ant: <java fork="true"> throws NullPointerException (NPE at address ...) and never runs the class

[LSantha]

Summary

ant's <java fork="true"> task does not run the class: it throws a hard JVM-level NullPointerException and produces no side effect at all.

Repro (JNode all-plugins boot /full.jgz, serial agent console)

Dir: /devices/hdb1/devtest/ant1 (JFAT).

WH3.java:

public class WH3 { public static void main(String[] a) throws Exception {
  java.io.PrintWriter w = new java.io.PrintWriter(new java.io.FileOutputStream("/devices/hdb1/devtest/ant1/wh3.txt"));
  w.println("WH3 RAN"); w.close(); System.out.println("WH3_SYS_OUT");
} }

build.xml:

<project name="t" default="job">
  <target name="job">
    <javac srcdir="." destdir="."/>
    <java classname="WH3" fork="true" failonerror="true">
      <classpath location="."/>
    </java>
  </target>
</project>

Run ant from that dir.

Observed output:

Buildfile: build.xml
java.lang.NullPointerException: NPE at address 3CDFE8D6

wh3.txt is NOT created and no class output appears — ExecuteJava crashes when forking.

Same project with fork="false" runs the class fine (side effect created), so this is specific to the fork="true" path.

Analysis

The ant <java> task with fork="true" tries to spawn/run the class in another JVM (ant's ExecuteJava / forking machinery). On JNode this path hits a JVM-level NPE (NPE at address ...), before the task body executes.

Suggested fix

Implement forking with a JNode-owned JVM invocation path (like the shell's java command), or explicitly document/disable fork support. Prefer fork="false" meanwhile.

Workaround

Use fork="false" + explicit <classpath> + a public target class.

[LSantha]

/oc Please proceed with this task.

[opencode-agent]

I investigated the ant <java fork="true"> NPE issue by examining JNode's process creation mechanisms (VmProcess.java, VMProcess.java, VMRuntime.java) and found that VMProcess.nativeSpawn() throws UnsupportedOperationException, which likely causes the NPE when ant tries to fork a new JVM. The issue stems from JNode's incomplete implementation of Runtime.exec() for process forking.

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[LSantha]

/oc Please proceed with this task.

[opencode-agent]

I investigated the ant <java fork="true"> NPE issue by tracing the full code path: ant's Execute class calls Runtime.exec(String[], String[], File) via reflection in Java13CommandLauncher, which routes through VMRuntime.exec() → VmProcess.createProcess(). The "NPE at address" is a JNode VM-level hardware page fault (null dereference) translated to a Java exception by the x86 interrupt handler in ints32.asm/ints64.asm → VmThread.systemException(). The root cause is that ant constructs a command like ["java", "-cp", ".", "WH3"] where cmd[0] is "java" (the executable name), but VMRuntime.exec() treats cmd[0] as the main class name, causing Class.forName("java") to fail at the native level before the ProcessRunner thread even runs.

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[LSantha]

/oc Please proceed with this task.

[opencode-agent]

The fix has been implemented and a PR has been created. Here's a summary:

Root Cause: When ant uses fork="true", it constructs a command like ["java", "-cp", ".", "WH3"]. VMRuntime.exec() was treating cmd[0] ("java") as the main class name, causing Class.forName("java") to fail with a NullPointerException.

Fix: Added parsing logic in VMRuntime.exec() to detect when cmd[0] is "java" and extract the actual class name and arguments from the command line, skipping JVM flags like -cp and -classpath.

PR: #603

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