From a06062fefbdbaec6addbb61851721379f1de6916 Mon Sep 17 00:00:00 2001
From: ebenders <devnull@localhost>
Date: Thu, 8 Sep 2011 12:37:48 +0300
Subject: [PATCH] Added reading of sections and decoding their name from the
 string table

---
 elftools/elf/elffile.py  | 55 +++++++++++++++++++++++++++++++++++++---
 elftools/elf/sections.py | 26 +++++++++++++++++++
 z.py                     | 34 ++++++++++++++++---------
 3 files changed, 100 insertions(+), 15 deletions(-)
 create mode 100644 elftools/elf/sections.py

diff --git a/elftools/elf/elffile.py b/elftools/elf/elffile.py
index 29dc095..11d3704 100644
--- a/elftools/elf/elffile.py
+++ b/elftools/elf/elffile.py
@@ -7,9 +7,12 @@
 # This code is in the public domain
 #-------------------------------------------------------------------------------
 
-from .structs import ELFStructs
+from cStringIO import StringIO
+
 from ..exceptions import ELFError, ELFParseError
-from ..construct import ConstructError
+from ..construct import ConstructError, CString
+from .structs import ELFStructs
+from .sections import Section
 
 
 class ELFFile(object):
@@ -22,7 +25,7 @@ class ELFFile(object):
                 boolean - specifies the target machine's endianness     
 
             header:
-                the complete ELF file header
+                the complete ELF file header
     """
     def __init__(self, stream):
         self.stream = stream
@@ -31,6 +34,21 @@ class ELFFile(object):
             little_endian=self.little_endian,
             elfclass=self.elfclass)
         self.header = self._parse_elf_header()
+        self._stringtable = self._get_stringtable()
+    
+    def num_sections(self):
+        """ Get the number of sections in the file
+        """
+        return self['e_shnum']
+    
+    def get_section(self, n):
+        """ Get the section at index #n from the file (Section object)
+        """
+        section_header = self._get_section_header(n)
+        name = self._get_section_name(section_header)
+        return Section(section_header, name, self.stream)
+    
+    #-------------------------------- PRIVATE --------------------------------#
     
     def __getitem__(self, name):
         """ Implement dict-like access to header entries
@@ -64,6 +82,37 @@ class ELFFile(object):
         else:
             raise ELFError('Invalid EI_DATA %s' % repr(ei_data))
     
+    def _section_offset(self, n):
+        """ Compute the offset of section #n in the file
+        """
+        return self['e_shoff'] + n * self['e_shentsize']
+    
+    def _get_section_header(self, n):
+        """ Find the header of section #n, parse it and return the struct 
+        """
+        self.stream.seek(self._section_offset(n))
+        return self._struct_parse(self.structs.Elf_Shdr)
+    
+    def _get_section_name(self, section_header):
+        """ Given a section header, find this section's name in the file's
+            string table, and return it as a normal Python string.
+        """
+        offset = section_header['sh_name']
+        self._stringtable.seek(offset)
+        return CString('').parse_stream(self._stringtable)
+    
+    def _get_stringtable(self):
+        """ Find the file's string table section, read it and return the string
+            table as a StringIO object pointing to the section's contents.
+        """
+        # Find the section header for the stringtable header, and read the 
+        # section's contents from it
+        #
+        stringtable_section_num = self['e_shstrndx']
+        stringtable_header = self._get_section_header(stringtable_section_num)
+        self.stream.seek(stringtable_header['sh_offset'])
+        return StringIO(self.stream.read(stringtable_header['sh_size']))
+    
     def _parse_elf_header(self):
         """ Parses the ELF file header and assigns the result to attributes
             of this object.
diff --git a/elftools/elf/sections.py b/elftools/elf/sections.py
new file mode 100644
index 0000000..4fb4249
--- /dev/null
+++ b/elftools/elf/sections.py
@@ -0,0 +1,26 @@
+#-------------------------------------------------------------------------------
+# elftools: elf/sections.py
+#
+# ELF sections
+#
+# Eli Bendersky (eliben@gmail.com)
+# This code is in the public domain
+#-------------------------------------------------------------------------------
+
+class Section(object):
+    def __init__(self, header, name, stream):
+        self.header = header
+        self.name = name
+        self.stream = stream
+    
+    def data(self):
+        """ The section data from the file.
+        """
+        self.stream.seek(self['sh_offset'])
+        return self.stream.read(self['sh_size'])
+
+    def __getitem__(self, name):
+        """ Implement dict-like access to header entries
+        """
+        return self.header[name]
+
diff --git a/z.py b/z.py
index e959632..c74a4ff 100644
--- a/z.py
+++ b/z.py
@@ -9,24 +9,34 @@ stream = open('binfiles/z.elf', 'rb')
 
 efile = ELFFile(stream)
 
+print 'num', efile.num_sections()
+sec = efile.get_section(39)
+#~ print sec.header
+print sec.name
+print sec['sh_type']
+print map(ord, sec.data())
+
+#~ print sec.stream
+#~ print map(ord, efile._stringtable)
+
 #~ print efile.header
 #~ print dir(efile)
 #~ print efile['e_type']
 
-shtable_offset = efile['e_shoff']
-strtable_section_offset = shtable_offset + efile['e_shstrndx'] * efile['e_shentsize']
+#~ shtable_offset = efile['e_shoff']
+#~ strtable_section_offset = shtable_offset + efile['e_shstrndx'] * efile['e_shentsize']
 
-# get to the section header for the sh string table
-print strtable_section_offset
-stream.seek(strtable_section_offset)
-sheader = es.Elf_Shdr.parse_stream(stream)
-print sheader
+#~ # get to the section header for the sh string table
+#~ print strtable_section_offset
+#~ stream.seek(strtable_section_offset)
+#~ sheader = es.Elf_Shdr.parse_stream(stream)
+#~ print sheader
 
-# yay, looks correct!!
-stream.seek(sheader.sh_offset)
-buf = stream.read(sheader.sh_size)
-for c in buf:
-    sys.stdout.write('%02X' % ord(c))
+#~ # yay, looks correct!!
+#~ stream.seek(sheader.sh_offset)
+#~ buf = stream.read(sheader.sh_size)
+#~ for c in buf:
+    #~ sys.stdout.write('%02X' % ord(c))
 
 
 
-- 
2.30.2