[NaCl SDK] Refactor create_nmf.py

Most of the complex logic is moved to elf.py or get_shared_deps.py (each with
their own simpler tests). These changes will make it easier to handle
generating a multi-platform NMF.

BUG=none
R=sbc@chromium.org

Review URL: https://codereview.chromium.org/161613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255474 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 99 insertions, 0 deletions

diff --git a/native_client_sdk/src/tools/lib/elf.py b/native_client_sdk/src/tools/lib/elf.py
new file mode 100644
index 0000000..2011a2b
--- /dev/null
+++ b/native_client_sdk/src/tools/lib/elf.py
@@ -0,0 +1,99 @@
+# Copyright 2014 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.
+
+"""Helper script for extracting information from ELF files"""
+
+import struct
+
+
+class Error(Exception):
+  '''Local Error class for this file.'''
+  pass
+
+
+def ParseElfHeader(path):
+  """Determine properties of a nexe by parsing elf header.
+  Return tuple of architecture and boolean signalling whether
+  the executable is dynamic (has INTERP header) or static.
+  """
+  # From elf.h:
+  # typedef struct
+  # {
+  #   unsigned char e_ident[EI_NIDENT]; /* Magic number and other info */
+  #   Elf64_Half e_type; /* Object file type */
+  #   Elf64_Half e_machine; /* Architecture */
+  #   ...
+  # } Elf32_Ehdr;
+  elf_header_format = '16s2H'
+  elf_header_size = struct.calcsize(elf_header_format)
+
+  with open(path, 'rb') as f:
+    header = f.read(elf_header_size)
+
+  try:
+    header = struct.unpack(elf_header_format, header)
+  except struct.error:
+    raise Error("error parsing elf header: %s" % path)
+  e_ident, _, e_machine = header[:3]
+
+  elf_magic = '\x7fELF'
+  if e_ident[:4] != elf_magic:
+    raise Error('Not a valid NaCl executable: %s' % path)
+
+  e_machine_mapping = {
+    3 : 'x86-32',
+    40 : 'arm',
+    62 : 'x86-64'
+  }
+  if e_machine not in e_machine_mapping:
+    raise Error('Unknown machine type: %s' % e_machine)
+
+  # Set arch based on the machine type in the elf header
+  arch = e_machine_mapping[e_machine]
+
+  # Now read the full header in either 64bit or 32bit mode
+  dynamic = IsDynamicElf(path, arch == 'x86-64')
+  return arch, dynamic
+
+
+def IsDynamicElf(path, is64bit):
+  """Examine an elf file to determine if it is dynamically
+  linked or not.
+  This is determined by searching the program headers for
+  a header of type PT_INTERP.
+  """
+  if is64bit:
+    elf_header_format = '16s2HI3QI3H'
+  else:
+    elf_header_format = '16s2HI3II3H'
+
+  elf_header_size = struct.calcsize(elf_header_format)
+
+  with open(path, 'rb') as f:
+    header = f.read(elf_header_size)
+    header = struct.unpack(elf_header_format, header)
+    p_header_offset = header[5]
+    p_header_entry_size = header[9]
+    num_p_header = header[10]
+    f.seek(p_header_offset)
+    p_headers = f.read(p_header_entry_size*num_p_header)
+
+  # Read the first word of each Phdr to find out its type.
+  #
+  # typedef struct
+  # {
+  #   Elf32_Word  p_type;     /* Segment type */
+  #   ...
+  # } Elf32_Phdr;
+  elf_phdr_format = 'I'
+  PT_INTERP = 3
+
+  while p_headers:
+    p_header = p_headers[:p_header_entry_size]
+    p_headers = p_headers[p_header_entry_size:]
+    phdr_type = struct.unpack(elf_phdr_format, p_header[:4])[0]
+    if phdr_type == PT_INTERP:
+      return True
+
+  return False