feat(crashtracking): J9 register parsing

Parse the GPINFO register section (1XHREGISTERS / 2XHREGISTER tags)
from J9/OpenJ9 javacore crash dumps mirroring what was done for HotSpot.

Register format:
  1XHREGISTERS   Registers:
  2XHREGISTER      RIP: 00007F8B7C0B3D7D   (x86-64)
  2XHREGISTER      PC:  0000FFFF98B9FB6C   (aarch64)

Added crash dumps from IBM J9 (Java 8) and IBM Semeru / OpenJ9 (Java 11)
that were obtained using Docker and this crashing program:

```java
import sun.misc.Unsafe;
import java.lang.reflect.Field;
public class Crash {
    public static void main(String[] args) throws Exception {
        Field f = Unsafe.class.getDeclaredField("theUnsafe");
        f.setAccessible(true);
        Unsafe unsafe = (Unsafe) f.get(null);
        unsafe.putInt(0L, 42); // SIGSEGV -> GPF dump
    }
}
```

```
docker run --rm -v /tmp/j9-crash-test:/work ibmjava:8-sdk \
  bash -c "cd /work && javac Crash.java && \
           java -Xdump:java:events=gpf,file=/work/javacore.ibmj9.txt Crash"
```

```
docker run --rm -v /tmp/j9-crash-test:/work ibm-semeru-runtimes:open-11-jdk \
  bash -c "cd /work && javac Crash.java && \
           java -Xdump:java:events=gpf,file=/work/javacore.openj9.txt Crash"
```

Author: bric3

dd-java-agent/agent-crashtracking/src/main/java/datadog/crashtracking/parsers/J9JavacoreParser.java

@@ -7,6 +7,7 @@
 import datadog.crashtracking.buildid.BuildInfo;
 import datadog.crashtracking.dto.CrashLog;
 import datadog.crashtracking.dto.ErrorData;
+import datadog.crashtracking.dto.Experimental;
 import datadog.crashtracking.dto.Metadata;
 import datadog.crashtracking.dto.OSInfo;
 import datadog.crashtracking.dto.ProcInfo;
@@ -21,8 +22,10 @@
 import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
 import java.util.ArrayList;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
@@ -36,6 +39,7 @@
  *
  * <ul>
  *   <li>TITLE - Contains dump event type and timestamp
+ *   <li>GPINFO - General information including OS level and CPU architecture
  *   <li>ENVINFO - Environment info including process ID
  *   <li>THREADS - Thread information and stack traces
  * </ul>
@@ -58,6 +62,7 @@ public J9JavacoreParser() {
   // Section markers
   private static final String SECTION_MARKER = "0SECTION";
   private static final String SECTION_TITLE = "TITLE";
+  private static final String SECTION_GPINFO = "GPINFO";
   private static final String SECTION_ENVINFO = "ENVINFO";
   private static final String SECTION_THREADS = "THREADS";
 
@@ -78,13 +83,19 @@ public J9JavacoreParser() {
   private static final Pattern NATIVE_STACK_PATTERN = Pattern.compile("4XENATIVESTACK\\s+(.+)");
   private static final Pattern EXCEPTION_DETAIL_PATTERN =
       Pattern.compile("1TISIGINFO.*[Dd]etail\\s+\"(.+?)\".*");
+  // Matches register entries in J9 GPINFO section, e.g.:
+  // 2XHREGISTER      RDI: 0000000000000001  (x86-64)
+  // 2XHREGISTER      R29: 0000FFFF990CDB50  (aarch64)
+  private static final Pattern REGISTER_ENTRY_PARSER =
+      Pattern.compile("([A-Za-z][A-Za-z0-9]*)\\s*:\\s*([0-9a-fA-F]+)");
   // Date time formatter for J9 format: YYYY/MM/DD at HH:MM:SS
   private static final DateTimeFormatter J9_DATETIME_FORMATTER =
       DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss", Locale.ROOT);
 
   enum Section {
     NONE,
     TITLE,
+    GPINFO,
     ENVINFO,
     THREADS,
     OTHER
@@ -104,6 +115,8 @@ public CrashLog parse(String uuid, String javacoreContent) {
     boolean incomplete = false;
     boolean foundThreadSection = false;
 
+    Map<String, String> registers = null;
+
     String[] lines = NEWLINE_SPLITTER.split(javacoreContent);
 
     for (String line : lines) {
@@ -140,6 +153,17 @@ public CrashLog parse(String uuid, String javacoreContent) {
           }
           break;
 
+        case GPINFO:
+          if (line.startsWith("1XHREGISTERS")) {
+            registers = new LinkedHashMap<>();
+          } else if (registers != null && line.startsWith("2XHREGISTER")) {
+            final Matcher m = REGISTER_ENTRY_PARSER.matcher(line);
+            while (m.find()) {
+              registers.put(m.group(1), "0x" + m.group(2));
+            }
+          }
+          break;
+
         case ENVINFO:
           // Extract process ID
           Matcher pidMatcher = PID_PATTERN.matcher(line);
@@ -257,9 +281,20 @@ public CrashLog parse(String uuid, String javacoreContent) {
     Metadata metadata = new Metadata("dd-trace-java", VersionInfo.VERSION, "java", null);
     Integer parsedPid = safelyParseInt(pid);
     ProcInfo procInfo = parsedPid != null ? new ProcInfo(parsedPid) : null;
+    Experimental experimental =
+        (registers != null && !registers.isEmpty()) ? new Experimental(registers) : null;
 
     return new CrashLog(
-        uuid, incomplete, datetime, error, metadata, OSInfo.current(), procInfo, sigInfo, "1.0");
+        uuid,
+        incomplete,
+        datetime,
+        error,
+        metadata,
+        OSInfo.current(),
+        procInfo,
+        sigInfo,
+        "1.0",
+        experimental);
   }
 
   private static Integer safelyParseInt(String value) {
@@ -276,6 +311,8 @@ private static Integer safelyParseInt(String value) {
   private static Section detectSection(String line) {
     if (line.contains(SECTION_TITLE)) {
       return Section.TITLE;
+    } else if (line.contains(SECTION_GPINFO)) {
+      return Section.GPINFO;
     } else if (line.contains(SECTION_ENVINFO)) {
       return Section.ENVINFO;
     } else if (line.contains(SECTION_THREADS)) {

dd-java-agent/agent-crashtracking/src/test/java/datadog/crashtracking/parsers/J9JavacoreParserTest.java

@@ -16,6 +16,7 @@
 import java.util.UUID;
 import java.util.stream.Collectors;
 import org.junit.jupiter.api.Test;
+import org.tabletest.junit.TableTest;
 
 public class J9JavacoreParserTest {
 
@@ -67,6 +68,26 @@ public void testParseGpfCrash() throws Exception {
     assertNotNull(crashLog.osInfo);
   }
 
+  @TableTest({
+    "scenario            | resource                          | pcRegister | spRegister",
+    "IBM J9 8 (amd64)    | sample-ibmj9-8-javacore-gpf.txt   | RIP        | RSP       ",
+    "OpenJ9 11 (aarch64) | sample-openj9-11-javacore-gpf.txt | PC         | SP        "
+  })
+  public void testParseRealGpfCrash(String resource, String pcRegister, String spRegister)
+      throws Exception {
+    final CrashLog crashLog =
+        new J9JavacoreParser().parse(UUID.randomUUID().toString(), readFileAsString(resource));
+
+    assertFalse(crashLog.incomplete);
+    assertEquals("SIGSEGV", crashLog.sigInfo.name);
+    assertEquals(11, crashLog.sigInfo.number);
+
+    assertNotNull(crashLog.experimental);
+    assertFalse(crashLog.experimental.ucontext.isEmpty());
+    assertTrue(crashLog.experimental.ucontext.containsKey(pcRegister));
+    assertTrue(crashLog.experimental.ucontext.containsKey(spRegister));
+  }
+
   @Test
   public void testParseOomCrash() throws Exception {
     // Given