[Mac/GN] Add a new linker_driver.py option to save unstripped linker output.

This declares a new GN arg save_unstripped_output that can be enabled if
enable_stripping=true. If true, then an unstripped copy of the linker output
will be saved in the output directory with an ".unstripped" suffix.

BUG=628052
R=mark@chromium.org

Review-Url: https://codereview.chromium.org/2157573002
Cr-Commit-Position: refs/heads/master@{#406110}

build/config/mac/BUILD.gn

@@ -48,6 +48,10 @@ config("compiler") {
   cflags_objc = cflags_c
 
   ldflags = common_mac_flags
+
+  if (save_unstripped_output) {
+    ldflags += [ "-Wcrl,unstripped," + rebase_path(root_out_dir) ]
+  }
 }
 
 # This is included by reference in the //build/config/compiler:runtime_library

build/config/mac/symbols.gni

@@ -21,4 +21,13 @@ declare_args() {
   # linked target and apply custom -Wcrl,strip flags. See
   # //build/toolchain/mac/linker_driver.py for more information.
   enable_stripping = is_official_build
+
+  # Save unstripped copies of targets with a ".unstripped" suffix. This is
+  # useful to preserve the original output when enable_stripping=true.
+  save_unstripped_output = false
+}
+
+if (save_unstripped_output) {
+  assert(enable_stripping,
+         "save_unstripped_output=true requires enable_stripping=true")
 }

build/toolchain/mac/BUILD.gn

@@ -104,10 +104,16 @@ template("mac_toolchain") {
     # If dSYMs are enabled, this flag will be added to the link tools.
     if (enable_dsyms) {
       dsym_switch = " -Wcrl,dsym," + rebase_path(root_out_dir) + " "
+      _dsym_output =
+          "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM/"
     } else {
       dsym_switch = ""
     }
 
+    if (save_unstripped_output) {
+      _unstripped_output = "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.unstripped"
+    }
+
     tool("cc") {
       depfile = "{{output}}.d"
       precompiled_header_type = "gcc"
@@ -232,7 +238,10 @@ template("mac_toolchain") {
       depend_output = tocname
 
       if (enable_dsyms) {
-        outputs += [ "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM/" ]
+        outputs += [ _dsym_output ]
+      }
+      if (save_unstripped_output) {
+        outputs += [ _unstripped_output ]
       }
     }
 
@@ -263,7 +272,10 @@ template("mac_toolchain") {
       ]
 
       if (enable_dsyms) {
-        outputs += [ "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM/" ]
+        outputs += [ _dsym_output ]
+      }
+      if (save_unstripped_output) {
+        outputs += [ _unstripped_output ]
       }
     }
 
@@ -287,7 +299,10 @@ template("mac_toolchain") {
       ]
 
       if (enable_dsyms) {
-        outputs += [ "{{root_out_dir}}/{{target_output_name}}{{output_extension}}.dSYM/" ]
+        outputs += [ _dsym_output ]
+      }
+      if (save_unstripped_output) {
+        outputs += [ _unstripped_output ]
       }
 
       default_output_dir = "{{root_out_dir}}"

build/toolchain/mac/linker_driver.py

@@ -31,6 +31,10 @@ import sys
 #         "... -o out/gn/obj/foo/libbar.dylib ... -Wcrl,dsym,out/gn ..."
 #       The resulting dSYM would be out/gn/libbar.dylib.dSYM/.
 #
+#   -Wcrl,unstripped,<unstripped_path_prefix>
+#       After invoking the linker, and before strip, this will save a copy of
+#       the unstripped linker output in the directory unstripped_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
@@ -135,6 +139,29 @@ def RunDsymUtil(dsym_path_prefix, full_args):
   return [dsym_out]
 
 
+def RunSaveUnstripped(unstripped_path_prefix, full_args):
+  """Linker driver action for -Wcrl,unstripped,<unstripped_path_prefix>. Copies
+  the linker output to |unstripped_path_prefix| before stripping.
+
+  Args:
+    unstripped_path_prefix: string, The path at which the unstripped 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(unstripped_path_prefix):
+    raise ValueError('Unspecified unstripped output file')
+
+  linker_out = _FindLinkerOutput(full_args)
+  (head, tail) = os.path.split(linker_out)
+  unstripped_out = os.path.join(unstripped_path_prefix, tail + '.unstripped')
+
+  shutil.copyfile(linker_out, unstripped_out)
+  return [unstripped_out]
+
+
 def RunStrip(strip_args_string, full_args):
   """Linker driver action for -Wcrl,strip,<strip_arguments>.
 
@@ -178,6 +205,7 @@ argument's -Wcrl,<sub_argument> and the second is the function to invoke.
 """
 _LINKER_DRIVER_ACTIONS = [
     ('dsym,', RunDsymUtil),
+    ('unstripped,', RunSaveUnstripped),
     ('strip,', RunStrip),
 ]