WIP: Graal native-image build of Java Schnorr Example

To build native image use:

./gradlew secp256k1-examples-java:nativeCompile

Build currently fails on macOS with:

Error: Support for the Foreign Function and Memory API is currently available only on the AMD64 architecture

Note: the Arena.ofConfined() change should probably not be merged to `master`,
but is currently necessary to work with native-image.

README.adoc

@@ -99,6 +99,20 @@ Run the script:
 
 * `./secp256k1-examples-java/build/install/secp256k1-examples-java/bin/secp256k1-examples-java`
 
+== Build and run a native image (AMD64-only with Graal JDK 22)
+
+To build using GraalVM `native-image`:
+
+. Make sure you have GraalVM 22 or later installed
+. Make sure `GRAALVM_HOME` points to the Graal JDK 22 installation
+. `./gradlew secp256k1-examples-java:nativeCompile`
+
+To run the compiled, native executable:
+
+. `export LD_LIBRARY_PATH="$HOME/.nix-profile/lib:$LD_LIBRARY_PATH"`
+. `./secp256k1-examples-java/build/schnorr`
+. Don't blink!
+
 == Building with Nix
 
 NOTE:: We currently only support setting up a development environment with Nix. In the future we hope to support a full Nix build.

secp256k1-examples-java/build.gradle

@@ -13,6 +13,9 @@ dependencies {
     implementation project(':secp256k1-api')
     runtimeOnly project(':secp256k1-bouncy')
     runtimeOnly project(':secp256k1-foreign')
+
+    // This is only needed for ForeignRegistrationFeature and the native-image build
+    implementation group: 'org.graalvm.sdk', name: 'nativeimage', version: '24.0.0'
 }
 
 jar {
@@ -34,3 +37,38 @@ run {
     systemProperty "java.library.path", findProperty("javaPath") ?: "${userHome}/.nix-profile/lib"
     jvmArgs += '--enable-native-access=org.bitcoinj.secp256k1.foreign'
 }
+
+configurations {
+    nativeToolImplementation.extendsFrom implementation
+}
+
+def mainClassName = "org.bitcoinj.secp256k1.examples.Schnorr"
+
+jar {
+    manifest {
+        attributes  'Implementation-Title': 'Schnorr Signature Example',
+                'Main-Class': mainClassName,
+                'Implementation-Version': archiveVersion.get()
+    }
+}
+
+// Compile a native image using GraalVM's native-image tool
+// Graal must be installed at $GRAALVM_HOME
+tasks.register('nativeCompile', Exec) {
+    dependsOn jar
+    workingDir = projectDir
+    executable = "${System.env.GRAALVM_HOME}/bin/native-image"
+    args = ['--verbose',
+            '--no-fallback',
+            '-cp', "${-> configurations.nativeToolImplementation.asPath}", // Lazy configuration resolution
+            '-jar', jar.archiveFile.get(),
+            '-H:Path=build',
+            '-H:Name=schnorr',
+            '-H:+ForeignAPISupport',
+            '--features=org.bitcoinj.secp256k1.examples.ForeignRegistrationFeature',
+            '--enable-native-access=ALL-UNNAMED',
+            '-H:+ReportUnsupportedElementsAtRuntime',
+            '-H:+ReportExceptionStackTraces'
+    ]
+}
+

secp256k1-examples-java/src/main/java/org/bitcoinj/secp256k1/examples/ForeignRegistrationFeature.java

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2023-2024 secp256k1-jdk Developers.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.bitcoinj.secp256k1.examples;
+
+import org.graalvm.nativeimage.hosted.Feature;
+import org.graalvm.nativeimage.hosted.RuntimeForeignAccess;
+
+import java.lang.foreign.FunctionDescriptor;
+import java.lang.foreign.Linker;
+
+import static java.lang.foreign.ValueLayout.*;
+
+/**
+ *
+ */
+public class ForeignRegistrationFeature implements Feature {
+    public void duringSetup(Feature.DuringSetupAccess access) {
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.ofVoid());
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_INT, JAVA_INT));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_LONG, JAVA_INT));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_INT, JAVA_INT, JAVA_INT));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_LONG, JAVA_LONG, JAVA_LONG));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_LONG));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_LONG));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_LONG, JAVA_INT));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(JAVA_INT, JAVA_LONG, JAVA_LONG));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.ofVoid(JAVA_LONG, JAVA_LONG));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.ofVoid(JAVA_LONG));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.ofVoid(JAVA_INT, JAVA_INT));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.of(ADDRESS, JAVA_INT, JAVA_INT), Linker.Option.firstVariadicArg(1));
+        RuntimeForeignAccess.registerForDowncall(FunctionDescriptor.ofVoid(JAVA_INT), Linker.Option.captureCallState("errno"));
+    }
+}

secp256k1-foreign/src/main/java/org/bitcoinj/secp256k1/foreign/Secp256k1Foreign.java

@@ -73,7 +73,7 @@ public Secp256k1Foreign(int flags) {
     }
 
     public Secp256k1Foreign(int flags, boolean randomize) {
-        arena = Arena.ofShared();
+        arena = Arena.ofConfined();     // Changed from `ofShared` for use in Graal native-image tools
         /* Before we can call actual API functions, we need to create a "context". */
         ctx = secp256k1_h.secp256k1_context_create(flags);