Disable process advice until after agent tracer is registered

This avoids a potential reentrant situation when tracer debug is enabled:
1. The full `Config` is logged during startup in its constructor
2. This includes any lazy config fields, such as the `hostname`
3. If the host is not available in the environment/host-files then
   `Config` calls the `hostname` command using `Runtime.exec(...)`
4. The `Runtime.exec(...)` call is intercepted by the process advice
5. The process advice calls `Config.get()` to see if RASP is enabled
6. `Config.get()` returns `null` as the config is still being built

The resulting NPE is caught before it escapes to the application,
but it still results in log-spam that could confuse investigations.

Author: mcculls

dd-java-agent/instrumentation/java/java-lang/java-lang-1.8/src/main/java/datadog/trace/instrumentation/java/lang/ProcessImplStartAdvice.java

@@ -3,22 +3,20 @@
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
 import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.bootstrap.instrumentation.api.java.lang.ProcessImplInstrumentationHelpers;
-import java.io.IOException;
 import net.bytebuddy.asm.Advice;
 
 class ProcessImplStartAdvice {
   @Advice.OnMethodEnter(suppress = Throwable.class)
-  public static AgentSpan startSpan(@Advice.Argument(0) final String[] command) throws IOException {
+  public static AgentSpan beforeStart(@Advice.Argument(0) final String[] command) {
     if (!ProcessImplInstrumentationHelpers.ONLINE) {
       return null;
     }
 
-    if (command.length == 0) {
+    if (command.length == 0 || !AgentTracer.isRegistered()) {
       return null;
     }
 
-    final AgentTracer.TracerAPI tracer = AgentTracer.get();
-    final AgentSpan span = tracer.startSpan("appsec", "command_execution");
+    final AgentSpan span = AgentTracer.startSpan("appsec", "command_execution");
     span.setSpanType("system");
     span.setResourceName(ProcessImplInstrumentationHelpers.determineResource(command));
     span.setTag("component", "subprocess");
@@ -29,7 +27,7 @@ public static AgentSpan startSpan(@Advice.Argument(0) final String[] command) th
   }
 
   @Advice.OnMethodExit(suppress = Throwable.class, onThrowable = Throwable.class)
-  public static void endSpan(
+  public static void afterStart(
       @Advice.Return Process p, @Advice.Enter AgentSpan span, @Advice.Thrown Throwable t) {
     if (span == null) {
       return;

dd-java-agent/instrumentation/java/java-lang/java-lang-1.8/src/main/java/datadog/trace/instrumentation/java/lang/RuntimeExecStringAdvice.java

@@ -1,20 +1,23 @@
 package datadog.trace.instrumentation.java.lang;
 
+import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.bootstrap.instrumentation.api.java.lang.ProcessImplInstrumentationHelpers;
-import java.io.IOException;
 import net.bytebuddy.asm.Advice;
 
 class RuntimeExecStringAdvice {
   @Advice.OnMethodEnter(suppress = Throwable.class)
-  public static void beforeExec(@Advice.Argument(0) final String command) throws IOException {
-    if (command == null) {
-      return;
+  public static boolean beforeExec(@Advice.Argument(0) final String command) {
+    if (command == null || !AgentTracer.isRegistered()) {
+      return false;
     }
     ProcessImplInstrumentationHelpers.shiRaspCheck(command);
+    return true;
   }
 
   @Advice.OnMethodExit(suppress = Throwable.class, onThrowable = Throwable.class)
-  public static void afterExec() {
-    ProcessImplInstrumentationHelpers.resetCheckShi();
+  public static void afterExec(@Advice.Enter boolean checking) {
+    if (checking) {
+      ProcessImplInstrumentationHelpers.resetCheckShi();
+    }
   }
 }