Convert jni_layer_llama.cpp from fbjni to pure JNI

[Copilot]

Summary

Removes fbjni dependency from the LLM Android JNI layer, enabling broader compatibility and simpler builds without Facebook's JNI wrapper library.

Changes:

• LlmModule.java: Replace HybridData with native handle pattern (long pointer)
• jni_layer_llama.cpp: Complete rewrite using pure JNI
  • New ExecuTorchLlmNative class holds native state
  • New CallbackHelper manages JNI callback lifecycle with proper global refs
  • All methods now extern "C" JNI functions with explicit RegisterNatives
• jni_helper.h/cpp: Add pure JNI overload for throwExecutorchException(JNIEnv*, ...)
• jni_layer.cpp: Pass JNIEnv* to register_natives_for_llm()

The fbjni-based codepath is preserved behind EXECUTORCH_HAS_FBJNI macro for backward compatibility.

Test plan

Existing Android JNI tests cover the LlmModule interface. The behavioral contract is unchanged—only the underlying JNI implementation differs.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• dl.google.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED --add-exports=jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED --add-opens=java.xml/javax.xml.namespace=ALL-UNNAMED -XX:MaxMetaspaceSize=384m -XX:+HeapDumpOnOutOfMemoryError -Xms256m -Xmx512m -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en (dns block)
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --add-opens=java.base/java.util=ALL-UNNAMED --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED --add-opens=java.base/java.nio.charset=ALL-UNNAMED --add-opens=java.base/java.net=ALL-UNNAMED --add-opens=java.base/java.util.concurrent.atomic=ALL-UNNAMED -Xmx2048m -Dfile.encoding=UTF-8 -Duser.country -Duser.language=en -Duser.variant -cp /home/REDACTED/.gradle/wrapper/dists/gradle-8.2-bin/bbg7u40eoinfdyxsxr3z4i7ta/gradle-8.2/lib/gradle-launcher-8.2.jar -javaagent:/home/REDACTED/.gradle/wrapper/dists/gradle-8.2-bin/bbg7u40eoinfdyxsxr3z4i7ta/gradle-8.2/lib/agents/gradle-instrumentation-agent-8.2.jar org.gradle.launcher.daemon.bootstrap.GradleDaemon 8.2 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

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Original prompt

Submit a new PR using the changes from the git history (commits b5bc13d and 2660810

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[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16519

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