?] {
    const $iftrue = $jp.label.decl;
    const $iffalse = $jp.nextStatement;

    if (!context.labels.has($iftrue.name)) {
      this.#processLabelStmt($iftrue, context);
    }

    let ifTrueHead: FlowNode.Class;
    const label = context.labels.get($iftrue.name);
    if (label !== undefined) {
      ifTrueHead = label;
    } else {
      const trueNode = this.#createTemporaryNode();
      ifTrueHead = trueNode;
    }

    let ifFalseHead: FlowNode.Class;
    let ifFalseTail: InstructionNode.Class | undefined;

    [ifFalseHead, ifFalseTail] = this.#processJp($iffalse, context);
    context.preprocessedStatementStack.push([ifFalseHead, ifFalseTail]);

    return [this.#graph.addCondition($jp, ifTrueHead, ifFalseHead)];
  }

  #processSwitch(
    $jp: Switch,
    context: ProcessJpContext,
  ): [SwitchNode.Class, InstructionNode.Class?] {
    const $labelRef = $jp.getChild(1);
    if (!($labelRef instanceof LabelReference)) {
      throw new Error("Switch statement must include a label reference");
    }
    const $switchDecl = ($labelRef as LabelReference).decl.nextStatement;
    const defaultCase = $jp.nextStatement;

    const node = this.#graph
      .addNode()
      .init(new SwitchNode.Builder($jp))
      .as(SwitchNode.Class);

    const $children = $switchDecl.children;
    let previousCase: CaseNode.Class | undefined = undefined;

    const childrenRefs: LabelReference[] = [];

    if ($switchDecl instanceof PackedSwitch) {
      for (const childRef of $children) {
        if (!(childRef instanceof LabelReference)) {
          throw new Error(
            "Packed switch directive children must be label references",
          );
        }

        if (!context.labels.has(childRef.decl.name)) {
          this.#processLabelStmt(childRef.decl, context);
        }

        childrenRefs.push(childRef as LabelReference);
      }
    } else if ($switchDecl instanceof SparseSwitch) {
      for (const element of $children) {
        if (!(element instanceof SparseSwitchElement)) {
          throw new Error(
            "Sparse switch directive children must be sparse switch elements",
          );
        }

        const childRef = element.label;
        if (!(childRef instanceof LabelReference)) {
          throw new Error(
            "Sparse switch element must contain a label reference",
          );
        }

        if (!context.labels.has(childRef.decl.name)) {
          this.#processLabelStmt(childRef.decl, context);
        }

        childrenRefs.push(childRef as LabelReference);
      }
    }

    for (const child of childrenRefs) {
      const label = context.labels.get(child.decl.name);

      if (label !== undefined) {
        const currentCase = this.#graph.addSwitchCase(
          child as LabelReference,
          label,
          label, // False node doesn't matter for now, since it will change
        );

        if (previousCase === undefined) {
          node.nextNode = currentCase;
        } else {
          previousCase.falseNode = currentCase;
        }

        previousCase = currentCase;
      }
    }

    const preProcessedStatement = this.#processJp(defaultCase, context);
    context.preprocessedStatementStack.push(preProcessedStatement);

    if (previousCase === undefined) {
      node.nextNode = preProcessedStatement[0];
    } else {
      previousCase.falseNode = preProcessedStatement[0];
    }

    return [node];
  }

  #processLabelStmt(
    $jp: Label,
    context: ProcessJpContext,
  ): [LabelNode.Class, LabelNode.Class] {
    if (context.labels.has($jp.name)) {
      const label = context.labels.get($jp.name);
      if (label !== undefined) {
        return [label, label];
      }
    }

    const node = this.#graph
      .addNode()
      .init(new LabelNode.Builder($jp))
      .as(LabelNode.Class);

    context.labels.set($jp.name, node);

    return [node, node];
  }

  #processGoto($jp: Goto, context: ProcessJpContext): [GotoNode.Class] {
    const node = this.#graph
      .addNode()
      .init(new GotoNode.Builder($jp))
      .as(GotoNode.Class);

    if (!context.labels.has($jp.label.decl.name)) {
      this.#processLabelStmt($jp.label.decl, context);
    }

    const label = context.labels.get($jp.label.decl.name);
    if (label !== undefined) {
      this.#connectArbitraryJump(node, label);
    }

    return [node];
  }

  #processCatchDirective($jp: Catch, context: ProcessJpContext) {
    context.tryCatchDirectives.push($jp);

    return this.#addInstruction(new StatementNode.Builder($jp));
  }

  #createTemporaryNode($jp?: Joinpoint): UnknownInstructionNode.Class {
    const node = this.#graph
      .addNode()
      .init(new UnknownInstructionNode.Builder($jp))
      .as(UnknownInstructionNode.Class);
    this.#temporaryNodes.push(node);
    return node;
  }

  #addInstruction(
    builder: NodeBuilder<InstructionNode.Data, InstructionNode.ScratchData>,
  ): [InstructionNode.Class, InstructionNode.Class] {
    const node = this.#graph.addNode().init(builder).as(InstructionNode.Class);
    return [node, node];
  }

  #addReturnStmt(
    builder: NodeBuilder<ReturnNode.Data, ReturnNode.ScratchData>,
  ): [ReturnNode.Class] {
    const node = this.#graph.addNode().init(builder).as(ReturnNode.Class);
    return [node];
  }

  #addThrowStmt(
    builder: NodeBuilder<ThrowNode.Data, ThrowNode.ScratchData>,
  ): [ThrowNode.Class] {
    const node = this.#graph.addNode().init(builder).as(ThrowNode.Class);
    return [node];
  }

  #connectArbitraryJump(from: InstructionNode.Class, to: FlowNode.Class) {
    from.nextNode = to;
  }
}

interface ProcessJpContext {
  labels: Map<string, LabelNode.Class>;
  preprocessedStatementStack: Array<[FlowNode.Class, InstructionNode.Class?]>;
  tryCatchDirectives: Catch[];
}