Support turning on debug after the native image has been built

dd-java-agent/instrumentation/graal/native-image/build.gradle

@@ -27,6 +27,8 @@ apply plugin: "idea"
 }
 
 dependencies {
+  compileOnly project(':dd-java-agent:agent-logging')
+
   main_java11CompileOnly group: 'org.graalvm.nativeimage', name: 'svm', version: '20.0.0'
 }
 

dd-java-agent/instrumentation/graal/native-image/src/main/java/datadog/trace/instrumentation/graal/nativeimage/VMRuntimeInstrumentation.java

@@ -5,7 +5,12 @@
 
 import com.google.auto.service.AutoService;
 import datadog.trace.agent.tooling.Instrumenter;
+import datadog.trace.api.Config;
+import datadog.trace.logging.GlobalLogLevelSwitcher;
+import datadog.trace.logging.LogLevel;
 import net.bytebuddy.asm.Advice;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 @AutoService(Instrumenter.class)
 public final class VMRuntimeInstrumentation extends AbstractNativeImageInstrumentation
@@ -36,6 +41,16 @@ public boolean injectHelperDependencies() {
   public static class InitializeAdvice {
     @Advice.OnMethodEnter(suppress = Throwable.class)
     public static void onEnter() {
+      if (Config.get().isDebugEnabled()) {
+        // was this native image originally built with debug off?
+        Logger configLogger = LoggerFactory.getLogger(Config.class);
+        if (!configLogger.isDebugEnabled()) {
+          // patch logger level and re-log configuration details
+          GlobalLogLevelSwitcher.get().switchLevel(LogLevel.DEBUG);
+          configLogger.debug("New instance: {}", Config.get());
+        }
+      }
+
       datadog.trace.agent.tooling.nativeimage.TracerActivation.activate();
     }
   }