Add a new python file to help diagnose backtrace failures in the field.

It will be installed in the LLDB.framework and can be loaded with

  (lldb) script import lldb.macosx

after which a "unwind-diagnose" command will be registered.  Select
the thread which has a bad backtrace and run this command -- a lot
of information about the stack frames, and an alternate backtrace
algorithm, will be used.  The information will often be sufficient
for a remote person to figure out why the backtrace failed.
<rdar://problem/13679300> 

llvm-svn: 180077

lldb/examples/python/unwind_diagnose.py

+#!/usr/bin/python
+
+# This implements the unwind-diagnose command, usually installed in the debug session like
+#   script import lldb.macosx
+# it is used when lldb's backtrace fails -- it collects and prints information about the stack frames,
+# and tries an alternate unwind algorithm, that will help to understand why lldb's unwind algorithm did
+# not succeed.
+
+import commands
+import optparse
+import os
+import platform
+import re
+import shlex
+import sys
+
+try: 
+    # Just try for LLDB in case PYTHONPATH is already correctly setup
+    import lldb
+except ImportError:
+    lldb_python_dirs = list()
+    # lldb is not in the PYTHONPATH, try some defaults for the current platform
+    platform_system = platform.system()
+    if platform_system == 'Darwin':
+        # On Darwin, try the currently selected Xcode directory
+        xcode_dir = commands.getoutput("xcode-select --print-path")
+        if xcode_dir:
+            lldb_python_dirs.append(os.path.realpath(xcode_dir + '/../SharedFrameworks/LLDB.framework/Resources/Python'))
+            lldb_python_dirs.append(xcode_dir + '/Library/PrivateFrameworks/LLDB.framework/Resources/Python')
+        lldb_python_dirs.append('/System/Library/PrivateFrameworks/LLDB.framework/Resources/Python')
+    success = False
+    for lldb_python_dir in lldb_python_dirs:
+        if os.path.exists(lldb_python_dir):
+            if not (sys.path.__contains__(lldb_python_dir)):
+                sys.path.append(lldb_python_dir)
+                try: 
+                    import lldb
+                except ImportError:
+                    pass
+                else:
+                    print 'imported lldb from: "%s"' % (lldb_python_dir)
+                    success = True
+                    break
+    if not success:
+        print "error: couldn't locate the 'lldb' module, please set PYTHONPATH correctly"
+        sys.exit(1)
+
+# Print the frame number, pc, frame pointer, module UUID and function name
+def backtrace_print_frame (target, frame_num, addr, fp):
+  process = target.GetProcess()
+  addr_for_printing = addr
+  if frame_num > 0:
+    addr = addr - 1
+
+  sbaddr = lldb.SBAddress()
+  sbaddr.SetLoadAddress(addr, target)
+  module_description = ""
+  if sbaddr.GetModule():
+    module_filename = ""
+    module_uuid_str = sbaddr.GetModule().GetUUIDString()
+    if module_uuid_str == None:
+      module_uuid_str = ""
+    if sbaddr.GetModule().GetFileSpec():
+      module_filename = sbaddr.GetModule().GetFileSpec().GetFilename()
+      if module_filename == None:
+        module_filename = ""
+    if module_uuid_str != "" or module_filename != "":
+      module_description = '%s %s' % (module_filename, module_uuid_str)
+
+  addr_width = process.GetAddressByteSize() * 2
+  sym_ctx = target.ResolveSymbolContextForAddress(sbaddr, lldb.eSymbolContextEverything)
+  if sym_ctx.IsValid() and sym_ctx.GetSymbol().IsValid():
+    function_start = sym_ctx.GetSymbol().GetStartAddress().GetLoadAddress(target)
+    offset = addr - function_start
+    print '%2d: pc==0x%-*x fp==0x%-*x %s %s + %d' % (frame_num, addr_width, addr_for_printing, addr_width, fp, module_description, sym_ctx.GetSymbol().GetName(), offset)
+  else:
+    print '%2d: pc==0x%-*x fp==0x%-*x %s' % (frame_num, addr_width, addr_for_printing, addr_width, fp, module_description)
+
+# A simple stack walk algorithm that follows the frame chain after the first two frames.
+def simple_backtrace(debugger):
+  target = debugger.GetSelectedTarget()
+  process = target.GetProcess()
+  cur_thread = process.GetSelectedThread()
+
+  backtrace_print_frame (target, 0, cur_thread.GetFrameAtIndex(0).GetPC(), cur_thread.GetFrameAtIndex(0).GetFP())
+  if cur_thread.GetNumFrames() < 2:
+    return
+
+  cur_fp = cur_thread.GetFrameAtIndex(1).GetFP()
+  cur_pc = cur_thread.GetFrameAtIndex(1).GetPC()
+
+  # If the pseudoreg "fp" isn't recognized, on arm hardcode to r7 which is correct for Darwin programs.
+  if cur_fp == lldb.LLDB_INVALID_ADDRESS and target.triple[0:3] == "arm":
+    for reggroup in cur_thread.GetFrameAtIndex(1).registers:
+      if reggroup.GetName() == "General Purpose Registers":
+        for reg in reggroup:
+          if reg.GetName() == "r7":
+            cur_fp = int (reg.GetValue(), 16)
+
+  frame_num = 1
+
+  while cur_pc != 0 and cur_fp != 0 and cur_pc != lldb.LLDB_INVALID_ADDRESS and cur_fp != lldb.LLDB_INVALID_ADDRESS:
+    backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
+    frame_num = frame_num + 1
+    next_pc = 0
+    next_fp = 0
+    if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386" or target.triple[0:3] == "arm":
+      error = lldb.SBError()
+      next_pc = process.ReadPointerFromMemory(cur_fp + process.GetAddressByteSize(), error)
+      if not error.Success():
+        next_pc = 0
+      next_fp = process.ReadPointerFromMemory(cur_fp, error)
+      if not error.Success():
+        next_fp = 0
+    # Clear the 0th bit for arm frames - this indicates it is a thumb frame
+    if target.triple[0:3] == "arm" and (next_pc & 1) == 1:
+      next_pc = next_pc & ~1
+    cur_pc = next_pc
+    cur_fp = next_fp
+  backtrace_print_frame (target, frame_num, cur_pc, cur_fp)
+
+def unwind_diagnose(debugger, command, result, dict):
+  # Use the Shell Lexer to properly parse up command options just like a
+  # shell would
+  command_args = shlex.split(command)
+  parser = create_unwind_diagnose_options()
+  try:
+    (options, args) = parser.parse_args(command_args)
+  except:
+   return
+  target = debugger.GetSelectedTarget()
+  if target:
+    process = target.GetProcess()
+    if process:
+      thread = process.GetSelectedThread()
+      if thread:
+        lldb_versions_match = re.search(r'lldb-(\d+)([.](\d+))?([.](\d+))?', debugger.GetVersionString())
+        lldb_version = 0
+        lldb_minor = 0
+        if len(lldb_versions_match.groups()) >= 1:
+          lldb_major = lldb_versions_match.groups(1)
+        if len(lldb_versions_match.groups()) >= 5:
+          lldb_minor = lldb_versions_match.groups(5)
+
+        print 'Unwind diagnostics for thread %d' % thread.GetIndexID()
+        print ""
+        print "lldb's unwind algorithm:"
+        print ""
+        frame_num = 0
+        for frame in thread.frames:
+          if not frame.IsInlined():
+            backtrace_print_frame (target, frame_num, frame.GetPC(), frame.GetFP())
+            frame_num = frame_num + 1
+        print ""
+        print "============================================================================================="
+        print ""
+        print "Simple stack walk algorithm:"
+        print ""
+        simple_backtrace(debugger)
+        print ""
+        print "============================================================================================="
+        print ""
+        for frame in thread.frames:
+          if not frame.IsInlined():
+            print "--------------------------------------------------------------------------------------"
+            print ""
+            print "Disassembly of %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
+            print ""
+            if lldb_major > 300 or (lldb_major == 300 and lldb_minor >= 18):
+                if target.triple[0:6] == "x86_64" or target.triple[0:4] == "i386":
+                  debugger.HandleCommand('disassemble -F att -a 0x%x' % frame.GetPC())
+                else:
+                  debugger.HandleCommand('disassemble -a 0x%x' % frame.GetPC())
+            else:
+              debugger.HandleCommand('disassemble -n "%s"' % frame.GetFunctionName())
+        print ""
+        print "============================================================================================="
+        print ""
+        for frame in thread.frames:
+          if not frame.IsInlined():
+            print "--------------------------------------------------------------------------------------"
+            print ""
+            print "Unwind instructions for %s, frame %d" % (frame.GetFunctionName(), frame.GetFrameID())
+            print ""
+            debugger.HandleCommand('image show-unwind -n "%s"' % frame.GetFunctionName())
+
+def create_unwind_diagnose_options():
+  usage = "usage: %prog"
+  description='''Print diagnostic information about a thread backtrace which will help to debug unwind problems'''
+  parser = optparse.OptionParser(description=description, prog='unwind_diagnose',usage=usage)
+  return parser
+
+if __name__ == '__main__':
+    print 'This is not meant to be run from the command line, import it into lldb with a command like "script import lldb.macosx"'
+elif getattr(lldb, 'debugger', None):
+    lldb.debugger.HandleCommand('command script add -f lldb.macosx.unwind_diagnose.unwind_diagnose unwind-diagnose')
+    print 'The "unwind-diagnose" command has been installed, type "help unwind-diagnose" for detailed help.'