[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.
+#
+# The command passed to the linker_driver.py 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.
+#
+#   -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.
+  try:

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

I’d move the try up to include the call of the compiler driver, so that even if
the compiler driver is totally busted and can’t be started, we’ll still remove
any preexisting linked image on our own.

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

Done.

+    for action in _LINKER_DRIVER_ACTIONS:
+      name = action[0]
+      if name in linker_driver_actions:
+        linker_driver_actions[name](args)
+  except Exception, e:
+    # If a linker driver action failed, remove the linker output to make the
+    # build step atomic.
+    try:
+      os.unlink(_FindLinkerOutput(compiler_driver_args))
+    except RuntimeError:

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

Why isn’t this just “except:”?

os.unlink is most likely going to fail with OSError, which doesn’t derive from
RuntimeError. But we want to re-raise the original interesting exception no
matter why os.unlink failed.

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

This was to only capture the exception from _FindLinkerOutput. This has been
restructured, though.

+      # Re-raise the original exception, since it may be more interesting than
+      # failing to find the output flag.
+      raise e
+      return
+
+    # Re-report the original failure.

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

Actually, since this is what you want to do no matter what, how about:

try:
  subprocess.check_call(compiler_driver_args)
  for …
except:
  try:
    os.unlink(…)
  finally:
    raise

This is also nice because you no longer need to specify Exception on the except.

+    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.
+  """
+  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')
+  subprocess.check_call(['xcrun', 'dsymutil', '-o', dsym_out, linker_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.
+  """
+  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

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

Not true.

% echo 'int main(int argc, char* argv[]) {return 0;}' > t.c
% clang -c t.c
% clang t.o
% ls
a.out	t.c	t.o

The default in the absence of -o is a.out in the current directory.

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

This comment is true for our build.

[Mark Mentovai, 2016/05/20 19:41:11]

Robert Sesek wrote:
Word it so that it’s correct, then, because I’m still reading it as saying that
ld requires -o, not that our build always provides -o.

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