Use chain-loading for Linux nacl_helper

chrome/nacl/nacl_helper_bootstrap_munge_phdr.py

Index: chrome/nacl/nacl_helper_bootstrap_munge_phdr.py
diff --git a/chrome/nacl/nacl_helper_bootstrap_munge_phdr.py b/chrome/nacl/nacl_helper_bootstrap_munge_phdr.py
new file mode 100755
index 0000000000000000000000000000000000000000..66f39fdf8afa27cc4be8052f0e63bb79a6bf7c89
--- /dev/null
+++ b/chrome/nacl/nacl_helper_bootstrap_munge_phdr.py
@@ -0,0 +1,39 @@
+#!/usr/bin/python
+# Copyright (c) 2011 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.
+#
+# This takes three command-line arguments:
+#       MUNGE-PHDR-PROGRAM      file name of program built from
+#                               nacl_helper_bootstrap_munge_phdr.c
+#       INFILE                  raw linked ELF file name
+#       OUTFILE                 output file name
+#
+# We just run the MUNGE-PHDR-PROGRAM on a copy of INFILE.
+# That modifies the file in place.  Then we move it to OUTFILE.
+#
+# We only have this wrapper script because nacl_helper_bootstrap_munge_phdr.c
+# wants to modify a file in place (and it would be a much longer and more
+# fragile program if it created a fresh ELF output file instead).
+
+import optparse

[Mark Seaborn, 2011/08/30 20:12:25]

Not used.

+import shutil
+import subprocess
+import sys
+
+
+def Main(argv):
+  if len(argv) != 4:
+    print 'Usage: %s MUNGE-PHDR-PROGRAM INFILE OUTFILE' % argv[0]
+    sys.exit(1)
+  [prog, munger, infile, outfile] = argv
+  tmpfile = outfile + '.tmp'
+  shutil.copy(infile, tmpfile)
+  result = subprocess.call([munger, tmpfile, '1'])

[Mark Seaborn, 2011/08/30 20:12:25]

Nit: Maybe do:
segment_num = '1'
result = subprocess.call([munger, tmpfile, segment_num])

+  if result != 0:

[Mark Seaborn, 2011/08/30 20:12:25]

You can use subprocess.check_call().  Then you don't need this check.

+    print '%s failed with %d' % (munger, result)
+    sys.exit(result)
+  shutil.move(tmpfile, outfile)
+
+if __name__ == '__main__':
+  Main(sys.argv)

[Mark Seaborn, 2011/08/30 20:12:25]

FWIW, I think it's preferable to do "Main(sys.argv[1:])"