[Mac/GN] Implement dSYM generation and stripping.

build/toolchain/mac/linker_driver.py

Index: build/toolchain/mac/linker_driver.py
diff --git a/build/toolchain/mac/linker_driver.py b/build/toolchain/mac/linker_driver.py
new file mode 100755
index 0000000000000000000000000000000000000000..50ba540c34b877ebd9f74e398013cd47ddf190cc
--- /dev/null
+++ b/build/toolchain/mac/linker_driver.py
@@ -0,0 +1,187 @@
+#!/usr/bin/env python
+
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import os
+import os.path
+import shutil
+import subprocess
+import sys
+
+# The linker_driver.py is responsible for forwarding a linker invocation to
+# the compiler driver, while processing special arguments itself.
+#
+# Usage: linker_driver.py clang++ main.o -L. -llib -o prog -Wcrl,dsym,out
+#
+# On Mac, the logical step of linking is handled by three discrete tools to
+# perform the image link, debug info link, and strip. The linker_driver.py
+# combines these three steps into a single tool.
+#
+# The command passed to the linker_driver.py should be the compiler driver
+# invocation for the linker. It is first invoked unaltered (except for the
+# removal of the special driver arguments, described below). Then the driver
+# performs additional actions, based on these arguments:
+#
+#   -Wcrl,dsym,<dsym_path_prefix>
+#       After invoking the linker, this will run `dsymutil` on the linker's
+#       output, producing a dSYM bundle, stored at dsym_path_prefix. As an
+#       example, if the linker driver were invoked with:
+#         "... -o out/gn/obj/foo/libbar.dylib ... -Wcrl,dsym,out/gn ..."
+#       The resulting dSYM would be out/gn/libbar.dylib.dSYM/.
+#
+#   -Wcrl,strip,<strip_arguments>
+#       After invoking the linker, and optionally dsymutil, this will run
+#       the strip command on the linker's output. strip_arguments are
+#       comma-separated arguments to be passed to the strip command.
+
+def Main(args):
+  """Main function for the linker driver. Separates out the arguments for
+  the main compiler driver and the linker driver, then invokes all the
+  required tools.
+
+  Args:
+    args: list of string, Arguments to the script.
+  """
+
+  if len(args) < 2:
+    raise RuntimeError("Usage: linker_driver.py [linker-invocation]")
+
+  # Collect arguments to the linker driver (this script) and remove them from
+  # the arguments being passed to the compiler driver.
+  linker_driver_actions = {}
+  compiler_driver_args = []
+  for arg in args[1:]:
+    if arg.startswith(_LINKER_DRIVER_ARG_PREFIX):
+      # Convert driver actions into a map of name => lambda to invoke.
+      driver_action = ProcessLinkerDriverArg(arg)
+      assert driver_action[0] not in linker_driver_actions
+      linker_driver_actions[driver_action[0]] = driver_action[1]
+    else:
+      compiler_driver_args.append(arg)
+
+  linker_driver_outputs = [_FindLinkerOutput(compiler_driver_args)]
+
+  try:
+    # Run the linker by invoking the compiler driver.
+    subprocess.check_call(compiler_driver_args)
+
+    # Run the linker driver actions, in the order specified by the actions list.
+    for action in _LINKER_DRIVER_ACTIONS:
+      name = action[0]
+      if name in linker_driver_actions:
+        linker_driver_outputs += linker_driver_actions[name](args)
+  except:
+    # If a linker driver action failed, remove all the outputs to make the
+    # build step atomic.
+    map(_RemovePath, linker_driver_outputs)
+
+    # Re-report the original failure.
+    raise
+
+
+def ProcessLinkerDriverArg(arg):
+  """Processes a linker driver argument and returns a tuple containing the
+  name and unary lambda to invoke for that linker driver action.
+
+  Args:
+    arg: string, The linker driver argument.
+
+  Returns:
+    A 2-tuple:
+      0: The driver action name, as in _LINKER_DRIVER_ACTIONS.
+      1: An 1-ary lambda that takes the full list of arguments passed to
+         Main(). The lambda should call the linker driver action that
+         corresponds to the argument and return a list of outputs from the
+         action.
+  """
+  if not arg.startswith(_LINKER_DRIVER_ARG_PREFIX):
+    raise ValueError('%s is not a linker driver argument' % (arg,))
+
+  sub_arg = arg[len(_LINKER_DRIVER_ARG_PREFIX):]
+
+  for driver_action in _LINKER_DRIVER_ACTIONS:
+    (name, action) = driver_action
+    if sub_arg.startswith(name):
+      return (name,
+          lambda full_args: action(sub_arg[len(name):], full_args))
+
+  raise ValueError('Unknown linker driver argument: %s' % (arg,))
+
+
+def RunDsymUtil(dsym_path_prefix, full_args):
+  """Linker driver action for -Wcrl,dsym,<dsym-path-prefix>. Invokes dsymutil
+  on the linker's output and produces a dsym file at |dsym_file| path.
+
+  Args:
+    dsym_path_prefix: string, The path at which the dsymutil output should be
+        located.
+    full_args: list of string, Full argument list for the linker driver.
+
+  Returns:
+      list of string, Build step outputs.
+  """
+  if not len(dsym_path_prefix):
+    raise ValueError('Unspecified dSYM output file')
+
+  linker_out = _FindLinkerOutput(full_args)
+  (head, tail) = os.path.split(linker_out)
+  dsym_out = os.path.join(dsym_path_prefix, tail + '.dSYM')
+
+  # Remove old dSYMs before invoking dsymutil.
+  _RemovePath(dsym_out)
+  subprocess.check_call(['xcrun', 'dsymutil', '-o', dsym_out, linker_out])
+  return [dsym_out]
+
+
+def RunStrip(strip_args_string, full_args):
+  """Linker driver action for -Wcrl,strip,<strip_arguments>.
+
+  Args:
+      strip_args_string: string, Comma-separated arguments for `strip`.
+      full_args: list of string, Full arguments for the linker driver.
+
+  Returns:
+      list of string, Build step outputs.
+  """
+  strip_command = ['xcrun', 'strip']
+  if len(strip_args_string) > 0:
+    strip_command += strip_args_string.split(',')
+  strip_command.append(_FindLinkerOutput(full_args))
+  subprocess.check_call(strip_command)
+  return []
+
+
+def _FindLinkerOutput(full_args):
+  """Finds the output of the linker by looking for the output flag in its
+  argument list. As this is a required linker argument, raises an error if it
+  cannot be found.
+  """
+  return full_args[full_args.index('-o') + 1]
+
+
+def _RemovePath(path):
+  """Removes the file or directory at |path| if it exists."""
+  if os.path.exists(path):
+    if os.path.isdir(path):
+      shutil.rmtree(path)
+    else:
+      os.unlink(path)
+
+
+_LINKER_DRIVER_ARG_PREFIX = '-Wcrl,'
+
+"""List of linker driver actions. The sort order of this list affects the
+order in which the actions are invoked. The first item in the tuple is the
+argument's -Wcrl,<sub_argument> and the second is the function to invoke.
+"""
+_LINKER_DRIVER_ACTIONS = [
+    ('dsym,', RunDsymUtil),
+    ('strip,', RunStrip),
+]
+
+
+if __name__ == '__main__':
+  Main(sys.argv)
+  sys.exit(0)