pxb1988/dex2jar · error · RuntimeException

Fail to assemble

Error message

Fail to assemble ${file}

What it means

Jasmins.parse(Path) reads a Jasmin assembly (.j) file and feeds it to the ANTLR-based parser. If the parser raises a RecognitionException (invalid Jasmin syntax), parse wraps it in a RuntimeException with the message 'Fail to assemble <file>' and the original exception as cause. This converts a parser error into an unchecked exception that propagates up through Jasmin2JarCmd.

Solutions

  1. Read the cause (RecognitionException) stack trace for the exact line/column of the syntax error.
  2. Fix the Jasmin source at the reported line (mnemonic, directive, or operand issue).
  3. Verify the file is genuine Jasmin assembly and not a class/dex/jar renamed to .j.
  4. Compare syntax against a known-good .j sample for the dex2jar version in use.
  5. If needed, catch RuntimeException around Jasmins.parse and report/skip the offending file.

Example fix

// before
ireturn 0   // ireturn takes no operand -> RecognitionException

// after
iconst_0
ireturn
Defensive patterns

Strategy: try-catch

Validate before calling

// Basic sanity check before parsing
if (!file.toString().endsWith(".j") || Files.size(file) == 0) {
    throw new IllegalArgumentException("Not a plausible Jasmin source: " + file);
}

Try / catch

try {
    ClassNode cn = Jasmins.parse(file);
} catch (RuntimeException e) {
    Throwable cause = e.getCause(); // RecognitionException with line/column
    System.err.println("Syntax error in " + file + ": " + cause.getMessage());
}

Prevention

When it happens

Trigger: Calling Jasmins.parse(file) on a .j file containing malformed Jasmin directives, bad instruction mnemonics, or wrong operand syntax that ANTLR cannot recognize; also invoked indirectly when d2j-jasmin2jar processes a directory containing an invalid .j file.

Common situations: Hand-written Jasmin files with typos, files generated for a different assembler syntax, corrupted/renamed non-Jasmin files given a .j extension, or Jasmin grammar differences from the version of dex2jar being used.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

AI-assisted analysis of pxb1988/dex2jar@b5bda4fb49 (2026-09-08). Data as JSON: /api/errors/59512634e63c4e54. Report an issue: GitHub.

Appendix: source

Thrown at d2j-jasmin/src/main/java/com/googlecode/d2j/jasmin/Jasmins.java:35

package com.googlecode.d2j.jasmin;

import org.antlr.runtime.ANTLRReaderStream;
import org.antlr.runtime.ANTLRStringStream;
import org.antlr.runtime.CommonTokenStream;
import org.antlr.runtime.RecognitionException;
import org.objectweb.asm.tree.ClassNode;

import java.io.*;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;

public class Jasmins {
    public static ClassNode parse(Path file) throws IOException {
        try (BufferedReader bufferedReader = Files.newBufferedReader(file, StandardCharsets.UTF_8)) {
            return parse(file.toString(), bufferedReader);
        } catch (RecognitionException e) {
            throw new RuntimeException("Fail to assemble " + file, e);
        }
    }

    public static ClassNode parse(String fileName, Reader bufferedReader) throws IOException, RecognitionException {
        ANTLRStringStream is = new ANTLRReaderStream(bufferedReader);
        is.name = fileName;
        JasminLexer lexer = new JasminLexer(is);
        CommonTokenStream ts = new CommonTokenStream(lexer);
        JasminParser parser = new JasminParser(ts);
        return parser.parse();
    }

    public static ClassNode parse(String fileName, InputStream is) throws IOException, RecognitionException {
        return parse(fileName, new InputStreamReader(is, StandardCharsets.UTF_8));
    }
}

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