[Mac/GN] Implement dSYM generation and stripping.

build/toolchain/mac/linker_driver.py

+#!/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 subprocess
+import sys
+
+# The linker_driver.py is responsible for forwarding a linker invocation to
+# the compiler driver, while processing special arguments itself.
+#
+# 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.

[Mark Mentovai, 2016/05/20 15:42:41]

Ask Nico whether there’s any chance of adding these to the compiler driver so
that we can drop this wrapper.

[Robert Sesek, 2016/05/20 19:09:55]

Acknowledged. Per offline chat, clang, when driving the full compile+link, can
produce a dSYM for you with -g, that part is probably reasonable, but maybe not
stripping. Will ask when Nico returns next week.

+#
+# The invocation of the linker_driver.py is first passed unaltered, except for
+# the removal of the special driver arguments, described below. The driver
+# arguments control what other steps occur after the image link.
+#
+#   -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.

[Mark Mentovai, 2016/05/20 15:42:41]

dsym_path_prefix is a directory, and the name + .dSYM gets appended? It’d be
helpful if you gave an example here that said where linker output and the .dSYM
would go.

[Robert Sesek, 2016/05/20 19:09:55]

Done.

+#
+#   -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.
+
+_LINKER_DRIVER_ARG_PREFIX = '-Wcrl,'
+
+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)
+      linker_driver_actions[driver_action[0]] = driver_action[1]
+    else:
+      compiler_driver_args.append(arg)
+
+  # 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:

[Dirk Pranke, 2016/05/20 01:47:19]

this should probably be wrapped in a try: ... finally: ... block that deletes
the binary if one of the steps fails, to be somewhat atomic and help avoid
confusing ninja.

[Robert Sesek, 2016/05/20 15:15:36]

Done.

+    name = action[0]
+    if name in linker_driver_actions:
+      linker_driver_actions[name](args)
+
+
+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.
+  """
+  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.
+  """
+  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')

[Mark Mentovai, 2016/05/20 15:42:41]

Does dsymutil trash the .dSYM before writing a new one? Easy way to check: put
some garbage files in a .dSYM bundle, then run dsymutil again to produce a new
one. If it doesn’t, then we should trash an existing .dSYM first before running
dsymutil.

[Robert Sesek, 2016/05/20 19:09:55]

It "kind of" does. If you put extra things in the bundle it doesn't seem to
care, but it does overwrite an existing dSYM file (probably to support the
--update argument). Now clobbering it.

+  subprocess.check_call(['xcrun', 'dsymutil', '-o', dsym_out, linker_out])

[Mark Mentovai, 2016/05/20 15:42:42]

If (this or) a later step fails, the .dSYM that you produced should be trashed.

[Robert Sesek, 2016/05/20 19:09:55]

Yeah, this was on my mind when writing it. At the time I couldn't find an
elegant solution, but that's now fixed.

dSYM generation is at least somewhat smart, though, and builds the output in a
mkdtemp dir before moving it into the final location.

+
+
+def RunStrip(strip_args_string, full_args):

[Mark Mentovai, 2016/05/20 15:42:41]

We may at some point want an option to save the original unstripped image
somewhere. I’ve wanted that before, but we couldn’t do it easily because Xcode
constrained us.

[Robert Sesek, 2016/05/20 19:09:55]

Acknowledged.

+  """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.
+  """
+  strip_args_list = strip_args_string.split(',')
+  strip_command = ['xcrun', 'strip'] + strip_args_list
+  strip_command.append(_FindLinkerOutput(full_args))
+  subprocess.check_call(strip_command)
+
+
+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.
+  """
+  for (i, arg) in enumerate(full_args):
+    if arg == '-o':
+      return full_args[i+1]
+  raise RuntimeError('Unable to locate linker output file')
+
+
+"""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 = [

[Mark Mentovai, 2016/05/20 15:42:41]

Can you move this up so that it’s after _LINKER_DRIVER_ARG_PREFIX?

[Robert Sesek, 2016/05/20 19:09:55]

No because they reference functions declared later. Moved the arg prefix down so
they can be friends, though.

+    ('dsym,', RunDsymUtil),
+    ('strip,', RunStrip),
+]
+
+
+if __name__ == '__main__':
+  Main(sys.argv)
+  sys.exit(0)