[lldb/crashlog] Add support for Last Exception Backtrace

This patch adds support to the "Last Exception Backtrace" to the
`crashlog` command.

This metadata is homologous to the "Application Specific Backtrace",
however the format is closer to a regular stack frame.

Since the thread that "contains" the "Last Exception Backtrace" doesn't
really exist, this information is displayed when requesting an extended
backtrace of the crashed thread, similarly to the "Application Specific
Backtrace".

To achieve that, this patch includes some refactors and fixes to the
existing "Application Specific Backtrace" handling.

rdar://113046509

Differential Revision: https://reviews.llvm.org/D157851

Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>

lldb/examples/python/crashlog.py

@@ -586,10 +586,15 @@ class JSONCrashLogParser(CrashLogParser):
             self.parse_threads(self.data["threads"])
             if "asi" in self.data:
                 self.crashlog.asi = self.data["asi"]
+            # FIXME: With the current design, we can either show the ASI or Last
+            # Exception Backtrace, not both. Is there a situation where we would
+            # like to show both ?
             if "asiBacktraces" in self.data:
                 self.parse_app_specific_backtraces(self.data["asiBacktraces"])
             if "lastExceptionBacktrace" in self.data:
-                self.crashlog.asb = self.data["lastExceptionBacktrace"]
+                self.parse_last_exception_backtraces(
+                    self.data["lastExceptionBacktrace"]
+                )
             self.parse_errors(self.data)
             thread = self.crashlog.threads[self.crashlog.crashed_thread_idx]
             reason = self.parse_crash_reason(self.data["exception"])
@@ -792,11 +797,22 @@ class JSONCrashLogParser(CrashLogParser):
         return True
 
     def parse_app_specific_backtraces(self, json_app_specific_bts):
-        for idx, backtrace in enumerate(json_app_specific_bts):
-            thread = self.crashlog.Thread(idx, True, self.crashlog.process_arch)
-            thread.queue = "Application Specific Backtrace"
-            if self.parse_asi_backtrace(thread, backtrace):
-                self.crashlog.threads.append(thread)
+        thread = self.crashlog.Thread(
+            len(self.crashlog.threads), True, self.crashlog.process_arch
+        )
+        thread.queue = "Application Specific Backtrace"
+        if self.parse_asi_backtrace(thread, json_app_specific_bts[0]):
+            self.crashlog.threads.append(thread)
+        else:
+            print("error: Couldn't parse Application Specific Backtrace.")
+
+    def parse_last_exception_backtraces(self, json_last_exc_bts):
+        thread = self.crashlog.Thread(
+            len(self.crashlog.threads), True, self.crashlog.process_arch
+        )
+        thread.queue = "Last Exception Backtrace"
+        self.parse_frames(thread, json_last_exc_bts)
+        self.crashlog.threads.append(thread)
 
     def parse_thread_registers(self, json_thread_state, prefix=None):
         registers = dict()

lldb/examples/python/scripted_process/crashlog_scripted_process.py

@@ -178,7 +178,7 @@ class CrashLogScriptedThread(ScriptedThread):
         self.idx = self.backing_thread.index
         self.tid = self.backing_thread.id
         if self.backing_thread.app_specific_backtrace:
-            self.name = "Application Specific Backtrace - " + str(self.idx)
+            self.name = "Application Specific Backtrace"
         else:
             self.name = self.backing_thread.name
         self.queue = self.backing_thread.queue