[2020-02] [merp] Add API methods for getting hashcode/reason of last crash (#19978)

* [merp] Add API methods for getting hashcode/reason of last crash

* Add test

* Review feedback and cleanup

Co-authored-by: Alexis Christoforides <alexis@thenull.net>

2 files changed, 73 insertions, 3 deletions

diff --git a/mcs/class/corlib/Mono/Runtime.cs b/mcs/class/corlib/Mono/Runtime.cs
index f59a7e93891..c85a3a3b1f5 100644
--- a/mcs/class/corlib/Mono/Runtime.cs
+++ b/mcs/class/corlib/Mono/Runtime.cs
@@ -27,6 +27,7 @@
 //
 
 using System;
+using System.IO;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -255,6 +256,43 @@ namespace Mono {
 			}
 		}
 
+		static string get_breadcrumb_value (string file_prefix, string directory_str, bool clear)
+		{
+			var allfiles = Directory.GetFiles (directory_str, $"{file_prefix}_*" );
+			if (allfiles.Length == 0)
+				return string.Empty;
+
+			if (allfiles.Length > 1) {
+				// it's impossible to tell which breadcrumb is the last one (let's not trust filesystem timestamps)
+				// delete the multiple files so at least next crash can make sense
+				try {
+					Array.ForEach (allfiles, f => File.Delete (f) );
+				} catch (Exception) { }
+
+				return string.Empty;
+			}
+
+			if (clear)
+				File.Delete (allfiles [0]);
+
+			var filename = Path.GetFileName (allfiles [0]);
+			return filename.Substring (file_prefix.Length + 1);
+		}
+
+		static long CheckCrashReportHash (string directory_str, bool clear)
+		{
+			var value = get_breadcrumb_value ("crash_hash", directory_str, clear);
+			if (value == string.Empty)
+				return 0;
+			else
+				return Convert.ToInt64 (value, 16);
+		}
+
+		static string CheckCrashReportReason (string directory_str, bool clear)
+		{
+			return get_breadcrumb_value ("crash_reason", directory_str, clear);
+		}
+
 		[MethodImplAttribute (MethodImplOptions.InternalCall)]
 		static extern void AnnotateMicrosoftTelemetry_internal (IntPtr key, IntPtr val);
 
diff --git a/mono/tests/merp-crash-test.cs b/mono/tests/merp-crash-test.cs
index a33010e59cf..d534a64fae5 100644
--- a/mono/tests/merp-crash-test.cs
+++ b/mono/tests/merp-crash-test.cs
@@ -65,6 +65,7 @@ class C
 			Crashers.Add(new Crasher  ("MerpCrashSignalKill", MerpCrashSignalBus));
 			Crashers.Add(new Crasher  ("MerpCrashSignalSegv", MerpCrashSignalSegv));
 			Crashers.Add(new Crasher  ("MerpCrashSignalIll", MerpCrashSignalIll));
+			Crashers.Add(new Crasher ("MerpCrashTestBreadcrumbs", MerpCrashTestBreadcrumbs, validator: ValidateBreadcrumbs));
 		}
 
 		public static void 
@@ -88,6 +89,22 @@ class C
 				throw new ValidationException (String.Format ("incorrect fail fast message (expected: {0}, got: {1})", failfastMsg, s));
 		}
 
+		public static void ValidateBreadcrumbs (object json)
+		{
+			var monoType = Type.GetType ("Mono.Runtime", false);
+			var m = monoType.GetMethod ("CheckCrashReportReason", BindingFlags.NonPublic | BindingFlags.Static);
+			var m_params = new object [] { "./", false };
+			string o = (string)m.Invoke(null, m_params);
+			if (o != "segv")
+				throw new Exception ("Crash report reason should be 'segv'");
+
+			m = monoType.GetMethod ("CheckCrashReportHash", BindingFlags.NonPublic | BindingFlags.Static);
+			long hash = (long)m.Invoke (null, m_params);
+
+			if (hash == 0)
+				throw new Exception ("Crash hash should not be zero");
+		}
+
 		[DllImport("libtest")]
 		public static extern void mono_test_MerpCrashSnprintf ();
 
@@ -222,6 +239,12 @@ class C
 			mono_test_MerpCrashUnhandledExceptionHook ();
 		}
 
+		public static void
+		MerpCrashTestBreadcrumbs ()
+		{
+			mono_test_MerpCrashSignalSegv ();
+		}
+
 
 		private static object jsonGetKey (object o, string key) => (o as Dictionary<string,object>)[key];
 		private static object jsonGetKeys (object o, params string[] keys) {
@@ -273,8 +296,6 @@ class C
 	public static void 
 	TestValidate (string configDir, bool silent, Action<object> validator = null)
 	{
-		DumpLogCheck (expected_level: "MerpInvoke"); // we are expecting merp invoke to fail
-
 		var xmlFilePath = String.Format("{0}CustomLogsMetadata.xml", configDir);
 		var paramsFilePath = String.Format("{0}MERP.uploadparams.txt", configDir);
 		var crashFilePath = String.Format("{0}lastcrashlog.txt", configDir);
@@ -319,7 +340,7 @@ class C
 			} catch (CrasherClass.ValidationException e) {
 				throw new Exception (String.Format ("Validation failed '{0}', json: {1}", e.Message, crashFile));
 			} catch (Exception e) {
-				throw new Exception (String.Format ("Invalid json: {0}", crashFile));
+				throw new Exception (String.Format ("Invalid json  ({0}:{1}): {2}", e.GetType(), e.Message, crashFile));
 			}
 
 			File.Delete (crashFilePath);
@@ -328,6 +349,8 @@ class C
 			Console.WriteLine ("Crash file {0} missing", crashFilePath);
 		}
 
+		DumpLogCheck (expected_level: "MerpInvoke"); // we are expecting merp invoke to fail
+
 		if (!xmlFileExists)
 			throw new Exception (String.Format ("Did not produce {0}", xmlFilePath));
 
@@ -368,6 +391,15 @@ class C
 
 		if (expected_level != levels [result])
 			throw new Exception (String.Format ("Crash level {0} does not match expected {1}", levels [result], expected_level));
+
+		// also clear hash and reason breadcrumbs
+		convert = monoType.GetMethod("CheckCrashReportHash", BindingFlags.NonPublic | BindingFlags.Static);
+		var hash_result = (long) convert.Invoke(null, new object[] { "./", true });
+		convert = monoType.GetMethod("CheckCrashReportReason", BindingFlags.NonPublic | BindingFlags.Static);
+		var reason_result = (string) convert.Invoke(null, new object[] { "./", true });
+
+		if (reason_result == string.Empty)
+			throw new Exception("Crash reason should not be an empty string");
 	}